Electric field activated combustion synthesis in the Ti + Al system under terrestrial and reduced gravity conditions

Abstract

The electric field-activated combustion reaction between Ti and Al was investigated under terrestrial and microgravity conditions with different ignition modes. Samples were reacted with and without an igniter layer and the effects of pre-ignition heating and convective heat transfer on combustion wave velocity were investigated for both cases. The contribution of these effects relative to the effect of the electric field was found to depend on the strength of the field, being less significant at high applied fields. The threshold level of the electric field for the formation of stable combustion waves was higher under reduced gravity conditions and increased further in the top ignition experiments; these observations were attributed to the decrease of preheating to the sample due to the reduction of gravity driven convection effects. Observations on the distribution of the molten reactant (aluminum) in quenched and self-extinguished samples were analyzed in terms of the contribution of forces of gravity, surface tension, and viscosity through calculations of the Bond (Bo) and Capillary (Ca) numbers. The results showed the dominance of the surface tension contribution even under microgravity conditions. Marangoni flows are influenced by concentration gradients due to differences in the Ti content in the molten aluminum.