CA1107926A - Silicon carbide fibers having a high strength and a method for producing said fibers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for producing a silicon carbide fiber having a high tensile strength which comprises (1) preparing a spinning solution from at least one organosilicon high molecular weight compound having a softening point of higher than 50°C, in which silicon and carbon are the main skeleton components, and spinning said spinning solution into a fiber, (2) preliminarily heating the spun fiber at a temper-ature of 350°-800°C under vacuum or a non-oxidizing atmosphere to volatilize low molecular weight compound contained therein, and (3) baking the thus treated fiber at a temperature of 800°-2,000°C under vacuum or at least one non-oxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas, to form said silicon carbide fiber.

Description

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The present invention is a divisional of Canadian patent application No. 250,637 filed on April 21, 1976 and relates to silicon carbide fibers having a high strength and a method for producing said fiBers.
Silicon carBide is a compound shown by a chemical formula of SiC and i5 usually produced in a block form by reacting SiO2 with C at a high temperature of about 1,900-2,200C.
Accordingly, it is necessary in order to produce a silicon carbide molding having a particularly de~ined shape lQ that the above described hlock is pulverized and a binder is added to the pulverized silicon carbide and the resultin~ mixture : is molded and then si`.ntered.
However, it has been impossible to produce fibrous silicon carbide moldings through the above described process.
United States Patent 3,433,725 discloses: a method for producing : -silicon carbide fibers by reacting carbon fibers with SiC14 gas which is being supplied, ~ithin a temperature range of 800- :
1,20QC. United $tates Patent 3,403,008 also teaches production of silicon carbide fibers and moldings, in which viscose rayon tows are i:mmersed in liquid silicon tetrachloride to form rayon silicate and then the formed rayon silicate i~s baked up to 1,Q00-2,000.C at a rate of 5QC~hr. under vacuum of 1-10 mmHg in a tubular oven to form silicon carbide ~i.bers.. Ho~ever, in th.e silicon c~rhide fibers produced in the above. descri.bed process, cry-stal grains of $iC constituti`ng the fibers are lar~e, the strength is 1QWt the di`ameter o~ the fi~ers i.s relatively large, the production cost i.s high and the application is considerably limited.

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The present invention provides a method for producing a silicon carbide fiber having a hi.gh tensile strength which comprises (1) preparing a spinning solution from at least one organosilicon high molecular weight compound having a softening point of higher than 50C, in which silicon and carbon are the main skeleton components, and spinning said spinning solution into a fiber,

(2) preliminarily heating the spun fiber at a temper-ature of 350-800C under vacuum or a non-oxidizing atmosphere ~ to volatilize low molecular weight compound contained therein, and

(3) baking the thus trea~ed fi~er at a temperature of 800-2,000C under vacuum or at least one non-oxidizing ; atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas, to form said silicon car~ide fiber.
In particular, according to the present invention, a silicon carbide fiber having a high strength.can be produced by the following steps:
(1l a step for producing or~anosilicon high. molecular weight compounds, in which silicon and car~on are the main skeleton components, ~y polycondensation reaction through at least one already- weIl known process of addition of a poly-condensation catalyst, irradiation and heating, C2~ a step for obtainlng organosil$~cQn hi.gh molecular weight compounds, of which a softeni.ng poi.nt is. higher than 5~C, C31 a 5*ep for producing a spinnIng solution from said organic high molecular ~eight compound ~nd spinning said , 7C~2~

solution into fiber, (~) a step for preliminarily heating the spun fiber under vacuum or a non-oxidizing atmosphere, and (5) baking the thus treated fiber at a high temper-ature under vacuum or atmosphere of inert gas, CO gas or hydrogen gas to form SiC fibers.
The present invention also provides a method for producing a silicon carbide fiber having a high tensile strength which comprises:
(A) subjecting at least one organosilicon compound selected from (1) a compound having only Si-C bond, (2) a compound having Si-H bond in addition to Si-C bond, (3) a compound having Si-X bond, X being halogen, (4) a compound having Si-N bond, (5) a compound having Si-oR bond (R=alkyl or aryl), (6) a compound ha~ing Si-OH bond, (7) a compound having Si-Si bond, (8) a compound having Si-O-Si bond, (.9~ an ester of organosilicon compound and (10) a peroxide of organosilicon compound, to polycondensation to produce an organosilicon high molecular weight compound, in which silicon and carbon are the main skeleton components, (B) reducing the content of low molecular weight compound mixed together with said high molecular welght compound by treating the mixture with at least one treatment selected from the group o~ treatments consisting of contacting said mixture w-ith a suitable solvent, a~ing ~aid mixture at a temper-ature of 5Q-700C and distilling said mixture at a temperature of 100-500C, to produce an organosilicon hi.gh. molecular weight compound having a soften~ng point of higher th.an 50C, 7~3~6 (C) preparing a spinning solution from said obtained organosilicon high molecular weight compound and spinning said spinning solution into a fiber, (D) preliminarily heating the spun fiber at a temper-ature of 350-800C under vacuum to volatilize remaining low molecular weight compounds, and (E) baking the thus treated fiber at a temperature of 800-2,000C under vacuum or at least one non-oxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas.
The present invention further provides a method for producing a silicon carbide fiber having a high tensile strength which comprises:
(A) subjecting at least one organosilicon compound selected from (1) a compound having only Si-C bond, (2) a compound having Si-H bond in additlon to ~i-C bond, (3) a compound having Si-X bond, X being halogen, (4~ a compound having Si-N bond, (5) a compound having Si-OR bona (.R=al~yl or aryl), (6) a compound having Si-OH bond, (7~ a compound having Si-Si bond, (8) a compouna having Si-O-Si bond, (.9~ an ester of organosilicon compound and ~10~ a peroxide of organosilicon compound, to polycondensation to produce an organosilicon high molecular weight compound, in which silicon and carbon are the :~
main skeleton components, ~ reducing the content of lo~ molecular weight compound mixed together with.said high. molecular weight compound by treating the mixture ~ith at least one treatment selected from the group of treatments consis:ting of contacting said , ,t,~j~X~

mixture with a suitable solvent, aging said mixture at a temper-ature of 50-700C and distilling said mixture at a temperature of 100-500C, to produce an organosilicon high molecular weight compound having a softening point of higher than 50C, (C) preparing a spinning solution from said obtained organosilicon high molecular weight compound and spinning said spinning solution into a fiber, (D) heating the spun fiber at a temperature of 50-400C under an oxidizing environment to form an oxide layer on 10 the fiber surface, (E) preliminarily heating the spun fiber at a temperature of 350-800C under a non-oxidizing atmosphere to volatilize remaining low molecular weight compound, and (F) baking the thus treated fiber at a temperature of 800-2,000C under vacuum or at least one non-oxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas.
According to another aspect of the present inventlon there is provided continuous silicon carbide fibers having 20 tensile strength of 200-800 Kg/mm2, Young's modulus of 10-40 ton/mm2 and resistant to corrosion and oxidation and showing no decrease in the tensile strength and Young's modulus at a temperature of 800C to 1,400C, which are composed of ultra-fine grain silicon carbide having an average grain size of less than 0.1 ~.
The organos~l~con compounds of th.e s~tarting materials for producing the organosilicon hi;gh mole.cul~r ~eight compounds, in whi.ch silicon and carbon are th.e main skele.ton components, -"'7''3~

and which are to be used for the spinning can be classified into the following groups (1)(10).
(1) Compounds having only Si-C bond:
Silahydrocarbons, such as R4Si, R3Si(R'SiR2)nR'SiR3, carbonfunctional derivatives thereof belong to this group.
For example, (CH3)4Si, (CH2=CH)4Si, (CH3)3SiC = CSi(CH3)3, 2 5 ( 2)4' (C2H5)3SicH2cH2cl~ (C6H5)3siC02 R\ / CH2 R R\ / CH2 R CH2 R , R CH2 2 <~2 Cl ~ CH ~ Cl, ( 3)3Si ~ Si(CH3)3, 3~æ~

3) 3 2 ~-CH2Si (CH3) 3r CH =CH-si-e~3-si-cH=cl~2~

H2 ( 3) 2 f I s i, H2C\ ~CH2 ,(CH3) 2Si ~ Si (CH3) 2 Si CH2 R R

(2) Compounds having Si-H bond in addition to Si-C bond:
Mono-, di-, and triorganosilanes belong to this group.
For exa~ple, (C2H5) 2SiH2, (CH2) 5siH2 ' (CH3) 3SiCH2Si (CH3) 2H, ClCH2SiH3, H--Si ~3 si--H,EI--Si--~--Si-CH=C

si~ si, 21 1 2 1 1i / CH3 (CH3)2Sl Si(CH3~2, (CH3)2si / \ H

(3) Compounds having Si-X bond; X being halogen:
Organohalogensilanes.
For example, CH2=CHSiF3~ C2H5SiHC12, (CH3)2(ClCH2)Si5i(CH3)2Cl, (C6H5)3SiBr~

Cl-Si-CH -C~ -Si-Cl, 1 2 2 ~ C125i SiC12 R R \ C-C \

C12si\ SiC12

(4) Compounds having 5i-N bond:
Silylamines belong to this group.
For example, R H~
/~ \=,/ CH=CH2 Si ~ (C~3)2N-SIi-N(C~3)2 R NH ~ CH3

(5) Si-oR organoalkoxy (or aroxy) silanes:
For example, (CH3)2Si(OC2H5)2, C2H5siC12(0C2H5)~
p-ClC6H40Si(CH3)3, / ~

` R O

~,

(6) Compounds having Si-OH bond:
Organosilanes.
For example, (C2H5)3SiOH, CCH3)2Si~OH~2~ C6~5Si(OH)3, (HO)(CH3~2SiCH2Si(CH3)2 ~ tOH~, HO--5i~Si--OH
R R

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(7) Compounds having Si-Si bond:
For example, (CH3)3SiSi(CH3~2Cl, (CH3)3SiSi(CH3)3, (c6H5)3sisi(c6Hs)2si(c6H5)2 / CH2 Si(CH3)2 CjH2 Si(.CH3~2 / CH2 \
CH2 / Si(CH3)2 , (- 3~2S Si(.CH3)2 CH2 \ / Si(CH3)2, (CH3~2 Si(CH3i2 CH2 \ Si~ 3 / Si\CH3~2 S i ~ /
(CH3~2 Si (CH.312 CH2 ~.CH3~2 CH2 Si(.CH3~2 CH2 Si \

CH2 / Si(.CH3~2 , 2 Si Si(CH3)3 Si (CH3~2 (- 3)2 (81 Co~pound~ h.~Ying ~I-O-Si ~ond:
Organo~Uox~nes.
For example, 7'~

(CH3) 3SiOSi (CH3) 3, HO(CH3) 2SiOSi (CH3) 20H, C12 (CH3) SioSi (CH3) ClOSi (CH3) C12, [ (C6H5) 2Sio] 4, CH2=c(cH3)co2cH2si ' (C~3)2cH202 ( 3 2 R2Si-CH2-SiR2 2 1 2 Sl iR2 2 i CH2 SiR2 , R2Si--O--SiR2 CH2 o R2 S i \ S i R2 R2 S l Sl i R2 O O , O O
\ / \ /
SiR2 SiR2 R2 S i--CH2--S i R2 H2 f-- C 2 - .
O O
R2Si-- O--SiR2 , o (9) Esters of organosilicon compounds-Esters formed from silanols and acids.
(:CH3~2Si(OCoCH3)2 a) Peroxides of organosilicon compounds:
(CH3~3SiOOC ~ (CH3) 3, (CH31 3sioosi (.CH3) 3 In the aboye ~ormulae, R sho~$ alkyl or ary~l groups.

From these starting mater.ials are produced organo-silicon high molecular weight compounds, in which silicon and carbon are the main skeleton components. For example, compounds having the following molecular structures are produced.

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(a) -Si - (C)n - Si - O-(b) -Si - O - (C)n - O-(c) -Si - (C)n-(d) The compounds having the above described skeleton components (a~ - (c) as at least one partial structure in linear, ring and three dimensional structures or mixtures of the compounds having the above described skeleton components (a~ - (c).
The compounds having the above descri~ed molecular structure are, for example as follo~s.

(.al -Si - CC]n - Si - O-.
n - 1, poly(:silmethylenesiloxanel, n - 2, poly(~silethylenesiloxanel, n = 6, poly(silphenylenesiloxane), (bl -Si - O - (:C)n - O-n ~ 1, poly(methyleneoxy~iloxanel t , J\7~2I~

n = 2, poly(ethyleneoxysiloxane), n = 6, poly(phenyleneoxysiloxane), n = 12, poly(diphenyleneoxysiloxane) (c) - Si - (C)n -n = 1, polysilmethylene, n = 2, polysilethylene, n = 3, polysiltrimethylene, n = 6, polysilphenylene, n = 12, polysi.ldiph.enylene (d) The compounds having the above described skeleton components as at least one partial structure in linear, ring and three dimensional structures or mixtures of the compounds having the above described skeleton components (a~ - (.c).
The production of the organosilicon high molecular weight compounds in which silicon and carbon are the main skeleton components from the starting materials of the organosilicon compounds belonging to the above described groups (1~ - (10~ can be effected by polycondensation attained ~y suhjecting the organosilicon compounds belonging to the. a~ove de~cri.bed groups ~ (10~ to at least one of irradiation, heati.ng and addition of a catalyst for the pol~condensation.
For example, some ~ell known reaction formulae for obtaining the above described or~ano.silicQn h~gh molecular weight compounds from the above described starting materi.als belonging ~ 7~

to the groups (1) - ~10) through at least one of addition of the catalyst, irradiation and heating, are exemplified as follows.

(1) CH3 / CH2 /CH3r fEI3 Si SiKOH~ -Si-CH -CH3/ CH / CH CH3 n \ / \ fH3 Si CH2 Heating> -- li CH2CH2CH2 CH3 CH2 _CH3 _ n (3) CH ~ 3i-H+HC-CH H2PtC16 ~i~fi- (CH2)2 CH3 CH3 H3 CH3 ~ n . _ 4) CIH3 f~3 (1) H20 CIH3 CIH3 -Cl--Si--CH2CH2--Si-Cl ~ l-f i-CH2CH2~ O~ _ H3 CH3 l _CH3 CH3 - n : _ / \ ~ CH Heating) l~ O li O ~
CH3 NHPh CH3 n Si + HO ~ o f. ~ ~ n - ' : : ' `

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(7)CH~--Sl-OH ~ ~3 CH3

(8)(CH3) 27i-CH2 1 i (CH3) 2 I f O O H2S04 -- C 2 i O
~ l l (CH3) 2Si-CH2-Si (CH3) 2 _CH3 CH3 n

(9)CH2 H / S (CH hv ~ Polymer (C 3)2S \ ~ ~

(CH3~2Si-Si(CH3)2

(10) 1 3 1 3 Cl Cl Cl - Si - Si - Cl Heating ~ -Si-CH2-Si-CH2-3 3 3 3 n A more detailed explanation will be made with respect to the thermal polycondensation reaction. At least one organo-silicon compound selected from the ahove descri~ed groups (1~ -(10) is polymerized within a temperature range of 200-1,500C
under vacuum, an inert gas, hydrogen gas, C0 gas, C02 gas, a hydrocarbcn gas or an organosilicon compound gas, if necessary, under pressure to produce the organosilicon high molecular weight compounds in ~hi:ch silicon and carbon are the main skeleton components.
The reason why the above described reaction should be effected within the temperature range of 2Qa-1,5Q0C is "~

as follows. When the temperature is lower than 200C, the synthesis reaction does not sat.isfactorily proceed, while when the temperature is higher than 1,500C, the product becomes SiC
compound and it is impossible to form fibers in the succeeding step, so that the temperature range must be 200 to 1,500C
and best results can be obtained within the temperature range of 300-1,200C.
In the above described synthesis reaction, a radical initiator of less than 10% may be ad~ed to the above described starting material. The above described radical initiators are, for example, benzoyl peroxide, di-tert.-butyl peroxyoxalate, di-tert.-butyl peroxide, azoisobutyronitrile and the like. The above described synthesis reaction does not al~ays need these radical initiators, but their use permits a lo~eri.ng of the temperature for starting the reaction by the succeeding heating or the obtaining of a reaction product having an increased average molecular weight.
When oxygen i.s present upon heating in the above described synthesis reaction, the radi.cal polycondensation reaction does not occur due to oxygen or even i.f said reaction occurs, the reaction stop~ in the cours:e, s.o that th.e poly-condensation reacti.on must be effected b.y heating under a vacuum or at least one environment selected from the group consisting of an inert, gas, hydrogen gas, CO yas, CO2 gas, a hydrocarbon gas, and an organosilicon comp~und gas..
In the thermal polycondensation re.action, a pressure is generated, so that it is not always. nece.ssary to apply particularly a pres.sure but ~hen a pressure is: appli~d, such `~ J

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pressure may be applied b~ means of at leas-t one of an inert gas, hydrogen gas, CO gas, CO~ gas, a hydrocarbon gas and an organosilicon compound gas.
A mechanism in which the organosilicon high molecular weight compounds in which silicon and carbon are main skeleton components, are produced by the above described synthesis reactionr will be explained hereinafter, for example, in the case of synthesis from methylchlorosilane.
Methyl group of methylchlorosilane is decomposed into a methyl free radical and silyl free radical by the heating.
The methyl free radical takes out hydrogen from methyl group bonded to silicon to form carbon free radical and methane gas is formed. On the other hand, hydrogen free radical is formed from methyl group bonded to silicon and at the s.ame time carbon free . radical is also formed. Presumably, the silyl free radical and the carbon free radical formed as. described above hond to form silicon-carbon bond and the organosilicon high molecular ~- weight compounds can be formed based on the above described reaction and the above described hydrogen free radical becomes hydrogen gas.
In draw~ngs ~hi.ch illustrate th.e present inyention:
Figure 1 is a di~gram of an e~odiment of apparatus for producing the organos~licon high. molecular ~ei.ght compounds;
Figure 2 shows a rel~ti.on of th.e. xesi.dual weight to the heating temperature.~hen the high molecular ~elght compounds containing lo~ molecular ~ei.ght compc.unds are h.eated;
Figure 3 sh.ows a ~elation of the xesi.dual ~eight to the heating temperature ~hen the hi.gh molecular ~ei.gh.t com~ounds ~ ~7C~6 containing low molecular weight compounds are heated under vacuum;
Figure 4 shows X-ray dif~raction patterns when the silicon high molecular weight compound fibers are heated at various temperatures;
Figure 5 shows a relation of the tensile strength to the heating temperature when the spun fibers according to the present invention are heated from 700C to 2,000C;
Figure 6 shows a relation of the tensile strength to the baking temperature when the spun fibers are baked under no tension;
Figure 7 shows a relation o$ the tensile ~trength to the baking temperature when the spun fibers are baked under a tension;
Figure 8 shows a relation of the tensile s.trength to the baking temperature when the spun fibers are baked while applying ultrasonic wave;
Figure 9 shows a relation of the tensi,le strength to the baking temperature when the spun fibers are baked ~hile applying a tension together with ultrasonic ~ave;
Figures lQ and 11 show electron dlffraction photo-graphs of the silicon carbide fibers ob~tained ~y baking under a tension or no tension, respectively;
Fi,gure 12 shows: relati,ons of the tensile strength and the Young's modulus to the diameter of the si,li.con carbide fiber according to the present i,nventlon; ~ :.
Figure 13 i,s a diagram sho~i,ng variations of the ~ `
tensile strength and tne Youngls modulus based on temperature .
.

