Low cost, high break elongation graphitized carbon fibers having low degree of graphitization are inert to bromine at room or higher temperatures, but are brominated at -7 to 20 C, and then debrominated at ambient. Repetition of this bromination-debromination process can bring the bromine content to 18 percent. Electrical conductivity of the brominated fibers is three times of the before-bromination value

Hung, Ching-Cheh

English

NASA Technical Reports Server

United States Patent [191 
Hung 
[I 11 Patent Number: 5,059,409 
[45] Date of Patent: Oct. 22, 1991 
[54] BROMINATED GRAPHITIZED CARBON 
[75] Inventor: Ching-Cheh Hung, Westlake, Ohio 
[73] Assignee: The United States of America as 
FIBERS 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 443,289 
[22] Filed: Nov. 30, 1989 
Related U.S. Application Data 
[63] Continuation-in-part of Ser. No. 219,016, Jul. 14, 1988, 
abandoned. 
[51] Int. ( 3 . 5  .............................................. COlB 31/04 
[52] U.S. Cl. .................................... 423/448; 423/439; 
423/460; 252/502 
[58] Field of Search ............... 423/439, 448, 460, 489; 
252/502; 510/160, 240, 253 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,089,754 5/1963 Nedopil ............................... 423/448 
3,409,563 11/1968 Olstowski ............................ 423/448 
3,539,372 11/1970 Hardy et al. ........................ 423/460 
3,931,392 1/1976 Deitz ................................... 423/448 
3,969,489 7/1976 Wu ...................................... 423/446 
4,388,227 6/1983 Kalnin .............................. 423/447.7 
4,565,649 1/1986 Vogel .................................. 423/448 
4,749,514 6/1988 Murakami et al. .................. 423/449 
OTHER PUBLICATIONS 
Dresslhaus et al., “Intercalation Compounds of Graph- 
ite”, Advances in Physics, 1981, vol. 36, No. 2, pp. 
Chung et al., “Are Brominated Thornel P-100 Crabon 
Fibers Intercalated?”, pp. 125-126. 
Hooley et al., “The Intercalation of Bromine in Graphi- 
tized Carbon Fibers and Its Removal”, Carbon, vol. 16, 
Primaly Examiner-Robert Kunemund 
Attorney, Agent, or Firm-Gene E. Shook; John R. 
Manning; James A. Mackin 
139-152, 266-276. 
NO. 4, 1978, pp. 251-257. 
[571 ABSTRACT 
Low cost, high break elongation graphitized carbon 
fibers having low degree of graphitization are inert to 
bromine at room or higher temperatures, but are bromi- 
nated at -7” to 20” c . ,  and then debrominated at ambi- 
ent. Repetition of this bromination-debromination pro- 
cess can bring the bromine content to 18%. Electrical 
conductivity of the brominated fibers is three times of 
the before-bromination value. 
1 Claim, 3 Drawing Sheets 
RESISTIVITY 
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TEMPERATURE (C) 
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Vogel, U.S. Pat. No. 4,565,649 is concerned with a 
process for producing graphite fibers with high electri- 
cal conductivity. The summary of the invention points 
that the fiber is a composition of graphite, Bronsted acid 
5 including hydrogen fluoride or hydrogen bromide, and 
a metal fluoride. Graphites can be used which have a 
low degree of crystallinity. 
DISCLOSURE O F  THE INVENTION 
According to the present invention the bromination 
process is conducted in a relatively low temperature 
range. Such a range extends between the melting point 
of bromine and temperature for liquid bromina- 
tion, and -150  c. to o" c. for vaporous bromination. 
15 The graphitized carbon fibers to be brominated at these 
temperatures can be less expensive and have higher 
break elongation values than those used in prior art 
larger interplanar spacings. These fibers may be either 
BROMINATED GRAPHITIZED CARBON FIBERS 
ORIGIN O F  THE INVENTION 
The invention described herein was made by an em- 
ployee of the U.S. Government and may be manufac- 
tured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefore. 
