AU606177B2

AU606177B2 - New polycarbosilane useful for the manufacture of ceramic products and articles based on silicon carbide

Info

Publication number: AU606177B2
Application number: AU18760/88A
Authority: AU
Inventors: Bruno Boury; Leslie Carpenter; Robert Corriu
Original assignee: Rhone Poulenc Chimie SA
Current assignee: Rhodia Chimie SAS
Priority date: 1987-07-10
Filing date: 1988-07-06
Publication date: 1991-01-31
Anticipated expiration: 2008-07-06
Also published as: FI883273A0; FR2617854B1; CN1031535A; FI883273A; NO883055L; KR890002284A; DK381088D0; IL87002A0; NO883055D0; FR2617854A1; BR8803443A; IL87002A; AU1876088A; EP0300862A2; EP0300862A3; JPH01156986A; ZA884834B; DK381088A; PT87948A

Description

COMMONWEALTH OF AUSTRALIA PATENT ACT 1952 COMfLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE CLASS INT. CLASS Application Number: Lodged: Complete Specification Lodged: Accepted: Published: y~ p Priority: 040 0 S0 0 o A 0 a 0 0 0 00 Q 0 *0 O tt Related Art-: NAME OF APPLICANT: RHONE-POULENC CHIbtIE ADDRESS OF APPLICANT: 25, Quai Paul Doumer, 92408, Courbevoie, France.

NAME(S) OF INVENTOR(S) Robert CORRIU Bruno BOURY Leslie CARPENTER t A 6 4 ADDRESS FOR SERVICE: DAVIES COLLISON, Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: "NEW POLYCARBOSILANE USEFUL FOR THE MANUFACTURE OF CERAMIC PRODUCTS AND ARTICLES BASED ON SILICON CARBIDE" The following statement is a full description of this invention, including the best method of performing it known to us -1la The present invention provides a new polycarbosilane, and a process for its manufacture.

The new polycarbosilane is useful in the manufacture of ceramic products and articles based on silico,, carbide, especially ti the form of fibres.

The idea of preparing ceramic products, filled or othe:wise, based on silicon carbide from organosilicon compounds is noi novel. In the case of the preparation of ceramic products containing silicon carbide by heat S 10 degradation of organosilicon polymers, many articles and °o patents have been published.

For example, French Patent No, 2,308,650 discloses a process for the preparation of polycarbosilanes by pyrolysis in an autoclave of polysilanes obtained by reaction of S 15 molten sodium or liti lum metails with dimethyldichlorosilane in a solvent (xylene). The polycarbosilanes thus obtained S can then be heated to generate 0 silicon carbide.

In the particular case where it is desired to obtain 'i-C fibres, the basic scheme described in this document may be summarized as follows: I I nMe 2 Sicl 2 ,>si i-CH2n-,polycarbositane fibre- Si-C fibre Me H (Me methyl radical, 6 heat treatment;.

Al 2 However a process of this kind has a number of disadvantages both in respect of its use and in respect of the products obtained. Firstly, it makes it necessary to employ very large quantities of molten sodium during the polysilane preparation stage (2 tons of Na per ton of Si-C produced).

In addition, e stage of conversion of polysilanes into polycarbosilanes requires very high reaction temperatures and pressures and very long reaction times 400-470'C; P: 80-110 atm; t: 10-15 hours).

Lastly, the polycarbosilanes obtained by t-his process offer weight yields of ceramic material which may apear inadequate (of the order of 60% by weight), bearing in mind the theoretical yield capable of being obtained with products of this type (70% by weight).

All these disadvantages make the preparative process, on the one hand, and the polycarbosilane precursors described in this document, on the other hand, particularly ill-suited to an industrial-scale production of ceramic materials based on silicon carbide.

The objective of the present invention is therefore problerfS' to solve the above -prblamrs and to produce a simple, effective, economical and easily feasible means for PO o Cctr-b.os \ko.or e obtaining po yai4ies in a wide variety of forms (filaments, moulded articles, coatings, films, and the like), which, on 3 3 being pyrolysed, give ceramic products in a high weight yield.

