M A T E R I A L S O F CONSTRUCTION
Carbon and Graphite
engineering materials of construction, carbon and graphite are unique, in that a wide range of physical properties exist without significant change in chemical composition. Raw materials, forming procedures, and temperature treatments all make important contribution to the ultimate physical properties of graphite. Thus, chemically, carbon and graphite are the purest and simplest of materials of construction, but the achievement of a given set of physical properties is a complex, difficult- to-control operation. T h e continuing investigations of the structure and properties of graphite on a large scale are due mainly to the needs of nuclear energy and, more recently, rocketry. -411 kinds of tools and devices are being used to determine the fundamental nature of carbon and graphiteeven the noises emitted during deflection. T h e materials are being subjected in the laboratory to extremes of temperature-from nearly absolute zero to more than 4000’ C. An unusual number of significant new A M O N ,
W . M. GAYLORD, author of our biannual reviews of developments in carbon and graphite since 1951, has been associated with chemical products marketing of National Carbon Co., a division of Union Carbide Corp., since 1943. Gaylord has also authored a number of articles on absorption and corrosion resistance of carbon. He is a graduate of Yale University, B.E. in chemical engineering 1942, and i s a registered professional engineer and member of AIChE.
developments have occurred during the past two years. I n the field of new materials there are graphite cloth and carbon wool. These materials appeared with little warning. Uses for them challenge the imagination. Many new kinds of coatings for carbon and graphite provide resistance to oxidation and erosion at high temperatures. Other coatings greatly improve the wearresistant properties of carbon and graphite. For joining carbonaceous materials with a high strength, high temperatureresistant bond, a new cement is being marketed. When cured, the cement is essentially carbon. Having far-reaching implications, a new processing technique shortens the manufacturing time of carbon from 8 weeks to 8 minutes-a factor of 10,000. A total of 176 exchanger-years is covered in a significant report on the performance of 16 impervious graphite heat exchangers in a severe temperature and corrosion application. Publication of Russian work in the field of carbon and graphite is increasing. If the papers seen to date are representative, it does not appear that their technology is as advanced or specialized as in the United States.
General T h e forming and baking of industrial carbon products by current methods require 3 to 8 weeks. The time per piece is reduced to minutes by a new process based on resistance baking at National Carbon Co.’s new 6000-ton-per-year plant. I n a hydraulic press the carbon shapes are baked at 2000° F. by passing a 3000- to 100,000-ampere current through the piece.
Graphite whiskers have been produced by two processes. ,4 consumable electrode arc has been used to make whiskers u p to 1.6 cm. long and 10 microns in diameter. Tensile strengths are a t least 20,000 p.s.i. and the electrical conductivity is nearly as high as that of the single crystal graphite. The whiskers are crystalline and it is likely that the structure consists of wrapped-up cylindrical sheets of graphite layer planes ( 7 A ) . At the University of Chicago welldeveloped graphite whiskers up to 1.33 mm. long and 0.1 mm. in diameter have been made by decomposing hydrocarbons on electrically heated carbon filaments. They exhibit fibrous structure, with the graphite planes parallel to the whisker axis ( 6 A ) . Looking considerably to the future. it has been demonstrated that graphite can be made from anthracite. However. an economical means of removing ash must be found to make anthracite competitive with petroleum coke under present conditions ( 2 4 ) . Two processes for producing industrial graphite have been illustrated with flow sheets. One traces the manufacture of nuclear graphite, which ends in a combination graphitization and purification furnace that uses Freon as the purifying gas ( 4 A ) . T h e new facilities that satisfy the demand for largr diameter carbon and graphite in the 45 to 60-inch range are shown on the second flow sheet ( 3 A ) . An estimate has been made of graphite’s present and future d a c e in “space” (54. A recent paper discusses the production of low permeability graphite by impregnation with furfural alcohol resin and deposition of carbon from gaseous hydrocarbons ( 7 A ) .
