CA1060161A - Process for producing an improved graphite body having a low coefficient of thermal expansion - Google Patents

Abstract

PROCESS FOR PRODUCING AN IMPROVED GRAPHITE BODY
HAVING A LOW COEFFICIENT OF THERMAL EXPANSION

ABSTRACT OF THE INVENTION
A process for producing an improved graphite body having a very low longitudinal coefficient of thermal expan-sion which comprises continuously processing a carbonaceous pitch having a mesophase content of at least 40 per cent by weight into a shaped, oriented body by extrusion, spinning, or calendering; heating the shaped body produced in this manner in an oxidizing atmosphere to thermoset the body to an extent which will allow the body to maintain its shape upon heating to more elevated temperatures; further heat-ing the thermoset body in an oxygen-free atmosphere to a carbonizing temperature to produce a highly oriented coke;
admixing the coke produced in this manner with a thermo-plastic carbonizable binder; and then extruding the result-ing mixture into a desired shape which is in turn carbonized and graphitized. The resulting body has a longitudinal (with grain) coefficient of thermal expansion which is lower than that of like shapes prepared in the same manner from an identical binder and coke produced from the same precursor pitch by conventional delayed coking techniques.

Description

~vo ~L0ti~6~ ~

BACKGROUND OF THE INVENTION

1) Field of the Invention -This invention relates to a process for prod~cing an improved graphite body, such as a graphite electrode;
having a very low longitudln~l coefficient of thermal expan-sion.

2~ Description of the Prior Art ~
Graphite ~hapes h~ving low coefficients of thermal ~ ~ -expansion, such as graphite electrodes, are generally pre-pared by admixing an oriented coke with a thermopla~tic carbonizable binder, ~uch as R coal tar pitch or ~ petro-leum pitch, extruding or lding the resulting mixture into a desired shape, and then carboni~ing and graphiti~g the shaped article to produce a graphite body. The oriented coke employed in such proces~ is ordinarily produced by the c~rbonization o~ a selected feedstock in a delayed coker.
. . ~
Although the shaped graphite articles produced in thi~
m~nner have low coefficients of thermal expansion, me~ns for further reducing the coefficients of thermal expansion of such gr~phite articles have been const~ntly sought so ~ ~
as to lmprove the performance of these article~ .Ln the high ~-temperature surroundings in which they are employed.
Graphite shapes can also be produced as descrlbed by Grindstaf~ et al~ ln U,S, patent 3,787,541 by heating a hydro-carbon feed for a time su~icient to ~orm a pitch containing at .

least 75 per cent mesoph~se, extruding the mlxture into desired shape. and then carbonizin~ and graphitizing the shaped body. However, both high temperatures and pr~ssures are required to extrude large bodie~ by thls technique, and upon graphitlzation such bod~es, like graphite bodies pro- ;
duced by conventional technlques, hsve lh~gher than d~sired coefficients of thermal expansion.

SUMMARY OF THE INVENTION
In accordance with the present invention, it has now 10 been found that an improved graphite body having a very low longitudinal coefficient of thermal expansion ~an be pre-pared by contlnuously processing a carbonaceous pltch having a mesophase content of at least 4Q per cent by weight into a shaped, oriented body by extruslon, spinning, or calen-; dering; heating the shaped body produced in this manner in an ox~dizing atmosphere to thermoset the body to an extent which wlll allow the body to maintain its shape upon heat-ing to more elevated temper~tures; further heating the ther-moset body in an oxygen-free atmosphere to a carbonlzing temperature so as to remove hydrogen and other volatiles and produce a highly oriented coke; ~dmixing the coke pro-duced in this manner wlth a thermoplastic carbonizable blnder; ~nd then extruding the resulting m~xture into a : desired shape which is in turn carbonized and graphitized.
Mesophase pitches are pitches which have been ~ transformed, ln whole or in part, to a liquid crystal or :

