Articles you may be interested inThe role of microstructure refinement on the impact ignition and combustion behavior of mechanically activated Ni/Al reactive composites

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The feasibility of synthesizing the titanium aluminides Ti 3 Al and TiAl through field-activated, selfpropagating combustion synthesis is demonstrated. A self-sustaining combustion wave can be initiated only when the imposed field is above a threshold value for each of these two aluminides. At the threshold values, wave propagation resulted in an incomplete reaction between the metals and the products, which contained several phases in addition to the desired one. As the field strength was increased, the reaction approached completion and the amounts of the secondary phases decreased. At a sufficiently high field, a single-phase product was obtained in the case of Ti 3 Al, but, in the case of TiAl, the product contained Ti 3 Al as a secondary phase even with the highest imposed field. The effect of reactant compact density was investigated for the case of Ti 3 Al synthesis. At a fixed value of imposed field, the degree of reaction completion and the conversion to the desired phase increased as the relative density decreased. These observations are discussed in light of the role of the electric field in activating the self-propagating combustion synthesis reactions and the effect of relative density on this activation. The results show that the synthesis by self-propagating high-temperature synthesis (SHS) can be optimized by the combination of field strength and relative density.

We report on the effect of an electric field on the self-propagating reaction between silicon and carbon to synthesize β-SiC. In the absence of a field at a threshold level, no self-sustaining reaction is observed, and as the applied voltage increases, a linear increase in the velocity of the reaction wave is observed. This first demonstration of the effect of fields on such reactions is explained in terms of a model in which the role of the field is confined to the reaction zone.

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