Silicides, and Borides

Borides of Nb and Ta have been reviewed67 and a method for their preparation from boron and metal oxide has been reported.68 

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Carbides, Silicides, and Borides. UReC2 x has been prepared and characterized by X-ray powder diffractometry.645... 

Within the classes of silicide and boride a much wider range of structural types is encountered. 

B. Aronsson, T. Lundstrom, and S. Rundqvist, Borides, Silicides and Phosphides, Methuen, London, U.K., 1965. 

Hydrides of the types AnHi (An = Th, Np, Pu, Am, Cm) and AnHs (Pa —> Am), as well as ThaHis (i.e. ThHs.yj) have been so obtained but are not very stable thermally and are decidedly unstable with respect to air and moisture. Borides, carbides, silicides and nitrides (q.v.) are mostly less sensitive chemically and, being refractory materials, those of Th, U and Pu in particular have been studied extensively as possible nuclear fuels.Their stoichiometries are very varied but the more important ones are the semi-metallic monocarbides, AnC, and mononitrides, AnN, all of which have the rock-salt structure they are predominantly ionic... 

In general, many metals and alloys (e.g. of Al, Ta and Mo) can be deposited on metallic and some non-metallic substrates. M may also be a metal compound having special useful properties (e.g. borides, nitrides, oxides, silicides and carbides), or even a non-metal such as Si (as in Ihrigising ). 

Schrey, F., Gallagher, P., and Levy, R., Selective Silicide or Boride Film Formation by Reaction of Vapor Phase TiC with Silicon or Boron, J. Electrochem. Soc., 1137(5) 1647-1649 (May 1990)... 

Aronsson B, Lundstrom T, Rundqvist S (1965) Borides, silicides and phosphides. Methuen, London... 

Parth6, E. and Chabot, B. (1984) Crystal structures and crystal chemistry of ternary rare earth-transition metal borides, silicides and homologues. In Handbook on the Physics and Chemistry of Rare Earths, ed. Gschneidner Jr., K.A. and Eyring, L. (North-Holland, Amsterdam), Vol. 6, p. 113. 

In earlier work, it was found for borides, silicides and nitrides that specific activity, expressed as total rate of methane consumption per unit surface area, plummeted with increasing surface area of the catalyst samples.1718 The same relationship was also found for transition metals carbides (Figure 16.4). It should be noted the dependence of specific activity on surface area rather than catalyst composition is unusual for heterogeneous catalytic reactions. In addition, it can be found that the reaction order in the oxidant is perceptibly in excess of 1 (Tables 16.8 and 16.9). Such an order is hard to explain in terms of common mechanism schemes for heterogeneous catalytic oxidative reactions. 

Another way of production is the coating of c-BN by electro-less plating with Ni-P, Ni-B, Ni-Fe-P, Ni-Cr-P, Ni-Cu-P, or Ni-W-P alloys, and mixing these powders with >1% of various carbides, borides, nitrides, silicides, and/or oxides. These powders are compacted and pre-sintered at 700-900 °C. Finally, hot-isostatic pressing at 1000-1400 °C and 1000-2000 bar is performed to reduce porosity [264]. 

E. Parthe and B. Chabot, Crystal structures and crystal chemistry of ternary rare earth-transition metal borides, silicides and homologues 113... 

Such a dependence is frequently observed experimentally in the oxida-tion of transition metals forming volatile oxides, and also of their alloys, carbides, nitrides, borides, silicides and other chemical compounds.350 365 An example taken from the work of E.A. Gulbransen and K.F. Andrew389 is presented in Fig. 5.22. 

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