Note: Descriptions are shown in the official language in which they were submitted.
13033
7 ~ 6~ ~
~ he inven~ion rela~es to ~ mes~phase pitch
deri~ed carbon fiber ~nd pastlcular~y t~ a carbon fiber
which h~s been bor~n~ted and lntercalated with calcium.
It iB well known to 6pi~ a mes~phase pitch into
a fiber, thermoset the pitch fiber ~y heatin~.~t in air,
. ~ and carbo~ize ~che thermoset pitch fiber by heating the thermo-
6et pitch fiber in an inert gaseous environment to an elevated
temperature. ~-
It is preferable ~o use mesophase pi~ch rather
than isotropic pitch for producing the carbon fibers because
~he mesophase pitch derived c~rbon fiber possesses excellent
mechanical properties. Furthermore, it is preferable to use
a mes~phase pitch having a mesophase conten~ of ~t least
about 70% by weight or the proce~s.
Carbon fiber~ have found a wide range of commer-
cial uses. In certain uses, it is desirable to use carbon
fibers which possess both excellent mechanical properties
and good electrical conductivity. The electrical conducti-
vity is usually described in terms of resi~tivity. Typically,
a mesophase pitch derived carbon fiber which has been carbon-
ized to a temperature of ~bout 2500C has a resisti~ity of
abou~ 7 microohm-meters ~nd ~ Young~s modulus of about 413.6
GPa. The ~ame carbon fiber heat treated ~o about 3000DC has
a resistivity of about 37 3 microohm~meter~.
The cost for obtaining temperatures of 2500~C and
particularly 3000~C is very higho Not only ls i~ costly to
expend the energy ~o reach the high ~empera~ures, but the
equipmen~ needed to reach such high temperatures is cos~ly
and deteriorates r~pidly due to the elevated temperatures.
2.
i 13033
~3l73~;~)g
The pre~ent invention allows the production of
a mesophase pitch derived carbon fiber having ~ resi~tivity
~f less than about 2 microohm-meter with a maximum heat
tre~tin~ temperature of from about 2000C to about 23~0C
and preferably about 1 microohm-meter.
The present invention relates to a m~sophase pi~ch
_ derived carbon fiber which has been boronated and intercalated
with calcium.
The preferred embodiment teaches a calcium ~o boron
weight ratio of abou~ 2:1 in the carbon fiber.
In the absence of boron, the calcium does not
intercalat~ into the carbon fiber very well. Even very small
amounts of boron enhance the intercalation of the calcium.
Generally, 0.1% by weight boron or even less is sufficient
to improve substantially the intercalation of calcium into
the carbon fibers.
For any given amount of boron in a carbon fiber, the
resistivity generally increases as the amount of intercalated
calcium increases at the low end, below a calcium to boron
weight ratio of 2:1. It is believed that the ~oron
acts as an acceptor and the calcium ~cts as an electron donor.
The interaction between the boron and the calcium is such
that a maximum re~is~ivity is reached and then the resistivity
is reduced ~ntil a minimum is reached for a calcium to boron
weig~t ratio of sbout 2:1. Apparently high conductivity is
associated with the donor st~te. As the amount of calcium
increases so that the ratio is greater than 2:1, the resistiv-
ity increases because a multiple phase condition exists.
Generally, if one were to boronate a carbon fiber
ln the absence of calcium, the maximum amount o boron which
could be introduced intD the carbon fiber is abou~ 1.2% by
weight. The presence of the intercalated calcium, howe~er,
~ubstantially ~ncreases the max~mum amount of boron. It is
, 13033
3 6~ ~
expected that about 10% by weight or more ~f boron can be
introducgd in~o the carbon fiber in the presence of the
intercalated c~lcium. In addition, ~t ~6 expected that ~s
~uch as 20% by weight ~f calcium can be intercalated int~
the carbon fiber in ~he presence of the boron._
- .Surprisingly, the boron and calc~um can be int~o-
d~ced ln~o the carbon fiber without chemically ~eacting with
~he carbon fiber ~o that a ~ingle phase i~ maintained_
Heat treatments at elevated temperatures can result in the
formation of a new phase, calcium borographite
~ t i~ believed that the presence of the intercalated
calcium results in cr~ss-~inking between layer planes in the
carbon fiber and improved mechanical properties are obtained.
Excellent values for tensile ~trength and Young'c modulus
are obtained for the calcium intercalated boronated fibers
even though relatively low process temperatures are used.