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:` ' ' ` ~

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of the silicon carbide fiber according to the present invention;
Figure 14 shows an X-ray diffraction pattern of the silicon carbide fiber baked at 1,500C;
Figures 15-17 are X-ray diffraction photographs of Pin hole method of the silicon caxbide fiber of the present invention;
Figure 18 is a diagram showing relations of the average grain size of SiC crystal and the tensile strength of the silicon carbide fiber of the present invention to the baking temperature;
Figure 19 is a diagram showing a relation of the tensile strength to the average grain size of SiC crystal o~
the silicon carblde fiber of the present invention;
Figures 20-23 sho~ photographs obtained by observing SiC crystal in the silicon carbide fiber of the present invention through a super h.igh voltage electron microscope; and :Figure 24 is a diagram of an em~odiment of apparatus for continuously effecting the method of the present invention.
An embodiment of apparatus for the above described synthesis reaction is a stationary autocla~e. I:n this case, ;the heating temperature i5 preferred to be 30Q-5~0C. Another embodiment for the above described synthes.is reacti.on is shown in Figure 1. In th~:s dra~ing, from a valve 1, the starting material is $ed ~nto a h.e~ting reaction column 2, wh.erein the heating is effected at a temperature of 3Q0-1,500C, prefera~ly 500-1,20QC, a part of th.e organosili.con high molecular ~eight compound for producin~ sili.con carbide f~bers of the present i.nvent;on among the reaction pxoducts i~ discharged from the ~. , --19-- :

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reaction column through a valve 3 and low molecular weight compounds formed in the heating reaction column 2 are fed into a separating colu~n 5 through a valve 4 and in said column 5 distillation and separation are effected and the formed gas is discharged from the column through a valve 6 and a high molecular weight compound is taken out from the column through a valve 7.
The low molecular weight com~ounds separated in the tower 5 are circulated into the heating reaction column 2 through a valve 8.
The reason why the organos.ilicon high molecular weight compound in which silicon and carbon are the main skeleton , components, are used for the starting material of spinning in the method of the present invention is that if ~ilicon or carbon is present as a side chain, this side-element is easily separated and volatilized b~ heating, while the skeleton consisting of silicon and carbon components i.s not easily decomposed and volatilized by the heating and sili.con and carbon bond at a high temperature to form silicon carbi.de.
The organosilicon high molecular weight compounds produced by the above described reactions, in wh.i.ch silicon and carbon are the main skeleton components, contain low molecular weight compounds soluble in an alcohol, ~uc~ as methyl alcohol, !:
ethyl alcohol, and the li.ke or acetone and tne ll.ke and the softening point o~ the resulting organic sili.cone high molecular weight compounds depends upon the: content o~ the lo~ molecular wei.ght compounds and there are the cases whRre the softening po~nt becomes hi`~her than 5QC and sai`d point ~,eco.~es lo~er than 5Q~C. As menti`,oned h.ereinaftex, tne s.o~teni~ng Point mus~t be hi.~her than 5Q.C for t~e s~ta,rti`ng materlal o~ sp~nni,ng.

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The low mulecular weight compounds soluble in the solvent are mainly -the low molecular weight compounds having an average molecular weight o~ 200-800, and when such compounds are present in a large amount, the softening point of the organosilicon high molecular weight compounds is less than 50C
and in the step of preliminary heating of the spun fibers under vacuum, the above described low molecular weight compounds melt and stick together with intermediate compounds having a slightly larger molecular weight than the low molecular weight compounds and further melt and bond with high molecular weight compounds having a larger molecular weight than the above intermediate compounds, whereby the shape of the spun fiber is lost. In the fiber obtained by spinning organosilicon high molecular weight compounds having a softeni.ng point of higher than 50C, wherein the content of the lo~ molecular weight compound is small, the major portion of the above described low molecular weight compounds volatilizes upon the prellminary heating under vacuum and the shape of fiber can be maintained.
In addition, when the spun fiber are su~jected to heating at a low temperature under an oxidizing atmosphere for formation of an oxide layer as explained hereinafter, the heating must be effected at a temperature of higher than 50C. The fibers formed from the organosilicon high molecular weight compounds having a softening point lower than 50C will melt and stick with one another, ~hen the oxIdized layer is formed, and the shape of the fibe~s will thus be lost.
In general, as: the molecular ~e.ight of an organo-silicon compound increase~, the boi.li`ng point hecomes h.igher '7~ 6 and even if heatin~ is effectecl under vacuum, the volatilizatlon becomes difficult. For example, the boiling point of Si6C14H36 (molecular weight: 372) under a reduced pressure of 1 mmHg is 150-153C, while the boiling point of SigC27H74 (molecular weight: 650) under a reduced pressure of 1 mmHg is 245-300C
and even if the organosilicon compound havir.g a larger molecular weight than that of SigC27H74 is heated under vacuum, such a compound does not substantially volatilize. For example, a solid organosilicon high molecular weight compound obtained by heating dodecamethylcyclohexasilane at 400C for 48 hours under argon atmosphere in an autoclave is diss-olved in hexane and the resulting solution is mixed with acetone and the product which is not dissolved in acetone, is produced. ~ relation of the heating temperature to the residual we~ght when the resulting product is heated under vacuum (:1 x 10 3 mmH.g~, is shown in Figure 2. As seen from Figure 2 the ~eight decrease is not substantially o~served at the heating temperature from room temperature to about 500C. The residual ~eight when the above described high molecular wei:ght compound containing a low molecular weight compound soluble in acetone is. heated under vacuum, is shown ~n Figure 3. As seen from Fi.gure 3, the weight decrease becomes large above 200C and at a temperature of about 5Q0C the weight decreas.e becomes e~en larger. The reason why the weigh.t decrease of th.e high.molecular wei~ght co~pound containing the low molecular weight compound soluhle i.n acetone becomes larger ab.ove 2Q0C, is based on ~he fact that the lo~
molecular ~eigh.t compound contai.ned in the high molecular wei.gh.t compound volati`lizes.

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It has been found that when a larger amount of low molecular weight compoun~ is contained and the softening point of the organic silicone high molecular weight compound is lower than 50C, the content can be decreased by the following means.
In the first means, the organosilicon high molecular weight compound in which silicon and carbon are the main skeleton components, is treated with a solvent of alcohols, such as methyl alcohol and ethyl alcohol or acetone to extract the low molecular weight compounds and to obtain the high molecular weight compounds having a softening point of higher than 50C.
In the production of spinning solution of the above described high molecular weight compound, in order to improve the softening point and viscosity it is possible to add the above described extracted low molecular w.eight compound to the high molecular weight compound, which is not extracted and remains, in such a range that the softening point does not become lower than 50C.
In the second means, the organosi.licon high molecular weight compound in which silicon and carbon are the main skeleton components, is sufficiently aged under vacuum or an atmosphere of air, oxygen, an inert gas, CO gas, ammonia gas, C02 gas, a hydrocarbon gas or an organosili.con compound gas, if necessary ~:
under pressure at a temperature range of 5Q-70~C to polymerize the low molecular weight compounds in the organosili.con high molecular wei`ght compound and to form the ~igh molecular ~eight compound having a softeni.ng poi.nt of h.i.gh.ex th.an sac. The atm.osphere for ef~ecting the aging is, for example, as indicated above vacuum, air, oxygen, an inert gas:, h~dxogen gas, CO gas, .. -23-'7~

ammonia gas, CO2 gas, a hydrocarbon gas or an organosilicon compound gas and, if necessary the agi.ng can be effected under pressure. When air, oxygen or ammonia gas is used, oxygen or nitrogen atom has cross-linking function, by which the low molecular weight compound is polymerized, so that these gases can be advantageously used. The above described various gas atmospheres are not always limited to one kind of gas and a mixed atmosphere of two or more gases may be used but in this case it is not desirable to mix gases~ which react with each other.
The above described aging may be carried out under vacuum, atmospheric pressure or pressure; under vacuum an evaporation of the low molecular weight compound is promoted while under pressure the low molecular weight compound having a molecular weight of less than 1,00.0 contained in the organo-silicon high molecular weight compound is not volatilized but is polymerized to form the high. molecular wei.ght compound, so that the yield of production is impro~ed.
When the temperature for aging the aboye described organosilicon hlgh molecular weight compound is. lo~er than 50C, the pol~merizati.on reaction is extremely 510w and such a temper-ature is not economic. On the other hand, if s:ald temperature exceeds 70ac, the above described h.igh molecular ~eight compound is ~lolently decomposed, 50 that the. aging tempexature must be withln a range of 5a-7~0c. The preferred tempexature range for agi`ng vari`es depending upon the kind of atmosphere, the kind of startlng material, the a~erage ~oleculax ~ei~ht o~
starting matexlal and the: like. Howe~er, under an a~r, oxygen 7~

or ammonia gas atmosphere, the desirable result can be obtained at a temperature of 80-300C while under an inert gas, hydroyen gas, CO gas, CO2 gas, a hydrocarbon gas, or an organosilicon compound gas atmosphere, the preferable result can be obtained at a temperature of 120-450C.
The required time for said aging relates to the aging temperature and when the temperature is high, the required time may be short; at a high temperature, decomposition and an excessive cross-linking reaction occur so that when the heatlng temperature is high, it is necessary to effect the heating for a short time. Ho~-ever, when the heating temperature is low, the heating time must be long. A better result can be ob.tained, when the heating i,s effected at a lo~ temperature for a long time and in general, the required time of 0.5-lQ0 hours is preferred under the a~ove described preferred temperature.
The a~ove described aging vari:es the molecular weight of the organosili.con hi.gh -molecular weight compoun~ and can make the spinning easy and the strength of the spun fi.lament can be improved.
2u In the thi:rd means, the low molecular wei.ght compound can be removed ~y dist~llatlon. This distillation includes distillati.on under atmospheri.c press~ure where m the distillation temperature can be high. H.o~e~er, in the di$ti11ation under vacuum the molecular weight compound can be. removed at a lower temperature than that ~n the dist~llation under atmospheric pres.s,ure. The distillation temperature is preferred to be lQû,-500C and when the distillation is effected at a temperature of lower than laOC, th.e low molecular wei.ght compound cannot : -25-be satisfactorily removed, while when the temperature is higher than 500C, the distillation temperature is too high and the polycondensation reaction proceeds to such an extent that the obtained organosilicon high molecular weight compound cannot be spun into filament.
In the present invention, when the organosilicon high molecular weight compounds obtained from the above described various organosilicon compounds by the well known polycondensa-tion process, have a softening point of higher than 50C, such organosilicon high molecular weight compounds can be directly used as the spinning material. Such organo~ilicon high molecular weight compounds are dissolved in a sol~ent or melted by heating to form a spinning solution, which is spun into a fiber. The resulting fibers are preliminarily heated at a temperature of 350 to 800C under vacuum and the preliminarily heated fibers are baked at a temperature of 80Q-2,000C under at least one non-oxidizing atmospheres to produce si.li.con carbide fibers having high strength. according to the present invention.
The organos~l~con high molecular ~eight compounds having a low content of the a~ove described molecular weight compounds are dissol~ed in a solvent capa~le of dLssol~ing the organosilicon high. molecular weigh.t compounds:, ~or ex~mple, ~enzene, toluene, xy~lene, ethylbenzene, styrene, cumene, pentane, hexane, octane, cyclopentadiene, cyclohexane, cyclohexene, methylene chIoride, chIoroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-d~chloroethane, meth.ylchloroform, 1,1,2-tri.chloroethane, hexach.Ioroethane, chlorobenzene, dichloro-henzene, ethyl ether, dioxane, tetrah.ydrofuran, methyl acetate, , , 7~i6 ethyl acetate, acetonitrile, carbon disulfide and the like, to produce a spinning solution, which is filtered to remove harmful substances in the spinning, such as macrogel, impurities and the like, and then the spinning solution is spun in a dry process by means of a spinning apparatus for synthetic fibers generally used and the spun fibers are subjected to a large draft to obtain fine fiber.
In this case, when the atmosphere in the spinning tube of the spinning apparatus is a mixed atmosphere of the saturated vapor of at least one of the above de~cribed solvents with air or an inert gas, heated air, a heated inert gas or steam, the solidification of spun fibers in the spinning tube can ~e controlled.
In additi.on to the production of the spinning solutlon by using the above des:cribed solvents, the above described organosilicon high molecular weight compounds having a softening point of higher than 50C can be heated and melted and the melt is filtered to remove the harmful subs:tar:ces in the spinning, ~ such as macrogel, impurities and the like and the thus treated 20 melt is spun through the a~ove described s:pinning apparatus. The temperature of the melt in the spinni.ng varies depending upon the softening point of the organosilicon high molecular weight compounds., but the temperature range of 5Q-4QClC i5 adYantageoUS.
In the above descri~ed spinn~ng apparatus, ~f neces$ary, there is provided ~i.th. a spinning tube and in the spinning tube in wh.ich. atmosphere i.s air, an inert gas., a h.eated air, a heated inert gas or steam, a large draft, applied to obtai.n fine fibers.
The spinning rate in s~id melt spinning vari.es depenaing upon an avera~e molecular we.ight, a molecular weight distribution and the molecular structure of the organosilicon high molecular weight compound, but is preferred to be 50-5,000 m/min.
The spun fibers are sub]ected to the preliminary heating at a temperature of 350-800C under vacuum. The object of the preliminary heating is as follows. The spun fibers contain a small amount of the low molecular weight compounds.
The low molecular weight compounds formed in the polycondensation reaction and by the decomposition reaction owing to heating can act as a solvent which dissolves the spun fibers and if a baking at a high temperature as explained hereinafter is carried out in such a way that these low molecular weight compounds are present, the spun fibers are dissolved and the shape of the fibers cannot be kept. Accordingly, these lo~ molecular weight : compounds should be evaporated by the preliminary h.eating.
The time of the preliminary heating should be enough to fully remove these low molecular weight compounds.
In the above descr;~ed preli~inary heati.ng under vacuum, evaporation of the easi.ly volatile components becomes violent a~ove 5Q0.C and th~ evaporation be.comes ~eak at about 700C as seen from Fi`gure 2. ~hen th.e baking at a high temper-ature is carried out after the low molecular ~ei.~h.t compounds have been evaporated and removed by the prelimi.naxy heating, the reaction for forming ~-ilicon carb.ide favourably p~oceeds and the silicon car~ide f~ers h.aving a h.igh:s;txength can be obtained.
In the b.aking at a high temperature, th.e. original formation of silicon carbide i.s obs:erYe.d from ab.out 8aQC by ~ ~ 3J~

X-r~y diffraction as shown in Eigure 4. When the temperature is further raiscd, tlle crystal of sil.icon carbide grows.
However, when the temperature exceeds 2,000C, silicon carbide decomposes, so that the temperature in the baking at a high temperature must be 800-2,000C.
In the practice of the pxesent invention, baking at a high temperature may be effected under various atmospheres.
After the preliminary heating up to about 800C under vacuum in order to evaporate the easily volati.le components, the baking effected at a temperature of 800-2,000C under an inert gas, CO gas or hydrogen gas atmosphere can provide silicon carbide fibers having a high strength.
The tensile strength when the si.licon carbide fibers are heated at a temperature of 700-2,aQaC is shown in Figure 5 and the heating at a temperature of ltQOa-1,5QQC provides the maximum tensile strength. The result af X-ray diffraction shows that the state of amorphous, semi-amorphous, or ultxa fine grain silicon carbi.de is maintained up to 1,50QC and ~hen the temperature exceeds 1,50QC, silicon c~rbi.de crys.tal grows, so that the strength decreas~es. Accordin~l~, hi~h ten~ile strength can be obtai.ned ~n the: for~ of the amorphous, s.emi.-amorphous or ultra fine grain s:ilicon car~ide.
Furthermore, it has been found th~t ~hen the spun fibers are h.eated under an o~dizi.ng atmosphere at a lo~ temper-ature of 50-5aQaC, p~rticularly, 15Q-3QQC fox seyeral mi.nutes to lQ houxs pr~or to the: preIiminary-heatin~, a thin ~xi.de layer is formed on the surface of the fibexs and the fihers are not me.lted at the succeeding preI~inary he~ting and the stickiness 3~2~

of mutual fibers can be prevented. If such a heating treatment at a lo~ temperature under an oxi.dizing atmosphere is carried out, it is not always necessary to effect the succeeding preliminary h~ating treatment under vacuum and the preliminary heating can be carried out under a non-oxidizing atmosphere, such as an inert gas, CO gas, hydrogen gas, a hydrocarbon gas or an organosilicon compound gas.
The atmosphere in the above described heating at a low temperature is preferred to be oxidizing gaseous atmosphere selected from the group consisting of air, ozone, oxygen, chlorine gas and bromine gas. If the heating under the above described gaseous atmosphere is carried out at a temperature of lower than 50C, said oxide layer cannot ~e formed on the fibers, while at a temperature of higher than 40ac the oxida-tion of the fibers is too great, so th.at the temperature range of 50-400C is preferable. The time for such. a heating step depends upon the temperature and is from several minutes to 10 hours.
As the atmosphere for this heating step an aqueous solution of KMnO4, K2Cr2O7, H2O2 and the oth.er inorganic peroxides can be used and in this case, the temperature is preferred to ~e from room temperature to lQ0C and the time is preferred to be Q.5 to 10 hours.
When a tensi.on is applied in th.e a~ove described heating under an oxi.dizing atmosphexe, a satisactoxy amount of tens.ion i.s such an amount that the ~ave-foxmed shri.nkage of the spun fi~ers: can be preyented ~ut In order to practically effect th.e heating at a lo~ tempexature unde.r a tensïQn, a tension of 7~