STATEMENT O F  COPENDENCY 
This application is a continuation-in-part of applica- 
tion Ser. No. 219,016 which was filed July 14, 1988, 
now abandoned. 
TECHNICAL FIELD 
nated graphitized carbon fibers having small crystallites 
10 
This invention is concerned with pitch-based bromi- processes because they can have smaller crystallites and 
and large interplanar spacings. The invention is particu- 20 pristine fibers or previously brominated. Bromination of 
larly directed to such fibers having improved proper- these fibers at these temDeratureS increases their electri- 
ties. cal conductivity. 
In the past, brominated graphitized carbon fibers 
have beenfabricated by submerging highly graphitized 
pristine graphite fibers in liquid or saturated vaporous 25 
ing from 5 minutes to many days. This was followed by 
debromination at ambient conditions for 1-20 days. FIG. 1 is a graph showing the electrical resistivity of 
This method produced brominated small crystallite, large interplanar spacing brominated 
graphitized carbon fibers which contained about 18% 3o graphitized carbon fiber as a function of bromination 
bromine by weight. The fibers produced by this process temperature. 
were about five times more electrically conductive than FIG, 2 is a graph showing the bromine to carbon 
the pristine fibers. weight ratio of small crystallite, large interplanar spac- 
One of the disadvantages of this conventional process ing brominated graphitized carbon fiber as a function of 
is that it is limited to highly graphitized carbon fibers 35 bromination temperature. 
having large crystallites, small interplanar spacing and 
low break elongation values. Typically the break elon- 
gation values are about 0.31%- This fiber is not only 
expensive, but also difficult to Process for engineering 
purposes. The less expensive, easier to process fibers 40 figure is 18%. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
The advantages and novel features of the invention 
bromine at room temperature for a period Of time rang- will be more fully apparent when read in connection 
with the accompanying drawings wherein; 
FIG. 3 is a graph showing the electrical resistivity of 
small crystallite, large interplanar spacing brominated 
graphitized carbon fiber as a function of fiber diameter. 
The bromine to carbon weight ratio of the fibers for this 
- 
having small crystallites, larger interplanar spacing and 
high break elongation values are inert to bromine under 
the conditions of the conventional method. 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
It is, therefore, an object Of  the present invention to According to the present invention, brominated 
provide brominated graphitized carbon fibers from less 45 graphitized carbon fibers having lower degrees of 
graphitized, less expensive fibers as the starting material graphitization than prior art fibers are produced. The 
which produces a product having an improved break graphite fibers to be brominated can be either pristine 
elongation values. fibers or fibers previously brominated. 
The fibers with "lower degree of graphitization" are 
50 tbose fibers having interplanar spacing iv the 3.40-3.45 BACKGROUND ART 
Ukaji et al, U.S. Pat. NO. 3,925,263 is directed to a A range and crystallite size in the 30-70 A range. These 
process for reacting fluoride with graphite fibers. The compare to the prior art fibers for bromination, where 
carbon material may be either in amorphous or crystal- the interptanar spacingo and the crystallite sizes are 
line form, and the reaction is carried out at 250"-600" C. 3.37-3.39 A and > 100 A, respectively. 
The graphitized carbon fibers are first cooled to a 
process for fluorination of carbon by contact with flue- temperature between -7.2" C., which is the melting 
rine gas. The carbon powder is in either amorphous or point of bromine, and room temperature. Refrigeration 
crystalline form and it is reacted at temperatures as low apparatus having the ability to control bromination 
as 250" C. temperature in this range has been found to be accept- 
Tiedmann, U.S. Pat. No. 4,036,786 describes a fluon- 60 able. By way of example, test tubes containing graphi- 
nated carbon composition which has significantly in- tized carbon fibers in direct contact with liquid bromine 
creased specific resistance. The material is utilized in are placed in the coolant container of a recirculation 
electrical resistors. cooler. The cooler has the ability to control the temper- 
Aramaki et al, U.S. Pat. No. 4,438,086 is concerned ature of the coolant in the -20" C. to +75" C. range. 