~ - 3 -~, , ~0~

so-called "mesoptlase" state. Such pitches by nature contain easily oriented molecules, and when these pitches are extruded, spun, or calendered lnto a deslred shape, the pitch molecules are preferentlally aligned along the len~th of the shaped body (with grain or parallel to the direction of the elongation), When the shaped body is thermoset and then heated in an oxygen-free atmosphere to a carbonlzing temperature, a highly oriented coke is obtained. I~ this coke is then admixed with a thermo- ~ -plastic carbonizable binder, and the mixture extruded lnto a deslred shape which is in turn carbonized and graphltlzed, the resultin~ body has a longitudinal (with ~rain) coefficient of thermal expansion whlch i8 lower than thnt Or llke shapes prepared ln the same manner from an identical blnder and coke produced ~rom the same precursor i~pitch by conventional delayed coking techniques, The ~
longltudlnal (with graln) coe~ficients of thermal expansion ~ -Or such shapes at room temperature have been found to be less than 0.1 x lO 6/oC and, in some instances, to have ~ `~
a negative value approaching the in-plane value Or single crystal graphite (-L5 xlO-~/C.~, e.g., as low as -0.7 x 10-6/C.
Suctl low coefricients Or thermal expansion have never been observed heretorore in fabricated graphite bodies, When natural or synthetlc pltches havlng an aromatic base are heated under quiescent conditions at a temperature ~`
of about 350C,-500C., either at constant temperature or wlth gradually lncreasing temperature, small lnsoluble `"

~ . :. . . :

1~6~ ~ 6 liquid spheres begin to appear in the pitch which gradually increase in slze as heating is continued. When examined by electron diffraction and polarlzed light technlques, these spheres are shown to consist of layers of oriented molecules aligned in the same direction. As these spheres contlnue to grow ln size as heatlng is continued~ they come in contact with one another and gradually coalesce with each other to produce larger masses of aligned layers. As ; coalescence continues, domains of aligned molecules ~ch larger than those of the original spheres are formed. These ,i~
domains come together to form a bulk mesophase wherein the transit~on from one oriented domain to another sometimes occurs smoothly and continuously through gradually curving lamellae and sometimes through more sharply curvI~g lamellae. ;`
The differences ln orientation between the domains create a complex array of polarized light extinction contours in the bulk mesophase corresponding to various types of linear discontinuity in molecular alignment. The ultimate size of the oriented domains produced is dependent upon the viscosity, and the rate of increase Qf the visco~ity, of the mesophase from which they are formed, which, in turn are dependent upon the particular pltch and the heating rate. In certain pitches, domains having sizes in excess of one hundred microns and as large as several thousand microns are pro~uced. In other pitches, the YiSCoSity of the mesophase is such that only limited coalescence and structural rearrangement of layers occur, so that the ulti-mate dom~in size does not exceed one hundred microns.

_ 5 _ ~ ~6~ 1 6 The highly oriented, optically anisotropic, in~oluble material produced by treating pitches in this manner h~s been given the term "mesophase", and pitches containing ~ ~ -such material are known a~ "mesophase pitches". Such pitches, when he~ted above their softening points, are mi$tures of .
two immiscible liquids, one the optically anisotropic, oriented me~ophase portion, and the other the i~otropic non-mesophase portlon. The term "mesophase" is derived ~rom the Greek "mesos" or "intermediate" ~nd indicates the pseudo-` 10 cryst~lline nature of this highly-oriented, optic~lly aniso-troplc materlal.
Carbon~ceous pitches having a mesophase content of at least 40 per cent by weight are suitable for processing into shaped oriented bodies w~ich can be thermw~t and carbonized to produce highly oriented coke ~uita~le for use in the pre~ent invention. In order to obtain the desired product from such pitch. however, the mesopha~e contained therein must, under quiescent conditlonsl fonm a bulk ~e80- ~`
phase havLng large coalesced domains, i.e., domain~ of ; 20 ali8~ed molecules in excess of one hundred microns. Pitches which fonn stringy bulk mesophase ~nder quiescent conditions, having ~all oriented domRin~, rather than large coalesced domalns, are unsuitable. Such pitches form mesophase having -`
; a high vi8co~ity which undergoes only limited coale~cense, : ' insufficien~ to produce large coale~ced domains having size~ in excess of one hundred mic~ons. In~te~d, 9mall oriented domains of mesophaae ~gglomerate to producc c:lumps .