0.001-5 Kg/mm provides a good result. If a tension of less than 0.001 Kg/mm2 is applied, it is impossible to maintain such a tension that the fiber does not loosen, while if a tension of more than 5 Kg/mm2 is applied, the tension is too large and the fibers are broken, so that the tension is preferred to be 0.001-5 Kg/mm2.
When the low molecular welght compounds are evaporated by the above described preliminary heating, the fibers shrink and bend but this bending can be prevented by applying a tension during the preliminary heating. In this case, the tension may be in such an amount that even if the fibers shrink in the above described preliminary heating, the formation of ~ave-shaped bending can be prevented and a good result can be obtained within a range of 0.001 to 20 Kg/mm . If a tension of less than 0.001 Kg/mm2 is applied to the filaments., it is impossible to prevent the loosening of the fibers, wh.ile wh.en a tension of more than 20 Kg/mm2 is applied, the tensi.on is too large and the fibers are broken, so that the tension appli.ed to the fibers -~
during the preliminary heating ls preferred to be O.Q01-20 Kg/mm .
It has ~een found that if a tensi.on of 0~001 to 100 Kg/mm is applied to the fibers in th.e above. described baking at a high temperature of 80Q-2,000C, the ori.entati.on of silicon carbide crystal in the fibers is improved and that the strength of th.e fibers ~aked at a temperature of hi.gher than 1,5aOC
under a tensi.on i.s appreci.abIy higher th.an th.at of the fibers baked under no tension load. Wh.en th.e tensi.on i.s. le$s than O.Q01 Kg~mm2, the effect of tension i.5 not o~$eryed, ~hile even '7~

if a tension of more than 100 K~/mm2 is applied, the effect does not vary and wllen the bakin~ is effected under a tension of 0.01~50 Kg/mm2, the stren~th becomes maximum. When the baking temperature is low, e.g. 800C, the tension to be applied to the fibers is low, for example, 0.1 Kg/mm2. When the baking temperature is raised and at the same time the tension is gradually increased, for example, when the baking is completed under a tension of 30 Kg/mm2, the orientation of silicon carbide crystal is improved and silicon carbide fibers having a high strength can be obtained.
In the method of the present invention, the stress to be applied during baking is obtained by tension, twisting or bending.
With respect to silicon carbide fibers obtained by baking the fibers at a high temperature under no stress and obtained by baking the fibers at a high temperature under a stress, the tensile strengths are compared hereinafter.
Fibers having a diameter of about 10 ~, after being .
subjected to the preliminary heatlng, were baked under a tension of 5 Kg/mm2 and other fibers having the same diameter, after being subjected to the preliminary heating, were baked under no tension. The diameter of these silicon carbide fibers does not vary. However, the tensile strengtn of the silicon carbide fibers baked under no tension suddenly decreases from (a baking temperature of~ ab.out 1,500C as shown in Figure 6, while the tensile strength reduction Gf the s~illcon carbide fi~ers baked under a tens:i.on of 5 Kg~mm is small even at a temperature of hi.gher than 1,50.0C as shown in Figure 7 and si`.li.con carbide fibers having a high strength can thus be obtained.
When the baking at a high temperature is effected while applying ultrasonic wa.ve to the fibers, the strength of the obtained silicon carbide fibers is improved. The ultrasonic wave having a frequency of 10 KHz to 30 MHz can be advantageously used. If an ultrasonic wave of less than 10 KHz is used, the ` object of improving the strength cannot be attained, while if an ultrasonic wave of more than 30 mega~lz is used, the frequency is too large to improve the strength. The preferred frequency of the ultrasonic wave to be applied in the present invention is 20 KHz to 5 MHz. The strength of the silicon carbide fibers baked at a temperature of 800-2,000C ~hile applying ultrasonic wave by means of an ultrasonic generator having an output of 100 W at a frequency of 500 KHz is sho~n in Figure 8 and as seen from Figure 8 the silicon carbide fibers havi,ng a constant strength can be obtained withi.n a temperature range of 1,800 to 2,000C.
If the above described tensi.on and ultrasonic ~ave ~, are simultaneously applied to th.e si.licon car~ide fibers, the orientation of silicon carbide crystal is- appreci.ably improved, crystal growth.occurri,ng in a uni,form direction. ~i.li.con carbide fibers having an excellent orientati.on of si`,licon carbide crystal can thus be obtained. As an em~odiment of b,aking at a high temperature under both the function of the. tension and the ultrasonic ~ave, a relation of the tens~le strength.to the baki.ng : temperature when the fibers having a diameter of 10. ~ are baked at 8Q0-2,QaOQC, with applicati.on of a tension of 5 Kg/mm,2 and an ultrasonic waYe of an output of lQQ ~at 30Q KH:z, is shown in ~ J~t~

Figure 9. As seen from ~i~ure 9, even in silicon carbide fibers baked at about 2,000C the decrease of tensile strenyth is not substantial and silicon carbide fibers having a high strength can be produced.
The orientation of silicon carbide crystal in silicon carbide fibers obtained by baking the fibers under a tension was determined by electron diffraction. As such an embodiment, the electron diffraction of silicon carbide fibers baked at 2,000C
under a tension of 5 Kg/mm2 is shown in ~igure 10. The electron diffraction of silicon carbide fibers baked at 2,0~0C under no tension is shown in Figure 11. In the above described electron diffraction photographs (Figures lQ and 11), th.e innermost diffraction ring is formed based on (111) plane of silicon carbide crystal, but in the case of the bak.ing treatment under no stress, the orientation of the s-ilicon carhide crystal in silicon carbide fibers is irregular as shown in Fi.gure 11 and the crystals oriented in ~11 directions are mixed, so that the strength of the electron diffraction is uni.form in all directions of 360 and the diffraction ring is uniform in the electron diffraction strength in all porti.ons of the ring and therefore the blackness of the diffraction ring is uniform, ~hi.le, as shown in Figure 10 in the electron diffracti.on of the silicon carbide fibers baked under a tensi.on, the. ri.ng i.5 larger in the diffrac-tion strength only at a part of the dif~ractiQn ring, so that the blackness of the di~f$ract~on ring is very~deep at a part and it can ~e seen that the orientat~.on of the silicon caxbide crystal in the fibers is very go~d. Since the orientation of the silicon carbide crystal is h;~gh., the strength o$ the crystclline silicon , .

7t~

carbide fibers obtained by baking under a tension does not significantly decrease as compared with the strength of non-crystalline silicon carbide fibers obtained by baking at a temperature of lower than 1,500C.
In the present invention, it has been found that the silicon carbide fibers obtained by the preliminary heating at a low temperature and the baking at a high temperature often contain free carbon. However, when the fibers are burnt at a temperature of 600-1,700C under an oxidizing atmosphere, the free carbon can be oxidized and removed. I:f such a burning under an oxidizing atmosphere is effected at a temperature of lo~er than 600C, the free carbon cannot be oxidized, while ~hen said burning is effected at a temperature of higher than 1,700C, the free carbon can be easily oxidized, but a reaction for forming SiO2 proceeds, so that such temperatures are not desirable.
The time for oxidizing the free carbon depends upon the oxidizing temperature and the already treated temperature of the fibers.
For example, wh.en the fibers burnt at 1,200C i~ treated under ~ an oxidizing atmosphere at 800C, 0.1-3 hours is preferable and :~ 20 in general, it is prefer~ble to effect such a treatment at a low - temperature for a relati~ely long time.
The silicon car~ide fi~ers according to the present invention can be used i.n monofil~ment, yarn, robbing and cable.
The silicon carbide fibers~ according tQ the present invention are mainly formed from ultra fine grains of e-~ic : crystal and the average grain sizes of the crystals of the fibers obtained by bak~ng at a temperature of l,lOUaC, 1.,3Q0.C and 1,500C under vacuum are about 2Q A, 30 A, and 80 A and the , . . . .
`

`7~

silicon carbide ~i~ers composed of such ultra fine grains of SiC
crystals have never been heretofore known.
The tensile strength of the silicon carbide fibers according to the present invention is 200-800 Ky/mm2 and Young's modulus is 10-40 ton/mm2. The tensile strength and the Young's modulus were determined with respect to silicon carbide fibers obtained by baking at 1,300C under vacuum and the result is shown in Figure 12. The tensile strength and the Young's modulus become larger, as the diameter of the fibers becomes smaller. Furthermore, as the diameter is smaller, the silicon `
carbide fibers become more flexible.
The tensile strength and Young's modulus at a high temperature of the silicon carbide fibers according to the present invention were determined up to a temperature of 1,400C
under vacuum and the obtained results are shown in Figure 13.
As seen from Figure 13, the tensile strengtn and the Young's modulus of the silicon carbide fibers according to the present invention do not vary at all from room temperature to 1,400C
and the silicon carbide fibers of the present invention are inorganic fibers whi:ch can be satis;factorily used from room temperature to 1,400C.
The silicon carbide fibers of the present invention are high in corrosion resistance and, in fact/ are not corroded at all, even if the f~bers are imme~sed in hot hydrofluoric acid, a hot mixture o~ hydrofluoric acid and sulfuric acid, or hot aqua regia and the tens-~le strength and Young's modulus before and after the immersi.ng do not var~ at ~11.
The antioxi.dati.on ch.aracteri.stics of fibers according .

to the present invention was determined by heating the silicon carbide fibers of the present invention at 1,200C for 100 hours in air but the fibers were not substantially oxidized and the tensile strength and the Young's modulus before the heating at 1,200C were unaffected even after the heating at 1,200C.
The Young's modulus of the silicon carbide fibers according to the present invention is higher than that of the carbon fibers having the highest Young's modulus among various presently known fibers and is about 6 times that of the glass fibers.
In the diffraction curve determined by X-ray diffraction method with respect to tne silicon carbide fibers obtained by baking at 1,500QC under vacuum, there are three diffraction peaks of 2~~36, 60 and 72 as shown in Figure 14 an~ it can be seen that the silicon carbide crystal in the fibers is ~-5iC crystal.
Furthermore, the silicon carbide fibers baked at the above described various temperatures were measured by Pin hole method X-ray diffraction and the obtained diffraction photographs are shown in Figures 15 to 17.
Figure 15 is the diffraction ph~tograph of the silicon carbide fibers baked at 1,200C under ~acuum, Figure 16 is the diffraction photograph of the silicon carbide fi~ers baked at 1,300C under vacuum and Figure 17 is the diffraction photograph of the silicon carbi.de fi~ers baked at l,5QQC under vacuum.
The ring in the most inside among th.~ di.ffraction rings in the di.ffraction photograph is formed based on ~111). plane of ~-SiC crystal and as~ the bak~ng temperature ~i`s raised, the diffraction r~ng becomes cleax and this sho~s the gro~th.of '79,'~

~-SiC crystal. Since the diffraction spot is not observed in the diffraction ring, it is apparen-t that ~-SiC crystal is very small grain.
The average grain size of SiC crystal can be calculated from the following formula:

O.9 x ,g X COS~

L : average grain size (A) A : X-ray wave length (A) ~ : width at half-maximum intensity (RadlanJ
~ : Brag angle The grain size of SiC crystals in ~ilicon carbide fibers baked at various te~peratures was calculated from the above formula. The average grain size of SiC crystal in tne silicon carbide fibers baked at 1,200C under vacuum is about 20 A, the average grain size of SiC crystal of the silicon carbide fibers baked at 1,300C under vacuum is about 30 A and the : average grain size of SiC crystal of the silicon carbide fibers baked at 1,500C under vacuum is about 80 A. A relation of the baking temperature to the average grain size of SiC crystal in 20 the silicon carbide fi~ers is- shown in Tigure 18 and as the baking temperature hecomes higher, the average grain size of SiC crystal becomes larger.
~ n the silicon carbide f~bers according to the present invention, as the baki.ng temperature in the production becomes higher, the tensile strength decreases and the average grain 6~ 6 size of the crystal becomes larger. A relation of the baking temperature to the tensile strength and a relation of the tensil.e strength to the average grain size if SiC crystal are shown in Figures 18 and 19, respectively. From these Figures, it is apparent that the grain size of the crystal and the tensile strength are in an inverse relationship and the reason why the silicon carbide fibers according to the present invention are very high in the tensile strength is presumably based on the fact that the silicon carbide fibers are constituted of the ultra fine grain crystals heretofore unknown.
SiC crystal in the silicon carbide fibers according to the present invention, which was obtained by baking at 1,500C under vacuum, was okserved by an electron microscope of an ultra high voltage of an accelerating voltage of 1,000 KV
and the obtained photographs are shown in Figures 20-23.
Figure 20 is a photograph of the silicon carbide fiber taken in 5,000 magnification and this shows that the s:urface of the fiber is very smooth. Figure 21 shows a ph~tograph of the silicon carbide fiber taken in 20,000 magnification and since the electron penetrates only the thin peri.phery portion, an image of SiC crystal grain can be observed and a verY small number of the grains having 100-1,000 A ~re present between the grains of an average grain size of about sa A which are distributed in the entire of the fiber. Figure 22 shows a photograph of a cut end of the silicon carkide fiber taken in 20,000 magnification and a very small num~er of the large grains hayi:ng lOQ-l,OOQ A are pres.ent between the gra~.ns. h.aYing about 50`A which are di.stribute~ in the entire of the fiber. Figure 23 .

` 7'32~

is a photograpll of a cut end of the silicon carbide fiber taken in 50,000 magnification and the grains having about 50 A are uniformly distributed and a very small number of large grains having 100-1,000 A are present between said ultra fine grains, but it can be seen that the grains mainly constituting the silicon carbide fiber are the ultra fine grains having about 50 A.
That is, the silicon carbide fibers according to the present invention are constituted with ultra fine grain of crystals.
The present invention will be explained in more detail.
For a better understanding of the invention, reference is taken to the accompanying drawings, wherein, as indicated above:
Figure 1 is a diagram of an e~bodiment of apparatus for producing the organosilicon high molecular ~eight compounds;
Figure 2 shows: a relatlon of the residual weight to the heating temperature when the hi`.gh l-~lolecuiar ~eight compounds containing low molecular weight compounds: are heateai ; 20 Figure 3 shows a relation of the res.idual weight to theheating temperature when the high molecular wei.ght compounds containing low molecular weight compounds are heated under vacuum;
Figure 4 shows X-ray di.ffractl.on p~tterns w.hen the silicon high molecular weight compound fib.ers are heated at various temperatures;
F;gure 5 sho~s a relation of the tensile s.trength to the heating temperature when the spun fibers. according to the present invention are h.eated from 7~QC to 2,OQQC;

Figure 6 shows a relation of the tensile strength to the baking temperature when the spun fibers are baked under no tension;
Figure 7 shows a relation of the tensile strength to the ba.~ing temperature when the spun fibers are baked under a tension;
Figure 8 shows a relation of the tensile strength to the baking temperature when the spun fibers are baked while applying ultrasonic wave;
Figure 9 shows a relation of the tensile strength to the baking temperature when the spun fibers are baked while applying a tension together with ultrasonic wave;
Figures 10 and 11 show electron diffracti.on photo-graphs of the silicon carbide fibers obtained by baking under a tension or no tension, respectively;
Figure 12 snows relations of the t~nsile strength and the Young's modulus to the diameter of th.e silicon carbide fiber according to the present invention;
Figure 13 is a diagram showing vari.ations of the tensile strength and the Young's modulus based on temperature of the silicon carbide fiber according to the present invention;
Figure 14 shows an X-ray diffracti.on pattern of the ; silicon carbide fiber baked at 1,5QQC;
Figures 15-17 are X-ray di.ffraction photographs of Pin hole method of the s-ilicon carbide fiber of the present invention;
Figure 18 is a diagram showing relations of the average grain size of SiC crystal and the tensi.le strength of the si.licon .

'7~,~$

carbide fiber of the present invention to the baking temperature;
Figure 19 is a diagram showing a relation of the tensile strength to the average grain size of SiC crystal of the silicon carbide fiber of the present invention;
Figures 20-23 show photographs obtained by observing SiC crystal in the silicon carbide fiber of the present invention through a super high voltage electron microscope; and Figure 24 is a diagram of an embodiment of apparatus for continuously effecting the method of the present invention.
The following Examples are given for the purpose of illustration of this invention and are not intende~ as limita-tions thereof.
Example 1 10 g of dodecamethylcyclohexasilane [(Me2Si~6] was fed in an autoclave and air in the autoclave was purged with argon gas and the polycondensation was effected at 400C under a pressure of about 40 atmospheres for 48 hours to obtain the organosilicon high molecular weight compounds of the present invention. The formed high molecular weight compounds were permitted to cool at room temperature and then these compounds were admixed with ether to form ether solution. Said ether solution was taken out from the autoclave and ether was evaporated to obtain 6.6 g of a solid product. This solid product was dissolved in benzene and the solution was spun into fibers.
The benzene solu~le product had an average molecular weight of more than l,5QQ.
lQ g of this organosilicon hi~gh moleculax weight compound was dissolved in lOQ cc of n-hexane and to the resulting 7$,~

solution was added 300 cc of acetone and the insoluble portion was about 60%. This insoluble portion was dissolved in benzene and the resulting solution was spun in a dry process at a spinning temperature of 20C at a spinning rate of 100 m/min. to obtain the organosilicon high molecular weight compound fibers having a diameter of 10 ~. The fibers were fully dried and then subjected to the preliminary heating to a temperature of 800-1,000C in about 2-48 hours, in average time of 12 hours under vacuum (1 x 10 3 mmHg) to obtain the fibers having black metal luster in a yield of 40-60%. The thus treated fibers were baked up to 1,800C under argon atmosphere to obtain silicon carbide fibers.
A relation of the residual weight to the heating temperature up to the above descri~ed 1,000C is shown in ; Figure 2.
The tensile strength of the fibers heated to 1,800C
was 98 Kg/mm2 and the tensile strength of the fibers heated to 1,000C was 810 Kg/mm2 and Young's modulus was 34 ton/mm2.
Example 2 10 g of linear polydimethylsilane Me Me [ ~
Me Me produced from dimethyldichlorosilane was charged in an autoclave and heated under argon atmosphere at 400C under a pressure of 5~ atmospheres for 48 houxs. The reaction product ~as dissolved in ether and the solution obtained ~y remoYing the insoluble : : : : .
.

