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
  • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
  • D01F9/24—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • 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
• • 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
  • D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
  • D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
  • G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
  • G01B21/04—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness by measuring coordinates of points
  • G01B21/047—Accessories, e.g. for positioning, for tool-setting, for measuring probes

Definitions

• a rapid continuous process is provided for the conversion of a predominantly amorphous carbonaceous fibrous material containing at least 75 percent carbon by weight (preferably at least 90 percent carbon by weight) to a uniform fibrous material of predominantly graphitic carbon.
• the carbonaceous fibrous material is passed through a reducing flame which imparts a minimum fiber temperature of at least 1,900 C. while the fibrous material is under tension at least sufficient to prevent visible sagging.
• the reducing flame is generated by a fuel-oxidant mixture, e.g. an acetylene and oxygen mixture.
• a fuel-oxidant mixture e.g. an acetylene and oxygen mixture.
• Long lengths of graphite yarns having substantially uniform properties, e.g. graphitic composition, Youngs modulus, and tenacity, may be produced through the use of the present process.
• Graphite fibers are defined herein as fibers which consist essentially of carbon and which have a predominant X-ray diffraction pattern characteristic of graphite.
• Amorphous carbon fibers are defined as fibers in which the bulk of the fiber weight can be attributed to carbon and which exhibit an essentially amphorous X-ray diffraction pattern.
• Graphite fibers generally have a much higher modulus and a higher tenacity than do amorphous carbon fibers and in addition are more highly electrically and thermally conductive.
• conductive graphitization Another prior art approach to graphitizing amorphous carbon fiber, called conductive graphitization, involves passing a yarn over electrically conductive contacts.
• an amorphous carbon fiber is advanced over a pair of spaced electrically conductive rollers while passing an electric current through the advancing fiber to raise it to graphitization temperature.
• a controlled atmosphere of nitrogen, argon, or mixtures thereof generally must be provided around the fiber while undergoing direct resistance heating.
• equipment must commonly be provided to scrape off or otherwise remove residues on the contact rollers.
• arcing tends to occur at the point of departure of the yarn resulting in local overheating and evaporation of portions of the yarn.
• a carbonaceous fibrous material suitable for graphitization according to the method of this invention has (I) at least 75 percent of its fiber weight attributable to carbon, and preferably at least 90 percent of its fiber weight attributable to carbon, (2) a relatively amorphous X-ray diffraction pattern, and (3) structural integrity for at least two seconds at a fiber temperature of I,900 C.
• the carbonaceous fibrous material selected for use in the present process may be formed by a variety of techniques which are known in the art. Such carbonaceous fibrous materials are generally formed by first stabilizing an organic polymeric fibrous material and subsequently pyrolyzing or carbonizing the same under conditions whereby its fibrous configuration is maintained.
• Organic polymeric fibrous materials of varied chemical constitution can be selected as precursors from which the carbonaceous fibers utilized in the process are derived including such diverse types as cellulosics, e.g. regenerated cellulose, cotton, and cellulose acetate; nitrogenous heterocyclics such as polybenzimidazoles; and acrylics consisting primarily of recurring acrylonitrile units.
• the preferred acrylic is an acrylonitrile homopolymer; however, acrylonitrile copolymers may be selected which contain at least about mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith.
• Amorphous carbon yarns suitable for use in the process are commercially available.
• Organic polymeric fibrous materials of a cellulosic origin are commonly stabilized prior to carbonization by then'nal treatment in a nonoxidizing atmosphere, while fibrous materials of a nitrogenous heterocyclic or acrylic origin are commonly initially stabilized by heating in the presence of oxygen.
• Illustrative, carbonization procedures for organic fibrous precursors are disclosed, for example, in US. Pat. Nos. 3,053,775 to Abbott, 3,235,323 to Peters, 3,285,696 to Tsunoda, 3,313,596 to Hogg et al., and in French Pat. No. 1,430,803.
• the carbonaceous fibrous materials which graphitized in accordance with the present invention are preferably in yarn form. Appreciable lengths of continuous multifilament yarns are graphitized in a particularly preferred embodiment of the invention. Staple yarns may also be selected, however, these generally give correspondingly lower tensile properties than do the continuous filament yarns. ()ther fibrous assemblages, such as carbonaceous fabrics, may likewise be treated in accordance with the present invention as will be apparent to those skilled in the art.
