Microwave-induced reaction sintering of NiAl2O4

The microwave reaction sintering of NiAl2O4 ceramics to "high" density was achieved in about 15 min using a 2.45-GHz microwave source operating at 2 kW. At temperatures > 500 C, NiO absorbs microwaves more strongly compared to Al2O3, leading to anisothermal conditions in the powdered mixture. By preheating to > 500 C, the NiO + Al2O3 mixture attains temperatures of about 1400 C, and at this temperature, the mixture inter-reacts to form a dense compact of NiAl2O4 in just 15 min. A comparative study against conventional sintering showed that the microwave reactions are considerably faster due to the enhanced diffusion of the species associated with "anisothermal conditions" that exist in the mixture when exposed to a microwave field. 14 refs.