with a method and apparatus for the preparation of 65 The refrigerated graphitized carbon fibers or the 
graphite fluoride by contact reaction between carbon graphitized carbon fibers being refrigerated are exposed 
and fluoride gas. The carbon is either amorphous or to a liquid or vaporous bromine. Liquid bromine has the 
crystal and the reaction may take place as low as 200" C. advantages in the bromination process because vapor- 
Kome et al, U.S. Pat. No. 3,929,920 is directed to a 55 
5,059,409 
3 4 
ous bromine reacts with fibers slowly due to the very mal expansion, and thermal conductivity of this fiber 
low vapor pressure in the low temperature range uti- due to bromination are within the error of the measur- 
lized in the bromination process. ing instrument. Table 1 shows the structural, chemical 
Vaporous bromine may be used instead of liquid bro- and physical properties of this fiber, which is Amoco 
mine if a Slower rate Of reaction iS acceptable. VapOrOUS 5 p-55, before and after the low temperature bromination. 
bromine may be preferred if controlling liquid bromine, 
which is a hazardous material, presents a problem. 
The effects of the bromination temperature on the 
electrical resistivity and the mass of less graphitized &brominating previously brominated-debrominated 
fibers are shown in the drawings. Conventional graphi- io fibers may produce further gains in the bromine con- 
tized carbon fibers known commercially as Amoco P-55 tents. n i S  is especially true if the fibers are in large 
utilizing conventional proc$sses. These fibers have ia- 41 grams of previously described Amoco p-55 graphi- 
However, these commercial fibers were brominated 15 fabric were in direct contact with -70 c. saturated 
with the improved process at a temperature between vaporous bromine for 7 days. The fibers were de- 
-5" C. and 20" C. for liquid bromination, or between brominated in room air for two days to produce a prod- - 15" C. and 20" C. for vaporous bromine. uct with a 4.9% bromine to carbon weight ratio. The FIG. 1 shows the effect of the bromination tempera- fibers were placed in direct contact with -7" C. satu- ture on the electrical resistivity of the P-55 fibers. The 20 
resistivity ofthe pristine fibers to be brominated is about rated vaporous bromine again for another 5 days and 
850 pa cm. The resistivity of graphite fibers bromi- debrominated in room air for 2 days which resulted in a 
nated by liquid bromine is shown by the line 10 while product with a 5.9% bromine to carbon weight ratio. 
the resistivity of those fibers brominated by vaporous The fibers were then placed in direct contact with 
bromine is shown by the line 12. -7" C. liquid bromine for another 4 days and de- 
of the bromination temperature on the of the P-55 18% bromine carbon weight ratio. This is higher than 
fibers. The mass increase of the graphite fibers during the 14% from the Previously described Process illus- 
bromination using liquid bromine as a function of the trated in FIG. 2, where only one cycle of the bromina- 
bromination temperature is shown by the line 14. This 30 tbn-debromination Process was Performed. 