It has now been found that it is possible to obtain high weight yields of ceramic materials based on silicon carbide using the new composition of the invention, which consists of a polycarbosilane of the average formula: eo H o Si-CH 2

-CH

2

(I)

ii in which the average value of n is equal to at least 2.

The polycarbosilanes according to the invention, in a completely unexpected and surprising manner, produce weight yields of Si-C cf 67% or more, though stoichiometrically equivalent to the polycarbosilanes of patent FR 2,308,650.

The invention also provides a process for the preparation of the polycarbosilanes defined above, which comprises the following stages: comprises the following stages: reaction ESi-H/=Si-CH=CH 2 reducing the composition obtained at the end vof stage in an anhydrous medium using a chemical 1 reducing agent which replaces the chlorine atoms preent in i the said composition by hydrogen atoms.

Besides the fact that it makes it possible to dispense with the use of molten metals (lithium or sodium) and with working under very severe ope ating conditions, thus circumventing the disadvantages inherent in an application of this kind, the process of the invention has also enabled the Applicants to obtain, with excellent reproducihility, new polycarbonsilanes which, on being pyrolysed, offer quite remarkable weight yields of ceramic, which thus makes them particularly highly suitable for the manufacture of ceramic moulded articles based on silicon carbide.

In the process for the preparation of the novel polycarbosilanes of the invention, the starting material employed is a dichlorovinylhydrosilane, of formula

CH

2 =CH-SiHC1 This product may be prepared by any means known per se, for example by heating a mixture based on vinyltrichlorozilane, hexylsilane and tributylamine (US-A- 3,646,091) or by reaction of vinylmethoxydichlorosilane with diethylaluminium hydride (FR-A-2,035,609), or else by reaction of a dichlorosilane with a semistoichiometric quantity of ethylene (FR-A-2,054,357).

DichLorovinyLhydrosiLane is a liquid material, so o1' that a bulk polymerization of this material can be under- O^ 10 taken. It is obviously quite possible to perform this polymerization in an organic solvent medium.

o This polymerization is of a catalytic type and o corresponds to a hydrosilylation reaction between the =Si-H groups and the sSiCH=CH 2 groups of the starting 0 15 material. The reaction temperature is not critical; in the case of a bulk polymerization, it generally lies in Sa range from 50 0 C to 110 C; in a solvent medium, the limit corresponds to the reflux temperature of the solvent (hexane 68-69°C). Furthermore, in order to initiate this reaction it is preferable to apply slight heat to the reactant mixture.

The operation is generally performed at atmospheric pressure; higher or lower pressures are obviously aiot excluded.

Any metal or metallic compound, including metal complexes, which effectively promotes the addition of the .SiH groups to the =SiCHCH group may be employed as

I

6 a catalyst.

A great variety of such catalysts is known, including certain iron, nickel and cobalt carbonyl compounds.

5 The catalyst is preferably a metal from the plai tinum group (platinum, iridium, rhodium, ruthenium, osmium and palladium), introduced into the composition in the form of a fine metal, powder or preferably in the form of a complex in a proportion of 1 to 400 ppm, preferably of 10 to 250 ppm, calculated as the weight of catalyst metal.

It is possible to employ as a catalyst complexes of a metal from the platinum group, especially the platinum-olefin complexes as described in US Patents 3,159,601 and 3,159,662, the products of reaction of platinum derivatives with alcohols, aldehydes and ethers described in US Patent 3,220,972, the platinum-vinylsiloxane cata- Lysts described in French Patents 1,313,846 and its addition 88,676 and French Patent 1,480,409 and the complexes described in US Patents 3,715,334, 3,775,452 and 3,814,730, or a rhodium catalyst such as described in US Patents 3,296,291 and 3,928,629.

The preferred metals from the platinum group are platinum and rhodium; ruthenium, which is less costly, can also be employed.

