US3464843A - Pyrolytic graphite alloys and method of making the same - Google Patents

Description

M. BASCHE Sept. 2, 1969 PYROLYTIC GRAPHITE ALLOYS AND METHOD OF MAKING THE SAME Filed March 21, 1962 FIG! ' FIGZ INVENTOR. MALCOLM 303045 2) ATTOR EY United States Patent 3,464,843 PYROLYTIC GRAPHITE ALLOYS AND METHDD OF MAKING THE SAME Malcolm Basche, Newtonville, Mass, assignor, by mesne assignments, to Union Carbide Corporation, a corporation of New York Continuation-impart of application Ser. No. 124,440, July 17, 1961. This application Mar. 21, 1962, Ser. No. 181,313

Int. Cl. C23c 9/06 U.S. Cl. 11746 8 Claims This invention relates to alloys and more particularly to alloys comprising pyrolytic graphite and to methods of producing such alloys. This application is, in part, a continuation of copending application Ser. No. 124,440, filed July 17, 1961 now abandoned.

A principal object of the present invention is to provide novel alloys comprising pyrolytic graphite and at least one metal and/ or metalloid.

Another object of the present invention is to provide one or more processes for producing pyrolytic graphite alloys.

Still another object of the present invention is to provide novel alloys comprising pyrolytic graphite and boron.

A still further object of the present invention is to provide new and improved alloys comprising pyrolytic graphite and boron which may be used in heat shields.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others, and the products possessing the features and properties which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a schematic, flow diagram illustrating a process for producing pyrolytic graphite alloys; and

FIGURE 2 is a diagrammatic view of a halide generator which may be used in production of pyrolytic graphite alloys.

It has been discovered that alloys comprising pyrolytic graphite and a metal such as, for example, a refractory metal as tungsten, hafnium or the like, or alloys comprising pyrolytic graphite and a metalloid such as, for example, boron or silicon can be produced if a gaseous metal or metalloid compound, e.g. a halide is contacted with a gaseous hydrocarbon at a suitable temperature. Of the many pyrolytic graphite alloys which may be prepared in the above manner, alloys comprising pyrolytic graphite and boron are of particular interest since it has been found that such alloys exhibit very unusual characteristics.

For instance, the thermal conductivity of some of such alloys, is substantially less than that exhibited by pyrolytic graphite itself if the thermal conductivity is measured in the c direction, that is, the direction perpendicular to the surface of the deposit. It is also of interest to note that the electrical conductivity of such alloys is substantially greater than that of ordinary pyrolytic graphite if measured in the same direction. Pyrolytic graphite itself is essentially a highly oriented graphite which has a hexagonal layer structure in which the basal planes tend to align themselves parallel to the surface of the deposit. As such, pyrolytic graphite conducts electricity by charge carriers and thermal energy or heat by lattice "ice vibration. It is believed that the boron alloying material is disposed both interstitially and substitutionally in the graphite lattice. As a result of the boron interstitially deposited between the basal planes of graphite, the number of charge carriers for a given area are increased thereby increasing the potential conductivity of electricity in the same area. Also, the vibration of each of the basal planes of the pyrolytic graphite lattice is decreased by the presence of boron thereby suppressing the thermal conductivity of the lattice. It has been found that such alloys will transmit current in a direction perpendicular to the surface of the deposit without an excessive voltage drop while, at the same time, providing a thermal insulation against the transfer of an excessive amount of heat.

The alloys of the present invention find wide utility. For example, such alloys may be used in applications or devices where there is desired a coating or free-standing mass or body capable of withstanding high temperatures or possessing substantial strength at elevated temperatures or possessing substantial gas imperviousness or corrosion resistance or possessing combinations of the above properties. Such alloys may also be employed so as to utilize the electrical properties thereof. One important use of such alloys and particularly alloys comprising pyrolytic graphite and boron is as heat shields. It is often necessary to adapt delicate instruments or explosive devices with a suitable protective cover or shield which will insulate them against large changes in temperatures. A very eifective shield, which may be used for the purpose may be made of alloys comprising pyrolytic graphite and boron in view of the excellent insulating properties which such alloys exhibit.

