Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/145—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from pitch or distillation residues

Definitions

• This invention relates to carbon fibers and more particularly to continuous pitch-based carbon fibers having a high modulus and low electrical resistivity and methods for the production of such fibers, and to composites comprising such fibers.
• Carbon fibers have long been known, and methods for their production from a variety of precursors are well described in the art.
• Cellulosic precursors have been used for producing carbon fiber since the early 1960's, with rayon being the dominant carbon fiber precursor for nearly two decades.
• PAN polyacrylonitrile
• pitch the importance of rayon-based carbon fiber has declined. This shift has been due in part to the superior toughness, tensile strength and stiffness exhibited by both PAN-based and pitch-based carbon fiber.
• the conversion yield of rayon to carbon fiber is low, and the resulting carbon fiber is ordinarily lower in density than carbon fiber based on PAN or pitch, which further limits its potential uses.
• Polyacrylonitrile fiber when oxidized and carbonized under appropriate conditions, provides tough, high strength, high modulus carbon fiber.
• the overall conversion yield in producing fiber from PAN is good, and the finished fiber is capable of achieving the outstanding tensile strength needed for producing the high performance composite materials used in a variety of sports, automotive and aircraft applications.
• the tensile modulus of commercially available PAN-­based fiber does not generally exceed about 50 X 106 psi, which is somewhat deficient for use in applications that require a high degree of stiffness.
• PAN-based carbon fibers generally exhibit densities of less than 1.9, together with low thermal conductivity, ordinarily less than 200 w/m-°K, and high electrical resistivity.
• Pitch-based carbon fiber has generally been recognized as capable of providing greater stiffness and higher thermal conductivity than carbon fiber from other sources, and considerable effort has been directed toward the development of pitch-based ultra-high modulus carbon fibers with good thermal conductivity. Such carbon fibers could find immediate application in forming composites for use where good dissipation of electrical charges or heat is desired. In addition, the combination of high stiffness and good thermal conductivity with the negative coefficient of thermal expansion characteristically exhibited by pitch-based fibers would make such composites extraordinarily dimensionally stable.
• the continuous carbon fibers heretofore disclosed and described in the art including those carbon fibers having tensile modulus values as great as about 120 to 125 X 106 psi which have been designated as "ultra-high modulus", have generally exhibited densities of less than about 2.2 g/cc, thermal conductivities of less than about 1000 w/m-°K and electrical resistivities generally above about 1.8 micro-ohm-­ meter.
• the thermal conductivity ordinarily falls below about 700 w/m-°K, and the electrical resistivity is generally above 2.0 micro-ohm-meter.
• pitch-based carbon fiber having a tensile modulus substantially above about 125 X 106 psi, with single carbon fiber filament values as great 140 X 106 psi, these fibers also generally do not exhibit low electrical resistivity characteristics, and the thermal conductivity of these fibers is also reported to be low, generally below 1000 w/m-°K.
• Crystalline graphite has a density of about 2.26 g/cc, and generally exhibits excellent thermal conductivity, near 1800 w/m-°K, and low electrical resistivity, well below 1.5 micro-­ohm-meter.
• the art has not suggested the preparation of continuous carbon fibers from pitch or any other source with a density of 2.2 g/cc or greater, a thermal conductivity well above 1100 w/m-°K and an electrical resistivity significantly below 1.5 micro-ohm-meter, to as low as 1.2 micro-ohm-meter and lower.
• a carbon fiber having a density of about 2.2 or greater and an electrical resistivity below 1.5 micro-ohm-meter, together with a tensile modulus well above 125 X 106 psi and even as great as 130 X 106 psi or greater would be a substantial advance in the carbon fiber art.
• Such carbon fiber, and particularly fiber exhibiting a thermal conductivity greater than 1100 w/m-°K, would find immediate wide acceptance for use in a variety of composite applications, and would be particularly useful for composites in which good dimensional stability and low electrical resistivity are needed.
• the carbon fibers of this invention are high modulus, pitch-­based continuous carbon fibers having a very high thermal conductivity, and a low electrical resistivity.
• the carbon fibers and woven fabric reinforcement made from such fibers are particularly useful for the production of composites.