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reflectivity at 2600 A. T h e refractive index and the extinction coefficient also show absorption peaks near 2600 A
(3B). High Temperature Technology
gest Karbate impervious graphite shell and tube heat exchangers ever made. Shells are 45 inches in diameter
General Properties Pitzer and Clementi, University of California, have formed a corrected theory of the behavior of carbon in high temperatures. Previously it was held that carbon heated to vaporization would produce a monatomic carbon gas. T h e new theory holds that a gas with two or more atoms is produced above 2000' C. Immediate value of the information is to suggest that the temperature and efficiency a t which nuclear reactors can be operated can be raised ( 5 B ) . Precise measurements have established that permanent set and creep in commercial graphite depend logarithmically on time. As part of the same work, hysteresis loops for both forcedeflection and torque-twist have been determined. Noises during deflection have been studied for clues to the nature of creep and permanent sei (7B). I n the range 100 to 1000 kc. the attenuation and velocity of sound ivaves transmitted through carbon rods have been measured. T h e Young's modulus calculated from sound velocity is found to be close to: but slightly higher than, the measured static values ( 8 B ) . In a new study of the heat capacity of different graphites in the liquid helium
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temperature range, a special calorimeter was used. T h e authors concluded that both electronic and lattice-vibration theories are in good agreement with experiment. They also feel that in lampblack graphite the random stacking of layer planes can account for the specific heat in excess of chat of natural graphite. Estimated values of the elastic consrants of graphite are presented ( 2 8 ) . Friction has been in\-estigated in seal materials a i 10.000 feet per minute sliding velocity at mating surface temperatures of 500' F. Bodies molded Fvith materials of high graphite content made hard by improved molding methods and impregnation had acceptable friction and \ v e x properties. Carbon materials made graphitic by electrographitization gave high \Year and high friction (78). Photomicrographs are a promising tool in the study and control of structure of carbon products IJB). O'Driscoll and Bell have given an upto-date discussion of rhe effects of radiation on the physical, mechanical, and nuclear properties of graphite (6B). Over the wave length range of 6000 to 2300 A. graphite sho\vs a peak of
INDUSTRIAL AND ENGINEERING CHEMISTRY
Hove has reviewed the high temperature physical properties of graphite and interpreted them in the light of presentday knowledge of the mechanisms affecting these properties. The thermal and mechanical behaviors only are discussed. H e points out that graphite is comparatively unique among materials. in that there is always a property or group of properties which preclude calling it a metal, semiconductor, or ceramic. T h e polycrystalline nature of graphite is of paramount importance in interpreting the high temperature behavior of the material (2Cj. I n rocket nozzle insert studies, si1 icon nitride, silicon carbide, and zirconia-coated graphite were found to be superior to plain graphite (7C). Silicon-impregnated graphite was among the least affected of 34 ceramics tested as nozzle liners in a laboratory rocket motor (JC). Another study of the behavior of graphite or carbon-based materials in high flow rates of an oxidizing gas a t high heat flux and surface temperature showed minor differences in materials produced with normal variations in commercial technology. The most promising materials include graphite coated with pyrolytic carbon. graphite impregnated with aluminum fluoride, and graphite coated with silicon carbide or silicon nitride ( 3 C ) . T h e tensile properties of six grades of graphite at 2200' to 2700' C. have been determined. At 2500' a peak in the strength-temperature curve was noted a t about double room temperature strength. i\ll grades failed brittlely at 2200' C. with elongation less than 1%. At 2500" C . elongations u p to 5% were obtained; at 2750" u p to 207' (6C). T h e constant load tensile creep properties in the range 1650' to 2650' C. have becn reported. Exposures were u p to 8 hours in a helium atmosphere. Elongations u p to 407, occurred with density decreases u p to 17yG. The creep rate increases continuously with increasing temperature and did not sho\v a minimum corresponding to the peak found in the tensile strength a t about 2485" C. (5C). Based on its heat-absorption characteristics, graphite has been favorably compared to copper on a weight basis as a ballistic missile heat sink (7C).
