The aim of this research is to study the efficiency of both microwave-hydrothermal and combustion methods to synthesize CoAl2O4 spinel. To attain the objectives, precursor solutions of CoCl2·2H2O and AlCl3·6H2O were applied to prepare cobalt aluminate spinel by a microwave-hydrothermal method and the effects of pH (4, 8 and 12), residence time (1 and 2 h), and temperature of the digestion system (190 and 220 oC) on the properties of final powders were studied. Moreover, mixed solutions of Al(NO3)3·9H2O, Co(NO3)2·6H2O and glycine were used as a precursor in the combustion synthesis method and the effect of different molar ratios of fuel to nitrate (0.36, 0.56) and calcination temperatures (800, 1000 oC) were evaluated. The powders obtained were characterized by XRD, XPS, SEM, TEM, FT-IR and UV-Vis. The results show that CoAl2O4 spinel is not formed by the microwave-hydrothermal method under the variable conditions studied, while the combustion synthesis method is capable of producing nano-particles of CoAl2O4 spinel and according to the results of TEM and Scherrer's equation most of the particles have sizes less than 100 nm.

Keywords: Microwave- hydrothermal, Combustion, Spinel, CoAl2O4.