~'7~

portion was evaporated to obtain 4.3 g of a solid product. This solid product had an average molecular weight distribution of 500-15,000 and was dissolved in 50 cc of hexane. The resulting solution was mixed with 200 cc of acetone to obtain precipitates.
The precipitate was dissolved in benzene and the solution was spun in a dry porcess at 25C into fibers having a diameter of 10 ~.
The thus obtained fibers were heated gradually to 1,000C in 10 hours under vacuum. The tensile strength of the fibers was 723 Kg/mm2 and Young's modulus was 36 ton/mm2.
Example 3 10 g of poly(dimethylsiltrimethylene), [ Si - CH2CH2CH2 ]n' was dissolved in 100 cc of ben~ene~ and the resulting solution was mixed with 400 cc of acetone to obtain 68 g of precipitate.
The precipitate was dissolved in benzene, and the resulting solution was spun in a dry process at 30C into fibers having a diameter of 10 ~. The spun fibers were fully dried and then heated gradually from room temperatur to 800C in 4 hours under vacuum to obtain silicon carbide fibers having metal luster in a yield of 59.8%. The resulting silicon carbide fibers had a -strength of 610 Kg/mm2 and Young's modulus of 29 ton/mm2. The fibers were placed in a graphite crucible and ~aked up to 1,800C under a ti~ghtl~ sealed condltion. The thus treated fibers had a tensi`le strength of 80 Kg~mm2.

7'~

Example 4 50 ~ of poly(phenyleneoxysiloxane) was dissolved in 300 cc of benzene, and then 500 cc of acetone was added to the solution to obtain precipitates. The precipitates were dissolved in benzene, and the resulting solution was spun in a dry process at a spinning temperature of 50C at a spinning rate of 150 m/min. to obtain fibers having a diameter of 10 ~.
The fibers were heated from room temperature to 800C in 6 hours under vacuum (1 x 10 3 mmHg), and the heat treated fibers were further heat treated from 800C to 1,800~ under helium atmos-phere to obtain silicon carbide fibers. The fibers had a tensile strength of 89 Kg/mm2, and even when the fibers were kept in air at 1,500C for 100 hours, the fibers did noi change the weight. Therefore, the fibers had excellent oxidation resistance.
Example 5 30 g of poly(dimethylsilphenylene), ~- Si ~3 was dissolved in 200 cc of benzene, and the resulting solution was mixed with 500 cc of acetone to obtain 24.5 g of precipitate.
The precipitate ~as dissolved in benzene, and the resultlng solution was spun in a dry process at a tempera~ure of 40C
to obtain fibers having a diameter of 10 ~. The spun fibers were heated from room temperature to 8Q0C in 4 hours under vacuum to obtain fi`bers in a y~eId of 65%. The fibers ~ere .~

', '`'7'~

further hea~ treated from 800C to 2,000C under helium atmosphere to obtain f.ibers having a tensile strength of about 75 Kg/~,m2.
Even when the fibers were kept in air at 1,500C ~or 100 hours, the fibers did not change the weight, and the fibers had very excellent oxidation resistance.
Example 6 lO g of dodecamethylcyclohexasilane was fed in an autoclave and air in the autoclave was purged with argon gas : and the polycondensation reaction was effected at 400C for 48 hours under a pressure of 40 atmospheres. After completion of the reaction, the polycondensation product was permitted to cool at room temperature, and then added with ether to form ether solution. The ether solution was taken out from the autoclave and ether was evaporated to obtain 6.6 g of a solid high molecular weight compound having an average molecular weiyht of about 1,800 and containing 4Q% of acetone-soluble low molecular weight compounds. The solid high molecular weight compound was heated and aged at 300C for 8 hours while slowly stirring under atmospheric pressure in argon atmosphere to obtain an organosili.con hi.gh molecular weigh* compound having an average molecular weight o~ about 2,100.
The resulting organosilicon high molecular weight compound was dissolved in benzene~ and the benzene solution was spun in a dry process to obtain fi~ers. having a diameter of about lQ ~. The fihers ~ere gradually heate.d from room temperature to 80.0C in 6 h.ours under vacuum (l x lO 3 mmHg~
to effect the prelim~nar~ heating of the fi.bers, and then baked up to l,80QC to obtai.n silicon carbi.de fi.hers.

~L~Lf;~'7~26 The tensile strength of the fibers heated to 1,200C
was 630 Kg/mm and that of the fibers heated to 1,800C was 85 Kg/mm2.
Example 7 The same solid high molecular weight compound as obtained in Example 6 was heated and aged at 250C for 3 hours while slowly stirring in air to obtain an organosilicon high molecular weight compound having an average molecular weight of about 2,300. The resulting organosilicon high molecular weight compound was dissolved in xylene, and the xylene solution was heated at 42C and spun into fibers having a diameter of about 10 ~. The fibers were gradually heated from room tempexature to 800C in 6 hours under vacuum (1 x 10 3 mmHg~ to effect the preliminary heating of the fibers, and ~ihers having a diameter of about 8 ~ were obtained. The preliminarily heat treated fibers were baked up to 1,800C under argon atmosphere to obtain silicon carbide fibers having a tensile strength of 93 Kg/mm2 and Young's modulus of 38 ton/mm2. The tensile strength of the fibers baked at 1,000C was 740 Kg/mm2. When the fibers were kept at 1,500C $or 10~ hours in air, the fi~ers dld not change the weight.
Example 8 10 g of linear polydimethylsilane, Me Me Si~, Me Me synthesized from dimethyld~chlorosi.lane was fed in an autoclave, 37~'' b ~

and air in the autoclave was purged with argon, and the poly-condensation was effected at 400C for 48 hours under a pressure of SO atmospheres. The resulting polycondensation produc~ was dissolved in ether, and ether-insol~le portion was removed from the ether solution, and ether was evaporated to obtain 4.3 g of a solid high molecular weight compound having an average molecular weight of about 7,500. The compound was heated and aged at 240C for 2 hours under atmospheric pressure in gaseous ammonia atmosphere while slowly stirring to obtain a high molecular weight compound having an average molecular weight of about 8,400. The resulting high molecular weight compound was dissolved in benzene, and the benzene solution was spun into fibers having a diameter of about lO ~. The fibers were gradually heated from room temperature to 800~ in 4 hours under vacuum (1 x 10 3 mmHg~ to effect the preliminary heating of the fibers. The resulting fibers had a diameter of about 8 ~. The preliminarily heat treated fibers.were further baked up to 2,000C in a graphite crucible to obtain silicon carbide fibers, which had a tensile strength of 95 Kg/mm2. The fibers baked at 1,000C had a tensile strength of 810 Kg/mm2 and Young's modulus of 31 ton/mm2.
Example 9 Poly(diphenyleneoxysiloxane~ havin~ an a~erage molecular weight of ll,OQQ was heated and aged at 350C for 3 hours under a press~re of 1 atmosphere.s in hydrogen atmosphere while slowly s:ti`rri.ng to obtain a hi`gh.molecular weight compound having an average molecular weight of 14,QOQ. The compound was dissolved in benzene, and the benzene solution wa~ spun in a 7~

dry process into fibers having a diameter of about 10 ~. The fibers were ~xadually heated from room temperature to 800C in 6 hours under vacuum (1 x 10 3 mmHg) to effect the preliminary heating of the fibers. The resulting fibers had a diameter of about 8 ~. The preliminarily heat treated fibers were further baked up to 1,800C under vacuum to obtain silicon carbide fibers having a tensile strength of 80 Kg/mm2. The fibers baked at 1,000C had a tensile strength of a~out 780 Kg/mm2 and Young's modulus of 41 ton/mm2.
~xample 10 Methylchlorosilane was polycondensed according to Fritz's method [Angew. Chem., 79, 657 (1967)] to prepare a high molecular weight compound having an average molecular weight of 1,000. The high molecular weight compound was heated and aged at 400C for 8 hours under a pressure of 10 atmospheres in nitrogen atmosphere to obtain a high molecular weight compound having an average molecular weight of 2,500. The aged high molecular weight compound was dissolved in xylene, and the xylene solution was heated at 35C and spun into fibers having a diameter of about 10 ~. The fibers were gradually heated from room temperature to 800C in 4 hours under vacuum (1 x 10 3 mmHg) to effect the preliminar~ heating of the fibers. The resulting fibers had a diameter of about 8 ~. The fibers were further baked up to l,800C under argon atmosphere to obtain silicon ; carbide fibers having a tensile strength of 110 Kg~mm2. The fibers baked at 1,000C had a tensile strength of 750 Kg/mm2 ; and Young's modulus of 29 ton/mm2. Even when the fi~ers were kept at 1,500C for 100 hours in air, the fibers did not change the weight.
Exam~le 11 The same high molecular welght compound as synthesized in Example 10 was heated and aged at 290C for 3 hours under gaseous ammonia atmosphere. The aged high molecular weight compound had an average molecular weight of 2,400. The aged compound was dissolved in benzene, and the benzene solution was spun into fibers having a diameter of about 10 ~. The fibers were gradually heated from room temperature to 800C in 6 hours under vacuum to effect the preliminary heating of the fibers.
The fibers were further baked up to 1,800C under vacuum to obtain silicon carbide fibers having a tensile strength of 89 Kg/mm2. The fibers baked at 1,000C had a tensile strength of 780 Kg/mm2 and Young's modulus of 28 ton/mm2.
Example 12 10 g of octaphenylcyclotetrasilane was fed into an autoclave together with 0.1 g of benzoyl peroxide, and air in the autoclave was purged with argon gas, and the polycondensation was effected at 370C for 24 hours under a pressure of about 35 atmospheres. After completi`on of the reaction, hexane was added to the autoclave, and the po]ycondensation product was taken out from the autoclave in the form of hexane solution.
Insoluble portion in hexane was filtered off, and hexane was evaporated to obtain 7.1 g of solid high molecular weight compounds having an average molecular weight of about 8,000.
The high molecular weight compounds were dissolved in 100 cc of hexane, and the ~exane solution was added with 4a~ cc of acetone to obtain 6.3 g of acetone-insolu~le precipitate. The -5~-., ' ' :

7~,Z~;

precipitate was dissolved in benzene, an~ the benzene solutlon was spun in a dry process into fibers having a diameter of about 10 ~. The fibers were heated from room temperature to 800C in 6 hours under vacuum (1 x 10 3 mmHg) to effect the preliminary heating of the fibers. The preliminarily heated fibers were further baked up to 1,400C in a graphite crucible to obtain silicon carbide fibers having a tensile strength of 350 Kg/mm2 and Young's modulus of 25 ton/mm2.
Example 13 10 g of a mixture of cyclic dimethylpolysilanes having formulae of (Me2Si)5 and ~Me2Si)6 was fed into an autoclave together with 0.5 g of azoisobutyronitrile, and air in the autoclave was purged witn argon gas, and the polycondensation : was effected at 400C for 12 hours under a pressure of about 80 atmospheres. After completion of the r~action, benzene was added to the autoclave, and the polycondensation product was taken out from the autoclave in the form of benzene solution.
In soluble portion in benzene was filtered off and benzene was evaporated under a reduced pressure to obta~n 4.8 g of solid high molecular weight compounds having an average molecular weight of about 7,000. The high molecular weight compounds were dissolved in 50 cc of h.exane, and to the hexane solution was added 200 cc of acetone to obtain 3.~ g of acetone-insoluble precipitates. The precipitate was di~ssolyed in benzene, and the benzene solution was spun i.n a dry proces.s. into fibers having a di.ameter of about 10 ~. The ~ibers were gradually heated from roo~ temperature to 8QQC in 6 hou~s under yacuum (1 x 10. 3 mmHg~ to effect the prel~m~nary~heat~ng o~ the fibers.

The preliminarily heated :Eibers were furtner baked up to 1,800C
under vacuum. The tensile strength of the fibers baked at 1,300C was 7S0 Kg/mm2, and that of the fibers baked at 1,800C
was 95 K~/mm2. Even when the fibers baked at 1,300C were kept at 1,500C for 120 hours in air, the fibers did not change the weight.
Example 14 10 g of a mixture of cyclic dlphenylsilane of the formula (Ph2Si)4, that of the formula (Ph2Si)5 and linear s polydiphenylsilane was fed into an autoclave and air in the autoclave was purged with gaseous nitrogen, and the polycondensa-tion was effected at 380C for 50 hours under a pressure of about 60 atmospheres. After completion of the reaction, benzene was added to the autoclave, and the polycondensation product was taken OUt from the autoclave in the form of benzene ~.
solution, and the ~enzene solution was concentrated under a reduced pressure to obtain 6.9 g of solid high molecular weight compounds. The reSUlting high molecular ~eigh.t compounds .
were dissolved in 50 cc of benzene, and to the ~enzene solution was added 200 cc of acetone to obtain 4.8 g of acetone~insoluble precipitates. The precipitate was dissolved in benzene, and the benzene soluti.on was spun in a dry process into fibers having a diameter of about 10 ~. The fibers were gradually heated from room temperature to 8QaC in 6 hours undex vacuum (1 x 10 3 mmHg~ to obtain black fi~ers h.avi.ng me*allic luster.
The fibers were ~urther baked up to 1,5uQC under helium atmosphere to obtain sili.con carbide fi.bers havin~ a tensile strength. of 300. K`g~mm2.

~.

7~Z~;
Example 15 Fluidized hexamethyldisi.lane was fed into a reaction column heated to 850C at a feeding rate of 1 Q/hr. together with argon gas. The starting hexamethyldisilane was subjected to a decomposition reaction and a polycondensation reaction in the heated reaction column and formed into high molecular weight compounds, and at the same time low molecular weight compounds were formed. A part of the resulting high molecular weight compounds could be taken out from the heated reaction column.
Major part of the high molecular weight compounds was fed into a separating column together with the low molecular weight compounds, and gases and the low molecular weight compounds were separated from the high molecular wei.ght compounds in the column. The low molecular weight compound~ were again fed into the heated reaction column and recycled. The operation was continued for 10 hours and 5.4 Kg of high molecular weight compounds having an average molecular w.eight o~ about 3,500 was obtained.
From 10 g of the resulting high.molecular weight compounds, ethyl alcohol-soluble portion was. removed by means of a Soxhlet's extractor to obtain 7.8 g of eth~l alcohol-insoluble portion, which was used as a spinning material. The ethyl alcohol-insoluble portion was dissol~ed in xylene, and the solution was heated to 45C and spun i.nto fibers h.aving a diameter of about lQ ~. The spun fib.ers: ~ere h.eated from room temperature to 800.C in 6 hours undex vacuum to effect the preliminary heat~ng o~ the fibers. The fi~bers ~ere further bak.ed by h.eati`ng up to 1,3Q~C under axgon atmosph.ere. The -'7~6 tensile strengtll of the baked fibers was 450 Kg/mm and ~oung's modulus was 27 ton/mm2.
Example 16 Poly(silmethylenesiloxane) having the following formula and an average molecular weight of about 24,000 was used as a starting material.
CIH3 CIE~3 [ I i - CH2 - Si - O

A content of the low molecular weight compounds soluble in acetone contained in this high molecular weight compound was less than 5% and the softening point of this high molecular weight compound was 100C. This organosilicon high molecular weight compound was dissolved in benzene to form a spinning solution, which was spun into fibers having a diameter of about 10 ~. The spun fibers were subjected to a preliminary heating by raising the temperature from room temperature to ~ :.
800C in 4 hours under vacuum (:1 x la 3 mmHg~ and then baked ~:
by heating up to 1,800C under vacuum to obtai.n silicon carbide fibers having a diameter of about 8 ~. The tensile strength of the fibers baked at l,000C was a~out 5Q0 Kg/mm2 and the tensile strength of the f~bers baked at 1,8QQC was about 65 Kg/mm .
Example 17 PolyCsilarylenesilo~ane~ h.a~ing the follo~i.ng formula and an average molecular weight of 25,00.Q had a content of the low molecular weigh.t compounds soluble i.n acet~ne being less than 7~ and has a softening poi.nt of 180C.

..

,, .

7~

~ O - S - O ~

The organosilicon high molecular weight compound was dissolved in benzene and the resulting benzene solution was ; spun in a dry process to obtain fibers having a diameter of about 10 ~. The spun fibers were subjected to a preliminary heating by gradually raising the temperature from room tempera-ture to 800C in 6 hours under vacuum (1 x 10 3 mmH~) and then baked by raising the temperature up to 1,800C to form silicon carbide fibers. The tensile strength of the fibers baked at 1,100C was 530 Kg/mm2 and the tensile strength of the fibers baked at 1,800C was 70 Kg/mm2.
Example 18 A polysilmethylene having the following formula and an average molecular weight of a~out 27,000 had a content of : the low molecular weight compounds soluble in acetone being less than 3% and had a softening point of 210C.

[ "i - CH2 ]
:~ ~H

The organosilicon high molecular welght compound was dissolved in benzene and the resulting solution was spun in a dry process into fibers having a diameter of about 10 ~.
The spun fibers were su~jected to a preliminary heating by gradually raising the temperature from room temperature to 8Q0C in 6 hours under ~acuum C1 x lQ 3 m~H~ Then the fibers ~, . .

1J!7~

were baked by heating up to 1,800C under vacuum. The tensile strength of the fibers baked at 1,300C was 680 Kg/mm2 and the tensile strength of the fibers baked at 1,800C was 70 Kg/mm2.
Example 19 Polysiltrimethylene having the following formula and an average molecular weight of about 28,000 had a content of the low molecular weight compounds soluble in acetone being 4.5 and had a softening point of 230C.

fH3 [ I C 2 C 2 CH 2~

The organosilicon high molecular weight compound was dissolved in benzene and the resulting solution was spun in a dry process into fibers having a diameter of about lO ~. -The fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C in 6 hours under vacuum, and the thus treated fibers were baked by heating up to 1,800C under argon atmosphere. The tensile strength of the fibers baked at l~Qoaoc ~as. 580 Kg/mm2, and the tensile strength of the fi~ers baked at 1,8Q0C ~as 76 Kg/mm2.
Example 20 lO g of cyclic polysilane (Ph2Si)5 ~as ~ed in an ; autoclave and the gas-eous content of the autoclaVe ~as substituted with argon gas and then said pol~silane ~as reacted by heating at 420C for 48 hburs. After completion of the reaction, the reaction produc~ ~-as d~ssolved i~n benzene and the solution was taken out ~rom the autocla~e and the solu.ion 's~

was fi~t~red and then berlzene was evaporated under a reduced pressure to obtain 4.8 ~ of a solid high molecular weight compound. An average molecular weight of this high molecular weight compound was 18,000. The organosilicon high molecular weight compound had a content of the low molecular weight compound soluble in acetone being 5% and had a softening point of 130C. The organosilicon high molecular weight compound was dissolved in xylene, and the solution was heated at 50C to form a spinning bath, which was spun in a dry process into fibers having a diameter of about 10 ~. The spun fibers were subjected to a preliminary heating by raising temperature from room temperature to 800C in 6 hours under vacuum (1 x 10 3 mmHg) and baked by heating up to 1,800C to form silicon carbide fibers. The tensile strength of the fibers baked at 1,100C
was 480 Kg/mm2 and the tensile strength of the fibers baked at 1,800 C was 55 Kg/mm2.
Example 21 An apparatus for producing silicon carbide fibers as shown in Figure 24 was used and the entire gaseous contents of the apparatus was substituted ~ith nitrogen gas. A mixed starting material of about 65% of dimethyldichlorosilane, about 25% of methyltrichlorosilane, about 5% of trimethylchloro-silane and about 5~ of the other substances ~ere charged in a primary reaction column 1 heated at 750C at a rate of 5 l/hr.
The reaction product formed ;n this column was introduced into a di.stillation column 2 and the: gases consis;ti.ng mainly of propane and hydrogen were separated from liquid. The liquid ~as i.ntroduced into a secondary reaction column 3 heated at 850C

.

