FIELD-ACTIVATED COMBUSTION SYNTHESIS IN THE NB-SI SYSTEM

The activation of self-propagating combustion reactions in the Nb-Si s ystem was investigated using an electric field. Self-sustaining combus tion in elemental reactants with compositions corresponding to Nb5Si3 can be initiated only when the imposed field is above a threshold valu e of 7.4 V cm(-1). The mode of wave propogation and the nature of the product depended on the magnitude of the field. Under steady-state wav e propagation, the product contained the high temperature (beta) and l ow temperature (alpha) modifications of Nb5Si3. The relative concentra tion of these phases showed a dependence on the applied field and on t he relative density of the reactant compacts. The effect of Nb particl e size on the synthesis of Nb5Si3 was investigated and the feasibility of the synthesis of Nb/silicide composites was demonstrated.