Broadly, the precess of this invention comprises contacting at an elevated temperature and a reduced pressure a hydrocarbon gas and a volatile compound (e.g. a halide) of a metal or metalloid such as, for example, boron, silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten, uranium and the like to produce an alloy comprising pyrolytic graphite and a metal or an alloy comprising pyrolytic graphite and a metalloid. This invention also comprises a process wherein a suitable substrate is contacted with a hydrocarbon gas, e.g. methane and a gaseous metal halide e.g. tungsten halide or a gaseous metalloid halide e.g. boron halide at an elevated temperature and a reduced pressure thereby depositing an alloy on such substrate. In one embodiment of the invention, pyrolytic graphite alloys are produced by contacting at an elevated temperature a halogen gas, e.g. chlorine with a mass of a metal or metalloid and immediately thereafter contacting the halide produced with a gaseous hydrocarbon at an elevated temperature and a reduced pressure. In one preferred embodiment of the invention, alloys comprising pyrolytic graphite and boron are produced by contacting the vapors of a boron halide, e.g. boron trichloride and a hydrocarbon gas, e.g. methane at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of mercury.

The flow diagram of FIGURE 1 will be described in connection with the production of alloys comprising pyrolytic graphite and boron, it being understood that such description is also generally applicable to the production of other alloys of pyrolytic graphite.

The substance or substrate desired to be coated is mounted in the reaction furnace 12 which is of the type generally utilized in vapor depositions. The pressure within the furnace is then brought within the pressure range of 20 mm. of mercury or below at which time the temperature of the furnace is increased from room temperature to somewhere between about 1500 C. and

2300 C. After the pressure and temperature are established, a gaseous hydrocarbon in the form of methane, natural gas, ethane, propane, or benzene, from a suitable source or supply 14 is introduced into the feed line 16. This latter line 16 leads to injector 18 which is fitted into furnace 12 so that the injection end 20 thereof is in proximity to the substrate desired to be coated. At this point, a vaporous boron compound such as boron trichloride, which is obtained from a suitable boron trichloride generator or storage tank 22, is fed into the feed line 24. The feed line 24 is adapted with a shut off valve 26 and with valves 28 and 30 on either side of flowmeter 32. In this way, relatively true flow values are obtained on flow meter 32. The pressure within the furnace is indicated by pressure gauge 34. Line 24 is connected to the injector 18 at which point the gaseous reactants are comingled prior to introduction into the furnace 12. Under the above conditions, the carbon and boron liberated from their respective compounds are deposited on the substrate 10 in the form of an alloy comprising pyrolytic graphite and boron. The formulas which represent the overall process may be set forth as follows:

( l 3CH pyrolytic graphite+6H (2) 6H +4BCl boron+ l2HCl (3) Boron-j-pyrolytic graphite alloy After a suitable time, i.e. when a coating of desired thickness is obtained, the gaseous reactants are shut off and the temperature and pressure of the system are allowed to return to normal. At this point, the substrate which is coated with the alloy may be utilized as such, that is, the substrate may become part of the finished structure or the substrate may be removed or separated from the alloy coating to form a free-standing alloy mass or body of desired shape and size.

FIGURE 2 illustrates a halide generating system 36 adapted to produce metal or metalloid halide which is then immediately used in the process. The system 36 has many advantages. For example, it permits the production and use of a substantially uncontaminated halide since the halide once formed is immediately utilized and thus not subjected to contaminating conditions. Additionally, the system permits easy handling of the halide and accurate control of the flow of halide vapors. Furthermore, the system eliminates the need for halide storage and effects economies of operation due to producing the halide and immediately utilizing it. In this embodiment, a charge of particulate or finely divided material, for example, sponge, strips, turnings, powder, wire, or the like capable of being converted, i.e. halogenated to produce the desired metal or metalloid halide for the process, is placed in an enclosed container 40 surrounded by a heater 42 e.g. a resistance heater capable of heating the material to an elevated temperature sufficient to affect halogenation thereof, e.g. between about 200 C. and 1000 C. Within the container 40, the material 381s confined between a porous support plate 41 and a diffusion plate 43. The material 38 may comprise a metal or metalloid compound capable of being halogenated, e.g. boron carbide or preferably it comprises a metal or metalloid element selected from the group consisting of boron, silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uranium. A halogen, preferably chlorine, is accurately metered and fed through an inlet 44 and downwardly through the heated charge, e.g. niobium metal to produce the halide, e.g. niobium chloride. The halide vapors flow from the heated halogenator outlet 46 either to feed line 24 as described above in FIGURE 1 or directly to the injector 18.