~ . .

to e~fect the thermal polycondensation reaction and then the reaction product was charged into a separating column 4 and separated into gas, low molecular weight compounds and high molecular weight compounds. Among them the gas was discharged from the column through a valve 18, the low molecular weight compounds were fed into the secondary reaction column 3 through a valve 19 as a recycling material. The yield of the above described high molecular welght compound was 19~ and the average molecular weight was 2,400 and a content of acetone-soluble low molecular weight compounds was about 25~, so that the high molecular weight compound was fed into an aging vessel 5 through a valve 20 and aged at 350C for 4 hours under atmospheric pressure. Thereafter, the thus aged product was filtered with a filter 7 and compressed with a pump 8 ana spun through a spinneret 9 into fibers having a diameter of about 10 ~. The spinning temperature was about 40C and the spinning rate was 20 m/min. The spun fibers were subjected to the preliminary heating through a preliminary heating apparatus 10 under vacuum having a length of 4 m, where the outlet temperature was 800C, and then baked at 1,800C in a baking oven 11 under argon atmosphere having a length of 2 m, in which the center was 1,800C, to form silicon carbide fibers, which were wound up on a take-up device 12. The diameter of the formed silicon carbide fibers was about 7 ~, and the yield was about 11% based on the starting material. The tensile strength of the fiber was about 75 Kg/mm2. When the baking was effected at 1,100C, the tensile strengt~ was 480 Kg~mm2 and Young~s modulu$ was 29 ton/mm2.

i .

Example 22 Silicon carbide fibers were produced startlng from dimethyldichlorosilane in the same manner as described in Example 21.
The dimethyldichlorosilane was charged in the primary reaction column 1 heated at 780C at a rate of 8 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases consisting mainly of propane and hydrogen were separated from liquid. The liquid was introduced into the secondary reaction column 3 heated at 880C to effect the thermal polycondensation reaction. Then, the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds în the separating column 4.
The yield of the above high molecular weight compound was 27%, and the average molecular weight was 3,200, and the content of acetone soluble lo~ molecular weight compounds was 27~.
The high molecular weight compound was aged in the aging vessel 5, at about 380C for about 3 hours, filtered, pumped and spun through the spinneret 9 into fibers having a diameter of about 10 ~. The spinning temperature was about 45C and the spinning rate was about 40 m/min. These spun fibers were subjected to the preliminary heating through the preliminary heating apparatus 10 having a length of 4 m, an inlet temperature of room temperature and an outlet temperature of 800C under vacuum. Then, the thus treated fibers were baked up to l,8QQC in t~e baking oven 11 under vacuum to form silicon caxbide fibers ha~ng a diameter of about 7 u, which were wound up on the take-up device 12. The ~ield was about ~, , 7~

17~ based on the startlng material. The tensile strength of the fiber was 95 ~g/mm2. When the baking was effected at 1,000C, the tensile strength was 540 Kg/mm2 and Young's modulus was 31 ton/mm2.
Example 23 .
Silicon carbide fibers were produced starting from a mixture of about 78% of dimethyldichlorosilane, about 8% of methyltrichlorosilane, about 3% of trimethylchlorosilane, about 2~ of methyldichlorosilane and about 9~ of the other substances 10 in the same manner as described in Example 21.
The mixture was charged in the primary reaction column 1 heated at 750C at a rate of 6 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases containing rich propane and hydrogen were separated from liquid. The liquid was introduced into the secondary reaction column 3 heated at 850C to effect the thermal poly-condensation reaction. Then, the reaction product ~as separated : into gas, low molecular weight compounds anZ. high molecular weight compounds in the separating column 4.
The yield of the above high molecular weight compound : was 21% and the average molecular weight ~as. 2, 6ao and the content of acetone solu~le low molecular weight compounds was about 22~.
The high molecular weight compound was aged in the aging vessel 5 at 42QC for 3 hours, filtered ~ith a ~ilter 7, compressed wi.th a pump 8 and spun through tne s~pinneret 9 into fibers having a diameter of a~out 15 ~. These ~pun fibers were subjected to the prelimi.nar~ h.eati.ng through the preli.minary _6a-heating apparatus 10 under vacuum :Erom room temperatures up to 800C in 6 hours and then baked up to 1,800C in carbon monoxide gas to form silicon carbide fibers. The diameter o~ the formed silicon carbide fibers was about 11 ~. The yield was 13~ based on the starting material. The tensile strength of the fiber was 85 Kg/mm2. When the baking was effected at 1,100C, the tensile strength was 490 Ky/mm2 and Young's modulus was 26 ton/mm .
Example 24 Silicon carbide fiber~ were produced starting from a mixture of about 55~ of diphenyldichlorosilane, about 35% of diphenyltrichlorosilane and about 10% of the other substances in the same manner as described in Example 21.
The mixture was charged in the primary reaction column 1 heated at about 800C at a rate of 4 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases consisting mainly of chlorine were separated from liquid. Next, the liquid was introduced i.nto the secondary reaction column 3 heated at about 900C to ef~ect the thermal polycondensation reaction. Then, the reaction product was separated into gas, low molecular wei.ght compounds and high molecular weigh.t compounds. in the separating column 4.
The yield of the above high molecular weLgh.t compound was 24% and the average molecular weight was ab.out 5,0Q0 and the content of acetone soluble lo~ molecular ~eight compounds was about 5%.
The high molecular weight compound was directly $iltered with the filter 7 without feeding into the agi.ng ~ ~t~7~

vessel 5 and ~le~ spun through the spinneret 9 into fibers having a diameter oE about 10 1l . The spun fibers were subjected to the preliminary heating through the preliminary heating apparatus 10 having a length of 4 m, an inlet room temperature and an outlet temperature of 800C under vacuum and then baked up to l,800C under argon to form silicon carbide (SiC) fibers having a diameter of about 7 ~. The yield was 18% based on the starting material. The tensile strength of the fiber was 85 Kg/mm2. When the baking was effected at 1,100C, the tensile strength was about 430 Kg/mm2 and Young's modulus was 26 ton/mm2.
Example 25 Silicon car~ide fibers were produced startlng from tetramethylsilane in the same manner as described in Example 21.
The tetramethylsilane was charged in the primary reaction column 1 heated at 780C at a rate of 9 l/hr. The reaction product was introduced into the distlllation cc,lumn 2, wherein the gases consisting mainly of propane and hydrogen were separated from liquid. Next, the liquid was introduced into the secondary reaction column 3 heated at 880C to effect the thermal polycondensation reaction. Then, the reaction product was separated into gas, low molecular weight compoun~s and high molecular weight polym~rs in the separating column 4.
The yield of the above high molecular weight compound was 16~ and the average molecular weight was 2,800 and the content of acetone soluble low molecular weight compounds was 20%.
Then, the high molecular weight compound ~as aged in the aging vess.el 5 at about 360C for a~out 3 hours, filtered . -, . ..

with the filter 7, compressed with the pump 8 and spun through the spinneret 9 into fibers having a diameter of about 10 ~.
The spinning temperature was about 47C and the spinning rate was about 50 m/~in. These spun fibers were subjected to the preliminary heating through the preliminary heating apparatus 10 having a length of 4 m, an inlet room temperature and an outlet temperature of 800C under vacuum. Then, the fibers were baked up to 1,800C in the baking oven 11 under vacuum to form silicon carbide fibers having a diameter of about 7 ~, which were wound up on the take-up device 12. The yield was about 14% based on the starting material. The tensile strength of the fiber was 68 Kg/mm2. When the baking was effecled at 1,000C, the tensile strength was 420 Kg/mm2 and Young's modulus was 35 ton/mm2.
Example 26 Fifty grams of 1,3-disilacyclob.utane was placed ir~
an autoclave and, after air in the autoclave ~as purged with argon gas, polycondensation was effected at 410C for 48 hours.
After the complet;on of the reaction, the polycondensation product was taken up in benzene and then benzene was evaporated to obtain 41 g of solid high molecular weight compound. Since this compound contained 15% of acetone-soluble lo~ molecular weight compound, it was dissolved in 2Q0 cc of hexane and then added with 400 cc of acetone to o~tain 33 g of acetone-insoluble prec~pitate. Th.e precipitate was di.ssolved i.n benzene and spun into fi~ers having a d;ameter of about lQ ~ by a dry process. Th.e spun fi~e.rs were thoroughly dri.ed and th.en subjected to a prell~minary heating from room temperature to '' :. .
, l~p ;J~

800C under vacuum (1 x 10 3 mm~g) in 6 hours. Then, the thus treated fibers were baked up to 2,000C under argon atmosphere to form silicon carbide fibers. The tensile strength of the fiber was 48 Kg/mm2. When the baking was effected at 1,000C, the tensile strength was 430 Kg/mm2 and Young's modulus was 39 ton/mm .
Example 27 An organosilane high molecular weight compound was produced from tetramethyldisilphenylene [H~CH3)2Si-c6~4-si(cH3)2 ]
and acetylene with a catalyst of H2PtC16. This compound had an average m~lecular weight of about 6,uOO and a content of acetone-soluble low molecular weight compound of 15%. Then, 30 g of the organosilane high molecular weight compound was dissolved in 200 cc of benzene and the solution was then admixed with 400 cc of acetone to obtain 26 g of precipitate. The precipitate was heated to 150C and spun into fibers having a diameter of about 10 ~. These spun fibers were subjected to a preliminary heating from room temperature to 800C under vacuum in 4 hours and then baked from 8Q0C up to 2,000C under argon atmosphere to form silicon carbide fibers. The tensile strength of the fiber baked at 1,200C ~as 3~a Kg/mm2 and the tensile strength of the fiber baked at 2,OQ0C ~a5 63 Kg/mm2.
Example 28 Polycondensation ~,as effected ~ith N,N'-diphenyl-~CH-3 CbH5~
diaminodimethylsilane ~ Si < ~ and p-dihydroxybenzene ~CH3 NHC~H`5J

-to produce an organosilane high molecular weight compound. This compound had an average molecular weight of about 7,000 and a content of acetone-soluble low molecular weight compound of 12%.
After the low molecular weight compound was removed with ethyl alcohol in a Soxhlet's extractor, the residue was dissolved in benzene and spun into fibers having a diameter of about 10 ~ by a dry process. These spun fibers were thoroughly dried and subjected to a preliminary heating from room temperature up to 800C in 1 hour and then baked up to 1,800C under vacuum to form silicon carbide fibers. The tensile strength of the fiber baked at l,000C was 410 Kg/mm2 and the tensile strength of the fiber baked at 1,800C was 43 Kg/mm2.
Example 29 Silicon car~ide fibers were produced startlng from tetramethyldichlorodisilane in the same manner as described in Example 21.
The tetramethyldichIorodisilane was charged in the primary reaction column 1 heated at 750C at a rate of 11 l/hr.
The reaction product was introduced into the distillation column ~ 20 2, wherein the gases consisting mainly of propane and hydrogen ; were separated from liquid. Then, the liquid was introduced into the secondary reaction column 3 heated at 850C to ef~ect the thermal polycondensation reaction. Next, the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds in the s-eparating column 4.
The yieId of the above high molecular weight compound ~as 14% and the average molecular weight ~as 2,1aQ and the content of acetone soluble low molecular weight compoun~s ~as ~ 76~

about 28~.
The high molecular weight compound was aged in the aging vessel 5 at 350C under argon atmosphere for 6 hours, filtered with the filter 7, compressed with the pump 8 and then spun through the spinneret 9 into fibers having a diameter of about 10 ~. These spun fibers were subjected to the preliminary heating through the preliminary heating apparatus 10 with a length of 4 m and an outlet temperature of 800C under vacuum and baked at 1,800C in the baking oven 11 with a length of 2 m under argon atmosphere to form silicon carbide fibers, which were wound up on the take-up device 12. The silicon carbide fiber had a diameter of about 8 ~ and a yield of about 10% based on the starting material. The tensile strength of the fiber was about 45 Kg/mm2. When the baking was effected at 1,100C, the tensile strength was about: 430 Kg/mm2 and Youn~'s modulus was 33 ton/mm2.
Example 30 An organosilicon high molecular weight compound was produced by polycondensing p-bis~.oxydîmethylsilyl)benzene [HO(CH3)2SiC6H4Si(CH3~2OH] with pot.as:sium hydroxide catalyst.
This compound had an a~erage moiecular ~eight of 3,500 and a content of acetone-soluble low molecular ~.eight compound of about 21%. Then, 30 g of the hi.gh molecular ~eight compound was dissolved in 10.0 cc of benzene and the solution then was admixed with 300 cc of acetone to obtain 21 g of precipitate.
The precipitate ~as heated and spun i.nto f.ibers having a diameter of about 10 ~ by a dry process. The.se spun fi.bers ~ere subjected to a prelimi`nary heating from room temperature ~'iP'7~

up to 800C under vacuum in 4 hours and then baked up to 1,800C
under carbon monoxide atmosphere ko form silicon carbide fibers.
The tensile stren~th of the fiber baked at 1,000C was 420 Kg/mm2 and the tensile strength of the fiber baked at 1,800C
was 53 Kg/mm .
Example 31 Silicon carbide fibers were produced starting from diacetoxydimethylsilane [(CH3)2Si(OCOCH3)2] in the same manner as described in Example 21.
The diacetoxydimethylsilane was charged in the primary reaction column 1 heated at about 750C at a rate of 9 l/hr.
The reaction product was introduced into the distillation column 2, wherein the gases were separated from liquid. Then, the liquid was introduced into the secondary reaction column 3 heated at about 850C to effect the thermal polycondensation reaction. Next, the reaction product was. separated into gas, low molecular weight compounds and high molecular weight compounds in the separating column 4.
The yield of the above high. molecular wei.ght compound was 13% and the average molecular weight was ahout 1,8Q0 and the content of acetone soluble low molecular wei.gh.t substance : was about 35%.
The hi.gh molecular weight compound ~as. aged in the aging vessel 5 at 390C i.n air for 4 hours, fi.ltered with the filter 7 and then spun through th.e spinneret 9 into fibers having a diameter of about 10 ~. These spun fibers were s.ubjected to th.e ~rel:iminary heati.ng th~ough th.e prelimi.nary heati.ng apparatus lQ having a length. of 4 mm, an inle.t temperatu~e 7~

of room temperature and ~n out:let temperature of 800C under vacuum and then baked at 1,800C in -the baking oven ll under argon atmosphere to form silicon carbide fibers having a diameter of about 8 ~. The yield was about 9% based on the starting material and the tensile strength of the fiber was 48 Kg/mm2. When the baking was effected at l,lQ0C, the tensile strength was about 410 Kg/mm2 and Young's modulus was 37 ton/mm .
Example 32 Dodecamethylcyclohexasilane was heat treated in an autoclave at 400C for 48 hours to obtain organosilicon high molecular weight compounds. lO g of the organosilicon high molecular weight compounds was dissolved in 100 cc of n-hexane and to the solution was added 300 ~c of acetone and the insoluble portion was about 60%. This insoluble portion was dissolved in benzene and the resulting solution was spun in a dry process at a spinning temperature of 25C at a spinning rate of 100 m/min.
to obtain fibers having a diameter of 10 ~. The fibers were fully dried and then subjected to a preliminary heating by raising the temperature to 800C in about 6 hours. under vacuum (1 x 10 mmHg~.
- The thus treated fibers were baked by heating to 1,800C under argon atmosphere, while applying a tension of 5 Kg/mm2 to obtain silicon carbide fibers. The tensile strength of the silicon carbide fibers baked at l,8aOC was 28~ Kg/mm . The tensile strength of the silicon carbide fibers baked in the same manner as descri~ed above without applying the tension was 68 Kg/mm2. This shows th.at the baking at a high temperature under a tension notice.ably~increases the tensile 7~2~

strength .
Example 33 10 g of linear polydimethylsilane produced from dimethyldichlorosilane was fed into an autoclave and heated at 400C under a pressure of 50 atmospheres for 48 hours under argon atmosphere. The reaction product was dissolved in ether and an insoluble portion was removed and the resulting solution was evaporated to obtain 4.3 g of a solid product. This solid product had an average molecular weight of 5Q0-15,000 and was dissolved in 50 cc of hexane and to the resulting solution was added 200 cc of acetone to form precipitate. The precipitate was dissolved in benzene and the benzene solution was spun at 25C in a dry process into fibers having a diameter of about 10 ~.
The spun fibers were subjected to a preliminary heating by gradually heating up to 7Q0C in 6 hours under vacuum.
The thus treated fibers ~ere baked by raising the temperature from 700C to 2,000C while applying ultrasonic wave having a frequency of 2G0 KHz generated from a ultrasonic wave generator of an output of 100 W, to form silicon carbide fibers.
The tensile strength of the silicon carbide fiberq baked at lr700C was 293 Kg/mm2. The tensile strength of the silicon carbide fibers baked in the same manner as described above without applying the ultrasonic wave was 55 Kg/mm2.
Example 34 PolyCsilmethylenesiloxane~ having the follo~ing formula and an average molecular weIght of about 24,0Q0 ~as used as a starting material.