.
.. . . . ~.

~3u~

~60g 6~

or stringy masses wherein the ultlmate domaln ~ize doe~ not exceed one hundred microns. Certain pitches which polymerize very r~pidly are of this type.
Carbonaceous pitches having a me~opha~ cont~nt of at least 40 per cent by welght can be produced in accordance with known techniques by heatlng a carbo~aceous pi~ch in an inert atmo~phere at a temperature above about 350C. for a time ~ufficient to produce the desired quantity of me~opha~e. .
By sn inert atmosphere is meant an atmo~phere which does not react with the pitch under the heating conditions employed, such as nitrogen, argon, xenon, helium~ and the like. The heating period required to produce the desired me~ophase : content varie~ with the particular pitch and temperature ~ :
employed, with longer heatin8 periods required at lower temperature~ than at higher temperatures. At 350C.~ the minimum temperature generally required to produce mesophase,.
at least one week of heating is u~u~lly nece~8ary to pro-duce a mesophase content of about 40 per cent. At tempern-tures of from about 400C. to 450C., conversion to me~ophase proceeds more rapidly, and a 50 per cent me~ophase cQntent ~ :
can u~uslly be produced at such temperatures within about 1-40 hours. Such temperatures are preferred for this rea~on.
Temperatures above about 500C. are undesirable, and heating 8t this temperature should not be employed for more than about 5 mlnute~ to avoid conver~ion of the p~tch to coke.
; The degree ~o which the pitch ha~ been converted to ~esopha~e c~n readily be determ~ned by polariz~ad light ., . ~ .. ... . . .

10~ 1 6 ~ ;

micro~copy and ~olubility examinations. Except for cert~in non-me~ophase insolubles present in the origlnal pitch or which, ~n ~ome instances, develop on heating, the non-mesophase portion of the pitch is readily soluble in organic solvents such as quinollne and pyridine, while the mesophase portion i5 essentially insoluble. In the case of pitches which do not develop non-mesophase lnsolubles when heated, the insoluble content of the heat treated pitch over and above the ~nsoluble cont~nt of the pitch before it has been heat treated corresponds essentially to the mesophase con-ten~. ( ) In the c~se of pitche~ which do develop non-me~ophase i.nsolubles when heated, the ~nsoluble content of the heat treated pitch over and above the insoluble con-tent of the pitch before it has been heat treated is not solely due to the conversion of the pitch to mesophase, but also represents non-mesophase insolubles which ~re produced .
along with the me~ophase during the heat treatment. The presence or absence of mesophase can be visually observed by polarized llght mlcroscopy examination of the pltch .
(1) The percent of quinoline insoluble~ (Q.I.) of a given pitch 1~ determined by quinollne extraction at 75C. The per cent of pyridine insolubles (P.I.) i~ detenmined by Soxhlet extr~ction in boiling pyridine (115C.).
(2) The insoluble content of the untreated pitch is generally le~s than 1 per cent (except for certain coal t~r pitches) and c~nsists-largely of coke and aarbon black found in the original pitch.
` .

' 930~

~L06V~6i~ ~
(see, e.g., Brooks, J. D., and Taylor, G. H., "The Formation of Some Graphitizing Carbons," Chemistry and Physics of Carbon, Vol. 4, Marcel Dekker, Inc., New York, 1968, pp.
243-2~8; and Duboi~, J., Agache~ C., and White, J.L., "The Carbonaceous Mesophase Formed in the Pyroly~is of Graphitiz-able Organic Materials," Metallography 3, pp. 337~369, 1970).
The amounts of such mesophase may also be visually estimated in this manner.
Aromatic base carbonaceous pitches having a carbon content of from about 92 per cent by weight to about 96 per cent by weight and a hydrogen content of from about 4 per ;
cent by weight to about 8 per cent by weight are generally ~uitable or producing mesophase pitches which can be employed to produce the highly oriented bodies ~uitable for use in the present lnvention. Petroleum pitch and coal tar p~tch are preferred starting materlals. Petroleum pitch can be derived rom the thermal or catalytic cracking of petroleum fraction~. Coal tar pitch is similarly obtained by the destructive distillation of coal. Some pitches, such as fluoranthene pitch, polymerize very rapidly when heated and fail to develop large coalesced domains of mesophase, and nre,therefore, not suitable precursor materials.
After the desired mesophase pitch has been prepared, ;~
it is continuously proce~sed into a shaped body using the conventional techniques of extrusion, spinning, or ealender-ing. In order to prevent oxidation of the pitch9 it should be shaped in an oxygen-free atmosphere, BUCh as the in~rtt ; i.. .

