US2849275A - Production of refractory metal carbides - Google Patents

Description

Aug. 26, 1958 CARBON w. H. BLEECKER 2,849,275 PRODUCTION OF REFRACTORY METAL CARBIDES Filed Jan. 21; 1954 TITANIUM METAL l2 HYDRIDE FURNACE GRINDER r OVERISIZE 1 --2o SCREEN I8} -lH ANALYSIS 22 MIXER i 32 PRECARB. FURNACE 24 FEEDER TOTAL C ANALYSIS METAL CARBIDE BALL MILL l VACUUM CARBURIZING (2e BALL MILL 1 so as VACUUM CARBURIZI NG INVENTOR. William H. Bleeker United States Patent PRGDUCTION OF REFRACTORY METAL CARBIDES Application January 21, 1954, Serial No. 405,287 4 Claims. (Cl. 2314) This invention relates to improvements in the production of metal carbides and in particular to improvements in the production of titanium carbide.

Heretofore, titanium carbide has been produced commercially by reacting the raw material, titanium dioxide, with carbon to produce titanium carbide. This reaction usually took place under hydrogen at atmospheric pressure and resulted in an impure titanium carbide having an oxygent content seldom below one percent. Since the oxygen content of the titanium carbide, produced by the above method, was the source of considerable difliculty, especially in the lowering of the transverse rupture strength to a marked degree, the trend has been to try to produce titanium carbide substantially free from oxygen. In order to achieve this end, the industry has resorted to vacuum carburizing in an e ort to reduce the oxygen content of the resulting carbide. While vacuum carburizing showed some improvement, still the resultant titanium carbide usually possessed oxygen in amounts greater than one half percent.

While investigators have agreed that the prior art overall reduction of titanium dioxide with carbon takes place in two steps, the intermediate product being titanium monoxide, the reaction never goes to completion. Since the intermediate product of the reaction is titanium monoxide, and titanium carbide and titanium monoxide are isomorphous in crystallographic structure, a large range of solid solubility exists between them so that carburization under vacuum precludes the probability of obtaining titanium carbide having less than one half percent oxygen.

An object of this invention is to provide a method of producing titanium carbide containing less than 0.35% of retained oxygen.

Another object of this invention is to provide a method of producing titanium carbide using titanium metal as the starting material.

A more specific object of this invention is to provide a method of producing titanium carbide whereby titanium with carbon and a refractory carbide to produce a binary carbide having very little residual oxyge These and other objects will become apparent when read in conjunction with the accompanying drawing, the single figure of which is a schematic flow chart illustrating steps embodying features of the invention.

This invention, in broad terms,

titanium hydride to remove the oversized particles, mixing a predetermined mass of carbon with the titanium hydride and vacuum carburizing whereby the titanium hy- 2,849,275 Patented Aug. 26, 1958 dride is converted to titanium carbide having very little residual oxygen.

Referring to the flow chart illustrated in the drawing, reference may be had to the different steps of the process. In practice, titanium metal 10 in the form of solid metal or in the form of sponge is employed as the starting material. The titanium metal available in such forms is substantially free from oxygen. The titanium metal 10 is hydrided in a suitable furnace represented at 12 by heating to a temperature preferably between 325 C. to 350 C. for about four hours. During the heating and holding at temperature, dry hydrogen gasis passed into the furnace. The hydrogen gas, flowing over the heated titanium metal, unites with the titanium metal to form titanium hydride having the general formula TiH Where x is about 0.5. The titanium hydride thus produced contains about 2% hydrogen by'weight which renders the titanium very friable.

When cooled, the titanium hydride is comminuted as at 14 by means of grinding, ball milling or any other suitable means to reduce it to a desired particle size of about mesh or finer. Since finely divided titanium is quite pyrophoric, it is desirous to conduct the comminution under a protective atmosphere, as for example, argon, helium, or other non-inflammable, non-contaminating gaseous atmospheres to reduce fire hazard. While titatitanium hydride produces a variety of particle sizes of the titanium hydride.

ployed in practicing the process of this invention.

In order to determine the mass of carbon to be added' from a suitable supply 20 to the titanium hydride to pro duce titanium carbide, a sample of the undersized titanium hydride is analyzed as at 18 to content of the titanium hydride. This may be accomplished by heating the sample in vacuum at a temperature in excess of 900 C where the hydrogen is evolved.