• the carbon fibers of this invention are pitch-based continuous carbon fibers having a density of not less than 2.18 g/cc, a tensile modulus substantially above 120 X 106 psi, and an electrical resistivity below about 1.6 micro-ohm-meter. More particularly, the continuous carbon fibers of this invention have a density in the range of from about 2.18 g/cc to the limiting density of crystalline graphite, about 2.26 g/cc, a tensile modulus greater than 125 X 106 psi and an electrical resistivity below about 1.5 micro-ohm-meter.
• the continuous carbon fibers of this invention will have a density in the range of from about 2.2 to about 2.26 g/cc, a tensile modulus in the range of from about 125 X 106 psi to about 150 X 106 psi, and an electrical resistivity in the range of from 1.5 to about 0.95, more preferably from about 1.2 to about 0.95 micro-ohm-meter.
• the continuous carbon fibers of this invention exhibit a thermal conductivity generally in the range of about 950 to about 1800 w/m-°K, preferably above about 1000 w/m-°K, and still more preferably above about 1100 w/m-°K.
• the high density, low electrical resistivity carbon fibers of this invention may be further described as being highly oriented and graphitic.
• the fibers have a three-dimensional order and crystalline structure characteristic of polycrystalline graphite, as will be apparent from an examination of the X-ray diffraction pattern of the fibers. Although the precise relationships are not understood, the crystallite size and the degree of crystallite orientation in the fiber, as well as the degree of crystallinity, appear to affect the level of electrical resistivity and thermal conductivity that may be achieved.
• the high density carbon fibers of this invention may be produced from high purity, high softening temperature mesophase pitch using improved spinning techniques and a sequence of controlled heating steps whereby the pitch is spun to form a fiber, infusibilized and then carbonized.
• High purity, high softening temperature mesophase pitch suitable for use in producing the carbon fibers according to the practice of this invention can be obtained from petroleum hydrocarbon or coal tar sources.
• a variety of methods for preparing a suitable pitch are well known, including those disclosed in U.S. patents 3,974,264, 4,026,788, and 4,209,500, and any of these methods as well as the variety of solvent-­based methods known in the art may be employed for these purposes.
• Several methods have been used in the art to characterize the mesophase component of pitch, including solubility in particular solvents and degree of optical anisotropy.
• the mesophase pitch useful in the practice of this invention preferably comprises greater than 90 wt% mesophase, and preferably will be a substantially 100 wt % mesophase pitch, as defined and described by the terminology and methods disclosed by S. Chwastiak et al in Carbon 19 , 357 - 363 (1981).
• the pitch can also be described as having a high softening temperature, preferably greater than about 340° C, and more preferably above about 345° C, although when derived from coal tar sources a pitch having a somewhat lower softening temperature may also be useful.
• the pitch will be thoroughly filtered to remove infusible particulate matter and other contaminants that may contribute to the formation of defects and flaws in the fiber.
• the pitch is spun from the melt using conventional methods, in general by forcing the molten pitch through a spinnerette while maintaining the pitch at a temperature well above the softening temperature.
• the temperatures useful for spinning generally lie in a narrow range and will vary, depending in part upon the viscosity and other physical properties of the particular pitch being spun.
• melt-spinning will recognize that even though the pitch may be in a molten state, it may be too viscous or may have insufficient strength in the melt to form a filament and may even decompose or de-volatilize to form voids and other flaws when the pitch temperature is outside the temperature range useful for spinning that pitch.
• the pitch will preferably be spun at or near the highest temperature within in the effective range of spinning temperatures at which the pitch may be spun.
• the degree of orientation of the mesophase domains in the spun pitch fiber appears to increase in proportion to spinning temperature, and a high spinning temperature is therefore desirable to obtain the very high degree of orientation of the mesophase domains within the fiber structure for the purposes of this invention.
• pitch fibers having large, well-oriented mesophase domains tend form fibers comprising larger, more compact graphitic microcrystals upon being carbonized.
• the size, and particularly the length of the mesophase domains as determined by L c , and the degree of domain orientation in the pitch fiber appear in turn to be determined at least in part by the conditions employed for spinning the pitch fiber, with the domain size and degree of domain orientation in the pitch fiber as well as the density of the resulting carbon fiber appearing to increase as the temperature of fiber spinning is increased.