increase during bromination using vaporous bromine is FIG. 3 shows the resistivity-diameter relation of the 
shown by the line 16. 18% bromine fiber. The diameter of this brominated 
These graphs shown that at a bromination tempera- fiber is in the 10-13 pm range, while the before-bromi- 
ture of about 20" C., both the liquid and the vaporous nation diameter of the same fiber is in the 9-12 pm 
bromine have only slight effects on the resistivity of the 35 range. Also, the resistivity is uniform at about 400 
graphite fibers, even though the fibers increase in mass. pa-cm for the fibers with diameters smaller than 11 pm, 
This weight increase is about 1.95% for the fibers bro- decreases sharply to 320 pa cm for the fibers with 
minated by vaporous bromine and about 7% for those diameters in the 11-12 pm range. The resistivity be- 
brominated by liquid bromine. comes larger and relatively nonuniform for fibers with 
40 diameter greater than 12 pm. This indicates structural 
damages of large diameter fibers due to excessive bro- TABLE I 
mination. Therefore, optimization of repeated bromina- Structural, Chemical, and Physical Properties of the Small Crystallite, Large Interplanar Spacing Graphitized Carbon 
Fibers Before and After Low Temperature Bromination tion-debromination process is needed to increase the 
Before After bromine content, and therefore the electrical conductiv- 
45 ity, of a large quantity of fibers without causing fiber 
Interplanar Spacing (A) 3.42 3.43 structural damages. 
Crystallite size (A) 5 0  50 Any pitch-based fibers with- crystallite size aad inter- 
Bromine to carbon 0 14 planar spacings in the 30-70 A and 3.40-3.45 A ranges 
weight ratio (%) can be used as the starting materials for bromination. Tensile strength (Ksi) 215 215 
Modulus (Msi) 55 55 50 This includes, but not limited to, the Amoco P-55, 
Break Elongation (%) 0.5 0.5 which is used as an example in this disclosure. Other 
Thermal Conductivity (W/m-K) 100 100 pitch-based fibers with the above described structure 
can have physical properties different from those de- Electrical Resistivity 850 300 
W - c m )  
Diameter (pm) 9-12 9.5-12.5 scribed in Table 1. However, the effects of bromination 
Coefficient of Thermal - 1  - 1 55 remain unchanged. That is, after bromination the fibers 
contain 1418% bromine, have diameters 5-15% larger Expansion (ppm/"C.) 
than the before-bromination values, electrical conduc- 
These graphs further show that the fiber resistivity tivity 3 times the b5fore-bromination values, interplanar 
decreases to about one-third of its pristine value if the spacing 0.01-0.02 A larger than the before-bromination 
bromination is carried out at a temperature of about 60 values. The tensile strength, modulus, coefficient of 
-5"  C. for vaporous bromination, or at a temperature in thermal expansion, and thermal conductivity values 
the range of -5"  C. to 0" C. for liquid bromination. In remain unchanged. 
both cases the fibers gain about 14% weight, and the While several embodiments of the invention have 
fiber diameter increase due to bromination was about been disclosed it will be appreciated that various 
5%. X-ray data indicates that bromination causes the 65 changes and modifications may be made to the process 
interp!anar spacing of this fiber to increase from 3.42 to of the invention without departing from the spirit of the 
3.43 A. However, changes of crystallite size, tensile invention or the scope of the subjoined claims. 
strength, modulus, break elongation, coefficient of ther- 
ALTERNATE EMBODIMENT OF THE 
INVENTION 
fibers Cannot be brominated in a satisfactory manner quantity and/or are tightly packed. By way of example, 
terplanar 'pacing Of 3'42 A and crysta11ites Of 50 A. tized carbon fibers in the form of unidirectional weaved 
Referring now to FIG. 2, there is illustrated the effect 25 brominated for days to produce in a Product with an 
Bromination Bromination 
I claim: 
5,059,409 
5 6 
1. A brominated graphitized carbon fabric material 
a plurality of pitch-based rebrominated previously 
brominated-debrominated graphitized carbon fi- 
bers having a unidirectional weave, each of said 5 
fibers having changed by bromination. 
(b) a diameter between 11 pm and 12 pm, 
(c) a resistivity of 320 pa-cm, 
(d) an interplaaar spacing which is about 0.01 A to 
about 0.02 A more than before-bromination, and 
(e) a crystallite size which is substantially un- 
comprising 
(a) a bromine to carbon weight ratio of 18%, * * * * *  
15 
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25 
30 
35 
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45 
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55 
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Brominated graphitized carbon fibers

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