' ~ ',. ', ' ', "

016~

atmospheres descrlbed above. Rods, bars, fil~ment~, and ~ ;
sheets of oriented pitch having a diameter or thickness of up to about one mm., or more, can be conveniently pre~
pared in this manner. As noted above, however, in order to obtain oriented bodies whlch can be the~mose~ and car~onized ;~
to produce highly oriented coke3 the pitch employed must, under quiescent conditions, orm a bulk me~ophase having ~ ;
large coalesced domains.
The temperature at which the pitch i9 sh~ped depends, of course, upon the temperature at which the pitch exhibits a suitable viscosity, and at which the higher-melting me80-phase portlon of the pitch can be easily deormed and oriented.
Since the softening temperature of the pitch, and its Vi8-cosity at a given temperature, increa3e~ as the mesopha~e content of the pltch increases, the mesoph~e content should not be permitted to rise to a point which raises the soft-ening point of the pitch to excessive levels. For this reason, pitches having a mesophase content of more than about 90 per cent are generally not employed. Pitches having a meso-pha~e content of from about 40 per cent by weight to about 90 per cent by weight, can be readlly shaped at temperatures ,, : .
at which they exhibit a viscosity of from about 10 poises to about 10,000 poises, usually at from about 310C. to about 459C. Vi~cositles of rom about 10 poi5es to about 200 poises are suitable for fiber spinning. When extrusion techniques are employed, the pitch should have a viscosity of ~rom about 100 polses to about 1000 poises, while vi~cosities in the , ..... .

~30~
.

~6~ 1 6 ~
range of from about 200 poises to about 10,000 poises are suitable for calendering of the pitch.
The shaped bodies produced in thls manner are highly oriented materials having a high degree of preferred - orientation of their molecules parallel to the direction of the elongation (with grain), as shown by their X-ray diffrs~tion patterns. This preferred orientation is apparent from the short arcs which constitute the (002) band of the diffraction patterns. Microdensitometer scanning of the (002) bands of the exposed X-ray film indicate th~s preferred orientation to be generally from about 20 to about 35, usually from about 25 to about 30 (expressed as the full ; width at half maximNm of the azimuthal intensity distribution).
The sh~ped body produced in this manner is ~hen heated in an oxidizing atmosphere for a time sufficient to thermoset the body to an extent which will allow the body to maintain its shape upon heatlng to more elevated temperature~. The oxidizing atmosphere may be pure oxygen, nitric oxide, or any othar appropriate oxidizing atmosphere. Most conveniently, ;~
air is employed as the oxidizing atmosphere.
The time required to thermoset the shaped bod~e~ of ; the lnvention will, of course, vary with such factors as the ;~
particular oxidizing atmosphere, the temperature employed, the dimen~ions of the bodies, the particular pi~ch from which the bodies are shaped, and the ~esopha~e content of such pitch. G~nerally, however, thermosetting of such bodies can ba effected in rel~tively short periods of time~ u~ually :
'~ ' ,: ~ 11 -1 ~60 i ~ ~
in from about 5 minutes to about 120 mlrlutes.
~ he temperature employed to effect thermosetting o~
these bodies ~ust, of course,not exceed their softenlng temperstures. The maximum temperature which can be employed will thu~ depend upon the particular pitch from ~hich the bodies were shaped, and the mesophase content of such pitch.
The hl~her the mesophase content of the body, the higher will be its ~oftenlng temperature, and the higher the tem-perature which can be employed to effec~ then~osetting. At higher temperatures, of course, thermosetting can be ef~ected in les8 time than is possible at lower temperatures. Bodies having lower mesophase content, on the other hand, require relatively longer heat treatment at somewhat lower tempera-ture~
A minimum temperature of at least 2S0C. is generally necessary to effectively thermoset the shaped bodies produced in accordance with the invention. Temperatures ln excess of 400C. may cause melting and/or excessive burn-off of the bodies and should be avoided. Preferably, to~eratures of ?0 from about 275C. to about 390C. are employed. At such temperatures, the required amount of thermDsettin~ can usu ally be effected withln from about 5 minutes to about 120 minute~.
After the shaped body of the invention has been ther-mose~ as required, it is further heated to a carbonizing temperature, At a temperature of about 1000C., bodies having a carbon content greater than about 98 per cent by ~ight , . , ~0~016~ `