The process is carried out at a temperature at which a gaseous hydrocarbon will decompose to produce primarily pyrolytic graphite rather than pyrolytic carbon. The latter, when compared with pyrolytic graphite may be stated to lack strength, density, and imperviousness. The present process, wherein an alloy comprising pyrolytic graphite and a metal and/or metalloid is deposited on a suitably exposed substrate, has been found to be operative when the reactants are maintained at a temperature between about 1500* C. and 2300 C. Althrough the process is operative at a deposition temperature between about 1500 C. and 2300" C., it is preferred to carry out the process at a temperature between about 1800 C. and 2100 C. It has been found that the process is highly effective within the latter range, especially at about 1950 C.

The pressure of the system is used to obtain an even distribution of the gas over the entire surface of the article. Therefore, the pressure of the system is dependent to a large extent on the size and shape of the article that it is desired to produce. In any case, the process is operative at pressures up to 20 mm. of mercury. If the pressure is allowed to increase above 20 mm., a large amount of carbonaceous soot is formed in the system. Although the process is operative at pressures up to 20 mm. of mercury it is preferred to carry out the process at a pressure below about 10 mm. of mercury. It has been found that the process is highly effective at pressures below about 10 mm. of mercury and that products of high quality are obtained.

The hydrocarbon gas or gases which may be used in this process include any carbonaceous gas capable of depositing pyrolytic graphite on an exposed surface when subjected to a suitable decomposition temperature. For illustrative purposes, the hydrocarbon gas may be methane, natural gas, ethane, propane or benzene. The amount of hydrocarbon gas utilized in the system is dependent on the temperature and pressure of the system and the properties that are desired in the final product. When alloys rich in pyrolytic graphite are to be produced the ratio of hydrocarbon gas to metal halide or metalloid halide is large. For example, when producing alloys having a boron concentration between about 0.32 and 1.74 percent by weight, the amount of hydrocarbon gas utilized was between and 300 moles to every mole of boron trichloride that was introduced into the system. It is also of interest to note that the velocity of the hydrocarbon gas is dependent on the amount of hydrocarbon gas utilized in the system.

The metallic or metalloid compound which is introduced into the carbonaceous gas should be readily vaporized so that the quantity introduced can be metered and controlled. Boron trichloride is a good example of a material which may be utilized because it is a gas at room temperature. However, other materials may be used including volatile compounds of metalloids such as boron and silicon, and volatile compounds of metals such as, for example, tungsten, tantalum, niobium, molybdenum, vanadium, thorium, uranium, titanium, hafnium, zirconium, aluminum and the like. Preferably the volatile compounds are halides and more particularly chlorides, For example, there may be utilized the trichlorides of boron and aluminum, the tetrachlorides of zirconium, hafnium, uranium, silicon, thorium, and titanium, the pentachlorides of vanadium, niobium, molybdenum and tantalum, and hexachloride of tungsten, or other chlorides of the above. The ratio of metal halide or metalloid halide to hydrocarbon gas is not fixed but may vary over a wide range. The exact ratio utilized at any given time would depend to a large degree on the amount of metal or metalloid that is desired to place in the pyrolytic graphite lattice. The amount of metal and/or metalloid to be added to the pyrolytic graphite lattice may range from about 0.001 percent by weight to an amount necessary to produce a metal and/or metalloid rich alloy. Preferably, however, the total amount of metal and/or metalloid added to the pyrolytic graphite lattice ranges from about 0.01 percent by weight to about 5.0 percent by weight. it should be mentioned that pyrolytic graphite alloys may be formed containing only one metal or metalloid, or two or more metals or metalloids or a mixture of at least one metal and at least one metalloid.