By way of example, the catalysts based on H 2 PtCI 6 or those based on RhCl(P 3 3

C

6

H

5 are particularly 1 44 I MMW__ 7 suitable.

Analysis shows that the product obtained at the end of polymerization has the stoichiometry SiC 2

H

4

CI

2 and is a polydichlorosiethyLene of average formula: Cl 1 (Si-CH 2

CH

in which the average value n can vary from 2 to 100, and more particularly between 6 and 10. This product is a o.,4 white solid, very poorly soluble in the majority of the usual organic solvents.

10 This polydichlorosilethylene is then reduced by 0 o0 substituting hydrogen atoms for the chlorine atoms bonded 0 to the silicon atoms. To do this, a chemical reducing agent is employed in a quantity which is at least stoichiometric in relation to the chlorine present, the reduction being performed in an anhydrous medium such as ether.

Reducing agents which may be used are for example, all the compounds containing a hydride, insofar as these are capable of eliminating practically all the chlorine present in the polydichlorosilethylene. Lithium aluminium hydride, sodium borohydride or sodium hydride are thus suitable. Lithium aluminium hydride LiALH 4 is preferably employed. For a detailed description of the conditions of use of compounds of this type reference may be made in particular to Patent FR 2,487,364.

It is also possible to employ an alkali or 8 4 4n 4 #4 4 1 #4 4$ 4* 4441 aLkaline-earth cetal hydride such as a Lithium hydride, a calcium hydride or a magnesium hydride, mixed with at least one sequestering agent, according to a process such as described in Patent FR 2,576,902. In this case, lithium hydride LiH will advantageously be employed with a tris(3,6-dioxaheptyl)amine of formula: N 4CH 2

-CH

2 -0-CH 2

-CH

2

-O-CH

3 3 After complete reaction and removal of the solvents, a viscous, clear and transparent oil is obtained, which is soluble in most of the usual organic solvents.

The formula of this product has been determined by infrared (IR) and NMR (1H 13 C 29Si) analysis, and the polymerization value has been determined by ga, phase chromatography (GPC). This product, with a stoichiometry of 15 SiC 2

H

6 is thus a polydihydrosilethylene of average formula:

H

+Si-CH2-CH2 n in which the value n can vary between 2 and 100, and more particularly between 6 and One of the advantages of the polycarbosilane according to the invention lies in its remarkable ability, when pyrolysed, to produce silicon carbide in a very high weight yield, based on the starting material.

A dynamic thermogravimetric analysis (TGA) conducted under nitrogen from 0 C to 1,000°C and coupled with an IR and XR analysis shows that, during heat c i i 1

I-

9 treatment, volatile compounds (hydrogen, alkanes and C-C4 alkenes) are given off first of all, to end with amorphous silicon carbide at about 850 0 C and then, when this temperature has been exceeded, with a silicon carbide powder with more than 991_ by weight in the 0 crystalline form (no a phase detectable; very low SiO content).

In order to complete the conversion into 0 SiC it may be necessary to conduct the pyrolysis up to approximately 1,100-1,2000C.

The weight yield of silicon carbide goes up to 67%, or nearly 96% of the theoretical weight yield capable of being obtained for a polycarbosilane of SiC 2

H

6 stoichiometry.

This means that the p/lycarbosilanes according to the invention are .especially useful in the manufacture of ceramic products and articles containing at least a proportion of silicon carbide.

In the most general case (production of Si-C powders), a polycarbosilane according to the invention is then heated in an inert atmosphere or under vacuum, at a temperature of between 900 0 C and 1,500°C, until the polycarbosilane is completely converted into silicon carbide.

When the intention is to produce a shaped product (fibres, filaments, and the Liks), the polycarbonate is then given the shape of the desired article before heating is carried out so as to obtain a silicon carbidebased moulded ceramic article after heating.

A conventional ceramic filler may, of course, e a filler IT) i! also be added to the polycarbosilane of the invention, and this is done before the said shaping is carried out.

