Field-related effects in the microwave ignited synthesis of aluminides

Microwave ignited combustion synthesis can be used to achieve complete conversion of reactants and to obtain products with unique microstructures. However, this synthetic route suffers from usually poor reproducibility due to the possible electromagnetic field distribution-related ignition mechanisms. Ignition can occur by the direct heating of the reactants, or by their indirect heating by the use of microwave co-absorbers or due to the possible occurrence of breakdown phenomena. In this work, the effects of microwave ignition in regions of predominant electric or magnetic field is investigated in case of mixtures of powdered metal reactants, one of which is aluminium and the remaining is of ferromagnetic nature. These reactions, when a high heating rate is applied, are usually preceded by the formation of liquid aluminium, which then reacts with the other elements to form the intermetallics. The aim of the work is to improve the process reproducibility and to propose new strategies to optimise the synthesis of high purity aluminide intermetallics. Significant differences between ignition in predominant E or H field were experimentally observed, suggesting that the electromagnetic field-related effects could be proficiently exploited to control the kinetic and the microstructure of the final products.