Tantalum carbides preparation

Tantalum carbide is produced by carburization of the element or the oxide with carbon, ia a manner similar to the preparation of WC or TiC. Final carburization in a vacuum gives a golden yellow carbide, free of oxygen and nitrogen, that contains 6.1—6.3 wt % C and 0—0.2 wt % graphite. 

Tantalum Carbide, TaC, has been prepared by heating a mixture of tantalum pentoxide and carbon in a molybdenum boat at 1260° C. in a stream of hydrogen,2 or by the action of hydrogen and carbon monoxide on tantalum pentachloride. It is a dark grey or black substance which is insoluble in all acids, and bums to the pentoxide when powdered and heated in air. Density—13 96. It melts with decomposition at 4100° abs., which is probably the highest melting-point yet recorded for a chemical compound. Its hardness coefficient fees between 9 and 10. It is a good conductor of electricity.4 For its crystal structure see reference cited.5... 

Tantalum(V) bromide may be prepared by bromination of tantalum carbide or of mixtures of tantalum (V) oxide and carbon. It is most conveniently prepared by reaction between the elements,1 either at atmospheric pressure, using an inert carrier gas, or in vacuo. The reaction of bromine vapor with tantalum powder in a nitrogen atmosphere forms the basis of the procedure outlined below. 

Shkiro, V. M., Nersisyan, G. A., Borovinskaya, I. R, Merzhanov, A. G., and Shekhtman, V. S., Preparation of tantalum carbides by self-propagating high-temperature synthesis. Sov. Powd. Metall., 18,227(1979). 

Electrodeposition is one of a few techniques used to crystallize high-melting materials at convenient temperatures [e.g., tantalum carbide, TaC (mp 3900°C) and niobium carbide, NbC (mp 3500°C) are crystallized at 750°C]. The preparation involves electrolysis of melts containing Ta20s (or Nb205), Na2B407, Na2C03, NaF, and KF. 

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

L. R. Newkirk, R. E. Riley, H. Sheinberg, F. A. Valencia, T. C. Wallace, Preparation of Unidirectional Fiber Reinforced Tantalum Carbide Composites", Proc. 7th Int. Conf. on CVD, Electrochemical Society, Princeton, NJ, 1979, pp. 488-98. 

Tantalum carbide is very similar structurally and chemically to niobium carbide and is used as a protective coating for tantalum metal. It can be prepared by the CVD of a mixture of elemental Ta metal and methane or a mixture of tantalum pentachloride, methylchloride and hydrogen [10]. 

Vapour-phase Species. The chemical properties of carbon vapour have been reviewed by Skell et al The report describes the preparation of and compositions of the vapour and discusses the chemistry of the constituent species, particularly C, Cg, C3, and C4. Several papers describing detailed aspects of the chemistry of these vapour-phase species have also been published. Chemical reactions of C, Cg, and C3, formed by laser-induced vaporization of either graphite or tantalum carbide, with oxygen, hydrogen, or methane have been studied by means of time-resolved mass spectrometry and gas-phase titrations in an attempt to determine the relative abundances of these three species in the vapour phase (Table 1). The techniques developed and... 

Stem KH, Gadomski ST (1983) Electrodeposition of tantalum carbides from molten salts. J Electrochem Soc 130 300-305 Massot L, Chamelot P, Taxil P (2006) Preparation of tantalum carbide films by reaction of electrolytic carbon coating with the tantalum coating. J Alloys Comp 424(1-2) 199-203... 

Chamelot Massot P, Taxil P Preparation of tantalum carbide films by reaction of electrolytic carbon coating with the tantalum coating. J Alloys Comp... 

Tantalum carbide was first prepared by Joly in 1876 when the pentoxide or tantalites and Na2C03 were heated with carbon at about 1500°. The pentoxide has been a common starting material for modern investigations. 

R Zahneisen, C Russel. An electrochemicaUy prepared precursor for the formation of tantalum carbide. J Mater Sci Lett 13 20, 1994. 

Tantalum pentoxide is used in making high refractive index optical glass as a dielectric film on tantalum for its use as a capacitor component and rectifier and for preparing tantalum metal, its carbide, and many other tantalum compounds. 

Subsequent preliminary comparative studies of the behavior of an SiC based layer on Ta, Mo, Ti and steel substrates showed that better mechanical stability was obtained with a coating deposited on tantalum. This element was consequently considered to make PFCVD deposit/interlayer/steel stacks. Tantalum can be produced by physical vapor deposition (PVD), at variable thickness, with reproducible morphology. Note that preparation by chemical vapor deposition with or without plasma assistance (CVD or PECVD) is possible at low temperature but would require an optimization study in order to be compatible with the deposition conditions of the silicon carbide layer, the aim being to increase the mechanical stability. 

Table 2 shows the initial results for the catalytic dry reforming of methane using bulk carbides of niobium, tantalum, molybdenum and tungsten, prepared by CH4 TPR. The conversions and yields obtained over P-M02C and a-WC are very similar to those predicted by thermodynamic considerations, and thus these materials are efficient catalysts for methane dry reforming. At atmospheric pressure, deactivation was observed over both catalysts after about 8 hours on stream. Examination of the post-catalytic samples by powder XRD (Figure 2) revealed that as the reaction proceeded the active P-M02C was oxidised and converted to... 

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