Formation ternary carbides

There are few methods designed for the formation of multicomponent carbides. The methods adopted to produce binary or ternary carbides are applicable. 

Phase diagrams and formation of ternary carbides in R-B-C systems 115... 

The trends in ternary carbide formation in Fe base systems have been briefly reviewed by [1967Gol, 1990Ere]. Aspects of flic construction of diagrams of ternary systems formed by Cr and C with d-transition metals have been presented by [1996Bon, 1997Hil]. 

Tsu] Tsuchida, T., Formation of Ternary Carbide FcsMosC by Mechanical Activation and Subsequent Heat Treatmenf , J. Mater Sci., 36,1735-1740 (2001) (Crys. Structure, Experimental, Magn. Prop., 12)... 

The free energies of formation of some chromium carbides and ternary carbides of uranium with Cr, Mo and W were measured by the methane hydrogen equilibration technique developed earlier. 

The superior oxidation resistance was attributed to the involvement of the ternary carbide Ti2AlC, which has excellent oxidation resistance due to the different bonds between Ti-C and Ti-Al [207,208]. Due to the nature of this composite, oxide formation and growth on this ternary carbide will certainly influence the overall oxidation process of the composite, i.e., the Al203-rich scale formed on Ti2AlC could extend to the surfaces of other phases through lateral diffusion and growth processes and eventually cover the whole surface, enhancing the oxidation resistance of the composite. 

The increase in sensitivity from the pyrolytically coated tube has been noted by others [86] who cautioned against impregnation of the graphite tube with salts of elements which form stable carbides (Ta, Si, Nb, Zr, W, La). Decreased sensitivities for V have been obtained following such treatment which was attributed to the possible formation of ternary compounds between the impregnating element, vanadium and graphite, e.g. V—Ta—C. 

Binary and Ternary Compounds with Elements of Groups II, III, and V. 2f-ray electron spectroscopy has been used to probe the electronic structures of tungsten borides, nitrides and also some carbides and oxides. Enthalpies of formation AH°298.i5 the tungsten borides WB and W2B have been determined by fluorine calorimetry and are — 66.5 and — 68.2 kJ mol respectively. The theoretical possibilities of preparing M02B, a-MoB, MO2B5, WjB, a-WB, and W2B5 by chemical vapour deposition is discussed and MoXj (X = B or Be) have been prepared and examined by X-ray methods. ... 

The Si-B-C system was mainly investigated with view to the understanding of the sintering mechanisms of SiC with boron in combination with carbon and the sintering of boron carbide with silicon [4]. The silicon solubility of about 2.5 at.% in B4C at 2323 K and the comparatively low temperatures of liquid phase formation in the ternary system enhance the sintering of boron carbide. 

Carbides, Silicides, and Germanides. The standard heat of formation and the dissociation energy of TiCjCg) have been determined as — 730 9 and 160 + 8 kJ mol , respectively, using the mass spectrometric Knudsen effusion technique. The standard heat and entropy of formation of TijSijis) have been reported as — 580 kJ moP and 272 e.u., respectively. A thermodynamic analysis of the co-reduction of TiOj with Si02 by carbon at elevated temperatures has shown that the formation of TiSi is more probable than TiSij. Phase equilibria in the Ti-Nb-Ge ternary system have been investigated. ... 

Carbides.— The crystal chemistry of ternary and more complex carbides has been reviewed. The dissociation energies of gaseous metal dicarbides have also been reviewed and compared with those of the corresponding chal-cogenide systems for which information is available. The results of two mass-spectrometric investigations of the atomization energies ( atom,o) dissociation energies (Z)S), and enthalpies of formation (A/ff°... 

The ternary system W-C-Co is shown in Fig. 24 at 1423°C [102]. WC coexists with the Co phase and forms a pseudobinary lower melting eutectic between WC and Co. This eutectic facilitates full densification during liquid phase sintering. The carbon content must be kept close to the theoretical value because a decrease in total carbon content will lead to the formation of q carbides (W, Co>6C which are brittle and harmful to the performance of these materials. In modern hardmetals, also f.c.c. carbides such as TaC, NbC and TiC are admixed which increase the high-temperature performance. Figure 25 shows a microstructure of a modem WC/Co-based hardmetal containing about lOweight-% of f.c.c. carbides TiC, TaC, and NbC. 

Thermodynamic Data on Alloys , by Kubaschewski and Catterall, critically surveys data on some 400 binary and ternary metallic systems, with the term alloy interpreted to include transition-metal oxides, sulphides, carbides, nitrides, and phosphides. When available, values are given for the integral enthalpy and entropy of formation of the alloy, the relative partial molar enthalpy and entropy of one component, and the volume change on mixing. 

The atomization enthalpies (4//,) and the enthalpies of formation (,AH°) of ternary gaseous rare-earth carbides (kJ/mol). 

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