For example, a carbon fiber according to the invention which
has been produced using a proce~s temperature of about
2000~C possesses mechanical properties comparable to a con
ventional me~ophase pitch derived carbon fiber which has been
sub~ected to ~ process temperature of 3000C. In addition,
the carbon fiber according to ~he i~vention po~sesses much
low~r re~i~tivity compared to the co7lventional carbon fiber.
Surprisingly, the carbon fiber according ~o ~he i~-
vention possesses a relatively high interlayer spacing as
compared to ehe typical interlayer ~pacin~ of 3.37 Angstroms
of a carbon fiber which has been sub3ected eo a heat treat-
ment of about 3000C. According to the prior art, one would
expPct a deterioration of mechanical properties for larger
30 values of interlayer spacing for the earbon fibers. The
~36~Y 13033
maximum inter~ayer spacing occurs for a calcium to boron
weight ratio of a~out 2:1 as in the case for the minimum
resistivity.
Generally, about 0,5% by weight boron and about
1% by weight calcium provides a good quality carbon fiber
according to the invention.
The present lnvention also relates to the method
of producin~ a mesophase pitch deri~ed carbon fiber having a
low resistivity and excellent mechanical properties, and
comprises the steps of producing a mesophase pitch derived
carbon fiber ~om a mesophase pitch having a mesophase con-
tent of at least about 70% by weight mesophase, boronating
the fiber, and intercalating the fiber with calcium.
The steps for boronating and intercalating can be
carried out simultaneously or consecutively, boronating
being first.
The preferred em~odiment is to carry out the method
to produce a calcium intercalated boronat d carbon fiber
havin~ a calcium ~o boron weight ratio of about 2:1.
l'he boronating can be carried out with elemental
boron, boron compounds, or a gaseous boron eompound. A cal-
cium compound 6uch as CaNCN ca~ be used. Oxygen containin~
compounds of calcium are le~s desirable because of the poss-
ible detrimental effect of the oxygen on the carbon fiber.
Boronating up to about 1,2% by weight maintains a
single phase in the carbon fiber. Greater amounts of boron
tend to produce boron carbide, B~C.
In carrying ou~ the instant inYen~iOn, the carbon
fiber has a diameter of less than 30 microns and preferably
a~out 10 microns.
D
13033
3 ~ ~
Further ob~ect~ and sdvantsge6 of the invention
~ill be set forth in the following specification and in
p~rt will be obviou~ ther~fr~m without specifically bein~
referred to, the same being reallzed and ~ttained as pointed
out in ehe claims here~f,
Illustratlve, non~limiting example~ of the practice
of the invention are ~et out below. Numerous other examples
ean readily be evolved in the light of the guidin~ pr1nciples
and teachings c~ntained herein. The examples given hcrein
are intended to illustrate the invention and not in any
~ense limit t~e manner in which the invention can be prac-
ticed,
The examples were carried out using mesophase
pitch derived carbon fibers having diameters of about 8
microns. The mesophase pitch used to produce the fibers had
a mesophase content of about 80% by weight.
The car~on fiber~ were produced using conventional
methods and were carbonized to ~bout 1700C. Lower or higher
carbonizing ~emperatures could have been usedO The use of
carbon fibers made the handling of the ibers simple because
of the mechanical properties exhibited by carbo~ fibers.
The best mode used ~n the examples simultaneously
boronated and calcium intercalated the carbon fibers. This
does n~t preclude the advantage of c~nsecutive ~reatments
for commercial operations. The method used is as follows.
Finely ground gr~.~hi,:~, so-called graphi~e flour,
was blended with elemental boron powder. The weight per-
cent~ge of boron was selected to be abs~ut the- desired weight
percentage for the carbon fibers. This mix~ure amounted to
~bou~ 6~0 grams and was roll-milled or about 4 hour~ to
. . .
1303
mix and grind the graphite and bolsn ~horoughly, The
mixture was then calcined in an argon atmosphere at a
temperature of about 2500C for about one hour. Any
inert atmosphere ~uld have been satisfactory.
_ The boronated graphite flour was blended ~ith
CaNCN powder having particles less than about 4~ microns
to form a treatment mixture. The amount of CaMCN is_
determined by ~he amount of calcium to be intercalated.
The weight of the carbon fibers being treated
as compared to the amount of the treatment mixture used
is very small. As a result, the weight ~ercentage of
the boron in the treatment mixture is about the s~me
for the combinati~n of the carbon fibers and ~he treat-
ment mixture. This simplifies ~he selection of a pre-
determined weight percentage of boronating for the
carbon fibers.