bide, is slightly greater than 20%, it has now been found that a carbon content of about 19.5% yields the optimum results since it minimizes the amount of tin-reacted free Because of the rapidity of the titanium-carbon reaction e. less than 100 mesh, is em in vacuo, which reaction is highly exothermic and explosive in nature, coupled with the difficulties presented by the evolution of large volumes of hydrogen gas from the dissociation of titanium hydride above 450 C., it may be desirable toemploy a precarburizing step in the process as indicated at 24. The precarburizing treatment may be carried out by heating'the mixture of carbon and titanium hydride in an inclined rotary furnace (not shown) which is heated by induction. A protective atmosphere of pure hydrogen is generated by the rapid evolution of hydrogen from the titanium hydride at temperatures in excess of 850 C. The precarburizing step is preferably carried out at a temperature in the range between 850 C. and 1300 C. The resultant product will have a very low hydrogen content and in addition, the material will be carburized, thereby eliminating the violence of the titanium-carbon reaction, to be more fully described. This step may also tend to partially agglomerate the particles. In order to insure a more positive control over the ultimate product, the precarburized material may be analyzed as at 26 to determine the total carbon content of the mass. Since, with most of the hydrogen removed, the total carbon content may vary slightly from the preferred amount of about 19.5%, additions of either carbon or titanium hydride may then be made to adjust the composition for optimum results. After the additions, if any, of carbon or titanium hydride have been made, the material is further processed as will be more fully described hereinafter.

If substantially pure titanium carbide is to be the end product, the precarburized materials, after being adjusted for carbon content, are placed in a closed ball mill represented at 28 for homogenization. In this step, any agglomeration of the particles from the precarburization treatment is broken. In addition, a thorough blending of any additions which have been made for carbon adjustment after the precarburizing treatment is also accomplished.

The homogenized ingredients are removed from the ball mill 28 and placed in a suitable vacuum furnace to complete the carburizing as represented at 30. Since the temperature of the precarburizing treatment as at 24 is not high enough nor is the pressure low enough to expel substantially all of the gases, oxygen, hydrogen and nitrogen, it is desirable to subject the homogenized ingredients to a vacuum treatment. The vacuum treatment serves a two-fold purpose for in addition for effecting the removal of any of the remaining gaseous elements, it also permits the completion of the reaction of any unreacted ingredients remaining from the precarburization treatment 24. By thus converting any of the unreacted ingredients, the end product, titanium carbide, is more uniform and contains a minimum amount of free carbon as was referred to hereinbefore. The vacuum treatment is usually a batch operation wherein the ingredients are placed in the furnace and heated to a temperature in the range between 1800 C. and 2000 C. The furnace is supplied with a vacuum supplying means (not shown) so that a vacuum in the range between 1 and 100 microns may be maintained throughout the vacuum treatment. Since some of the hydrogen remains with the titanium after the precarburizing treatment, as well as oxygen and nitrogen which was present in the starting material, the vacuum is desired so that the gaseous products may be removed during this treatment thereby insuring optimum results.

Since titanium metal is the starting material in the process, the oxygen content of the resultant product, titanium carbide, is extremely low in contradistinction to titanium carbide produced by either the conventional titanium dioxide or the vacuum carburized titanium dioxide processes of the prior art. Titanium carbide produced by the process of this invention has consistently assayed less than 0.05% oxygen. While lattice parameter measurements have shown values of about 4.3275.A. and the extrapolated value of pure titanium carbide is placed at '4 4.330 A., it is apparent that the titanium carbide produced by the process of this invention is of unique purity. This is further substantiated by fluorescent analysis which reveals the absence of cations. The titanium carbide, thus produced, is suitable for use in the production of cemented carbides utilizing titanium carbide and a binder metal, or titanium carbide in addition to other refractory metal carbides with binder metals.

In another embodiment of this invention, the same results, that is, extremely pure titanium carbide, can be achieved by a slight variation in the overall process previously described. Referring again to the flow chart, the titanium metal 10 is hydrided as at 12, comminuted as as 14, screened as at 16, and mixed as at 22 with the predetermined mass of carbon from the supply 20 as was hercinbefore described. After thorough mixing as at 22, the step of precarburizing the ingredients as at 24 is omitted, and instead, the ingredients are placed in a feeder represented at 32 of any suitable type, for example, vibratory, mechanical, etc. which is connected to the vacuum carburizing furnace 30. The feeder 32 is operated at a predetermined rate, thereby metering the ingredients into the furnace for the vacuum carburizing treatment at 30 at a rate depending upon the size of the furnace; for example, it has been found that a vacuum furnace capable of accommodating a pound charge has been satisfactorily fed at a rate of between 10 to 20 pounds per hour. If the capacity of the furnace is larger, the feed rate may be accordingly increased and vice versa. The metering of the ingredients is an essential feature of this alternative process since, as was stated hereinabove, the titanium-carbon reaction is highly exothermic and takes place with explosive violence at about 900 C. However, if the ingredients are metered into the furnace 30 at a predetermined rate, as described in this alternative process, the reaction will take place continuously on a small mass at any one instant thereby controlling the violence of the exposive reaction. Thus, the ingredients are fed into the furnace which is heated to a temperature in the range between 1100 C. and 1300" C. without danger of violence from the explosive reaction. The furnace is also provided with an atmosphere of argon or hydrogen, usually at atmospheric pressure, before the titanium hydride and carbon are metered therein. The hydrogen from the titanium hydride is thus evolved in proportion to the rate of feed of the ingredients from the feeder 32. At the same time, the reaction between titanium and carbon occurs so that when all of the ingredients are in the vacuum furnace 30, the reaction of the titanium hydride and carbon has been completed and the titanium carbide is formed. Upon completion of the reaction, a vacuum in the range between 1 and 100 microns is applied and maintained within the furnace 30 and the temperature is raised to between 1800 C. and 2000 C. during the vacuum treatment.