The alloys of the present invention may be used in the form of coatings or as free-standing bodies or masses of any suitable size and shape. For example, the exterior surfaces of a device to be insulated against large changes in temperature may be protectively coated with a suitable thickness of, for instance, an alloy comprising pyrolytic graphite and boron. Likewise, a free-standing shape may be obtained by coating a suitable substrate, e.g graphite with a desired thickness of a pyrolytic graphite alloy and thereafter removing the substrate. For example, the interior surface of a graphite tube may be coated with a suit-able thickness of a pyrolytic graphite alloy and the graphite thereafter removed so as to form a free-standing alloy tube. Coherent deposits of an alloy of various thicknesses may be built up on, for example, fiat plates or discs so as to form fiat stock of alloy which may be utilized as such or modified as by machining to other shapes. It should also be mentioned that by using fluid bed or rotating drum techniques, particulate bodies or masses which can withstand temperatures above 1500 C. can likewise be coated with an appropriate pyrolytic graphite alloy. For instance, nuclear fuel particles, e.g. uranium dicarbide, may be coated with a suitable thickness of, for example, an alloy comprising pyrolytic graphite and zirconium or niobium. Likewise, particles of non-conducting materials may be coated with a suitable thickness of, for example, an alloy comprising pyrolytic graphite and boron. Such coated particles may be used in, for instance, resistance elements, e.g. resistors. Among the non-conducting base -material which may thus be coated, mention may be made of ceramic materials such as glass, oxides, such as silica, magnesia, alumina and the like. Whenever the term substrate is used in the specification and claims, it is to be taken in its broadest sense and to include within its meaning substances, masses, bodies, material or the like of any size and shape.

More detailed descriptions of producing pyrolytic graphite alloys are given in the following non-limiting examples set forth for the purpose of illustration.

Example I A graphite substrate having a flat deposition surf-ace was placed in position in a furnace of the type heretofore described and the furnace was subjected to a pressure of about 8 mm. of mercury, the temperature of the furnace was then raised to 1950 C. and then methane was introduced into the injector at a flow rate of 5 liters per minute. After the methane fiow had stabilized itself, boron in the form of boron trichloride was fed into the injector at which time it was comingled with the hydrocarbon gas. The flow rate of the boron halide was approximately 0.03 liter per minute. After the desired deposit thickness was obtained, the reactants were turned off and the furnace was allowed to return to room temperature. The substrate was removed from the alloy coating and specimens of the resulting fiat alloy plate were then tested and compared with similar flat plate specimens containing only pyrolytic graphite. Unless other wise indicated, the property data set forth in the following tables is at room temperature. It should be noted that the alloy property data set forth hereinafter represents only initial or preliminary values.

1 Contains 1.74% boron.

Numerous experiments were carried out utilizing the procedure set forth in Example I but in each case the conditions were varied as set forth in Table II which follows:

TABLE II Reactor Gas Flow, l./min. Pressure, p.s.i. Temp, Press,

mm. CH4 B01 CH BCI;

The above Table II illustrates that the process conditions may be varied over a wide range but, in each experiment, a similar coating was produced by the process.

Table III, which follows, sets forth the change in properties encountered when the boron content of an alloy is varied. The property data set forth in Tables III, IV, V, VI and VII for pyrolytic graphite represent-s average values.

TABLE III Alloy, percent by weight boron Density (g1u./cc.) 2. 21 2. 22 2. 21 2. 20 Electrical resistivity (ohm-cm):

c 0. 0266-0. 02679 0. 0189 0.70 a 243 10' 26BX10 284Xl0' sooxro- Bend strength (p.s.i.) a 37,000 33,000 18,000 Flexure modulus of elasticity (p.s.i.)

10 a 3. 78 6. 78 6. 82 4. 0 Thermal conductivity (B.t.u.-ft./ Itfl-hr, F.):

As compared to unalloyed pyrolytic graphite, the alloys comprising pyrolytic graphite and boron showed significantly higher bend strengths than pyrolytic graphite alone, as well as substantially lower a and c direction electrical resistivity and c direction thermal conductivity.

Although only pyrolytic graphite alloys having a boron content of between about 0.32 percent to about 1.74 percent by weight have been exemplified above, it should be mentioned that the boron content may be more or less, the preferred boron concentrations ranging from about 0.01 percent by weight to about 5.0 percent by weight.

