Study on the obtaining of cobalt oxides by thermal decomposition of some complex combinations, undispersed and dispersed in SiO2 matrix

In order to obtain cobalt oxides nanoparticles we have used the thermal decomposition of some carboxylate type precursors. These precursors were obtained by the redox reaction between cobalt nitrate and ethylene glycol, either bulk or dispersed in silica matrix. The redox reaction takes place by heating the Co(NO 3 ) 2 ·6H 2 O-C 2 H 6 O 2 solution or the Si(OC 2 H 5 ) 4 -Co(NO 3 ) 2 ·6H 2 O-C 2 H 6 O 2 gels. Thermal analysis of the Co(NO 3 ) 2 ·6H 2 O-C 2 H 6 O 2 solution and Si(OC 2 H 5 )-Co(NO 3 ) 2 ·6H 2 O-C 2 H 6 O 2 gels allowed us to establish the optimal value for the synthesis temperature of the carboxylate precursors. By fast heating of the solution Co(NO 3 ) 2 ·6H 2 O-C 2 H 6 O 2 , the redox reaction is immediately followed by the decomposition of the precursor, which represents an autocombustion process. The product of this combustion contains CoO as unique phase. We have obtained a mixture of CoO and Co 3 O 4 by annealing the synthesized carboxylate compounds for 2 h at 400°C. With longer annealing time (6 h), we have obtained Co 3 O 4 as unique phase. The XRD study of the crystalline phases resulted by thermal decomposition of the precursors embedded in silica matrix, showed that the formation of Co 2 SiO 4 and Co 3 O 4 , as unique phases, depends on the thermal treatment.