This operation permits the end productsi to be moulded ceramic articles containing silicon carbide as a binder.

i 5 Finally, the ceramic filler-polycarbosilane mixture described above can be employed for coating a sub- Sstrate of any shape (monolith, plate, fibre, and the Slike) and of various natures (metal, ceramic, glass, alloy, and the like) to obtain an article coated with a ceramic material containing silicon carbide after heating.

In the case where the above process results in powders, these can be-shaped and then 'sintered in a conventional manner to produce ceramic articles made of silicon carbide.

In the case where the above process results in fibres, these can be used as a rleinforcing structure for ceramic/cerimic or ceramic/metal composite materials.

i The following Examples illustrate the invention.

20 Example 1 This example illustrates one of the methods of preparatio. oa the dichlorovinylhydrosilane employed as starting material for the preparation of' the polycarbosilanes according to the invention.

20 g (0.1I mole) of phenylsilane (A SiH 3 and 101 g (0.628 mole) of trichlorovinylsilane are introduced i

I

.II K 11 into a 250-cm 3 single-necked flask fitted with a condenser.

i hwo-meth~fkosheZ hoker4,lc L' Y 5 cm of h444"nthilpnonorami e s redistiLled over sodium, are added to this mixture.

After stirring for half an hour under nitrogen, a first mixture of products containing chlorodihydrovinysilane, dichorovinyLhydrosi Lane and trichlorovinylsi lane (boiling range: 30-80 0 C) is distilled directly. A second distillation using a packed column permits 25 g of dichlorovinyhydrosilane to be isolated (boiling point at atmospheric pressore: 62 0

C)

The yield based on the initial trichlorovinylsilane is 37% by weight.

Example 2 This example illustrates the preparation of polydichlorosilethylene from a dichlorovinylhydrosilane.

g (0.16 mole) of a dichLorovinyhydrosilane prepared according to Example 1 and 30 pL of a solution of H 2 PtCL 6 -based catalyst diluted to a concentration of 3.7% by weight in 2-ethyhexanoL are mixed in a 100-cm 3 single-necked flask fitted with a large condenser and a nitrogen inlet.

To save time, the reaction is initiated by gentle heating.

The rea.tion is then exothermic and very fast.

After cooling, a white solid which has the SiC 2

H

4

CI

2 stoichiometry is obtained and is identified as being a poty c, Poydich Loros i lethylene of formuLa Ui 12 cI Cl Example 3 This example illustrates the last stage of prepar- Sation of the polycarbosilane according to the invention.

I 5 A second suspension obtained by adding 20 g of h the polydichlorosilethylene obtained according to Example i 2 to 150 cm of anhydrous ether is added under nitrogen to a first suspension obtained by adding 13.36 g (0.35 mole) of LiALH 4 to 250 cm 3 of anhydrous ether and kept at 0 0

C.

When the addition is complete the mixture is left at ambient temperature for 4 hours.

An acid hydrolysis is then performed in a waterice-HCl mixture.

The aqueous phase is extracted 3 times with 200 cm of ether. The ether phases art, ,b Ifned and are then dried over MgSO 4 The solvent is then removed in a rotary evapor- Sator.

Ii 20 7.7 g of an oily, clear and transparent residue are then obtained in an 82% yield based on the initial chloro polymer. This product, with SiC2H 6 stoichiometry, is identified as being a polydihydrosilethylene of formula:

H

i 1 13 in which the mean value n is between 2 and 8.

Example 4 This example illustrates the behaviour of the polycarbosilanes according to the invention when pyrolysed.

The final product obtained in Example 3 is first heated under nitrogen 4e4-.m-60 0 C to 450°C with a temperature rise of 1.5 0 C/min. A 2-hour plateau is maintained at 4500C.

At the end of this first stage, condensable volatiles have been formed, together with noncondensable volatiles:

H

2 starting at 0 0

C

2

H

4 starting at 4000C

C

2

H

6 starting at 400 0

C

These volatiles correspond to decomposition pro- ,'ucts of the carbon chain.