In another embodiment of this invention, a binary carbide consisting of binary crystals of titanium carbide and a metal carbide selected from the group consisting of tungsten, columbium, tantalum, and vanadium carbides is produced. In this particular embodiment the titanium metal 10 is hydrided as at 12, comminuted as at 14, screened as at 16, mixed as at 22 with carbon from the supply 20 and precarburized as at 24 as was hereinbefore described with reference to the previous embodiments and illustrated in the accompanying flow chart. After the total carbon analysis has been checked as at 26 and adjustments have been made by the addition of either titanium hydride or carbon to the mass, a predetermined mass of metal carbide, for example, tungsten carbide, is added from a supply 34 to the precarburized materials and all of the ingredients are placed in a closed ball mill 36 and milled until uniformly blended.

After the ingredients are substantially homogenized, they are placed in a suitable vacuum furnace 38 and heated to a temperature in the range between 1800 and 2000 C. A vacuum of about 1 to 100 microns is applied to the furnace 38 and maintained throughout the thermal cycle of the vacuum carburizing treatment. The binary carbide thus formed may be further processed in any suitable manner similar to the pure titanium carbide as was referred to hereinbefore.

The above-described process for preparing a binary carbide may be modified as illustrated in the accompanying flow chart. Thus, the titanium metal is hydrided as at 12, comminuted as at 14, screened as at 16, and mixed as :at 22 with the proper amount of carbon from the supply 20 as was previously described. After the ingredients are thoroughly mixed, they are then placed directly in the closed ball mill 36 with a predetermined mass of metal carbide from the supply 34, for example, tungsten carbide, Where they are milled until homogenized. The ingredients are then removed to the vacuum carburizing furnace 38 where they are slowly heated to a temperature in the range between 900 C. and 1100 C., the temperature range in which the titanium hydride and carbon is converted to titanium carbide. The furnace is supplied with pure hydrogen which is evolved from the dissociation of the titanium hydride. After carburization has been accomplished, the hydrogen atmosphere is removed and the furnace is supplied with a vacuum of about 1 to 100 microns after which the temperature is raised to a range between 1800 C. and 2000 C. for the vacuum.

It is to be noted that in the latter process described for the production of a binary carbide, the violence of the titanium-carbon reaction may be so minimized by the presence of the metal carbide addition to the mass that the step of vacuum carburizing can be accomplished without the use of 12. feeder 32 to meter the ingredients into the vacuum carburizing furnace 38. However, to insure a more positive control over the reaction as well as over the ultimate product, the use of .a feeder as was hereinbefore described, may be desirable.

There are several significant factors to be noted concerning this process and the products produced therefrom. Perhaps the foremost feature of this process is the purity of the titanium carbide component thus produced. Reference may be had to Table I comparing the purity of the product of the process of this invention as contrasted to the product produced by currently known convention-a1 processes.

Table I Percent Lattice Process Type Oxygen pararxneter,

Conventional T102 +2. 0 4. 305-4. 310 Vacuum carburized 'IiOz +1.0 4. 315 Hydride (this invention) 0.197 4. 3275 The accepted extrapolated value of the lattice parameter of pure titanium carbide is placed at 4.330 A. When the oxygen content of titanium carbide decreases, the lattice parameter increases and since a fluorescent analysis shows the absence of cations, it is apparent that the titanium carbide thus produced by the process of this invention, as described hereinafter, is of unique purity.

Further, by hydriding the metal, the fine powder which is desirable for the optimum results may be produced in a more stable form (hydride) thus reducing the hazard of handling the material in the pyrophoric metal powder form. Moreover, by employing the metal hydride and later decomposing it, the hydrogen thus released being extremely pure nascent hydrogen, exerts a refining influence on the ingredients as a whole. Also, the charge from the precarburizing furnace has a minimum of gas or gas-evolving reactants so that comparatively large masses may be vacuum processed in one batch. No special technique or special equipment is needed. The overall process, with its various embodiments provides a very flexible operation in the end product.