~iLi'7~PZ~;

tfi - CH2 - Si - 0 The organosilicon high molecular weight compound contained less than 5~ of the low molecular weight compound soluble in acetone and this compound was dissolved in benzene to form a spinning solution, which was spun into fibers having a diameter of about 10 ~. The spun fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C in 4 hours under vacuum.
The thus treated fibers were baked by heating from 800C to 2,Q00C, while applying ultrasonic wave having 300 KHz ,-by means of an ultrasonic wave generator of an output of 100 W
to obtain silicon carbide fibers. The formed silicon carbide fibers had a tensile strenyth of 275 Kg/mm2. The tensile strength of the silicon carbide fibers baked in the same manner without applying the ultrasonic wave was 64 Xg~mm2.
Example 35 Dodecamethylcyclohexasilane ~as heat treated in an autoclave at 400C for 48 hours to o~tain organosilicon polymers.
10 g of the silicon poly~ers was- dissolved in lQQ cc of n-hexane and to the solution was added 3Q0 cc of acetone and the ; insoluble portion was about 60%. This insoluble porti.on was - dissolved in benzene and the resulti,n~ solution was spun in a dry process at a spinning temperature of 25C at a spi.nning rate of 100 m/min. through.a spinnlng tube, to ~hi.ch a mixed gas of benzene, acetone and argon, the paxtial pres5uxes of benzene, acetone and argon beinq 0.5, 0.3 and 0.2 atmospheric pressures respectively, was introduced, to obtain fibers having a diameter of 10 Il. The fibers were heated in air at 150C for 30 minutes and then subjected to a preliminary heating by raising the temperature to 800C in about 6 hours under vacuum (1 x 10 3 mmHg).
The thus treated fibers were baked by heating to 1,800C under argon atmosphere to obtain silicon carbide fibers.
The tensile strength of the silicon carbide fibers baked at 1,800C was 68 Kg/mm2, and that of the silicon carbide fibers baked at 1,300C was 410 Kg/mm2 and Young's modulus was 28 ton/mm2.
Example 36 10 g of linear polydimethylsilane Me Me [ I i - Si~
Me Me produced from dimethyldichlorosilane was fed in an autoclave and heated at 400C under a pressure of 50 atmospheres for 48 hours under argon atmosphere. The reaction product was dissolved in ether and an insoluble portion was removed and the resulting solution was evaporated to obtain 4.3 g of a solid product. This solid product had an average molecular weight of 1,800 and was dissolved in 50 cc of hexane and to - the resulting solution was added 200 cc of acetone to form precipitate. The precipitate was dissolved in benzene and the benzene solution was spun at 25C in a dry process through a spinning tube, to which a gaseous mixture of benzene and air having a benzene partial pressure of 0.3 atmospheric pressure, -.

`7~Z~

was introduced, into fibers having a diameter of about 10 ~.
The spun fibers were heated at 200C for 15 minutes in air containing ozone and sub~ec-ted to a preliminary heating by gradually heating up to 700C in 4 hours under vacuum.
The thus treated fibers were baked by raising the temperature to l,800C under vacuum to form silicon carbide fibers. The tensile strength of the silicon carbide fibers baked at l,800C was 65 Kg/mm2.
Example 37 10 g of dodecamethylcyclohexasilane was fed in an autoclave and air in the autoclave was purged with argon gas and the polycondensation reaction was effected at 400C for 48 hours under a pressure of 40 atmospheres. After completion of the reaction, the polycondensation product was permitted to cool at room temperature, and then added with ether to form ether solution. The ether solution was taken out from the autoclave and ether was evaporated to obtain 6.6 g of a solid high molecular weight compound containing 40% of acetone-soluble low molecular weight compounds. The solid high molecular weight compound was heated and aged at 300C for 8 hours while slowly stirring under atmospheric pressure in argon atmosphere to obtain an organosilicon high molecular weight compound containing 5% of acetone-soluble low molecular weight compounds.
The resulting organosilicon high molecular weight compound was dissolved in benzene, and the benzene solution was spun in a dry process to obtain fibers having a diameter of about 10 ~. The fibers were heated at 200C for 30 minutes in air and then gradually heated up to 800C in 6 hours under ~7~2~

vacuum (l ~ 10 3 mm~g) to e~fect the preliminary heating of the fibers, and then baked up to 1,800C to obtain silicon carbide fibers.
The tensile strength of the fibers heated to 1,200C was 650 Kg/mm and that of the fibers heated to 1,800C was 85 Kg/mm .
Example 38 10 g of octaphenylcyclotetrasilane was fed in an autoclave together with 0.1 g of benzoyl peroxide, and air in the autoclave was purged with argon, and the polycondensation was effected at 320C for 24 hours under about 35 atmospheric pressure. After completion of the reaction, hexane was added to the autoclave, and the polycondensation product was taken out from the autoclave in the form of hexane solution.
Insoluble portion in hexane was filtered off, and hexane was - evaporated to obtain 7.1 g of solid high molecular weight ;~ compounds having an average molecular weight of about 4,000.
The high molecular weight compounds were dissolved in 100 cc of hexane, and the hexane solution was then admixed with 400 cc of acetone to obtain 6.3 g of acetone-insoluble precipitate.
The precipitate was dissolved in benzene, and the benzene solution was spun in a dry process through a spinning tube, to which a gaseous mixture of benzene and air having a benzene partial pressure of 0.3 atmospheric pressure, was introduced, into fibers having a diameter of about lO ~. The fibers were heated at 180C for 18 minutes in air and further heated up to 800C in 6 hours under vacuum (l x lO 3 mmHg) to effect the preliminary heating of the fibers. The preliminarily heated , . . . .

: : ..' .

'.'D7~'1'2S

fibers were ~urther baked up to 1,800C in a graphite crucible to obtain silicon carbide fibers. The fibers baked at 1,000C
had a tensile strength of 510 Kg/mm , and fibers baked at 1,800C had a tensile strength of 78 Kg/mm .
Example 39 lO g of a mixture of cyclic dimethylpolysilanes having formulae of (Me2Si)5 and (~e2Si)6 was fed in an autoclave together with 0.5 g of azoisobutyronitrile, and air in the autoclave was purged with argon, and the polycondensation was effected at 400C for 12 hours under a pressure of about 80 atmospheres. After completion of the reaction, benzene was added to the autoclave, and the polycondensation product was taken out from the autoclave in the form of benzene solution.
Insoluble portion in benzene was filtered off and benzene was evaporated under a reduced pressure to obtain 4.8 g of solid high molecular weight compounds having an average molecular weight of about 3,800. The high molecular weight compounds were dissolved in 50 cc of hexane, and the hexane solution was then admixed with 200 cc of acetone to obtain 3.9 g of acetone-insoluble precipitate. The precipitate was dissolved in benzene, and the benzene solution was spun in a dry process through a spinning tube, to which a gaseous mixture of benzene and air having a benzene partial pressure of 0.4 atmospheric pressure was introduced, into fibers having a diameter of about lO ~. The fibers were heated at 150C for 30 minutes in air and then gradually heated up to 800C in 4 hours under vacuum (l x 10 mmHg) to effect the preliminary heating of the fibers.
The preliminarily heated fibers were further baked up to 1,800C under vacuum. The tensile strength of the fibers baked 7~.'J '~

at l,300C was 390 Kg/mm2, and tha-t of the fibers baked at 1,800C was 95 Kg/mm .
Example 40 10 g of a mixture of cyclic diphenylsilane of the formula (Ph2Si)4, that of the formula (Ph2Si)5 and linear polydiphenylsilane was fed in an autoclave and air in the autoclave was purged with gaseous nitrogen, and the polycondensa-tion was effected at 380C for 50 hours under a pressure of about 60 atmospheres. After completion of the reaction, benzene was added to the autoclave, and the pol~condensation product was taken out from the autoclave in the form of benzene solution, and the benzene solution was concentrated under a reduced pressure to obtain 6.9 g of solid high molecular weight compounds. The resulting high molecular weight compounds were dissolved in 50 cc of benzene, and the benzene solution was added with 200 cc of acetone to obtain 4 8 g of acetone-insoluble precipitate. The precipitate was dissolved in benzene, and the benzene solution was spun in a dry process through a spinning tube, to which a gaseous mixture of benzene and argon having a benzene partial pressure of 0.25 atmospheric pressure was introduced, into fibers having a diameter of about 10 ~. The fibers were heated at 200C for 15 minutes in air containing ozone and then gradually heated up to 800C in 4 hours under argon atmosphere to obtain black fibers having metallic luster.
The fibers had a tensile strength of 420 Xg/mm2. The fibers were baked up to 1,300C under helium vacuum to obtain silicon carbide fibers. Then said fibers were heated at 800C for 2 hours in air. The tensile strength of the fibers baked at .

~';i7~

1,300C was 410 Kg/mm2, and that o~ the fibers baked at 1,800C
was 73 Kg~mm .
Example 41 Fluidized hexamethyldisilane was fed into a reaction column as shown in Figure 1 heated to 850C at a feeding rate of l l/hr. together with argon gas. The starting hexamethyldi-silane was subjected to a decomposition reaction and a poly-condensation reaction in the heated reaction column and formed into high molecular weight compounds, and at the same time low molecular weight compounds were formed. A part of the resulting high molecular weight compounds was able to be taken out from the heated reaction column. Major part of the high molecular weight compounds was fed into a separating column together with the low molecular weight compounds, and gases and the low molecular weight compounds were separated from the high molecular weight compounds in the column. The low molecular weight compounds were again fed into the heated reaction column and recycled. The operation was continued for lO hours and 5.4 Kg of high molecular weight compounds having an average molecular weight of about 3,500 was obtained.
From lO g of the resulting high molecular weight compounds, ethyl alcohol-soluble portion was removed by means of a Soxhlet's extractor to obtain 7.8 g of ethyl alcohol-insoluble portion, which was used as a spinning material. The ethyl alcohol-insoluble portion was heated to 145C and spun into fibers having a diameter of about lO ~. The spun fibers were heated from room temperature to 200C in 30 minutes in air and further heated up to 800C in 6 hours under vacuum to effect , 7 ~
the preliminary heatinq of the ~ibers. The preliminarily heated fibers had a tensile strength of 430 Kg/mm2. The thus treated fibers were further baked by heating up to 1,800C under argon atmosphere. The tensile strength of the baked fibers was 105 K~/mm .
Example 42 An apparatus for producing silicon carbide fibers as shown in Figure 24, was used and the entire gaseous contents of the apparatus was substituted with nitrogen. A mixed starting material of about 65~ of dimethyldichlorosilane, about 25% of methyltrichlorosilane, about 5% of trimethylchlorosilane, and about 5% of the other substances was charged in a primary reaction column 1 heated at 750C at a rate of 5 l/hr. The reaction product formed in this column was introduced into the distillation column 2, wherein the gases consisting mainly of propane and hydrogen were separated from liquid. The liquid was introduced into a secondary reaction column 3 heated at 850C to effect the thermal polycondensation reaction and then the reaction product was charged into a separating column 4 and separated into gas, low molecular weight compounds and high molecular weight compounds. The separated gas was discharged from the column through a valve 18, and the low molecular weight compounds were fed into the secondary reaction column 3 through a valve 19 as a recycling material.
The yield of the above high molecular weight polymer was 19% and the average molecular weight was 2,400 and the content of acetone soluble low molecular weight compounds was about 25%.

.
- ~ . .
- ':' ~ '' 7~

The hi~h molecular wci~ht compounds were fed into an aging vessel 5 through a valve 20 and aged at 340C for 4 hours under atmospheric pressure. Thereafter, the thus aged product was filtered with a filter 7, compressed with a pump 8 and then spun through a spinneret 9 into fibers having a diameter of about 10 ~. The spinning temperature was 100C and a mixture of benzene and air having a benzene partial pressure of 0.25 atmospheric pressure was supplied into the spinning tube and the spinning rate was 20 m/hr. These spun fibers were treated from room temperature up to 200C in air for 30 minutes, subjected to a preliminary heating through a preliminary heating apparatus 10 with a length of 4 m and an outlet temperature of 800C under vacuum and then baked to 1,800C in a baking oven 11 with a length of 2 m under argon atmosphere to form silicon carbide fibers, which were wound up on a take-up device 12. The diameter of the formed silicon carbide fibers was about 7 ~, the yield was about 11% based on the starting material and the tensile strength was about 75 Kg/mm . When the baking was effected at 1,100C, the tensile strength was 480 Kg/mm and Young's modulus was 41 ton/mm .
Example 43 Silicon carbide fibers were produced starting from dimethyldichlorosilane in the same manner as described in Example 42.
The dimethyldichlorosilane was charged in the primary reaction column 1 heated at 780C at a rate of 8 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases consisting mainly of propane and hydrogen -1~7~3.Z~

were separated from ll~uid. Next, the ].iquid was introduced into the secondary reaction column 3 heated at 880C to effect the thermal polycondensation reacti.on and then the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds in the separating column 4.
The yield of the above high molecular weight compounds was 27~ and the average molecular weight was 3,200 and the content of acetone soluble low molecular weight compounds was 20%.
The high molecular weight compoundswere aged in the aging vessel 5 at about 350C for about 3 hours, filtered with the filter 7, compressed with the pump 8 and then spun through the spinneret 9 into fibers having a diameter of about 10 ~.
The spinning temperature was about 45C and the spinning rate was about 40 m/hr. These spun fibers were heated from room temperature up to 200C in air containing ozone for 15 minutes, subjected to the preliminary heating through the preliminary heating apparatus 10 having a length of 4 m, an inlet room temperature and an outlet temperature of 800C under vacuum, and then baked at 1,800C in the baking oven 11 under vacuum to form silicon carbide fibers having a diameter of about 7 ~, which were wound up on the take-up device 12. The yield was about 17% based on the starting material and the tensile strength of the fibersbaked at l,800C was 95 Kg/mm2. When the baking was effected at 1,000C, the tensile strength was 430 Kg/mm2 and Young's modulus was 37 ton/mm .
Example 44 Silicon carbide fibers were produced starting from .

-79~
' . . '

11~7~

a mixture o~ about 78~ of climethyldichlorosilane, about 8~ of methyltrichlorosilane, about 3~ of trirnethylchlorosilane, about 2~ of methyldichlorosilane and about 9% of the other substances in the same manner as described in Example 42.
The mixture was charged in the primary reaction column 1 heated at 750C at a rate of 6 l/hr. The reaction product was introduced into the distillation column 2, wherein gases were separated from liquid. Next, the liquid was introduced into the secondary reaction column 3 heated at 850C to effect the thermal polycondensation reaction and then the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds in the separating column 4.
The yield of the above high molecular weight compounds was 21% and the average molecular weight was 2,600 and the content of acetone soluble low molecular weight compounds was about 22%.
The high molecular weight compounds were aged in the aging vessel 5 at 340C for 3 hours, filtered with the filter 7, compressed with the pump 8 and then spun through the spinneret 9 into fibers having a diameter of about 15 ~. The spinning temperature was 75C. These spun fibers were cut into a length of about 30 cm, heated from room temperature up to 150C in air for 30 minutes, subjected to the preliminary heating from room temperature to 800C under vacuum in 6 hours and then baked at 1,800C under carbon monoxide atmosphere to form silicon carbide fibers. The diameter of the formed silicon carbide fibers was about 11 ~ and the yield was 13% based on 1~)7~
the starting material. The tens.ile strength of the fiber was 85 Kg/mm2. When the baking was effected at l,100C, the tensile strength was 490 Kg/mm .
Example 45 Silicon carbide fibers were produced starting from a mixture of about 55% of diphenyldichlorosilane, about 35% of diphenyltrichlorosilane and about 10% of the other substances in the same manner as described in Example 42.
The mixture was charged in the primary reaction column l heated at about 800C at a rate of 4 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases consisting mainly of hydrogen and hydrocarbon were separated from liquid. Next, the liquid was introduced into the secondary reaction column 3 heated at about 900C to effect the thermal polycondensation reaction and then the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds in the separating column 4.
The yield of the above hish molecular weight polymers was 24% and the average molecular weight was about 5,000 and the content of acetone soluble low molecular weight substances was about 5%.
The high molecular weight compounds were filtered with the filter 7 without aging and then spun through the spinneret 9 into fibers having a diameter of about lO ~. These spun fibers were heated from room temperature up to 180C in air for 30 minutes, subjected to the pre~iminary heating through the preliminary heating apparatus lO having a length of 4 m, .

1~7~

an lnlet room temperaturc and an outlet temperature of 800C under vacuum and then baked at 1,800C in the baking oven 11 under a~gon atmosphere to form silicon carbide fibers having a diameter of about 7 ~. The yield of the fiber was 18% based on the starting material. The tensile strength of the fiber was 85 Kg/mm2. When the baking was effected at 1,100C, the tensile strength was 430 Kg/mm .
Example 46 Poly(silmethylenesiloxane) having the following formula and an average molecular weight of about 18,000 was used as a starting material.

-~ Si - CH - Si - O-~
1 2 I n A content of acetone soluble low molecular weight substance contained in this high molecular weight compound was less than 10% and said organosilicon high molecular weight compound was dissolved in benzene to form a spinning solution, which was spun into fibers having a diameter of about 10 ~
through a spinning tube using a mixed atmosphere of benzene and air and having a benzene partial pressure of 0.3 atmospheric pressure. These spun fibers were heated from room temperature up to 200C in air for 10 minutes, subjected to a preliminary heating from room temperature up to 800C under vacuum (1 x 10 3 mmHg) for 4 hours and then baked up to 1,800C under vacuum to form silicon carbide fibers having a diameter of about 8 ~. The tensile strength of the fiber baked at 1,000C was about 390 Kg/mm and the tensile strength of the 7~32S

fiber baked at 1,800C was about 65 Kg/mm2.
Example 47 Pol~(silarylenesiloxane) having the following formula and an average molecular weight of about 16,000 and a content of acetone soluble low molecular weight substance of less than 10%.

~ - I ~ ~

The organosilicon high molecular weight compound was dissolved in benzene to form a spinning solution. This spinning solution was spun into fibers having a diameter of about 10 ~
through a spinning tube using a mixed atmosphere of benzene and air having a benzene partial pressure of 0.3 atmospheric pressure by a dry process. These spun fibers were heated from room temperature up to 2Q0C in ozone for 10 minutes, subjected to a preliminary heating from room temperature up to 800C under vacuum ~1 x 10 3 mmHg) in 6 hours, and then baked up t~ 2,000C under argon atmosphere. Then the fibers were heated at 1,000C in air for 1 hour to remove free carbon. The tensile strength of the fiber baked at 1,300C ~as 390 Kg/mm2 and the tensile strength of the fiber baked at 2,OQ0C was 65 Kg/mm2.
Example 48 Polysilmethylene having the following formula and an average molecular weight of about 20,000 had a content of acetone soluble low molecular weight compounds of less than 6%.