The am~unt of calcium lntercalation must be
de~ermined experimentally by varying the amount of ~he
calcium compound used and the treatment time.
It should be recognized tha~ the vapor pressure
of the boron i~ much lower than ~he calcium. The
boronation is a result of the atomic diffusion whereas
th~ intercalation of calcium is a result of vapor
diffusion.
7.
13033
~ ~ 7 3 ~ g
For each example, six carbon fibers were used
and each fiber ~ad a length ~f about 10 cm. Each of the
carbon fibeIs was suspen~ed inside a ~raphite container using
a Draphite formO '~he graphi~e form maintained the carbon
fiber in a preselected position while the tre~*ment mixture
- was added.to the graphite container. The treatment mixture
was vibrated around each carbon fiber ~o obtain a uniform
and packed arran~ement. ~_
The six graphite containers were placed in a
graphite susceptor and heated inductively to a predetermined
maximum temperature for about 15 minutes. The furnace
chamber was evacuated to about 5 x 10-~ Torr prior to the
heat treatment and then purged with ar~on during the heating
cycle. An inert gas other than argon could be used.
The process could be carried out using BC13,
boranes or water sol~ble salts such as H3B03. In addition,
CaC12 could have b~en used. Of course, a wide range of other
compounds for supplying boron and calcium could be realized
easily experimentally in accordance with the criteria set
forth herein.
Examples 1 to 18:
Examples 1 to 18 were carried out to obtain about
0.5Y~ by weight of boron in the carbon fibers and varying
amounts of intercalated calcium. The maximum temperature
for the heat treatment was 2050~C,
Table 1 shows the results of the Examples 1 to 18.
The amount of the intercal2ted calcium vari~d from about
0.5% to about 3.6% by wPight. The Young's m~ulus for each
of the carbon ibers was extremely high and the tensile
strength was also very good. The resistivity showed a
13033
~L~L73~
m~nimum of ~bou 1.8 ~c~Dhm~ t~rs iEor about 1/D 'by w~ight
calcium. The lnte~layer ~pacirlg~ C~/2 ~as about a maximum
for ^chat v81Ue .
TABLE 1
0.5V/~ B~ron - ~oung~
Ca ~n Fiber ~esisti~ity Tens~leModulus ~c~/2
Example % t''L- ~G Pa G Pa R _
Do S 2 ~ 92 ~ 28 44E~-~ 3 ~ 4176
2 0~8 3~8 1~80 5513~4217
3 1 ~ O 1 ~ 81~ 33 4~33 ~ 4224
4 0~5~ 3~5 1~90 5453~4091
~i 0~6 2~7l~E30 5933~4158
6 0~7 3~6 1~88 ~i583~4174
7 0~7 4~3 1~69 64E~3~4219
B 0. 6 4~ 714 S6 4E~93 ~ 4229
9 0. 8 2 . 91 . S8 5~63 . 4248
0 . 9 1. ~ 8 614~ . 41g8
11 0~ 9 1 ~ 81~ 58 7Z43 ~ 4133
12 0 ~ 9 2 ~ O1 ~ 43 6~413 ~ 4147
13 1 ~ 2 1 ~ 5~L ~I 32 6343 ~ 4205
14 2 . 3 2 . 11 . 84 7383 . 4174
2 . 0 2 ~ 31 . 48 ~843 . 4141
1~ ~ 2 . 6 1. ~i . 44 6623 . 4062
17 ~ 1 . 41 . 25 6~-3 . 4~82
18 3~ 6 1 . 80 . 79 ~0 3 O 403~
13033
73
Examp le ~ 19 t~ 40
E~amples 19 to 40 ~ere carried out to obtain
about 1.0% by weight of boron ~n ~he carbon fibers and
Yaryin~ amounts of lntercalated calcium. The_maximum
temperature for the heat ~reatment was-2050~C
Table 2 shows the results of the Examples 19
to 40. By interpolation, it can be ~en that as in
Examples 1 to ~8, a calcium to boron weight ratio of
2:1 results in the lowest resistivity, about 1.1 micro-
ohm-meters, and a large value for the interlayer spacing.
10.