• the spinning temperature range for a particular pitch will generally rise as the softening temperature of the pitch is increased, and the use of mesophase pitch materials having a high softening temperature will thus be preferred.
• pitch tends to polymerize when heated, and to coke, particularly when exposed to an oxidizing environment while hot. Polymerization may in turn increase the melt viscosity of the pitch, making spinning difficult or impossible, while coking of the pitch forms infusible particles that contribute to flaws in the fiber and may block the spinnerette.
• the spinning process will therefore preferably be conducted using melting and heating operations designed and optimized to protect the molten pitch from exposure to air or other oxidizing conditions during the spinning operations, and to minimize the time the pitch is exposed to elevated temperatures.
• a variety of methods are known for converting pitch fiber to carbon fiber, including those described for example in U.S. patents 4,005,183, 4,209,500, 4,138,525 and 4,351,816, the teachings of which are incorporated herein by reference.
• the infusibilized pitch fiber is then carbonized by further heating in the absence of any oxidizing gas.
• the carbonizing steps may be carried out by heating the fiber in bulk, for example by winding the infusibilized yarn on a bobbin prior to the heating step, by a threadline operation, or by a combination of bulk and threadline operations.
• the carbonizing step has been conducted in the art by heating in the substantial absence of air or other oxidizing gases, and preferably in a substantially inert gas atmosphere, to a temperature in the range of from 1000° to 1900° C, and graphitizing by heating at further elevated temperatures.
• the heating steps are generally conducted to specified temperatures at a carefully controlled rate, particularly before and during the carbonizing step in order to avoid melting or otherwise causing damage to the fiber.
• the pitch fiber is infusibilized by treatment with a liquid oxidizing composition, preferably comprising aqueous nitric acid, and then carbonized.
• a liquid oxidizing composition preferably comprising aqueous nitric acid
• the subsequent carbonizing and graphitizing operations using pitch fiber infusibilized with liquid oxidizing composition may be be conducted according to the processes disclosed and described in the U.S. patents set forth herein above.
• the infusibilized fiber may be carbonized and graphitized in a single operation whereby the fiber is wound on a suitable spool and heated under controlled conditions to a temperature above 2000° C, preferably above 3000° C to accomplish the graphitization step.
• the liquid oxidizing composition comprises an aqueous solution of nitric acid.
• Nitric acid is relatively inexpensive and may be readily obtained in concentrated form from commercial sources.
• the concentrated acid will be diluted with water, preferably with deionized or distilled water to avoid introducing undesirable contaminants, to achieve the desired concentration.
• concentration of nitric acid employed will depend in part upon the length of time the pitch will be exposed to the nitric acid, as well as on the amount of aqueous nitric acid that will be added per unit weight of fiber and the degree of drying that will take place before the heat treatment is carried out. Although a concentration of as low as 10 wt% may be used, concentrations of at least 15 wt% will ordinarily be needed to achieve adequate oxidation and reduced fiber sticking. Still more preferred to accomplish adequate treatment in a reasonable length of time will be concentrations above about 20 wt% and preferably in the range of from about 20 to about 30 wt%.
• the time between the application of the acid to the pitch yarn and the heat treatment will be in the range of from one to about five days, a concentration of approximately 25 wt% will be suitable.
• the concentration of the nitric acid may be further increased above 30 wt% to as much as 40 wt%.
• the liquid oxidizing composition may include carbon black or colloidal graphite particles and a surfactant for these purposes.
• the particles serve to separate the pitch filaments and thereby reduce sticking, and the surfactant may be useful for maintaining the particles as a uniform dispersion in the composition, as well as aiding the flow of the oxidizing composition over the fibers.
• suitable anionic and nonionic surfactants are well known and widely available, typically including various water soluble sodium and ammonium salts of compounds such as tetramethyl oleic acid, lauric acid and the like.
• Other alternative surface treatments that may be useful include the application of a sizing composition to the pitch fibers, either with the liquid oxidizing composition or in a subsequent step.
• a variety of methods for applying the liquid oxidizing composition to the pitch fibers including dipping, spraying, misting and the like will be readily apparent to those skilled in the art.
• a rotating kiss wheel commonly employed for the application of sizing to fibers, may also be conveniently used for this purpose.