~Si - CH

.. ~

-~3-9~

The organosilicon high molecular weight compound was dissolved in benzene to form a spinning solution. This spinning solution was spun into fibers having a diameter of about 10 ~
through a spinning tube using a mixed atmosphere of benzene and air having a benzene partial pressure of 0.15 atmospheric pressure in a dry process. These spun fibers were heated from room temperature up to 200C in air for 30 minutes, subjected to a preliminary heating from room temperature up to 800C
under vacuum (1 x 10 3 mmHg) in 12 hours, and then baked up to 1,800C under vacuum. The tensile strength of the fiber baked at 1,300C was 415 Kg/mm2 and the tensile strength of the fiber baked at 1,800C was 70 Kg/mm2.
Example 49 Poly(dimethylsiltrimethylene) having the following formula and an average molecular weight of about 21,000 had a content of acetone soluble low molecular weight compound of less than 5%.

¦ 3 --~--Si- CH - CH2 - CH2 3 The organosilicon high molecular weight compound was dissolved in benzene to form a spinning solution. This spinning solution was spun into fibers having a diameter of about 10 through a spinning tube using a mixed atmosphere of benzene and air having a benzene partial pressure of 0.3 atmospheric pressure in a dry process.
These spun fibers were heated from room temperature up to 200C in air containing ozone for 15 minutes and subjected to .~ ~

7'1 1~g37~

a preliminary heating from room temperature up to 800C
under vacuum for 6 hours. The tensile strength of the fibers baked at l,000C was 390 Kg/mm2 arld the tensile strength of the fiber baked at 1,800C under argon atmosphere was 95 Kg/mm2.
Example 50 Silicon carbide fibers were produced starting from tetramethylsilane in the same manner as described in Example 42.
The tetramethylsilane was charged in the primary reaction column 1 heated at 780C at a rate of 9 l/hr. The reaction product was introduced into the distillation column 2, wherein gases consisting mainly of propane and hydrogen were separated from liquid. Next, the liquid was introduced into the secondary reaction column 3 heated at 880C to effect the thermal polycondensation reaction and then the reaction product was separated into gas, low molecular weight compounds and high molecular weight compounds in the separating column 4.
The yield of the above high molecular weight compounds was 16% and the average molecular weight was 2,800 and the content of acetone soluble low molecular weight compounds was 20%.
The high molecular weight compound was aged in the aging vessel 5 at about 360C for about 3 hours, filtered with : the filter 7, compressed with the pump 8 and then spun through the spinneret 9 into fibers having a diameter of about 10 ~.
The spinning temperature was about 147C and the spinning rate was about 50 m/min. These spun fibers were heated from room temperature up to 200C in air containing ozone for 15 minutes, subjected to a preliminary heating through the preliminary heating apparatus 10 having a length of 4 m, wherein an inlet 1~7~2~;

temperature was room temperature and an outlet temperature was 800C, under vacuum and then baked up to 1,800C in the baking oven 11 under vacuum to form silicon carbide fibers having a diameter of about 7 ~I~ which were wound up on the take-up device 12. The yield was about 14~ based on the starting material and the tensile strength of the fiber was 68 Kg/mm2.
When the baking was effected at 1,000C, the tensile strength was 420 Kg/mm2 and Young's modulus was 36 ton/mm2.
Example 51 Fifty grams of 1,1,3,3,-tetramethyl-1,3-disilacyclo-butane was charged into an autoclave and, after air inside the autoclave was purged with argon, polycondensation was effected at 410C for 48 hours. After the completion of reaction, the polycondensation product was taken up in benzene and then benzene was evaporated to obtain 41 g of a solid high molecular `~ weight compound. This high molecular weight compound contained 15% of acetone soluble low molecular weight compounds, so that it was dissolved in 200 cc of hexane and then was admixed with 400 cc of acetone to obtain 33 g of acetone insoluble precipitate.
~ 20 The precipitate was dissolved in benzene and then spun into fibers having a diameter of about 10 ~ through a spinning tube using a mixed atmosphere of benzene and air having a benzene partial pressure of 0.28 atmospheric pressure in a dry process.
These spun fibers were heated from room temperature up to 200C
in air for 30 minutes, subjected to a preliminary heating from room temperature up to 800C under vacuum (1 x 10 3 mmHg) in 6 hours and then baked up to 2,000C under argon atmosphere to form silicon carbide fibers. The tensile strength of the :
,.

~Y ~7~2~;

fiber baked at l,000C was 430 Ky/mm2 and the tensile strength of the fiber bake~ at 2, nooc was 48 Kg/mm~.
Example 52 Dodecamethylcyclohexasilane was heat treated in an autoclave at 400C for 48 hours to obtain organosilicon polymers.
100 g of the organosilicon polymers was dissolved in 100 cc of n-hexane and to the solution was added 700 cc of acetone to obtain about 60% of acetone insoluble portion. This insoluble portion was dissolved in xylene and the resulting solution was spun in a dry process at a spinning temperature of 34C through a spinning nozzle having a diameter of 250 ~ into a spinning tube wherein air was fed in a rate of 2 l/min., at spinning rate of 100 m/min. to obtain fibers having a diameter of 20 ~.
The spun fibers were heated in air at 200C for 30 minutes under a tension of 50 g/mm2. The thus treated fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C in 3 hours under a tension of 200 g/mm2 under vacuum (1 x 10 3 mmHg) and then baked by raising the '! ~ ' temperature up to 1,700C at a rate of increase of 200C/hr. ~-~
under argon atmosphere to obtain silicon carbide fibers having no bent portion. The tensile strength of the silicon carbide fibers baked at 1,700C was 45 Kg/mm2 and the tensile strength of the fibers baked at 1,300C was 415 Kg/mm~ and the strength of the fibers was uniform.
Example 53 100 g of linear polydimethylsilane produced from dimethyldichlorosilane was fed into an autoclave and heated at 400C under a pressure of 50 atmospheres for 48 hours under ~ .
argon atmosphere. The reaction product was dissolved in ether 7'~2~

and the insoluble portion was removed and the resulting solution was evaporated to obtain 58 g of a solid product. This solid product had an average molecular weight of 1,400 and was dissolved in 60 cc of hexane and to the resulting solution was added 400 cc of acetone to obtain an insoluble precipitate in a yield of 65%. This precipitate was dissolved in toluene and the toluene solution was filtered to form a spinning solution.
This spinning solution was spun in a dry process through a spinning nozzle having a diameter of 200 ~ into a spinning tube wherein air having a partial pressure of benzene of 0.01 was supplied, at a spinning rate of 150 m/min. at a spinning temperature of 25C into fibers having a diameter of 10 ~.
The spun fibers were heated in air containing ozone at 200C for 15 minutes under a tension of 50 g/mm2. The treated fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C in 4 hours under a tension of 100 g/mm under argon gas. Then, the fibers were baked by raising the temperature up to 1,800C at a raising temperature rate of 200C/hr. under argon atmosphere under a tension of 100 g/mm to obtain crystalline silicon carbide fibers. The tensile strength of the fibers baked at 1,000C
was 370 Kg/mm and the tensile strength of the fibers baked at 1,800C was 80 Kg/mm2. The thus obtained silicon carbide fibers had no bent portion and the tensile strength was uniform and the fibers were not substantially broken during the spinning.
Example 54 Dimethyldichlorosilane and sodium were reacted in toluene to obtain an insoluble polysilane compound. 100 g of this polysilane was charged in an autoclave and air in the - ~ -`7~.2ti autoclave was substituted with nitrogen gas and the polysilane was heated at 400C for 36 hours. The resulting product was dissolved in hexane and the resulting solution was taken out from the autoclave and filtered and then the hexane was distilled and removed. 55 g of the formed solid high molecular weight compounds was obtained. The softening point of the compounds was 38C, so that the solid compounds were dissolved in 50 cc of hexane and to the solution was added 385 cc of acetone and 28 g of precipitate insoluble in acetone was obtained. 2 parts of the precipitate insoluble in acetone was mixed with 1 part of the acetone soluble portion and the mixture was heated and melted and filtered to form a spinning bath, which was heated at 210C and spun through a nozzle having a diameter of 300 ~ at a spinning rate of 1,000 m/min. into fibers having a diameter of 10 ~. The spun fibers were h~ated from room temperature to 180C in 1 hour and maintained at 180C
for 30 minutes under a tension of 20 g/mm2 in air. The thus treated fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C in 3 hours under a tension of 100 g/mm2 under nitrogen gas.
Subsequently, the thus treated fibers were baked by raising the temperature from 800C to 1,300C in 2 hours to obtain silicon carbide fibers. The tensile strength of silicon carbide fibers baked at l,300C was 380 Kg/mm2 and there was no bent portion in the fibers, so that the silicon carbide fibers having a uniform tensile strength were obtained.
Example 55 100 g of dodecamethylcyclohexasilane was fed in an ... .

~ ~79~`~

autoclave and air in the autoclave was purged with argon gas and the polycondensation reaction was effected at 400C for 37 hours under a pressure of 40 atmospheres. After completion of the reaction, the polycondensation product was permitted to cool at room temperature and then was admixed with ether to form ether solution. The ether solution was taken out from the autoclave and the ether was evaporated to obtain 66 g of a solid high molecular weight compound. The high molecular weight compounds contained the low molecular weight compounds and the softening point was lower than 50C. The solid high molecular weight compounds were heated and aged at 300C for 3 hours while slowly stirring under argon atmosphere to obtain organic silicon high molecular weight compounds having a softening point of 190C.
The resulting organic silicon high molecular weight compounds were dissolved in xylene and the xylene solution was spun in a dry process through a spinning nozzle having a diameter of 300 ~ at a spinning temperature of 25C and at a spinning rate of 250 m/min. into a spinning tube, wherein air was introduced into fibers having a diameter of 10 ~. The spun fibers were heated by raising the temperature from room temperature to 190C
in 1 hour and keeping 190C for 15 minutes under a tension of 50 g/mm2. The thus treated fibers were subjected to the preliminary heating by raising the temperature from room temperature to 800C in 4 hours under vacuum while applying a tension of 200 g/mm2 and further baked by raising the temperature to 1,600C at a raising temperature rate of 300C./min. under vacuum. The tensile strength of the fibers baked at 1,200C

7~t2t~

was 410 Kg/mm2 and the tensile strength of the fibers baked at 1,600C was 105 Kg/mm2 and the fibers had no bent portion and the tensile strength of the fibers was very uniform.
Example 56 100 g of octaphenylcyclotetrafuran was fed in an autoclave together with 1 g of benzoyl peroxide and air in the autoclave was purged with argon gas and the polycondensation was effected at 350C for 24 hours under a pressure of about 35 atmospheres. After completion of the reaction, hexane was added to the atuoclave and the polycondensation product was taken out from the autoclave in the form of the hexane solution. Insoluble portion in hexane was filtered off and the hexane was evaporated to obtain 71 g of solid high molecular weight compounds having an average molecular weight of about 2,000. The high molecular -weight compounds were dissolved in 200 cc of hexane and to the hexane solution was added 1,000 cc of acetone to obtain 6.3 g of acetone insoluble precipitate. The precipitate was dissolved in toluene and the toluene solution was spun in a dry process through a spinning nozzle having a diameter of 250 ~ at a spinning temperature of 30C and at a spinning rate of 150 m/min. into fibers having a diameter of 10 ~. The spun fibers were heated in air to 220C for 18 minutes under a tension of 50 g/mm2.
The thus treated fibers were heated by raising the temperature from room temperature to 800C in ~ hours under argon atmosphere while applying a tension of 200 g/mm2. Then, the fibers were baked by raising the temperature up to l,800C in a graphite crucible to obtain silicon carbide fibers. The tensile strength of the fibers baked at l,000C was 350 Kg/mm2 and the tensile ~7~2~;

strength of th~ fibers baked at 1,800C was 78 Kg/mm2 and the fibers had 310 bent portion and the tensile strength was very uniform.
Example 57 100 g of a mixture of cyclodimethylpolysilanes having formulae of (Me2Si)5 and (Me2Si)6 was fed in an autoclave together with 3 g of azoisobutyronitrile and air in the autoclave was purged with argon gas and the polycondensation was effected at 360C for 12 hours under a pressure of about 80 atmospheres.
After completion of the reaction, benzene was added into an autoclave and the polycondensation product was taken out from the autoclave in the form of benzene solution. Insoluble portion in benzene was filtered off and benzene was evaporated under a reduced pressure to obtain 48 g of solid high molecular weight compounds having an average molecular weight of about 1,800.
The high molecular weight compounds were dissolved in 100 cc of hexane and to the hexane solution was added 700 cc of acetone to obtain 39 g of acetone insoluble precipitate. The precipitate was dissolved in xylene and the solution was filtered off to obtain a spinning solution. This spinning solution was spun in a dry process through a spinning nozzle having a diameter of 200 ~ at a spinning temperature of 45C and at a spinning rate of 200 m/min. into a spinning tube, wherein benzene having a partial pressure of 0.1 was introduced, into fibers having a diameter of 10 ~.
The spun fibers were heated at 190C in air for 30 minutes under a tension of 50 g/mm2. The thus treated fibers were subjected to a preliminary heating by raising the ~37~2~:i temperature from room temperature to 800C in 4 hours while applying a t~nsion of 200 g/mm2 al~d then baked by raising the temperature up to 1,300C at a rate of increase of 200C/hr.
under a tension of 100 g/mm2 to obtain silicon carbide fibers.
The tensile strength of the fibers baked at 1,300C was 410 Kg/~
mm . The above described silicon carbide fibers had no bent portion and the tensile strength of the fibers was very uniform.
Example 58 100 g of a mixture of cyclophenylsilanes having the formulae of (Ph2Si)4 and (Ph2Si)5 and linear polydiphenylsilane was fed into an autoclave and air in the autoclave was purged with nitrogen gas and the polycondensation was effected at 380C for 50 hours under a pressure of about 60 atmospheres.
After completion of the reaction, benzene was added into the autoclave and the polycondensation product was taken out from the autoclave in the form of benzene solution and the benzene solution was concentrated under a reduced pressure to obtain 69 g of the solid high molecular weight compounds. The result-ing high molecular weight compounds were dissolved in 100 cc of benzene and to the benzene solution was added 700 cc of acetone to obtain 48 g of acetone insoluble precipitate. The precipitate was dissolved in benzene and the benzene solution was spun in a dry process through a spinning nozzle having a diameter of 300 ~ into a spinning tube wherein air was introduced, at a spinning temperature of 25C and at a spinning rate of 100 m/min., into fibers having a diameter oE about 10 ~
The spun fibers were heated at 200C for 15 minutes in air containing ozone gas under a tension of 50 g/mm2. The 7~Z~i thus treated fibers were subjected to a preliminary heating by gradually raisillg the temperature up to 800C in 4 hours under argon gas while applying a tension of 500 g/mm2. The fibers were baked by raising the temperature up to l,800C under vacuum to obtain silicon carbide fibers. The silicon carbide fibers were heated at 800C for 0.5 hour in air. The tensile strength of the fibers baked at 1,300C was 410 Kg/mm2 and the tensile strength of the fibers baked at l,800C was 73 Kg/mm2. The above described silicon carbide fibers had no bent portion and the tensile strength of the fibers was very uniform.
Example 59 From hexamethyldisilane was produced the organosilicon high molecular weight compounds according to the present invention by using the apparatus as shown in Figure 1 under atmospheric pressure. Namely, hexamethyldisilane was fed in a fluid form into a reaction column heated at 850C at a feeding rate o 1 l/hr. together with argon gas. The starting hexa-methyldisilane was subjected to decomposition and polycondensa-tion reaction in the heated reaction column and formed into high molecular weight compounds and at the same time low molecular weight compounds were formed. A part of the resulting high molecular weight compounds was able to be taken out from the ; heated reaction column but the major part of the high molecular weight compounds was fed into a separating column together with the low molecular weight compounds and in the separating column, gases and the low molecular weight compounds were separated from the high molecular weight compounds. The low molecular weight compounds were again fed into the reaction ~7~2~i column and used as a rec~cling material. The operation was continued for 10 hours and 5.4 Kg of high molecular weight compounds having an average molecular weight of about 1,500 was obtained.
From 100 g of the resulting high molecular weight compounds, ethyl alcohol soluble portion was removed by means of Soxhlet's extractor to obtain 78 g of ethyl alcohol insoluble portion, which was used as a spinning material. The ethyl alcohol insoluble portion was dissolved in xylene and the solution was heated to 45C and spun through a spinning nozzle having a diameter of 250 ~ at a spinning rate of 100 m/min. into fibers having a diameter of about 10 ~. The spun fibers were heated by raising the temperature from room temperature to 200C in 30 minutes in air under a tension of 50 g/mm2.
The thus treated fibers were subjected to a preliminary heating by raising the temperature up to 800C
in 4 hours under a tension of 150 g/mm2 under vacuum. The thus treated fibers were baked by raising the temperature up to 1,400C under argon atmosphere under a tension of 100 g/mm2 to obtain silicon carbide fibers. The tensile strength of the obtained fibers was 430 Kg/mm2. The silicon carbide fibers had no bent portion and the tensile strength of long fiber was very uniform.
Example 60 An apparatus for producing silicon carbide fibers as shown in Figure 24 was used and the entire gaseous contents of the apparatus was substituted with nitrogen. A mixed starting ~L07'~

material of about 65~ of dimethyldichlorosilane, about 25% of methyltrichlorosilane, about 5% oE trimethylchlorosilane and about 5% of the other substances was charged in a reaction column 1 heated at 750C at a rate of 1 l/hr. to effect a thermal polycondensation reaction, whereby high molecular weight compounds and others were obtained. The reaction product was introduced into a distillation column 2, wherein the gases consisting mainly of methane and hydrogen were separated from liquid and high molecular weight compounds. Among them the gas was discharged out of the system and the liquid was again fed into the reaction column as a recycling material.
The yield of the above high molecular weight polymer was 34% and the average molecular weight was about 1,300 and the softening temperature was 35C.
The high molecular weight compounds were aged at 280C in nitrogen atmosphere for 4 hours, filtered and then spun through a spinning nozzle of 300 ~ at 190C at a rate of 1,000 m/min. into fibers having a diameter of 20 ~. In this case, hot air was blown into the spinning tube. These spun fibers were heated up to 150C in air containing ozone under a tension of 150 g/mm2 in 30 minutes and then maintained at 210C
in air for 15 minutes. The thus treated fibers were heated from room temperature up to 800C in nitrogen atmosphere under a tension of 500 g/mm2 in 3 hours and then baked up to 1,400C
under argon atmosphere to form silicon carbide fibers. The silicon carbide fibers had a tensile strength of 390 Kg/mm2 and uniformity of the tensile strength was very good because of no bent portion.