• a carbonaceous yarn When a carbonaceous yarn is selected as the starting material it may optionally be provided with a twist which improves its handling characteristics.
• a twist of about 0.1 to l t.p.i., and preferably about 0.1 to 0.7 t.p.i. may be conveniently utilized.
• a highly preferred reducing flame for use in the process is that resulting from an acetylene and oxygen mixture. With this reducing flame, the graphitizing step can be conducted in an open atmosphere.
• a further advantage of the acetylene-oxygen reducing flame is that is has a fairly constant high temperature which is independent, within limits, of the fuel-oxidant ratio.
• a carbon monoxide-oxygen flame also yields good results in an open atmosphere, although it is, of course, essential to provide adequate safety provisions for the operator under such conditions.
• Hydrocarbon fuels such as propane and butane, may be selected but the process does not proceed as smoothly as with acetylene or with carbon monoxide. However, in the presence of an inert blanketing gas, e.g. nitrogen, or argon, comparable stability may be achieved with hydrocarbon fuels.
• Molecular oxygen can be replaced in the fuel-oxydant mixture by a gaseous oxidant such as nitrous oxide although generally it is not advantageous to do so because of the convenience and ready availability of oxygen.
• Fuel-oxidant combinations can also be employed to produce the reducing flame which do not contain a hydrocarbon fuel, such as a carbon monoxide-hydrogen mixture and a hydrogen-chlorine mixture.
• Nonconventional flame sources such as augmented flames (cf. B. Karlovitz, International Science of Technology, June 1962, pp. 36-41); recombination flames, such as the atomic hydrogen torch (cf. 1. Langmuir, Industrial and Engineering Chemistry, June 1927, pp. 667-674); plasma torches; and the like; can also be employed to provide high temperatures. The temperature should not be so high, however, as to destroy the fibrous configuration.
• the fuel to oxidant ratio generally is a significant parameter in the present process.
• the graphitizing treatment is best carried out in a luminous flame obtained by keeping the amount of oxygen in the fuel mixture below the stoichiometric amount which is required to burn the fuel completely to carbon dioxide. Oxidation reactions within the flame are essentially limited to the combustible gas mixture, and the fibrous material traveling through the flame is exposed to an essentially reducing environment. The fibrous material can be destroyed by oxidation if the oxidant-fuel ratio is too high.
• the luminosity of the flame is believed to be caused by ionized carbon fragments in the flame resulting from incomplete combustion of the fuel. Less pyrolytic carbon will be deposited at higher oxygen to fuel ratios than at lower ratios.
• a deposit of pyrolytic graphite is desirable since it increases the high temperature stability of the resulting graphitic product.
• such a deposit is undesirable, e.g., where high adhesion to a matrix is desired.
• a surface protective layer of pyrolytic graphite alternatively can be formed in a separate step in which the fibrous material is heated to a high temperature in a controlled environment containing hydrocarbon vapors.
• temperatures in the flame zone refer to the temperature of the fibrous material as measured by an infrared radiation thermometer and not to a theoretical reducing flame temperature under adiabatic conditions, i.e. without withdrawal of heat by immersing a body into the reducing flame.
• the temperature of the fibrous material in the flame is generally significantly lower than the theoretical reducing flame temperature.
• the theoretical flame temperature of an oxygen-acetylene reducing flame is about 3,l00 C.
• An upper limit of about 2,500 C. for the fiber temperature of a yarn undergoing treatment is generally sufficient and safe.
• the amorphous carbonaceous fibrous material is passed through the reducing flame at a fast enough rate to avoid breaking. As the temperature of the reducing flame is increased, the minimum rate at which breakage is avoided also increases. This minimum speed can be determined for any given combination of amorphous carbonaceous fibrous material and specific reducing flame. The longer the residence time, the greater the extent of graphitization. Thermal degradation with graphite formation occurs within the reducing flame to the substantial exclusion of oxidative degradation. Optimum conditions are reached at the point where the loss of the fiber mass is lowest and the conversion of the remainder of the fibrous material to graphitic carbon is the highest. The two effects can be balanced favorably by adjusting the residence time and the fiber temperature. Subject to the nature of the reducing flame and other factors, residence times of about 2 to 24 seconds, and preferably about 6 to 17 seconds are generally suitable. An exemplary set of optimum conditions is a yarn temperature of 2,300 C. with a residence time of about 15 seconds.