are obtained. At temperatures in excess of about 1500C., these bodles are essentially completely carbonized. Such heating should be conducted in sn oxygen-free atmosphere, such as the inert atmospheres described above, to prevent `~
further oxidation of the body. Because these bodies have been infusibilized, they are capable o~ being carbonized free of support.
In order to en~ure that the expulsion o volatiles frvm the bodies durin~ carbonizatton doe~ not occur so rapidly as to di~rupt the structures thereof, the heating rate must be controlled so that the volatilization does not proceed at an excessive rate. Particular care must be taken in heat-ing the bodies to a temperature of about 500C. While very thin bodie~, e.g., fibers or sheets of from about 8-15 microns in diameter or thickness, can be heated to about 500C. fairly rapidly, e.g., in about 5 minutes, larger bodles of about 1 mm. diameter or thickness require longer heating schedules, ~ ;
i e.g., from about 8 hours to about 20 hours. After the initial expuls~on of volatiles up to about 500C. has been completed, the bodies may be heated to their final carbonizing tempera-ture, usually in the range of from about 900C to about 1500C., and u~ually within from about S minute to about ` 10 hours.
The coke bodies produced in this manner have a highly ~;
oriented structure characterized by the presence of carbon cryst~llites preferentLally aligned along the lengl:h~ of the bodie~ (with grain or parallel to the direction of :

~06~
elongation), as shown by the short arcs which constitute ~he (002) band of their X-ray diffraction patterns. Micro-densitometer ~canning of the (002) band of the exposed X-ray fllm indicates the preferred orlentation parameter (~WHM) of coke carbonlzed to about 1000C. to be less than about 45, usually from about 30 to about 40. Coke carbonized ~ ~
to about 1500C. has a higher degree of preferred orienta- ~;
tion, i.e., a preferred orientation parameter (FWHM) of from about 20 to about 30. Further improvement in the degr2e of preferred orientation i8 obtained by heatin8 the coke at still higher temperature~. If desired, such coke may be heated~ as described hereinbe~ore, to a graphitizing tem-perature In a range of from about 2500C. to about 3300C.
The oriented coke produced in this manner i~ then sdmlxed with a thermoplastic carbonizable binder to form ~ `
a mixture which i5 then extruded into a desired shape which is in turn csrbonized and grsphitized, in accordance with conventional techniques. The coke may be crushed or ~ized to facilitate admixture with the c~rboni2able blnder; how-ever, care ~hould be taken to mRintain the nspect ratio of the coke at at least 2:1 (by a~pect ratio of the coke is , . .
meant the ratio of the with grain dimension to the ~gain~t ~
grain dlmenYion). The graphi~lzed shape~ prepared in th~ 8 - ~ ~`
manner have been found to have longitudinal (wi~h grain) coefficients of thermal expansion which are lower tlhan those of llke ~h~pes prepared in the same manner from an identic~l binder and coke produced from the ~ame precur~or pitch by . ::

" - lb - ,,, ,, `' ,, . , ,. , ~ . . . .