~ 0 ~ 13Q33
TABL~ 2
lV/o Boron
Y~ung's
Ca in Fiber Resisti~ity Tensile M~dulus Col,2
Exampl.e ~ L- ~ G Pa _ G Pa _ A
19 1.5 4.8 1.89 6413.43~1
0.4 4.3 2.07 4763.4120
_ 21 0.5 2.3 1.9~ 77g.3.3833
22 1.3 4.3 2.53 7863.4348
23 1.~ 3.3 1.85 6923.~265
24 1.5 2.8 1.~3 7453.4638
1.6 3.4 ~.92 66g3.4564
26 1,~ 5.0 1.96 7173.4534
27 I,8 4.4 Z.12 6893.4610
28 1.6 2.3 2.1~ 7583.4540
29 1.8 3.0 1.52 ?173.4571
2.2 1.4 1.33 6273.45~9
31 ~.9 1.7 0.8~ 4483.4488
32 1.9 1.1 1.54 5863.4520
33 3.2 2.0 . 0.58 34~3.4549
34 2,5 1.5 1.15 55~3.4461
4.7 2.3 0.41 3583.4288
36 4.3 2.~ ~.39 33~3.~3~8
37 6.2 2.~ 0.50 2903.43~4
38 5.4 2O0 0.50 3523.44~2
39 6.5 1.7 0.56 4623.4486
8.9 2.2 0.70 5523.4392
13033
36~g
Examples 41 to 58:
Examples 41 to 58 were carried out to obtain
about 2.0~/~ by weight of b~r~n in the carbon fibers and
varyin~ amounts of intercalated c~lcium. The maximum
~empera~ure for the heat treatment was 1600C....
- ,Table 3 shows the r~sults of Examples 41 to 58;
The ~alues of the resistivity are not as good as
the Examples 1 to 40. The lowest resistivity is for ~
calci~m to boron weight ratio of abGut 2:1. The value for
the Young's modulus for each carbon iber is fairly higho
1~ .
, . . .
13033
~l736~
TABLE 3
2% Boron_ Young's
Ca in Fiber Resisti~i~y Tensile Modulus C~2
Example % ~L-V~ G Pa G Pa _ A
41 ~.2 7.5 2.62 400 3.4202
42 0.2 7~6 2.62 365 3 D 4242
~ 43 ' ~,3 7.7 2.48 338 3.4324
44 0.7 7.3 2.59 393 3.4283
1.2 6.8 . 2.29 407 3.4179
46 1.8 5.8 1.98 ~20 3.4209
47 2.3 7.1 1.86 ~27 3.4238
48 2.6 5.6 2.03 427 3.4383
49 2.6 4.0 2.38 414 3.436
3.3 4,2 1.97 400 3.4291
51 4cO 3.~ 2.~5 427 3.4483
52 S.l 3.3 1.96 434 3.4491
53 501 3.8 1.27 400 3.4444
54 6.4 4.0 1.32 448 3.4559
6.8 ~.2 1.~3 455 3.4326
56 8.0 4.7 1.13 420 3.4~86
57 8.5 3.5 1.16 510 3.4381
58 . 12.5 4.2 1.23 786 3.433
. 13q33
:~L73tiC~
Examples 59 to 7~:
~ xamples 59 to 75 were carried out to obtain
about 2.0% by weight of boron in the carbon fibers as in
~he Examples 41 to 58 exeept that the maximu~ temperature
fvr the heat treatment was 2050~C.
Table 4 shows the results of the Exa~ples 59 to
75.
The Examples 5~ to 75 produced much lower ~alues
for resistivity than the Examples 41 to 58. The lowest
resistivity and highest interlayer spacin~ can be inter-
polated to be at a calcium to boron weight ratio of about
2:1. The Young's modulus and ~ensile strength for each of
the carbon fibers is excellent.
1~.
.
, ~3033
3 ~73~
TABLE_4
2'70 Boron Young ' s
Ca in Fib er Re s i s t ivi ty Ten s i l e M~ du l us Co ~ 2
Example % ~ ~ G Pa _G Pa _A
59 O 2. ~ ~.25 6~9 3.381
0.7 2.5 1.6D - 593 3.4003
- 61 3. ~ 2.9 1.31 689 3, s3go
62 0.4 2.8 2.06 641 3.3964
6~ 0.6 2.9 2 12 620 ~-3,4950
lD 64 0.9 2.6 2.07 738 3.4302
~ . ~ 2.6 1,68 662 3.4489
66 2.9 2.8 1.60 5513 . 4717
67 3.1 2.6 2.11 586 3.4957
6~ 3.2 3.4 1.37 ~27 3.5077
69 3.5 2.5 1.73 ~79 3.5136
3.6 2.0 ~ .48 579 3.5222
71 4.8 1.5 0. ~9 510 3.5293
72 4.5 1. ~ 1 O 25 ~76 3,5349
73 5.1 1.5 1.52 565 3.5027
74 5.1 ~ .5 1.80 634 3. ~930
6. ~ 1.8 0.97 551 3.4886
13033
~ ~ 3 6
Examples ?6 to 93
Examples 76 to 93 were c~rr$ed out t~ obtain
about 2,0X by weight of boron $n the carbon fibers RS in
~he Example~ 41 to 75 except that the maximum temperature
or the heat treatmen~ wa~ about 2300~C.