~1~g7~2~

Example 61 Organosilicon high molecular weight compounds were produced starting from dimethyldichlorosilane in the same manner as described in Example 60.
The dimethyldichlorosilane was charged in the reaction column 1 heated at 780C at a rate of 1 l/hr. The reaction product was introduced into the distillation column 2, wherein the gases consisting mainly of methane and hydrogen were separated from liquid and high molecular weight polymers.
The yield of the above high molecular weight polymer was 24% and the average molecular weight was about 1,400, and the softening temperature was 45C.
The high molecular weight polymer was aged at 210C
in air for 2 hours with slow stirring to obtain a high molecular weight compound having a softening temperature of 180C. This high molecular weight compound was melted and filtered to obtain a spinning solution, which was spun into fibers having a diameter of 15 ~ through nozzles of 300 ~ at a spinning temperature of 200C at a spinning tube rate of 500 m/min. while blowing hot air into a spinning tube. These spun flbers were heated from room temperature up to 190C in air under a tension of 50 g/mm2 in 1 hour and maintained at 190C for 30 minutes and subjected to a preliminary heating from room temperature up to 800C in argon atmosphere under a tension of 200 g/mm2 in 3 hours and further baked up to 1,700C under argon atmosphere at a rate of 200C/hr. to form silicon carbide fibers. The tensile strength of the fibers baked at 1,300C was 400 Kg/mm2 and the tensile strength of the fibersbaked at l,700C was 85 Kg/mm2.

7~

The silicon carbide fibers had good strength properties because of no bent portion.
Example 62 Poly(silmethylenesiloxane) having the following formula and an average molecular weight of about 8,000 was used as a starting material.

~Si - CH2 - Si - 0~

The softening point of the above described high molecular weight compound was higher than 50C and this compound was melted and filtered to obtain a spinning melt.
This melt was spun through a spinning nozzle having a diameter of 300 ~ at a spinning temperature of 150C and a spinning rate of 500 m/min. into fibers having a diameter of 15 ~.
The spun fibers were heated by raising the temperature from room temperature to 150 C in 1 hour and maintaining 150C for 30 minutes in air containing ozone under a tension of 100 g/mm2.
The thus treated fibers were subjected to a preliminary heating by raising the temperature from room temperature to 800C

in 3 hours under vacuum and succeedingly, the temperature was raised to 1,400C at a raising temperature rate of 200C/hr.
to bake the fibers, whereby silicon carbide fibers were obtained.
The tensile strength of the fibers baked at 1,400C was 390 Kg/mm and the fibers had no bent portion, so that tensile strength was very uniform.

~ ~ 017~26 Example 63 Poly(silarylenesiloxane) having the following formula and an average ~olecular weight of 12,000 was used as a starting material.

~ O - S - O ~

The softening point of the above described high molecular weight compound was 180C and was melted and filtered to prepare a spinning melt. This melt was spun at a spinning temperature of 203C through a spinning nozzle having a diameter of 250 ~ at a spinning rate of 1,000 m/min. into fibers having a diameter of 10 ~.
The spun fibers were heated by raising temperature to 180 C in 1.5 hours and keeping 180C for 15 minutes in air under a tension of 200 g/mm2, subjected to a preliminary heating by raising the temperature from room temperature to 800C
in 3 hours under a tension of 400 g/mm in nitrogen gas. The thus treated fibers were baked by raising the temperature up to 1,700C at a raising temperature rate of 200C/hr. under argon gas to obtain silicon carbide fibers. In the above described silicon carbide fibers, the tensile strength of the fibers baked at l,000C was 340 Kg/mm2, the tensile strength of the fibers baked at 1,300C was 380 Kg/mm2 and the tensile strength of the fibers baked at 1,700~ was 65 Kg/mm2. The fibers had no bent portion and the tensile strength in the long fibers was very uniform.

_99_ 7¢3~

Example 64 Polysilmethylene having the following Eormula and an average molecular weight of about 4,000 was used as a starting material.

[ Si - CH

The above described high molecular weight compound had a softening point of lower than 50C and was aged at 390C
for 2 hours under a nitrogen gas and then filtered to prepare a spinning melt. This melt was spun through a spinning nozzle having a diameter of 200 ~ at a spinning temperature of 180C
and a spinning rate of 150 m/min. into fibers having a diameter of 10 ~. The spun fibers were heated by raising the temperature from room temperature to 160C in 2 hours in air and then subjected to a preliminary heating by passing through an oven having a length of 1 m, wherein the center portion was heated at 800C, while applying a tension of 500 g/mm2 under a nitrogen gas.
The thus treated fibers were baked by passing through an oven having a length of 2 m where the center portion was 2Q heated at 1,300C under argon gas to obtain silicon carbide fibers. The tensile strength of the fibers baked at 1,300C

was 340 Kg/mm2 and the fibers had no bent portion and the tensile strength in the long fibers was very uniform.
Example 65 Polysiltrimethylene having the following formula and an average molecular weight of about 6,00G was used as a ' , `

~792~;

starting material.

The above described polymer was heated and melted and then filtered. The filtered melt was spun through a spinning nozzle having a diameter of 240 ~ at a spinning temperature of 140C and a spinning rate of i,200 m/min. into fibers having a diameter of 10 ~.
The spun fibers were heated by raising the temperature to 130C in 1 hour and keeping 130C for 15 minutes in air containing ozone under a tension of 150 Kg/mm and then subjected to a preliminary heating by raising the temperature from room temperature up to 800C in 3 hours under vacuum. The thus treated fibers were baked by raising the temperature to 1,600C at a rate of increase of 200C/hr.
in argon gas to obtain silicon carbide fibers. The tensile strength of the fibers baked at l,000C was 310 Kg/mm2, the tensile strength of the fibers baked at l,300C was 380 Kg/mm2 and the tensile strength of the fibers baked at 1,600C
was 108 Kg/mm2. The fibers had no bent portion and the tensile strength of the fibers was very uniform.
Example 66 250 g of polysilane was charged into an autoclave of 1 Q and air in the autoclave was purged with argon gas and said polysilane was reacted at 470C for 14 hours while stirring. The reaction product was dissolved in n-hexane and 7~

such a solution was taken out from the autoclave and filtered.
Then, n-hexane was removed by reducing pressure by means of an aspirator to ~orm a viscous product. This product was concentrated at 260C under vacuum to obtain 130 g of silicon high molecular weight compounds having a softening point of 230C and an intrinsic viscosity of 0.5.
The high molecular weight compounds were heated to 280C and spun through a spinning nozzle having a diameter of 300 ~ at a spinning rate of 300 m/min. into fibers. The spun fibers were heated by raising the temperature from 10C to 150C in 2.5 hours and from 150C to 180C in 30 minutes and keeping 180C for 30 minutes under air under a tension of 20 g/mm to form oxide layer on the fiber surface. The thus treated fibers were baked by raising the temperature to 1,300C
at a rate of increase of 100C/hr. under a tension of 200 g/mm2 under vacuum and maintaining 1,300C for 1 hour to obtain silicon carbide fibers. The tensile strength of the fibers was 350 Kg/mm2 and the Young's modulus was 28 ton/mm2.
The silicon carbide fibers of the present invention having the tensile strength comparable with 300-400 Kg/mm2 - of piano wire, which is the highest in the tensile strength among steel materials, can be easily obtained and the specific gravity was about 3Ø The acid resistance, antioxidation and heat resistance of the fibers are excellent and the wetting to metals and alloys is better than that of carbon fibers and the reactivity with metals and alloys is poor, so that the fibers are very useful for fibrous materials of fiber reinforced metals, plastics and rubbers, electric heating . .

, .

7~

fibers, fire proof cloth, acid resistant membrane, atomic furnace material, airplane constructlon material, bridges, building material, nuclear fusion furnace material, rocket material, radiation element, abrasive cloth, wire rope, marine developing material, golf shaft material, sky stock material, tennis racket material, fishing rods, shoe bottom materials and the like.

Claims (39)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for producing a silicon carbide fiber having a high tensile strength which comprises:
(A) subjecting at least one organosilicon compound selected from (l) a compound having only Si-C bond, (2) a compound having Si-H bond in addition to Si-C bond, (3) a compound having Si-X bond, X being halogen, (4) a compound having Si-N bond, (5) a compound having Si-OR bond (R-alkyl or aryl), (6) a compound having Si-OHbond, (7) a compound having Si-Si bond, (8) a compound having Si-O-Si bond, (9) an ester of organosilicon compound and (10) a peroxide of organosilicon compound, to polycondensation to produce an organosilicon high molecular weight compound, in which silicon and carbon are the main skeleton components, (B) reducing the content of low molecular weight compound mixed together with said high molecular weight compound by treating the mixture with at least one treatment selected from the group of treatments consisting of contacting said mixture with a suitable solvent, aging said mixture at a temperature of 50° - 700°C and distilling said mixture at a temperature of 100° - 500°C, to produce an organosilicon high molecular weight compound having a softening point of higher than 50°C, (C) preparing a spinning solution from said obtained organosilicon high molecular weight compound and spinning said spinning solution into a fiber, (D) preliminarily heating the spun fiber at a temperature of 350°-800°C under vacuum to volatilize remaining low molecular weight compounds, and (E) baking the thus treated fiber at a temperature of 800°-2,000°C
under vacuum or at least one nonoxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas.

2. The method of claim 1 wherein said mixture of low molecular weight compound and high molecular weight compound is aged at a temperature of 50°-700°C.

3. The method as claimed in claim 2, wherein said aging for reducing the content of low molecular weight compound is effected under an atmosphere of air, oxygen or ammonia gas.

4. The method of claim 1 wherein the polycondensation is achieved by the addition of a catalyst selected from the group consisting of Na, KOH, H2SO4, H2PtCl6, benzoyl peroxide, di-tert.-butyl peroxy-oxalate, di-tert.-butyl peroxide and azoisobutyronitrile.

5. The method of claim 1 wherein the polycondensation is achieved by irradiation.

6. The method of claim 1 wherein the polycondensation is achieved by heating.

7. The method of claim 1 wherein said mixture of low molecular weight compound and high molecular weight compound is treated with a solvent that will preferentially dissolve low molecular weight compound.

8. The method of claim 1 wherein said mixture of low molecular weight compound and high molecular weight compound is distilled at a temperature of 100°-500°C.

9. The method of claim 1 wherein said spinning solution is prepared by dissolving said organosilicon high molecular weight compound in a solvent selected from the group consisting of benzene, toluene, xylene, ethyl-benzene, styrene, cumene, pentane, hexane, octane, cyclopentadiene, cyclo-hexane, cyclohexene, methylene chloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, methylchloroform, 1,1,2-trichloro-ethane, hexachloroethane, chlorobenzene, dichlorobenzene, ethyl ether, dioxane, tetrahydrofuran, methyl acetate, ethyl ether, ethyl acetate, acetonitrile and carbon disulfide.

10. The method of claim 1 wherain said spinning solution is prepared by melting said organo-silicon high molecular weight compound.

11. The method as claimed in claim 1, wherein said prelininary heating (step D) is effected under a tension of 0.001-20 Kg/mm2.

12. The method as claimed in claim 1, wherein said baking (step E) is effected under a tension of 0.001-100 Kg/mm2.

13. The method as claimed in claim 1 wherein said baking (step E) is effected under exposure to an ultrasonic wave having a frequency of 10KHz -20 MHz.

14. The method as claimed in claim 1 wherein after the baking in step (E) said fiber is heated at a temperature of 600°-1,700°C under an oxidizing atmosphere to remove free carbon contained in the filaments as CO2.

15. The method as claimed in claim 1, wherein said solvent for reducing the content of the low molecular weight compound is an alcohol or acetone.

16. A method for producing a silicon carbide fiber having a high tensile strength which comprises:
(A) subjecting at least one organosilicon compound selected from (1) a compound having only Si-C bond, (2) a compound having Si-H bond in addition to Si-C bond, (3) a compound having Si-X bond, X being halogen, (4) a compound having Si-N bond, (5) a compound having Si-OR bond (R-alkyl or aryl), (6) a compound having Si-OH bond, (7) a compound having Si-Si bond, (8) a compound having Si-O-Si bond, (9) an ester of organosilicon compound and (10) a peroxide of organosilicon compound, to polycondensation to produce an organosilicon high molecular weight compound, in which silicon and carbon are the main skeleton components, (B) reducing the content of low molecular weight compound mixed together with said high molecular weight compound by treating the mixture with at least one treatment selected from the group of treatments consisting of contacting said mixture with a suitable solvent, aging said mixture at a temperature of 50°-700°C and distilling said mixture at a temperature of 100°-500°C, to produce an organosilicon high molecular weight compound having a softening point of higher than 50°C, (C) preparing a spinning solution from said obtained organosilicon high molecular weight compound and spinning said spinning solution into a fiber, (D) heating the spun fiber at a temperature of 50°-400°C under an oxidizing environment to form an oxide layer on the fiber surface, (E) preliminarily heating the spun fiber at a temperature of 350°-800°C
under a non-oxidizing atmosphere to volatilize remaining low molecular weight compound, and (F) baking the thus treated fiber at a temperature of 800°-2,000°C
under vacuum or at least one non-oxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas.

17. The method of claim 16 wherein said mixture of low molecular weight compound and high molecular weight compound is treated with a solvent that will preferentially dissolve said low molecular weight compound.

18. The method as claimed in claim 17, wherein said solvent for reducing the content of low molecular weight compound is an alcohol or acetone.

19. The method of claim 16 wherein the polycondensation is achieved by the addition of a catalyst selected from the group consisting of Na, KOH, H2SO4, H2PtCl6, benzoyl peroxide, di-tert.-butyl peroxy-oxalate, di-tert.-butyl peroxide and azoisobutyronitrile.

20. The method of claim 16 wherein the polycondensation is achieved by irradiation.

21. The method of claim 16 wherein the polycondensation is achieved by heating.

22. The method of claim 16 wherein said mixture of low molecular weight compound and high molecular weight compound is aged at a temperature of 50°-700°C.

23. The method of claim 16 wherein said mixture of low molecular weight compound and high molecular weight compound is distilled at a temperature of 100°-500°C.

24. The method of claim 16 wherein said spinning solution is prepared by dissolving said organosilicon high molecular weight compound in a solvent selected from the group consisting of benzene, toluene, xylene, ethyl-benzene, styrene, cumene, pentane, hexane, octane, cyclopentadiene, cyclohexane, cyclohexene, methylene chloride, chloroform, carbon tetra-chloride, 1,1-dichloroethane, 1,2-dichloroethane, methylchloroform, 1,1,2-trichloroethane, hexachloroethane, chlorobenzene, dichlorobenzene, ethyl ether, dioxane, tetrahydrofuran, methyl acetate, ethyl acetate, acetonitrile and carbon disulfide.

25. The method of claim 16 wherein said spinning solution is prepared by melting said organo-silicon high molecular weight compound.

26. The method as claimed in claim 16 wherein said preliminarily heating (step E) is effected under a tension of 0.001-20 Kg/mm2.

27. The method as claimed in claim 16 wherein said baking (step F) is effected under a tension of 0.001-100 Kg/mm2 or ultrasonic wave having a frequency of 10 KHz-20MHz.

28. The method as claimed in claim 16 wherein said baking (step F) is effected under exposure to an ultrasonic wave having a frequency of 10 KHz-20 MHz.

29. The method as claimed in claim 16, wherein said heating for forming the oxide layer on the fiber surface (step D) is effected under a tension of 0.001-5 Kg/mm2.

30. The method as claimed in claim 16, wherein said oxidizing environment in the step (D) is air, ozone, oxygen, chloride gas or bromine gas.

31. The method as claimed in claim 16, wherein said oxidizing environment in the step (D) is an aqueous solution of KMnO4, K2Cr2O7 or H2O2.

32. A method for producing a silicon carbide fiber having a high tensile strength which comprises (1) preparing a spinning solution from at least one organosilicon high molecular weight compound having a softening point of higher than 50°C in which silicon and carbon are the main skeleton components, and spinning said spinning solution into a fiber, (2) preliminarily heating the spun fiber at a temperature of 350°-800°C
under vacuum or a non-oxidizing atmosphere to volatilize low molecular weight compound contained therein, and (3) baking the thus treated fiber at a temperature of 800°C-2,000°C
under vacuum or at least one non-oxidizing atmosphere selected from the group consisting of an inert gas, CO gas and hydrogen gas, to form said silicon carbide fiber.

33. The method of claim 32 wherein said spinning solution is prepared by dissolving said organosilicon high molecular weight compound in a solvent selected from the group consisting of benzene, toluene, xylene, ethylbenzene, styrene, cumene, pentane, hexane, octane, cyclopentadiene, cyclohexane, cyclohexene, methylene chloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, methylchloroform, 1,1,2-trichloro-ethane, hexachloroethane, chlorobenzene, dichlorobenzene, ethyl ether, dioxane, tetrahydrofuran, methyl acetate, ethyl acetate, acetonitrile and carbon disulfide.

34. The method of claim 32 wherein said spinning solution is prepared by melting said organosilicon high molecular weight compound.

35. The method as claimed in claim 32, wherein said preliminary heating (step 2) is effected under a tension of 0.001-20 Kg/mm2.

36. The method as claimed in claim 32, wherein said baking (step 3) is effected under a tension of 0.001-100 Kg/mm2.

37. The method as claimed in claim 32 wherein said baking (step 3) is effected under exposure to an ultrasonic wave having a frequency of 10 KHz-20 MHz.

38. The method as claimed in claim 32, wherein after the baking in step (3), the fibers are heated at a temperature of 600°-1,700°C under an oxidizing atmosphere to remove free carbon contained in the filaments as CO2.

39. A continuous silicon carbide fiber having tensile strength of 200-800 Kg/mm2, Young's modulus of 10-40 ton/mm2 and resistant to corrosion and oxidation and showing no decrease in the tensile strength and Young's modulus at B temperature of 800°C, to 1,400°C, which are composed of ultra-fine grain silicon carbide having an average grain size of less than 0.1µ.