Combustion Synthesis of Nanocomposite Powders Using A Mechanically Activated Process

The authors investigated aspects of nanocomposite structure formation in Fe+Al+Fe2O3 and Fe+Al+Cr2O3 powder mixtures during combustion synthesis using precursors formed as a result of mechanochemical interaction at the stage of preliminary mechanical activation of reactive mixtures. Despite the significant difference in thermal effects, two types of reactions (aluminothermic reduction of oxides and formation of intermetallics from elements, though in the trace amounts) can take place during mechanical activation. Local chemical concentrations at the interfaces and quick reaction kinetics in the nanometer scaled diffusion couples are probably responsible for the simultaneous passing the reactions in mechanically activated mixtures. Nanocomposite structure of the precursors with fine alumina inclusions allows forming end products inheriting structural morphology of the precursors in toto. Complete reduction of oxides with aluminum at the stage of mechanical activation is not a necessary condition for nanostructure preservation during the following self-propagating high-temperature synthesis. The last one is probably connected with the high rate of heterogeneous nucleation at the early stage of combustion and the optimized heat evolution and cooling conditions.