Alumina-aluminide alloys (3A) technology: I. Model development

The general reaction behavior of the 3A process under the thermal explosion mode of synthesis has been investigated via a continuum model. The continu um model uses mass and energy balances to predict temperature difference (T -s,T-avg - T-f) curves, as well as profile curves of the reactant conversio ns and sample temperature. In particular, the effect of the dimensionless p arameters associated with the rate of local heat generation (beta, the ther micity factor), the activation energy (gamma, the Arrhenius number), the ra te of heat redistribution (alpha, the modified thermal diffusivity), the ra te of heat transfer by convection (Bi, the Biot number or convective heat t ransfer parameter), and the rate of heat transfer by radiation (Omega, the radiative heat transfer parameter) were investigated, Conditions to control the reaction process, which should produce high-density final products, we re determined. It was found that the overall maximum temperature may be red uced for high gamma, low beta, high alpha, and high Bi and Omega. In terms of processing conditions, this may be obtained by reducing the initial reac tant concentrations, optimizing the particle size, using small sample sizes and high compaction pressure, and increasing the heat loss by using a high thermal conductivity inert gas.