• the composition may also be applied to the pitch yarn in bulk after the yarn has been accumulated, such as for example by dipping or spraying the bobbin wound with fiber. A relatively loose winding of the fiber on the bobbin will be desired to allow the composition to flow more freely through the fiber.
• the package or spool comprising the fiber wet with nitric acid may be heat treated directly.
• the wet fiber may contain as much as 50 wt% aqueous acid, requiring the evaporation of large quantities of water during the subsequent heating steps. It may therefore be desirable to allow the excess aqueous composition to fully drain from the spool, and to carry out an initial low temperature heating step to further dry the fiber.
• the drying step may be conducted in a separate operation carried out in a low temperature oven, or by placing the spool in the furnace and conducting an initial low temperature heating cycle with a sweep of inert gas to remove moisture before finally sealing the furnace, in order to reduce the potential for furnace blow-out or other furnace damage due to the presence of large quantities of steam.
• the heat treatment of the fiber infusibilized with aqueous nitric acid or similar liquid oxidizing composition may be conducted in a single heating step to a temperature in the range of 3000° - 3500° C to produce the high modulus fiber of this invention.
• the heat treatment will be conducted in a substantially non-reactive atmosphere to ensure that the fiber is not consumed.
• the non-reactive atmosphere may be nitrogen, argon or helium, however for temperatures above about 2000° C, argon and helium are preferred. Although the non-reactive atmosphere may include a small amount of oxygen without causing serious harm, particularly if the temperature is not raised too rapidly, the presence of oxygen should be avoided.
• yarn wet from being treated with liquid oxidizing composition will produce an atmosphere of steam when heated, which should be purged from the furnace before carbonizing temperatures are reached, inasmuch as steam is highly reactive at such temperatures. It may be desirable to include boron or similar graphitizing components in the furnace atmosphere and these will be regarded as non-reactive as the term is used herein.
• the heat treatment used in the carbonizing and graphitizing of pitch fibers infusibilized with aqueous nitric acid or similar oxidizing composition has three broad ranges which are important in deciding a heating schedule.
• the rate of temperature increase up to about 400° C should take into account that the pitch fibers may not become completely infusibilized until heated above that temperature, and too rapid heating may result in fiber deformation due to softening, fusion and disorientation of the mesophase. While the temperature increase above about 400° C may take place at a higher rate, it must be recognized that much of the gas loss that occurs during the pyrolysis or carbonizing process takes place as the fibers are heated in the range of 400° C to about 800° C, and too rapid an increase can result in damage due to evolving gases.
• the rate of heating may be much greater, and conducted generally at as rapid a rate as may be desired.
• a convenient heating schedule includes heating at an initial rate of 25° C/hr from room temperature to about 400° C, then at 50° C/hr from 400° to 800° C, and finally at a rate of 100° C/hr, or even greater if desired, over the range of from about 800° C to the final temperature.
• the heating schedule also is determined in part upon the type of fiber, the size of the spools, the effective loading of the furnace and similar factors. Various further adjustments may be necessary for use of specific equipment and materials, as will also be readily apparent to those skilled in the art.
• the heating of the fiber may in the alternative be conducted in a series of steps or stages, with cooling and storage of intermediate materials such as carbonized fiber for further processing at a later time.
• the infusibilized fiber may also be carbonized using conventional carbonizing processes such as those described herein above.
• test methods employed in the following examples for determining strand tensile properties for continuous carbon fiber are described in ASTM D4018 and D3800.
• Electrical resistivity for carbon fibers was determined by measuring the resistance per unit length of 50 and 100 cm lengths of the yarn using an ohm-meter, then calculating the yarn resistivity as the resistance multiplied by the cross-­sectional area.
• Cross-sectional area was in turn determined from the weight per unit length, measured according to ASTM D4018 and density, measured according to ASTM D3800 using o-­dichlorobenzene as the immersion liquid.
• Pitch fiber yarn having 2000 filaments was spun from a 351° C softening point mesophase pitch, using an average temperature of 401° C.
• the fiber was spun at an extrusion rate of 8.9 lb/hr and a takeup speed of 590 ft/min for 18 min, then at 12 lb/hr and 800 ft/min, to provide a total fiber weight of 4.1 lb.