. 9308 ~6 ~

conventional delayed coklng techniques Typlcally, the longltudinal (with ~rain) coefficients o~ thermal expansion Or such shapes at room temperature have been ~ound to be less than 0 1 x 10 6/oC and, in some instances, to have a negative value approaching the in-plane value o~ single crystal graphite, eJg , as low as -0,7 x 10-6~C Con-ventional graphlte shapes typically ha~e longitudlnal (wlth grain) coefrlclents o~ thermal expanslon of between 0, 5 x 10-6~C, and 1. 0 x 10-6/C, The crushed or slzed coke should be admixed wlth thermoplastic carbonizable aromatic binder, such as coal tar pltch or petroleum pitch, in an amount ~u~ficient to forrn a mixture containing rrom about 50 per cent by weight to about 80 per cent by welght coke and ~rom about 20 per cent by weight to about 50 per cent by weight binder~
Preferably, such mixture contains rrom about 55 per cent by weight to 75 per cent by weight coke and from about 25 per cent by welght to 45 per cent by weight binder A~ter a substantially homogeneous mixture has been obtained, the mlxture i8 extruded lnto a deslred shape by means Or an auger extruder or other conventional technique. Tempera-tures Or ~rom about 100C. to about 200C,, preferably rrom about 110C. to about 150C., are generally employed3 dependlng, of course, upon the temperature at whlch the mixture exhiblts a su~table vlscoslty, Carbonlzatlon of the shaped article may be er~ected by heating the artlcle in a substantlally oxyeen-free atmo~phere to a temper~ture su~flclently eleYated to expel Yolatile~
and reduce the blnder to a carbon residue which p~r~anently ,,. ; ~

6~ ~:

binds the aggregate body. A carbon-lzation temperature of about 100QC. i5 generally effective to drive o~f most of the vol~tlle matter and produce a body having a carbon ~ -content greater than about 98 per cent by welghtJ and ak temperatures in e~cess o~ about 1500"C., the body is essen~
ti~lly completely carbonized. The article should be heated gradually, of courseJ so as to expel the volatiles at a rate which will not rupture the structureO The time re-quired to e~fect carbonization wlthout rupturing the structure will, of course, depend upon the temperature and thickness of the articleJ wl~h periods o~ from about ` '~
10 hours to about 300 hours being sufflclenk for most structures. A graphitized body is produced by further heating at temperatures o~ *rom about 2500C. to about ~300C., preferably from about 2800C. to about 3000C.
. , .
Residence times at the graphitizing temperature of from about l minute to about 240 minutes are usuallg sufficient~
~he following examples are set ~orth for purposes o~
illustration so that those skilled in the art may be~ter understand the invention, It should be understood that ~hey are exemplary only~ and should not be construed as limiting the invention in any manner. All coefficient or thermal ;~ expansion values set ~orth in the examples and throughout the speci~ication are room temperature values.

:-; A commercial petroleum pitch was employed to produce ~, a pltch having a mesophase content of about 57 per cent by weight. The precursor pitch had a density o~ 1.24 g./cc., ~, .~ .
. - .~ i ,,"
.

10~ ~ 6 ~

a softening temperature of 120C., and contained 0.5 per cent by weight quinoline insolubles (Q.I. was determined by quinoline extraction at 75C.). Chemical analysis showed a carbon content of 93.3%, a hydrogen content of 5.63%, a sulfur content of 1.0% and 0.15% ashO :
The mesophase pitch was produced by heating the pre~
cursor petroleum pitch at a temperature of about 400C.
for about 15 hours under a nitrogen atmosphere. After heating, the pitch contained 57 per cent by weight pyri~
dine insolubles, indicating that the pitch had a meso~
phase content of close to 57 per cent (P.I. was deter- ~ .
mined by Soxhlet extraction in boiling pyridine).
A portion of this pitch was spun con~in~ously Lnto fiber about 15 microns.in diameter at a temperature of 390C. under ~ nitrogen atmosphere. Part of this fiber was then heated ~n an air-draft furnace to a temperature :~
of 275C. over a period of about one hour, where the temperature was maintained for about one more hour so as to thermoset the fiber. About 300 grams of the ther-moset fiber was then cut into one-inch lengths which were placed in a beaker and heated in a sagger to a temperature o 500C. at a rate of 60C. per hour, held at this temperature for 3 hours, and then cooled to room temperature. The fibers were then removed from the beaker and reheated in a graphite crucible to a temperature of 1000Co at a rate of 60C. per hour, where the temperature was maintained for 5 more hours.