Table S ~h~ws the result6 of the Examples 76 to
93.
The Examples 76 to 93 compare well with ~he
Examples 59 to 75.
. TABLE 5
2% Boron Young's
Ca in ~iber Resisti~7i~y Tensile M~dulus. Co~2
, Example _ % _ ~f~_nn_ _ Pa G Pa A
76 1 D 9 2.3 1.82 551 3.4385
77 2.5 2.5 1.1~ _~10 3.4585
78 1.1 2.3 0.~6 420 3.3896
79 1.1 2.6 1.70 572 3.4410
1.4 2;4 1.63 558 3.4339
~1 1.5 2.5 1.~9 724 3.44~2
82 1. S 2 . 3 2. 34 538 3 . 44D5
IB3 1 . 4 2 sl 3 ~ . ~9 ~2~ 3 . 4312
84 2~5 2.3 2.37 696 3.4~81
85, 2.5 ~.~ 2.30 682 3.4~71
867 2.~ 2.3 ~.30 724 3.4667
87 2.4 2O2 2~54 731 3.4752
8~ 2.~ 2.6 1.93 662 3.4913
8g 5.1 1~2 1.90 772 3.507~
~0 6.1 1.~ 1.91 -. ~89 3.~9g2
` ~1 5.7 1~2 1.9~ 890 ~,5232
~2 7.0 ~.2 1.~ ~58 3.4~54
93 ~ l.S 1.14 517 3.5159
1~ ~
~ ~7 3 ~ ~
While a maximum temperature for the heat treat-
ment can exceed 2300C, there is a reduction of mechanical
properties of the fibess when ~he maximum tempera~ure
exceeds 2500~C.
Examples 94 to 109:
Ex~mples 94 to 109 were carried out to obtain
about 5% by weight of boron in the carbon fibers. The maxi-
mum temperature for the heat trea~ment was abou~ 2050C.
Table 6 shows the results of the Examples 94 to
109.
The'Examples 94 to ios do not include the prefer- -
red calcium to boron wei~ht ratio but the trend of resisti-
vity versus calcium content shows the characteristic increase
in resis~ivity for a calcium to boron weight ratio less than
2:1. In addition, the interlayer spacing inCreasPs from a
calcium content of about 3.8% to 8.5% by wei~ht ~nd would
be expected to be a maximum at about 10% by weight in
accordance with the inYentiOn.
13033
TAB~E 6
5% Boron Young's
Ca in Fiber Resistivity Tensile Modulus Co~2
Example JO ~ n~ G PaG Pa A
94 ~.6 2.~ 1.43531 3.3928
2.0 ~ .6 1.70462 3.4435
96 3,2 2.6 1.27- 446 3.5160
~ g7 . 2.8 2.'6 1.58572 3.4830
98 3,~ 2.8 1.40531 3.4822
~9 4.3 2.8 ~ .61 503 -~ 3.5089
100 2;5 2.9 2 20~89 3.5134
101 3.2 3.0 1,57~00 3.5134
102 3.9 3- 3 2.21~58 3.5473
103 4.5 3.3 1. ~6 579 3.5306
104 408 3O4 0.88517 3.5367
105 _ 607 3.0 0.37317 3.5316
106 ~ 7 3. ~ 0.34290 3.5614
107 8.0 3.6 0.29241 3,57~1
108 8.0 3O4 ~79324 3.583
109 8.5 6.0 0.33186 3.6007
I wish it ~o be understood that I do no~ desire
to be limited to the exact details of construction shot~
and described, for obvious modification~ will vccur to a
pe~son skilled in the ~rt.
Having ~hus described the inven~ion, what I claim
as new and desire to be secured by Letters Patent, is as
follow.s:
18.
