Evaluation of two different methods to synthesize cobalt-aluminate spinel

The aim of this research is to study the efficiency of both microwave-hydrothermal and combustion methods to synthesizeCoAl2O4 spinel. To attain the objectives, precursor solutions of CoCl2·2H2O and AlCl3·6H2O were applied to prepare cobaltaluminate spinel by a microwave-hydrothermal method and the effects of pH (4, 8 and 12), residence time (1 and 2 h), andtemperature of the digestion system (190 and 220 oC) on the properties of final powders were studied. Moreover, mixedsolutions of Al(NO3)3·9H2O, Co(NO3)2·6H2O and glycine were used as a precursor in the combustion synthesis method and theeffect of different molar ratios of fuel to nitrate (0.36, 0.56) and calcination temperatures (800, 1000 oC) were evaluated. Thepowders obtained were characterized by XRD, XPS, SEM, TEM, FT-IR and UV-Vis. The results show that CoAl2O4 spinel isnot formed by the microwave-hydrothermal method under the variable conditions studied, while the combustion synthesismethod is capable of producing nano-particles of CoAl2O4 spinel and according to the results of TEM and Scherrer’s equationmost of the particles have sizes less than 100 nm.