N e w Materials A complete new dimension and concept in manufactured graphite-flexible fiber and fabric forms-have been in-
A new, automated plant now produces carbon shapes in minutes compared to weeks ordinarily required troduced. .4 unique process converts organic textile fiber forms directly to graphite with carbon content in excess of 99.97,. For development purposes graphite cloth 40 inches wide by 7 feet long is available a t $1.50 per square foot. Clean, strong, flexible carbon fibers 5 to 50 microns in diameter made by carbonizing rayon are available. Methane can be pyrolyzed a t 1150' to 1450' C. to make 0.1 to 4.0 micron whiskerlike fibers. They are said to provide better performance than granular carbon in a number of applications ( 2 0 ) . The Minnesota Mining and Manufacturing Co. has developed special silicon carbide coatings to protect graphite from abrasion and oxidation. Tested in the Mach 5 jet of exhaust gases from a n oxygen-kerosine flame a t 2750' C., a graphite-base material that holds dimensions 10 times longer than conventional graphite has been discovered (30).
An integrally bonded graphite coating 40 to 250 microns thick with a \-ickers hardness of 2000 has been developed for machined graphite parts. T h e melting point is over 2000" C. and the coating is smooth and wear-resistant. O n the other hand, graphite particles 10 to 40y0 by \\.eight added to silicon carbide produce a light-weight material having resistance to thermal shock combined with the desirable properties of silicon carbide. Shapes u p to 80 cubic inches are available ( 7 0 ) . For nuclear reactor use grades of graphite can be produced with 1/750,000 the permeability of ordinary graphite. I n one-helium cooled nuclear reactor concept under consideration, graphiteclad fuels will permit operating temperatures to 760' C. Compared with stainless steel-clad fuels limited to 565' C., reactor capacity will be increased one third ( 4 0 ) . A German firm is making. reactor grade graphite of 2.07 density by an undisclosed process starting with a mineral 20%, graphite. Graphite blocks 110 inches long. 20 inches wide, and 46l/2 inches thick are available. T h e development \vas stimulated by the production of aircraft honeycombed panels which require a support material during the brazing operation ( 3 0 ) . A new high-temperature graphite is being used for mainbearing oil seals and as bearing inserts in turbine blade pitch adjusting mechanisms in turbo-prop engines.
Applications I n the plasma arc torch which produces temperatures up to 16,000' C., coated graphite nozzles are used (78E). Chlorination. T h e reduction-chlo-
rination of ores at 1370' to 1650' C. can be carried out in a graphite tube resistance element and furnace chamber. Examples are chromite. spodumene, zircon: rutile. and boron oxide (76E). Copper. Beryllium-copper master alloy is produced in a three-phase carbon electrode vertical. arc-type reduction furnace. T h e sides and bottom are lined Lvith carbon brick. T h e hot meal is tapped into a graphite-lined ladle
(74E). Formaldehyde. The absorption towers of the Borden Co.'s ne\r formaldehyde plant are packed with carbon Raschig rings ( 3 E ) . I n the same plant, Impervite impervious graphite rupture disks have been in service 3 years a t 4 to 5 p.s.i., 120" C.: replacing former disks with a life of 1 year due to corrosion. I n Borden's vinyl acetate polymerization plant. service pressures range from 26 inches to 25 p.s.i.g. Previous rupture disks failed in 3 months because of fatigue but graphite disks have lasted 3 years so far ( 70E). Hydrochloric Acid. T h e vapor phase production of colloidal silica via silicon tetrachloride produces hydrogen chloride. I n Godfrey L. Cabot's new plant the first falling-film hydrogen chloride absorber constructed with 2-inch impervious graphite tubes is used to recover the hydrogen chloride from the hot. dilute gas stream (25E). I n the ne\v perchloroethylene plant a t St. Auban. France, the hydrochloric acid streams are circulated through impervious graphite block-type exchangers by impervious graphite pumps ( 5 E ) . Iron. Current practice in the use of carbon shapes, brick. and paste in and around foundry cupolas is detailed in a comprehensive report. Carbon refractories are recommended for lining cupola wells, tap holes, and slagging troughs (23E). T h e ten linings of a blast furnace are compared in another report. T h e last tbvo had carbon hearths and carbonaceous tap hole mix. These nvo linings gave far better service than the first eight ( 2 E ) . Miller has detailed the design and operation of a blast furnace with a carbon bosh lining. Smoother furnace operation, less cooler trouble. larger working volume. and lower fuel rates more than offset the higher cost of carbon bosh (79E). Nuclear. I n the Exer process for making uranium tetrafluoride from uranium ore leach liquors, impervious graphite was preferred for handling boiling hydrofluoric acid solutions ( 73E). Traces of dust are removed from a steam-hydrogen fluoride mixture by a steamjacketed. carbon tube filter in the Paducah plant producing uranium hexafluoride (E).I n the AEC feed materials production centers graphite is used for
