Field activated combustion synthesis of the silicides of vanadium

Abstract

The synthesis of vanadium silicides was investigated using the field-activated combustion synthesis technique. For all V–Si compounds, self-sustaining combustion reactions could be obtained when fields above a threshold value were imposed. Monophasic products were obtained only for the starting compositions V:Si=l:2 and V:Si=5:3. For all other compositions the reaction produced a polyphasic mixture. No significant variation of phase composition was observed with an increase in field strength. In contrast with other systems, the field was seen to have a weak effect on the combustion macrokinetic parameters. This was interpreted on the basis of the large electrical conductivity of the reaction products, driving a large part of the electric flux away from the reaction front. The reaction mechanism was investigated through the use of quenching experiments. Only the VSi 2 and V 5Si 3 phases were observed in the leading edge of the combustion front, with the other phases forming from solid–solid interactions in the afterburn. These results have been compared with observations relative to the mechanism of silicides formation in isothermal solid–solid and solid–liquid diffusion couples.