The production of other pyrolytic graphite alloys is exemplified in the following examples:

Example 11 A series of runs were made to produce flat plate alloy materials comprising pyrolytic graphite and niobium. In these runs, a chlorinator such as illustrated in FIGURE 2 was employed to form niobium chloride which was immediately fed to the deposition furnace and utilized. In carrying out these runs the container 40 of halide generating system 36 was charged with a suitable quantity of sponge, strips, wire or the like of niobium metal 38 and a graphite substrate 10 having a fiat deposition surface was placed in position in a furnace 12 of the type as heretofore described. The metal charge 38 in container 40 was brought up to a temperature on the order of about 400 C. while the temperature within the furnace 12 was raised to between about 2130 C. and 2150 C. Methane was introduced into the injector 18 at a flow rate of 3 liters per minute. Chlorine gas was introduced through inlet pipe 44 of the system 36 and brought into contact with the heated niobium charge. The niobium chloride vapors produced were fed via outlet pipe 46 and feed line 24 into the injector 18 at which time they were cominglegl with the methane and the mixture introduced into the furnace. The outlet pipe, feed line and injector were heated to a temperature between about 295 C. and 320 C. The flow rate of chlorine gas and the chlorination temperature were controlled so that the flow rate of niobium chloride to the injector and the furnace was maintained between about 0.01 and 0.02 liter per minute. During the deposition of the alloy on the heated substrate, the pressure within the furnace was maintained at about 5 mm. of mercury. After a suitable deposition time, the chlorine and methane flows were terminated and the furnace allowed to return to room temperature. In the runs carried out the deposition times ranged from about 19 hours to about 24 hours to produce alloy coatings having a thickness of from about 54 mils to about 90 mils. In each run, the substrate was removed from the alloy coating and specimens of the resulting flat plate were examined and tested. Table IV which follows indicates the alloys produced in the above series of runs and some of the properties thereof.

TABLE IV Alloy Bend Knoop hardness, Electrical resistivity, content, strength 100 gram tester ohm-cm. percent (p.s.i.) niobium a c a c a 0.00 18,000 84. 20. 0 0 700 500 10- 0.14 27,200 107, 26. 9 550 0.23. 27,650 113.7 24.0 540 10- 24,125 111.5 31.6 550X10- 23, 200 101.0 23. 8 0. 642 509x10- 17, 935 121. 5 30. 2 0.550 580 10- 18, 000 103. 5 25. 0 0. 605 480 10- 700 95. 5 31. 0 0. 542 473X10 13,700 97. 9 37. 4 0. 530 463 10- 19, 200 112. 5 32. 8 483X 10- As compared to unalloyed pyrolytic graphite, the alloys comprising pyrolytic graphite and niobium showed increases in bend strengths especially at low alloy contents, i.e. less than 0.5 percent as well as significant gains in a and c direction hardness.

A series of runs similar to Example IV were made to produce fiat plate alloy material comprising pyrolytic graphite and molybdenum. However, in these runs the container 40 was charged with strips, chunks or the like of molybdenum metal and the deposition times ranged from about 20 to 30 hours to produce alloy coatings having a thickness of from about 59 mils to about 105 mils. Table V which follows indicate the alloys produced and some of the properties thereof.

TABLE V Bend Knoop hardstrength ness 100 gram Alloy content,

Electrical resistivity percent molyb- A series of runs similar to Example IV were made to produce flat plate alloy material comprising pyrolytic graphite and tungsten. However, in these runs, the container 40 was charged with sponge, strips or the like of tungsten metal, the chlorinator temperature was maintained between about 395 C. and about 440 C., the

methane flow rates were 4 liters per minute, and the deposition times were on the order of about 50 hours to produce coatings having an average thickness of about 180 mils.

Table VI indicates the alloys produced and some of the properties thereof.

a and c direction hardness and in some cases, slightly higher bend strengths.

A run similar to Example IV was made to produce flat plate alloy material comprising pyrolytic graphite and aluminum. However, in this case, the container 40 was charged with sponge, strips or the like of aluminum metal, the methane flow rate was 3 liters per minute while the aluminum chloride flow rate was 0.05 liter per minute and the deposition time was 50 hours which resulted in a coating having an average thickness of about 169 mils. Table VII indicates the alloys produced and some of the properties thereof.