~u~ ~`

10~0 The fibers calcined in this manner were then milled to produce a flour consisting of particles wlth lengths up to -about 200 microns. l`he milled flour was blended with a 110C.
softening point coal tar pltch in a rat;o of 100 parts by weight of flour to 80 parts by weight of pitch (55 per cent -by weight flour and 45 per cent by weight binder). The result~
ing mixture was then placed in an auger extruder, the cham-ber of the extruder was evacuated, and the ~ixture was extruded into a rod 2 centimeters in diameter at a tempera-ture of about 120C. employing an extrusion pressure of between 100 psi. and 200 psi.
The extruded rod was then heated in a sagger to a tem-perature of 1000C. at a rate of 60C. per hour and held at this temperature for 2 hours, and then further heated to a temperature of 3000C. over a period of about 1 hour, and maintained at that temperature for 2 hours.
The rod produced in this manner was found to have a longitudinal (with grain) coefficient of thermal expansion of -0.67 x 10 6/oC. Evaluations were made from ~amples having dimensions of 1 cm. x 2 cm. x 12.7 cm., which had been cut with the grain of the rod.
On the other hand. a rod produced from t~e same binder pitch and coke produced from the same precursor pitch as the I coke produced in accordance with the above description, but ; in a conventional manner, was found to have a longitudinal (with grain) c~oefficient of thermal expansion of 0.67 x 10-6/C.

`
, ~:

~6V~

A portion of the mesophase pitch described in Example 1 was extruded continuously through a spinnerette containing 128 4-mil diameter holes at a temperature of about 370C., under a nitrogen atmosphere, to produce ilaments 50 to 85 microns in diameter. Part of these filaments were spread into a thin layer and passed through an air-draft furnace -~
set at 380C. The residence time of the filaments in the furnace was about 5 minutes. About 300 grams of the thermoset ;
filaments having lengths of from about 1-5 mms, was placed in a beaker and heated in a sagger to a temperature of 500C, at a rate of 60C. per hour, held at this tempera- ;
ture for 3 hours, and then cooled to room temperature. The filaments were then removed from the beaker and reheated ~ ;
in a graphite crucible to a temperature of 1000C. at a rate of 60C. per hour, where the temperature was maintained for 5 more hours.
., ~
The filaments calcined in this manner were then blended wlth a 110C. softening point coal tar pitch ln a ratio of 100 parts by weight of filaments to 51 parts by weight of ;~
pitch (66 per cent by weight filaments and 34 per cent by `~
weight binder). The resulting mixture was then placed in an auger extruder, the chamber of the extrudex was evacuated~
and the mixture was extruded into a rod 2 centimeters in ~-diameter at a temperature of about 120C. employing an extru~
sion pressure of about 340 psi.

'~ - 19 ~
'~.'' ~' ' :; ' ,: ~, ' 10t;~)161 The extruded rod was then heated in a sagger to a temperature of 1000C. at a rate of 60C. per hour and held ~ ` ;
at this temperature for 2 hours, and then further heated to a temperature of 3000C. over a period of about 1 hour, and maintained at that temperature for 2 hours~
The rod produced in this manner was found to have a longitudinal (with grain) coefficient of thermal expansion of -0.14 x 10 6/oC. Evaluations were made from samples havlng dimensions of 1 cm. x 2 cm. x 127 cm., which had been cut ` with the grain of the rod. -~
On the other hand, a rod produced from the s~me binder pitch and coke produced Erom the same precursor pitch as the coke produced in accordance with the above description, ;
but in a conventlonal manner, was found to have a longitudinal (with grain) coefflcient of thermal expansion of 0.67 x 10 ~C.
; .

