Note: Descriptions are shown in the official language in which they were submitted.
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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
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9308
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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
.
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.. . . . ~.
~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.
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(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.. .
9308
' ~ ',. ', ' ', "
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
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, ..... .
~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
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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
- 12 -
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~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
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:
~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
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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.
EXAMPLE 1
:-
; 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.,
- 16 -
~,
.~ .
. - .~ 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.
- 17 -
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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.
`
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- 18 -
~6V~
EXAMPLE 2
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 ~
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9308
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.
; .
EXAMPLE 3
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
.
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, . .
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
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., ~
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.
,
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