• a mixture containing aqueous nitric acid (25 wt%) and 35 g/l of carbon black was applied to the fiber during the spinning operation using a kiss wheel, adding 2.6 lbs to the final weight of the pitch fiber.
• the fiber was wound at a low crossing angle onto a graphite bobbin covered with a 1/4" thick carbon felt pad to give a diameter of 3.5".
• the final spool or package of fiber was tapered, 10" at the base and 4" at the top, and had an outside diameter of 6.5".
• the package was placed in the top position of an induction furnace and heated in an argon atmosphere at a rate of 25°/hr to 400° C, then at 50°/hr to 800° C, and finally at 100°/hr to 3200°C.
• the spool was held at 3200° C for one hour, then cooled.
• the fiber had the following strand properties: tensile strength 327,000 psi tensile modulus 125,000,000 psi yield 0.324 g/m density 2.20 g/cc resistivity 1.51 micro-ohm-meter
• Pitch fiber yarn having 2000 filaments was spun from a 355° C softening point mesophase pitch, using an average temperature of 412° C.
• the fiber was spun at an extrusion rate of 12 lb/hr and 850 ft/min, to provide a total fiber weight of 3.8 lb.
• a mixture containing aqueous nitric acid (25 wt%) and 35 g/l of carbon black was applied to the fiber during the spinning operation using a kiss wheel.
• the fiber was wound at a low crossing angle onto a graphite bobbin covered with a 1/4" thick carbon felt pad to give a diameter of 3.5".
• the final spool or package of fiber was tapered, 10" at the base and 4" at the top, and had an outside diameter of 6.5".
• the final weight of the pitch fiber package included 38 wt% aqueous acid mixture.
• the package was mechanically rotated and allowed to dry at room temperature to a moisture content of about 15 wt%, and then further to a final moisture content of less than 9 wt%.
• the package was placed in the induction furnace and heated in an nitrogen atmosphere at a rate of 25°/hr to 400° C, then at 50°/hr to 800° C, then to 1300° C and held for 24 hr before being cooled, removed from the furnace and placed in a second induction furnace.
• the package was again heated in an argon atmosphere at 100°/hr to 3230°C, held at 3230° C for 2 hr, then cooled.
• the fiber had the following strand properties: tensile strength 453,000 psi tensile modulus 136,000,000 psi yield 0.355 g/m density 2.21 g/cc resistivity 1.14 micro-ohm-meter
• the resistivity of the carbon fiber is remarkably low, indicating substantial improvement in thermal conductivity.
• the combination of good conductivity, characterized by a resistivity value less than 1.5 micro-ohm-meter and a high tensile modulus, greater than 125,000,000 psi, found for these fibers is considerably greater has been achievable in the art to this time, and is quite surprising.
• Pitch fiber yarn having 2000 filaments was spun from a 351° C softening point mesophase pitch, using an average temperature of 400° C.
• the fiber was spun at an extrusion rate of 15.4 lb/hr.
• the fiber was treated with aqueous nitric acid, wound on a bobbin and subjected to a first heat treatment substantially by the procedures of Example 2.
• the fiber was then threadline processed in a 2400° furnace for about 5 sec. using 600 g of yarn tension, wound in a parallel manner on a flanged graphite spool and heated in an argon atmosphere at 100°/hr to about 3310° C.
• the spool was held at about 3310° C for one hour, then cooled.
• the fiber had the following strand properties: tensile strength 376,000 psi tensile modulus 138,000,000 psi yield 0.311 g/m density 2.21 g/cc resistivity 1.47 micro-ohm-meter
• Pitch fiber yarn having 2000 filaments was spun from a 331° C softening point mesophase pitch, using an average temperature of 372° C.
• the fiber was spun at an extrusion rate of 12 lb/hr, and thermoset by heating in air at an average rate of 280° C/hr to 380° C and held for 5 min before being cooled to room temperature and wound onto a graphite bobbin.
• the package was placed in the induction furnace and heated in a nitrogen atmosphere at a rate of 50°/hr to 800° C, and finally at 100°/hr to 1300° C and held at that temperature for two hours before cooling.
• the fiber was threadline processed in a 2400° furnace for about 5 sec. using 600 g of yarn tension, then wound in a parallel manner on a flanged graphite spool and heated in an argon atmosphere at 100°/hr to 3080° C. The spool was held at 3080° C for two hours, then cooled.