crucibles for vacuum and production melting and as ingot molds for uranium (IE). By adding u p to 8 pounds per cubic foot of fine particles (less than 5 microns) ofgraphite tocarbon dioxide at 35 p.s.i.g., 150' C.. a t 40 feet per second velocity, heat transfer has been increased by a factor of 8 over carbon dioxide alone. Phosphorus and Phosphates. After .3 years' operation TVA's rotating phosphorus furnace \vas shut doivn for inspection. Erosion of the 41-inchthick carbon bottom averaged only 1 inch per year. S o hot spots, tap-outs, or major repairs have occurred so far. T h e roof and electrodes are fued, the crucible and contents rotate a t one revolution per 50 to 200 hours ( 6 E ) . Anorher rrport compares the life ol' linings in rotating and stationary phosphorus furnaces ( 2 2 E ) . TVX's pilot plant for converting ferrophosphorus to iron and phosphatic slag fertilizer uses a composite lining of graphite and magnesite to solve the furnace design problem. The phosphate slag is resisted by the graphitelined walls and magnesite in the hcarth resists the lowphosphorus iron ( J E ) . hlonsanto's new phosphate insecticides plant a t L-itro? L\', Va.? uses Karbate impervious graphite pipe in sever? corrosive services. particularly where hydrogen chloride is handled. Condensers are carbon block type and the vacuum ejectors have carbon nozzles (73E). Sulfuric Acid. T h e Moa Bay process for nickel extraction requires the handling of sulfuric acid leach liquors a t 400 to 500 p.s.i., 205" to 230" C. T h e leach vessels are lined \vith lead and acidproof brick faced with carbon brick cemented with National C-6 cement. The carbon brick is used because it does not spa11 (27E). Sixteen impervious graphite reboilers still in operation after 11 >-ears' handling 45 to 55% sulfuric acid u p to 150' C. show maintenance costs closely related to scaling and cleaning operations. Initially, 20 to 23 units per >-ear xvere cleaned and repaired. After a process change reduced carbon scale deposition, the reboilers needed maintenance only once every 21 months! on the average (77E). An impervious graphite cascade cooler in an insecticide plant has withstood for over 4 years the thermal shock of two or three batches a day of concentrated sulfuric acid a t 400' F. T h e tubes are a t 90' F. \vhen the batch starts through (SEI ' Three of the largest Karbate impervious graphite shell and tube heat exchangers ever made are used in OlinMathieson Chemical Corp.'s Beaumont,
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MATERIALS OF CONSTRUCTION Tex.. plant recovering sulfuric acid from petroleum refining acid sludge. Each 45.inch-diameter shell provides 2685 square feet of heat transfer surface (7E). T h e C . S . Industrial Chemicals’ neii plant for recovering spent sulfuric acid also uses graphite tube and shrll heat exchangers to cool wet sulfur dioxide gas
(77E). Tantalum and Columbium. Grauhite plays an important part in extraction ol tantalum and niobium. T h e carbides of both metals can be prepared by heating their oxide to 2000” C. with lampblack in graphite crucibles. T h e mixture is heated in vacuum by radiation of graphite resisrance elements. T h e electrolysis of potassium fluotantalate is carried out at 900’ C.. using graphite as the anode in the form of a rod or heated pot. An inductance heated pot at 1100’ C . is usrd to react aluminum and potassium fluotantalate to form A13Ta (24E). Titanium. Russian researchers using metallographic and tracer isotope methods have concluded that titanium loss in graphite crucibles can be controlled by using low porosity graphite, rapid melting, and minimization of superheat of the melt (72E). Carbon pickup in titanium melted in graphite crucibles has been reduced to 0.13 to 0.22% by Watertown Arsenal metallurgists. T h e technique used starts with a crucible having a protective “skull” of titanium at the bottom. Adjusting poTver input to hold a meniscus in the molten metal completes the process (2OE).