• the necessary apparatus for graphitization according to the present process is simple and should be so arranged that the fibrous material is exposed to a minimum of frictional contacts.
• a convenient arrangement is to continuously feed an amorphous carbonaceous yarn from a rotating-reciprocating bobbin through the reducing flame to an identically functioning takeup mechanism. Starting at the correct reciprocating position on the bobbin, the yarn is unwound without traverse movement and analogously rewound at the takeup side. Hence, random yarn motions are minimized. Further positioning of the yarn in the reducing flame can be accomplished with minimal action by two cylindrically shaped guides located before and after the reducing flame source. Feed and takeup bobbins can be driven by, for example solid-state controlled DC motors with r.p.m.
• a cruciform glass vessel fitted with cooling plates and a passage opening for the yarn can be employed.
• the yarn Before entering the burner module, the yarn may be put under constant tension as, for example, by passing it over a rubber-capped electromagnetic clutch and a skewed roll. The latter separates individual yam loops around the clutch and prevents abrasion by yarn to yarn contact.
• the geometry of the burner is also a factor in maximizing the effectiveness of the graphitization of the present invention.
• Two impinging flames originating from two standard conical tips significantly raise the temperature of the fibrous material passing therethrough.
• a particularly preferred embodiment of this technique is the impingement of the two flames on the tips of their inner cones at an angle of 45.
• the addition of more than two orifices does not have a beneficial effect.
• a series of burners such as to form a continuous reducing flame zone of increased lateral dimension may permit increased processing speeds or the processing of larger fibrous assemblages. Since residence time in the reducing flame is a major parameter, processing speed is significantly related to the length of the flame zone.
• Surrounding the conical tip with a cylindrical or globular reflector, constructed from polished stainless steel sheets, for example also significantly raises the yarn temperature.
• the volume flow of the fuel and oxidant through the burner should be as high as possible, consistent with good reducing flame stability, in order to maximize the moduli of the fibers.
• Tension during reducing flame treatment is recommended for the achievement of optimum properties as it prevents the tendency of the fibrous material to shrink.
• Shrinkage usually leads to relaxation of ordered structures and, thereby, causes a lowering of physical properties.
• Preservation of orientation and/or an increase in orientation, depending upon the magnitude of tension applied increases both the Youngs modulus and the tensile strength.
• the tension applied should be at least sufiicient to avoid visible sagging. Beyond the optimum tension the fibrous material may be damaged by still higher ten- SlOi'iS.
• Flamcproofing compounds may optically be applied to the carbonaceous fibrous material prior to its passage through the reducing flame.
• Such flame proofing or protective agents are not essential in order to effectively carry out the process of the invention.
• treatment of an amorphous carbonaceous yarn containing at least 75 percent carbon by weight (preferably 90 percent carbon) prior to passage through the reducing flame with an aqueous boric acid solution e. g. about 5 to 20 percent by weight
• an aqueous boric acid solution e. g. about 5 to 20 percent by weight
• Other materials which can be optionally employed include silicone oil (DOW 700), antimony salts, and the common bromineand chlorine-containing flame-proofing compounds.
• Graphite fibers produced according to the present process have a relatively higher average tensile strength and a much narrower distribution of individual break values than are generally obtainable by conductive graphitization. Particularly uniform fibers have been obtained when the present process is carried out with a carbonaceous fibrous material derived from a polybenzimidazole. Although we do not wish to be limited by the theory of this improvement, it appears to be due to two factors: (1) the flame healing of flaws by ionized carbon fragments in a luminous reducing flame, and (2) the reduced mechanical wear of the fibrous material in the reducing flame as contrasted to the frictional contact of the rollers during conductive graphitization.
• the data in table I illustrate the results obtainable in an embodiment of the invention employing an acetylene-oxygen flame source as the reducing flame.
• the carbonaceous yam employed was derived from a cellulosic yarn, possessed a slight twist, was sold commercially under the designation VYB-70l0 (Union Carbide), had a total denier of 680, and had the physical properties identified in table I.
• the yarn exhibited an amorphous X-ray diffraction pattern, and in excess of 90 percent of its fiber weight was attributable to carbon.
