Defect and Diffusion Forum Vols. 237-240

Abstract: This paper concerns an analysis of the transport processes at high temperature in anionic conducting oxides subjected to a chemical potential gradient or an applied electrical field. The general equations are given. The principle of the cationic kinetic demixing under a “generalized“ thermodynamical potential gradient is reviewed. Experimental results obtained with yttria-doped zirconia are reported. An experimental procedure for the determination of the oxygen diffusion coefficient in ionic and semiconducting oxides is also described. The results obtained with yttriastabilized zirconia are compared to both self diffusion and conductivity data. This has allowed us to obtain information concerning the defect structure.

Abstract: The results of direct kinetic measurements and SEM observations on formation of silicide phases in Mo-Si system at temperatures 1400-1700о С are presented in the work. It was shown, that the formation of MoSi2 proceeds by two different mechanisms and accordingly, two types of microstructures are formed: (i) a compact layer (usually with expressed columnar structure) by the reaction diffusion mechanism; and (ii) separated fine grains by crystallization in the volume of saturated Me-Si melt. A model of product formation is offered which allows to calculate the relative contributions of the two mechanisms of disilicide phase formation at various stages of interaction and to estimate the role each of them in the total process.