Process Equipment Development Absorbers. A German patent has been awarded to the designers of a graphite tower that produces hvdrochloric acid from chlorine, hydrogen. and lvater. T h e gases are burned at the base of the toiver in a bell-shaped chamber. A modification of the construction of falling film absorbers has been described ( 5 F ) . Cement. National C-6 cement is a new material based on a furfuryl alcohol (27E) composition that maintains a strong bond between carbon and graphite articles at temperatures u p to 1400’ C. ( 7 F ) . Furnaces. Carbon resistor tube furnaces l inch in diameter bv 12 inches long to 5 inches in diameter by 48 inches long are now available for work requiring temperatures to 2750’ C. ( S F ) . A new vertical style carbon-resistor type furnace for 1900’ to 2750” C. operation features automatic loading ( 7 F ) . Giler describes a vacuum melting furnace which uses graphite for all its components (@). Heat Exchanger. Impervious graphite low finned tubes with inner surface
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2.6 times that of a plain tube have been introduced. Graphite block-type heat exchangers are now available in loo-, 150-, and 200-square foot size lvith 3/4-inch diameter holes. There is a choice of two flow patterns and from one to 16 passes on both fluid sides ( 2 F ) . Impervious graphite plate-type heat exchangers have been improved by fitting them with adjustable and removable elbow connections (GF). T h e 1958 prices of Karbate impervious graphite floating head exchangers have been presented in graphical form. Fixed tube sheet Tvpe 304 stainless steel exchangers made by the same manufacturer carry about the same prices ( 3 F ) . Reys gives cost estimating data for impervious graphite heat exchangers, pumps. absorption equipment. pipe and fittings, towers, and rupture disks. Prices today are about the same as when impervious graphite equipment was first introduced in 1938 (8F). Nuclear Energy. A nuclear reactor using the principles of rotary kiln, construction has been patented in Germany. Rupture Disks. English-made graphite rupture disks are being distributed in the Vnited Srates. Tower Packing. Efficient Intalox saddle packing made of carbon is now being produced. They are particularl;. recommended for hot alkalies. hydrofluoric acid, and mixtures containing hydrofluoric acid.
Bibliography General (1A) Bacon, R., Bowman. J. C.. Buli. A m . Phys. Soc. 2, 131 11957). 12A) Boobar. M. G., ISD. Esc. CHE’II. 50, 27 (1958). (3.A) Chem. Eng. 65, No. 7, 128-31 (1958). (4A) Zbzd., 66, NO. 4, 118-19 (1959). (5A) Metal Progr. 74, No. 4, 96-113 (1958 1. (6A) Meier, L., 44th Quart. Rept. Inst Study of Metals, Univ. Chicago. Chicago. Ill., March 1957. (7A) LVatt, W.. Bickerdlke, R . L., others, .Vuclear Pouer4,86 (1959). General Properties ilB) .4ndrew, J . F., LVobschall, D. C.. Okada, J., Bull. Am. Phys. Soc. 4, 132 (1959) . (2B) Bowman, J. C.: Krumhansl, J. .A,. Phys. and Chem. Solids 6, 367-79 (1958). (3B) Humphreys-Owens, S., Gilbert, L. h.. Ind. Carbon and Graphite, Papers Cor,,f. London 1957, pp. 37-41. (4B) Martin, S. W.? Shea, F. L., J r . . IND.ENG.CHEM. 50,41 (1958,. i5B) Mzssiles and Rockets 5, No. 20, 49 (1959). (6B) O’Driscoll, \.V. G., Bell, J. C . . Nuclear Eng. 3, 533-7 (1958). (7B) Swikert, M. A , , A m . SOC.Lubrication E n ~ r s .Trans. 1, 115-20 (1958). (8B) ‘Wobschall, D. C., Hammill, H.. Bull. A m . Phys. SOC.4, 113 (1959).