• the yarn was passed in the open atmosphere through an acetylene-oxygen reducing flame in which the volume ratio of the gases was 1:1. The total flow rate was 1,500 ml./min.
• the data in table ll illustrate the results obtainable in an em I v bodiment of the invention employing a carbonaceous yarn derived from a polybenzimidazole yarn to form a graphite yarn.
• the exemplary polybenzimidazole was poly[2,2"(mphenylene)-5,5'-bibenzimidazole], commonly referred to as PB].
• the polybenzimidazole precursor can be conveniently prepared by the method of example ll of US. Pat. No. 2,895,948 to Brinker et al., or according to the teachings of US. Pat. No. 3,174,947 to Marvel et al.
• a yarn can be prepared from the exemplary polybenzimidazole by dry spinning from dimethylacetamide, for example, in a manner known to the art.
• the resulting PBl yarn is preoxidized by heating in air for about 6 minutes at 450 C. and subsequently carbonized at 800 C. in an inert atmosphere for a residence time of 8 minutes.
• the carbonized PBl yarn contained in excess of 90 percent carbon by weight, possessed a slight twist of about 0.5 t.p.i., had a total denier of 1,450, and exhibited an amorphous X-ray difiraction pattern.
• the same reducing flame source and processing conditions were employed as described in connection with the runs reported in table 1. Highly uniform physical properties were exhibited by the resulting graphite yarn.
• the run sreported table lIl illustratethe use of a different reducing flame source, i.e. a mixture of oxygen and propane, to produce graphite yarn.
• a different reducing flame source i.e. a mixture of oxygen and propane
• the same carbonaceous yarn as used in the runs reported in table I was employed.
• the yarn was passed through an oxygen-propane reducing flame in which the volume ratio of the gases was varied as indicated in table ill, and a fiber temperature of approximately 2,000 C. was imparted to the yarn. Sufficient tension was maintained upon the yarn to prevent visible sagging.
• the apparatus included a cruciform glass vessel with provision for maintaining a nitrogen atmosphere therein, and was fitted with cooling plates and passage openings for the fiber.
• a surface-mix propane-oxygen burner was mounted within the vessel. The data show the properties of the resulting graphite yarn (average of 10 single filament breaks) as a function of the oxygen-propane ratio and the yarn residence time in the reducing flame.
• the runs reported in table IV illustrate the results obtainable in an embodiment of the invention employing a carbonaceous yarn derived from a 760 continuous filament acrylonitrile homopolymer yarn to form a graphite yarn.
• the acrylonitrile homopolymer yarn had a twist of about 0.5 t.p.i.
• the carbonaceous yarn derived from an acrylonitrile homopolymer yarn exhibited the physical properties identified in table IV, and was formed by preoxidizing and carbonizing the precursor as described below.
• the acrylonitrile homopolymer was preoxidized in air in accordance with the teachings of US. Ser. No. 749,957, filed Aug. 5, 1968 of Dagobert E.
• the preoxidized yarn prior to carbonization was nonbuming when subjected to an ordinary match flame, but was incapable of withstanding the reducing flame utilized in the present process which imparts a highly elevated fiber temperature of at least l,900 C.
• the preoxidized yarn was carbonized to form a carbonaceous yarn exhibiting a total denier of approximately 1,000, an amorphous X-ray diffraction pattern, and a carbon content in excess of 90 percent by weight, by heating at 1,050" C. in a constant temperature muffle furnace containing a nitrogen atmosphere for about 2 minutes.
• the same reducing flamesource and processing conditions were employed as described in connection with the runs reported in table I. No visible sagging of the yarn was observed.
• Tables I, ll, Ill, and IV illustrate improved fiber properties achievable by the method in this invention.
• a continuous process for producing a predominantly graphitic fibrous material comprising continuously passing a carbonaceous fibrous material having:
• a continuous process according to claim 1 wherein the residence time of said carbonaceous fibrous material in said reducing flame is from about 6 to 17 seconds.
• a continuous process for producing a predominantly graphitic fibrous material comprising continuously passing a carbonaceous fibrous material having:
• a continuous process according to claim 12 wherein the residence time of said carbonaceous fibrous material in said reducing flame is about 6 to 1 7 seconds.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Inorganic Fibers (AREA)
• Carbon And Carbon Compounds (AREA)

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Cited By (7)

Citations (7)

• 1969
  • 1969-04-28 US US820008A patent/US3634035A/en not_active Expired - Lifetime
• 1970
  • 1970-04-22 GB GB1289047D patent/GB1289047A/en not_active Expired
  • 1970-04-27 DE DE2020404A patent/DE2020404C3/de not_active Expired

Patent Citations (7)

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