Tantalum carbide production

The four most important carbides for the production of hard metals are tungsten carbide [12070-12-17, WC, titanium carbide [12070-08-5] TiC, tantalum carbide [12070-06-3J, TaC, and niobium carbide [12069-94-2] NbC. The binary and ternary soHd solutions of these carbides such as WC—TiC and WC—TiC—TaC (NbC) are also of great importance. Chromium carbide (3 2) [12012-39-0], molybdenum carbide [12011-97-1], MoC, and... 

The industrial practice for the production of tantalum consists of two steps. In the first, the carbide is made by charging a graphite crucible with an intimate, pelletized mixture of lamp black and tantalum pentoxide and heating it in a high-frequency furnace under a dynamic vacuum (10 torr). In the next step, the ground carbide and the requisite amount of tantalum pentoxide are mixed, palletized, and fed to a reduction furnace where the reduction to the metal occurs. The formation of tantalum carbide as well as the reduction to the metal occur at about 2000 °C. The product leaving the reduction furnace is in the form of pellets or roundels (small cylinders) of porous metal, usually sintered together. 

The free energies of formation of the transition metal carbides are somewhat more negative than the free energies of formation of the actinide carbides. To facilitate separation of the actinide metal from the reaction products and excess transition metal reductant, a transition metal with the lowest possible vapor pressure is chosen as the reductant. Tantalum metal and tantalum carbide have vapor pressures which are low enough (at the necessary reaction temperature) to avoid contamination of the actinide metal by co-evaporation. 

Hafnium carbide has an extremely high melting point (3887 °C) and may find use as an alternative to tantalum carbide in the production of very hard metal components.28... 

Use Production of tantalum rare-element optical glass intermediate in preparation of tantalum carbide piezoelectric, maser, and laser applications dielectric layers in electronic circuits. 

DItantalum pentaoxide EINECS 215-238-2 Tantalic acid anhydride Tantalum oxide Tantalum oxide (TaaOs) Tantalum oxide dusts Tantalum penta oxide Tantalum pentoxide. Used in production of tantalum, tantalum carbide optical glass piezoelectric and laser applications dielectric layers in electronic circuits. White powder insoluble in H2O, soluble in HE LDso (rat orl) = 8000 mg/kg. Atomergic Chemefa/s Cabof Carbon Ltd. Cerac Sigma-Akirich Fine Chem. 

The separation of tantalum from niobium requires several complicated procedures. Commercial production of the element includes methods such as electrolysis of molten potassium fluotantalate, carbother-mic reduction of tantalum oxide, reduction of potassium fluotantalate with sodium, or oxidation of tantalum carbide at 800-900 °C, for example, in scrap from cemented carbides (Hammond 1986, Fichte and Roth-mann 1982). 

Major industrial uses of tantalum include the production of electrical components (mainly capacitors), superalloys, tantalum carbide, and in the chemical industry (Cunningham 2000). Its physical properties make tantalum an important component of superalloys (produced by combination with cobalt, iron, nickel, and titanium) commonly used in the aerospace industry. In the chemical industry, tantalum s corrosion resistance is taken advantage of in the production of heat exchangers, evaporators, condensers, pumps, and liners for reactors and tanks (Cunningham 2000). The recycling of industrial and obsolete tantalum-containing scrap represents approximately 20% of the total tantalum consumption in the US (Cunningham 2000). 

Gibson JO, Gibson MG, Production of carbon fiber - tantalum carbide composites, U.S. Pat., 4196230, Apr 1 1980. 

Tantalum carbide is produced industrially in appreciable quantity wdth a world production estimated at 500 tons annually (1994). The following is a summary of applications of tantalum carbide in production or development. More details are given in Ch. 16. 

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... 

The carbothermic reduction processes outlined so far apply to relatively unstable oxides of those metals which do not react with the carbon used as the reductant to form stable carbides. There are several metal oxides which are intermediate in stability. These oxides are less stable than carbon monoxide at temperatures above 1000 °C, but the metals form stable carbides. Examples are metals such as vanadium, chromium, niobium, and tantalum. Carbothermic reduction becomes complicated in such cases and was not preferred as a method of metal production earlier. However, the scenario changed when vacuum began to be used along with high temperatures for metal reduction. Carbothermic reduction under pyrovacuum conditions (high temperature and vacuum) emerged as a very useful commercial process for the production of the refractory metals, as for example, niobium and tantalum, and to a very limited extent, of vanadium. 

This transformation is carried out by intimately mixing metal oxide powders with carbon, again as with the pure metals, at temperatures between 1500-2300 K, with or without the presence of a hydrocarbon gas. The reactions of oxides with carbon are thermodynamically favored, but high temperatures are again needed because the transformations are limited by diffusion. The direct transformation of oxides to carbides is economically advantageous over the use of metals since the need to separately reduce the oxide phases is avoided. Wide application is found for the commercial production of carbides of molybdenum, tungsten, and tantalum. 

In this method metal chlorides or oxychlorides are made to react with gaseous hydrocarbons in the vicinity of a localized heat source (1400-2100 K). Clearly, the reaction is thermodynamically favorable (Tables 3 and 4). The method was first used by Van Arkel in 1923 with an incandescent tungsten filament to make carbides of tantalum and zirconium [40]. Although the reaction variables have been studied extensively, problems remain with control of the process and with low productivity. Application to catalyst synthesis has been moderate [41],... 

The dynamic membranes originally developed by Union Carbide are protected by three core patents U.S, 3977967, 4078112, and 4412921 (Trulson and Litz, 1976 Bibeau, 1978 and Leung and Cacciola, 1983) and their foreign equivalents. Those patents cover a broad range of metal oxides such as zirconia, gamma alumina, magnesia>alumina spinel, tantalum oxide and silica as the membrane materials and carbon, alumina, aluminosilicates, sintered metals, fiberglass or paper as the potential porous support materials. However, their marketed product, trade named Ucarscp membranes, focused on dynamic membranes of hydrous zirconium oxide on porous carbon support. 

The superconductivity and structure of some ternary molybdenum sulphides 258 the non-stoicheiometry of ZrS2 259 and the phase systems ZnCd-S, ZnHg-S, and CdHg-S260 have all been investigated. The reaction of carbon disulphide with the metals of the transition groups IV, V, and VI, has been studied.261 In most cases, the product of the reaction at 800—1000 °C is a sulphide (or more rarely a mixture of two sulphides), but in the case of the metals niobium and tantalum a mixture of carbides is produced. 

This technique has been used by Stokes and co-workers among others for tantalum and tungsten carbide synthesis and the authors have been concerned with a detailed analysis of the influence of the quenching rate on the form of the final product. This work has been extensively reported in Ref. Perhaps it would now be possible to analyse the experimental data taking into account thermodynamic and transport considerations. 

Corrosion of the plates not only detracts from their mechanical properties but also gives rise to undesirable corrosion products, namely, heavy-metal ions, which, when depositing on the catalysts, strongly depress their activity. The corrosion processes also give rise to superficial oxide films on the metal parts, and these cause contact resistance of the surfaces. For a lower contact resistance, metallic bipolar plates sometimes have a surface layer of a more stable metal. Thus, in the first polymer electrolyte membrane fuel cell, developed by General Electric for the Gemini spacecraft, the bipolar plates consisted of niobium and tantalum coated with a thin layer of gold. A bipolar plate could also be coated with a layer of carbide or nitride. 

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