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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t3C) Janes, M., Wright Air Develop. Center, Tech. Rep. WADCTR-58-395 (March 1958). (4C) Lynch, J. F., Bull. Am. Ceram. Soc. 37, 443-5 (1958). (5C)Martens, H . E., Jaffe, L. D., Button. D. D.. California Inst. Tech.. DA-04495-ORD-18 (hTov. 13, 1958). 16C) Martens, H. E., Jaffe, L. D., Jepson. J. O., Bull. A m . Phys. SOC. 2 , 266 (1957 . 7C) Stalder, J. R., Natl. Advisory Comm. Aeronaut NACA-TN-4141 (November 1957,. New Materials i1D) Ceram. Age 73, No. 4. 13-4 (1959) 12D) Chem. Engr. 64, h’o. 10. 172 11957). (3D) Zbzd., 65, No. 23, 178 (1958). (4D) Ibzd., 66, No. 3, 60 (1959). (5D)Elect. Equzpment Engr. 6, No. 9. 1 2 {1958). Applications (1E) Buntz, B. J., .4m. Inst.. ,Mining Petrol. Engrs., Inst. Metals Div., Sprc. Rept. Ser. 4, 17 (1957). i~2E)Carlson, J. W., Frey, A. E., Blast Furnace Steel Plant 46, 1279-86 (1958,. (3E) Chem. Engr. 64, No. 6, 148 (1957). (4E) Zbid., S o . 8 , pp. 160-2. (5E) Ibid.,65, No. 9, 116-19 (1958). (6E) Zbid.,No. 14, p. 74. (7E) Ibid., 66, No. 5, 106 (1959‘1. (8E) Ibid., No. 6, p. 141. (9E) Chem. Processing 21, No. 1, 76 (19581. (10E) Zbid., 22, No. 1, 33 (1959). (11E) Dillon, C. P., Chem. Engr. 66, Yo. 19: 184 (1958). (12E) Elyutin, V. P., Maurakh. M. A , , Pavlov, Yu. 4.,Primenenie Radioaktiz,. Izotopoou. Met. No. 34, 115-21 (1955). (13E) Greek, B. F.:Rosenberger, F. E.. I N D .E m . CHEW5 1 , 105-12 (1959). (14E) Higbie. K. B., Farmer, M. C., Chem. Eng. Proq. 54, No. 4, 51-4 (1958). (l5Ei Higgins, I. R.. Roberts, J. T . . Hancher, C. W., Marinsky, J. .A,, IND. ENG.CHEM. 50, 285-92 (1958). (16E) Loch, L. D., Chem. Engr. 65, No. 13, 105-9 (1958). i17E) hfeinhold, T. F., Schutz, C. E.; Chem. Processing 21, No. 5, 111-14 (1957). i18E) Metal Progr. 75, 108-9 (1959). (19E) Miller, E. K., Iron Steel Engr. 34, NO, 4, 91-4 (1957). (20E) Prod. Eng. 29, No. 5, 17 (1958). (21E) Simons, C. S., Chem. Engr. 66, S o . 2, 130-34 (1959). (22E) Striplin, M. hl., Potts, J. M , Marks, E. C., J . Electrochem. Soc. 106, 146-7 (19591. (23E) Tatum, G. B.. .tiadern Castings 32, 30.10, 58-64 (1957). (24E) Taylor, D. F.. Chem. Eng. Progr. 54, NO. 4, 47-50 (1958). ;25E) White, L. J., Duffy, G. J., 1 % ~ . E x . CHEM.5 1 , 232-8 (1959). Process Equipment Development t l F ) Ceram. Age 7 1 , KO. 4. 12 (19581. [ZF) Chem. Engr. 64, No. 11, 198 (1957). 13F) Zbid., 6 5 , No. 26, 64 (1958). (4F)Giler, R. R., Znd. Hpahng 25, 2236-48 (1958). (5F) IND. ENG. CHEM. 50, No. 3, 96.4 (1958). i6F) Ibid., No. 3. p. 102.4. (7F) National Carbon Co., Div. Union Carbide Corp., New York, Tech. Bull. S-7600-FG, Part 18 (June 1957). (8Fi Reys, J., Chem. Engr. 65, KO. 4 , 137-42 (1958). (9F) Steel 144, No. 8, 102 (1959).