TABLE VII Alloy con- Knoop hardness, 100 Electrical resistivity,

tent, per- Bend gram tester ohm-em.

cent strength aluminum (p.s.i.) a c a c a 18, 000 84. 0 20 0 0. 70 500X10 21, 400 98.4 24 7 0. 900x10- 27, 000 84. 8 27 4 0.88 5625x10- The content or concentration of metal or metalloid alloying material can be varied by suitable control of the reaction mix of hydrocarbon and metal or metalloid halide. Thus, although only pyrolytic graphite alloys having a metal or metalloid content of between about 0.002 percent to about 3.70 percent by weight have been exemplified in the several tables above, it is obvious that the content of the alloying material may extend over a wider range and that if desired alloys containing higher percentages of metal or metalloid than those illustrated can be readily prepared. Likewise, although the pyrolytic graphite alloys exemplified contain only a single metal or metalloid, it is evident that alloys containing two or more alloying materials may be produced by introducing two or more halides in suitable ratios into the furnace with the hydrocarbon.

As various changes may be made in the form, construction and arrangement of the parts herein described without departing from the spirit and scope of the invention and without sacrificing any of the advantages, it is understood that all matter herein is to be interpreted as illustrative and not in a limited sense.

What is claimed is:

1. The process of coating a substrate at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of mercury with a gaseous hydrocarbon and a volatile halide of an element selected from the group consisting of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uranium thereby depositing pyrolytic graphite and an element in the form of an alloy on said substrate.

2. A pyrolytic graphite alloy produced by contacting at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of mercury a gaseous hydrocarbon and a volatile halide of an element selected from the group consisting of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uranium.

3. The process of producing a pyrolytic graphite alloy which comprises contacting at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of mercury a gaseous hydrocarbon and a volatile halide of an element selected from the group consisting of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uranium.

4. The process of producing a pyrolytic graphite alloy which comprises contacting at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of mercury a gaseous hydrocarbon and a volatile chloride of an element selected from the group consisting of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uranium.

5. The process of producing a pyrolytic graphite alloy which comprises contacting at an elevated temperature a halogen gas with a mass of an element selected from the group consisting of silicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum, tugnsten and uranium, and immediately thereafter contacting the halide produced with a gaseous hydrocarbon at a temperature between about 1500 C. and 2300 C. and a pressure below about 20 mm. of

mercury.

6. The process of claim wherein said halogen gas comprises chlorine.

7. The process of producing an alloy of consisting essentially pyrolytic graphite and boron which comprises subjecting a reaction mixture consisting of gaseous hydrocarbon and boron trichloride to a temperature between about 1500 C. and 2000 C. and a pressure below about 20' mm. of mercury.

8. The process of producing an alloy of consisting essentially pyrolytic graphite and boron which comprises subjecting a reaction mixture consisting of methane and boron trichloride to a temperature between about 1500 C. and 2000 C. and a pressure below about 20 mm. of

mercury.

References Cited UNITED STATES PATENTS 2,671,735 3/1954 Grisdale et a1. 117-46 X 2,764,510 9/1956 Ziegler 1l7-46 X 2,810,365 10/1957 Keser 11746 X 2,810,664 10/1957 Gentner 117226 OTHER REFERENCES Grisdale et al.: Pyrolytic Film Resistors, Carbon and Borocarbon, in Bell System Technical Journal 30, pp. 305-313, April 1951.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 5, pp. 129-130, 1924.

RALPH S. KENDALL, Primary Examiner A. GOLIAN, Assistant Examiner US. Cl. X.R.

Claims (1)

1. THE PROCESS OF COATING A SUBSTRATE AT A TEMPERATURE BETWEEN ABOUT 1500*C. AND 2300*C. AND A PRESSURE BELOW ABOUT 20MM. OF MERCURY WITH A GASEOUS HYDROCARBON AND A VOLATILE HALIDE OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF SILICON, ALUMINUM, TITANIUM, ZIRCONIUM, HAFNIUM, THORIUM, VANADIUM, NIOBIUM, TANTALUM, MOLYBDENUM, TUNGSTEN AND URANIUM THEREBY DEPOSITING PYROLYTIC GRAPHITE AND AN ELEMENT IN THE FORM OF AN ALLOY ON SAID SUBSTRATE.

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