• the carbon fiber had the following strand properties: tensile strength 293,000 psi tensile modulus 102,000,000 psi yield 0.322 g/cc density 2.16 g/cc resistivity 2.73 micro-ohm-meter
• a commercial high modulus, continuous pitch-based carbon fiber was obtained from Amoco Performance Products Inc. as Thornel P-120 carbon fiber having a tensile strength of 364 kpsi, a tensile modulus of 122 X 106 psi, a resistivity of 1.801 micro-ohm-meter, a density of 2.173 g/cc, and a d spacing Co (004) of 3.375 ⁇ .
• the fiber was heat treated for about 2 hrs in a furnace held at 3330° C, after which the resistivity was 1.776 micro-ohm-meter, the density was 2.186 g/cc and the d spacing Co (004) was 3.371.
• a commercial high modulus, continuous pitch-based carbon fiber was obtained from Amoco Performance Products Inc. as Thornel P-100 carbon fiber having a tensile strength of 350 kpsi, a tensile modulus of 110 X 106 psi, a resistivity of 2.31 micro-ohm-meter, a density of 2.168 g/cc, and a d spacing Co (004) of 3.379 ⁇ .
• the tensile modulus was 110 X 106 psi
• the resistivity was measured as 2.05 micro-ohm-meter
• the density was 2.167 g/cc
• the d spacing Co (004) was 3.377 ⁇ .
• a heat treatment of the fiber for about 1 hr in an oven maintained at 3300° C gave a tensile modulus of 126 X 106 psi, a resistivity of 1.73 micro-ohm-meter and a density of 2.180 g/cc.
• a commercial high modulus, continuous pitch-based carbon fiber was obtained from Amoco Performance Products Inc. as Thornel P-75 carbon fiber having a tensile strength of 279 kpsi, a tensile modulus of 73 X 106 psi, a resistivity of 7.12 micro-ohm-meter, a density of 2.085 g/cc, and a d spacing Co (004) of 3.418 ⁇ .
• the tensile modulus was 113 X 106 psi
• the resistivity was measured as 2.52 micro-ohm-meter
• the density was 2.175
• the d spacing Co (004) was 3.382 ⁇ .
• a commercial high modulus continuous pitch-based carbon fiber was obtained from Amoco Performance Products Inc. as Thornel P-55 carbon fiber having a tensile strength of 315 kpsi, a tensile modulus of 56 X 106 psi, a resistivity of 8.73 micro-ohm-meter, a density of 2.035 g/cc, and a d spacing Co (004) of 3.429 ⁇ .
• the tensile modulus was 101 X 106 psi
• the resistivity was measured as 2.27 micro-ohm-meter
• the density was 2.163
• the d spacing Co (004) was 3.377 ⁇ .
• a heat treatment of the fiber for about 1 hr in an oven maintained at 3300° C gave a tensile modulus of 123 X 106 psi a resistivity of 1.81 micro-­ohm-meter and a density of 2.183 g/cc.
• the present invention is a pitch-­based continuous carbon fiber having a density of not less than 2.18 g/cc, a tensile modulus substantially above 120 X 106 psi, and an electrical resistivity below about 1.6 micro-­ohm-meter. More particularly, the invention is a continuous carbon fiber having a density in the range of from about 2.18 g/cc to the limiting density of crystalline graphite, about 2.26 g/cc, a tensile modulus in the range of from about 125 X 106 psi to about 150 X 106 psi, and an electrical resistivity in the range of from 1.5 to about 0.95.
• the thermal conductivity of the continuous carbon fibers of this invention lies in the range of about 950 to about 1800 w/m-°K, generally above about 1000 w/m-°K and more preferably above 1100 w/m-°K, and the fibers thus are particularly attractive for use in fiber reinforced composites where good dimensional stability and dissipation of heat is desired.
• the present invention is further directed to methods for making such carbon fiber and to composites comprising such carbon fiber. It will be recognized by those skilled in the art that further modifications, particularly in the processes described for making the continuous pitch-based carbon fibers of this invention, may be made without departing from the spirit and scope of the invention, which is solely defined by the appended claims.

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• 1989
  • 1989-12-01 CA CA 2004370 patent/CA2004370C/en not_active Expired - Lifetime
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