I claim:

1. In the production of titanium carbide, the steps comprising, heating titanium metal in an atmosphere of hydrogen at a temperature between 325 C. and 350 C. to form titanium hydride, mechanically comminuting the titanium hydride, screening the comminuted titanium hydride to obtain a predetermined particle size of no greater than mesh, adding a predetermined mass of carbon in the form of fine powder to the titanium hydride, mixing the titanium hydride and carbon to produce a substantially uniformly blended mixture, and vacuum carburizing the mixture at a temperature between 1800 C. and 2000 C.

2. In the production of titanium carbide, the steps comprising, reacting titanium metal with hydrogen at a temperature between 325 C. and 350 C. to form titanium hydride, mechanically comminuting the titanium hydride, screening the titanium hydride to obtain a predetermined particle size of less than 100 mesh, adding a predetermined mass of carbon in the form of fine powder to the titanium hydride of the predetermined particle size, mixing the titanium hydride and carbon to produce a substantially uniformly blended mixture, precarburizing the mixture at a temperature in the range between 850 C. to 1300 C. in an atmosphere of hydrogen, ball milling the precarburized mixture, and vacuum processing the precarburized mixture at a temperature in the range between 1800 C. and 2000 C. to convert the titanium hydride to titanium carbide containing less than 0.35% oxygen.

3. In the production of a binary carbide product, the steps comprising, reacting titanium metal with hydrogen at a temperature between 325 C. and 350 C. to form titanium hydride, mechanically comminuting the titanium hydride, screening the comminuted titanium hydride to obtain a predetermined particle size of no greater than 100 mesh, adding a predetermined mass of carbon to the titanium hydride. of the predetermined particle size, mixing the titanium hydride and carbon to produce a substantially uniformly blended mixture, adding a predetermined quantity of metal carbide selected from the group consisting of tungsten carbide, vanadium carbide, columbium carbide and tantalum carbide to the mixture of titanium hydride and carbon, ball milling to substantially uniformly blend the metal carbide and mixture, and vacuum carburizing at a temperature of 1800 C. to 2000 C. to convert the titanium hydride of the mixture to titanium carbide having less than 0.35% oxygen and produce a binary carbide product composed of titanium carbide and the metal carbide selected from the group consisting of tungsten carbide, vanadium carbide, columbium carbide and tantalum carbide.

4. In the production of a binary carbide product, the steps comprising, reacting titanium metal with hydrogen at a temperature between 325 C. and 350 C. to form titanium hydride, mechanically comminuting the titanium hydride, screening the comminuted titanium hydride to obtain a predetermined particle size of no greater than 100 mesh, adding a predetermined mass of carbon to the titanium hydride of the predetermined particle size, mixing the titanium hydride and carbon to produce a substantially uniformly blended mixture, precarburizing the mixture of titanium hydride and carbon in a hydrogen atmosphere, adding a predetermined quantity of metal carbide selected from the group consisting of tungsten carbide, vanadium carbide, columbium carbide and tantalum carbide to the precarburized mixture, ball milling the precarburized mixture and metal carbide to substantially uniformly blend the same, and vacuum processing the ball milled material at a temperature of 1800 C. to 2000 C. to convert the ball milled material to a binary carbide product composed of titanium carbide and the metal carbide selected from the group consisting of tungsten carbide, vanadium carbide, columbium carbide and tantalum addition to a substantial economy in carbide, said titanium carbide of the binary carbide product containing less than 0.35% oxygen.

References Cited in the file of this patent FOREIGN PATENTS France May 11, 1936 Germany Feb. 25, 1933 and Sons, New York, page 182.

Schwarzkopf et al., Refractory Hard Metals, 1953,

5 The Macmillan Co., New York, pages 49-50, 68, 91.

Claims (1)

1. IN THE PRODUCTION OF TITANIUM CARBIDE, THE STEPS COMPRISING, HEATING TITANIUM METAL IN AN ATMOSPHERE OF HYDROGEN AT A TEMPERATURE BETWEEN 325*C. AND 350*C. TO FORM TITANIUM HYDRIDE, MECHANICALLY COMMINUTING THE TITANIUM HYDRIDE, SCREENING THE COMMINUTED TITANIUM HYDRIDE TO OBTAIN A PREDETERMINED PARTICLE SIZE OF NO GREATER THAN 100 MESH, ADDING A PREDETERMINED MASS OF CARBON IN THE FORM OF FINE POWDER TO THE TITANIUM HYDRIDE, MIXING THE TITANIUM HYDRIDE AND CARBON TO PRODUCE A SUBSTANTIALLY UNIFORMLY BLENDED MIXTURE, AND VACUUM CARBURIZING THE MIXTURE AT A TEMPERATURE BETWEEN 1800*C. AND 2000*C.

Images