A commercial coal tar pitch was employed to produce a pitch having a mesophase content of about S5 per cent by weight. The precursor pitch had a density of 1.28 g./cc., ~ ;
a softening temperature of 113C., and contained 0.7 per cent by weight quinoline insolubles (Q.I. was determined by quino~
line extraction at 75C.). Chemical analysis showed a carbon content of 93.8V/o~ a hydrogen content of 4.70~/O~ a 3ulfur con-tent of 0.4/O~ and 0.007~/O ash.
The mesophase pitch was produced by heating the precur-sor coal tar pitch at a temperature of about 400C. for about 18 hours under a nitrogen atmo~phere. After heating, the .

, . .

lOG0161 ` ~
pitch contained 55 per cent by weight pyridlne insolubles, indicating that the pitch had a mesophase content of close to 55 per cent (P.I. was determined by Soxhlet extraction in boiling pyridine). ;
A portion of this pitch was spun continuously into fiber about 15 microns in diameter at a temperature of 400C. under a nitrogen atmosphere. Part of this fiber was then heated .~ 'f. . ~
in an air-draft furnace to a temperature of 275C. over a period of about one hour, where the temperature was main~
tained or about one more hour so as to thermoset the fiber.
; .
About 300 grams of the thermoset fiber was then cut into ~; ?
one-inch lengths which were placed in a beaker and heated , in a sagger to a temperature of 500C. at a rate of 60C. -i per hour, held at this temperature for 3 hours~ and then cooled to room temperature. The fibers were then removed from the beaker and reheated in a graphite crucible to a temperature of 1000C. at a rate of 60C. per hour, where the temperature was maintained for 5 more hours.
The fiber calcined in this m!anner was then milled to produce a flour consisting of particles with lengths up to about 200 microns. The milled flour was blended with a 100C.
softening point coal tar pitch in a ratio of 100 parts by weight of flour to 40 parts by weight of pitch (71 per cent by weight flour and 29 per cent by weight binder). The result ing mixture was then placed in an auger extruder, the chamber of the extruder was evacuated, and the mixture was e~truded into a rod 2 centimeters in diameter at a temperature of about ., ~

930~ .
, ~

120C. employing an extrusion pressure of between 440 psi.
and 460 psi.
~ he extruded rod was then heated lrl a sag~er tn a tem-per~ture of 1000C. at a rate of 60C. per hour ~nd held at this temperature for 2 hours, and then further heated to a temperature of 3000C. over a peri.od of about 1 hour, and maintained at that temperature for 2 hours.
The rod produced in this manner was found to have a longitudinal (with grain) coefficient of thermal expansion of O.06 x 10 6/oC. Evaluations were made from samples having dimensions of 1 cm. x 2 cm. x 12.7 cm., which had been cut wlth the grain of the rod.
On the other hand. a rod produced from the same binder pitch and coke produced from the same precursor pitch as :
the coke produced in accordance with the above descriptionf but in a conventional manner, was found to have a longitudinal .
~wieh gr.in) coeffirient of thermal expanslon of 0.52 x 10-6~C.

, - 22 - :

Claims (2)

WHAT IS CLAIMED IS:

1. In a process for producing graphite bodies having low longitudinal coefficients of thermal expansion which comprises admixing from 50 per cent by weight to 80 per cent by weight of an oriented coke with from 20 per cent by weight to 50 per cent by weight of a thermoplastic carbonizable binder, extruding the result-ing mixture into a desired shape, and then carbonizing and graphitizing the shaped article to produce a graphite body, the improvement which comprises producing a body having a longitudinal coefficient of thermal expansion of less than 0.1 x 10-6/°C. by employing a coke having an aspect ratio of at least 2:1 which has been prepared by continuously extruding a carbonaceous pitch having a mesophase content of at least 40 per cent by weight into a shaped body having pitch molecules preferentially aligned along its length, said pitch being one which under quiescent conditions forms a bulk mesophase having large coalesced domains in excess of one hundred microns, heating the shaped body in an oxidizing atmosphere at a temperature sufficiently elevated and for a time sufficiently prolonged to thermoset the body to an extent which will allow it to maintain its shape upon heating to more elevated temperatures, and the further heating the thermoset body in an oxygen-free atmosphere to a temperature sufficiently elevated to produce a highly oriented coke.

2. A process as in claim 1 wherein the oxidizing atmosphere employed to thermoset the shaped body is air.