The product is then heated from 450 to 9500C under nitrogen with a temperature rise of 1.5 0 C/min.

Volatile products are released: H2, CH 4

CH

4

C

2

H

6

C

3

H

6

C

3

H

8 and C 4

H

8 The elemental analysis of the product obtained at 950°C is as follows, in percentages by weight: Si C H Others 67.7 31.5 0.1 0.7 The product has therefore substantially the same elemental analysis as Si-C <Si 70% C I A

IA

-14 At about 1,100 0 C, XR rnaLysis permits onLy phase SiC to be detected. The weight yieLd of SiC is 67%, based on the start ing material

Claims

4. 15 The claims defining the invention are as follows: 1. A polycarbosilane of the average formula: Si-CH 2 -CH 2 (1) H in which the average value of n is equal to at "east 2, II 2 A polycarbos-lane according to claim 1, in which the value of n in formula is between 2 and 100. 3. A polycarbosilane according to claim 1, in which the value of n is from 6 to 10. 4. A process for the manufacture of a polycarbosilne as defined in claim 1, which comprises the following stages: polymerizing dichlorovin-ylhydrosilane in the presence of a catalytically effective quantity of a metal or of a metal compound which catalyses tne hydrosilylation reaction ESi-H/j=Si-CH 2 =CH 2 and reducing the composition obtained from stage in an anhydrous medium using a chemical reducing agent which replaces the chlorine aii:;os present in the said composition by hydrogen atoms. A process according to claim 4, in which the polymerization takes place in bulk.
6. A process according to claim 4, 7n which the polymerization takes place in solution in an organic solvent. t I U Iii o
7. 6, in whic of between
8. 7, in whic platinum,
9. catalyst b 9, in whi aluminium aluminium magnesium
11. lithium al
12. lithium hy employed.
13. pclycarbos described
14. carbide-ba heating a to 3 or ob :1i 9 q 0 09 0 or 9 9 9I 1 99 I II I 1 I 16 7. A process according to any one of claims 4 to 6, in which the polymerization takes place at a temperature of between 500C and 110 0 C. 8. A process according to any one of claims 4 to 7, in which the polymerization catalyst employed is based on platinum, palladium, rhodium, iridium, ruthenium or osmium. 9. A process according to claim 8, in which a catalyst based on hexachloroplatinic acid is employed. 10. A process according to any one of claims 4 to I o 9, in which the chemical reducing agent employed is lithium 0 r6 aluminium hydride, sodium borohydride, sodium hydride, aluminium hydride, lithium hydride, calcium hydride and magnesium hydride. 1° o 11. A process according to claim 10, in which o lithium aluminium hydride is employed. So*. 12. A process according to claim 10, in which eIi lithium hydride mixed with a tris(3,6-dioxaheptyl)-amine is employed. 13. A process for the preparation of a pclycarbosilane as claimed in claim 1 substantially as described in the Examples. 14. A process for the preparation of a silicon carbide-based ceramic product or article, which comprises heating a polycarbosilane as claimed in any one of claims 1 to 3 or obtainable by the process of any one of claims 4 to 1 1 7. rn C/ I_ 17 13, in an inert atmosphere or under vacuum at a temperature of between 900 and 1,500°C until the polycarbosilane has been converted into silicon carbide. A process according Lo claim 14, in which the polycarbosilane is shaped before the heating is performed so as to obtain a silicon carbide ceramic article after the heating.
16. A process according to claim 15, in which ceramic filler is mixed with the polycarbosilane before the S shaping is performed. I t 17. A process according to claims 15 or 16, in which the said shaping consists in coating a substrate. S8. A process for the pyrolysis of a polycarbosilane substantially as described in Example 4.
19. Ceramic products and articles containing silicon carbide, prepared by a process according to any one of claims 14 to 16.. j Dated this 17th day of October, 1990. i RHONE-POULENC CHIMIE SBy its Patent Attorneys .i DAVIES COLLISON iVw A f "T r /f