CHARACTERIZATION OF COBALT-ZINC HYDROXYCARBONATES AND THEIR PRODUCTS OF DECOMPOSITION

A series of cobalt-zinc hydroxycarbonate precursors with nominal Co/Zn atomic ratios of 0/100, 10/90, 20/80, 30/70, 40/60, 50/50, 70/30, 90/ 10 and 100/0 have been synthesized from their mixed metal nitrates and ammonium carbonate by a coprecipitation route. X-Ray and electron dif fraction studies of the precursors revealed that hydrozincite, Zn-5(CO 3)(2)(OH)(6), was the major phase at Co/Zn ratios less than or equal t o 30/70 and spherocobaltite, Co(CO3), predominated at Co/Zn ratios of 50/50 to 90/10. The Co/Zn 100/0 precursor formed only the metastable b asic carbonate Co(CO3)(0.5)(OH)(1.0). 0.1H(2)O. UV-VIS-NIR diffuse ref lectance spectroscopy revealed that the cobalt was present in the 2+ o xidation state in an octahedral environment in all the precursors. Dec omposition of the Co/Zn precursors at 350 degrees C resulted in the fo rmation of ZnO as the major phase at low Co loadings and Co3O4 as the major phase at high loadings. The highest surface areas were attained from the decomposition of basic cobalt carbonate or spherocobaltite co ntaining little or no zinc in solid solution. XPS studies of the oxide s revealed that only Co3+ and Zn2+ ions were present at the surface at Co/Zn ratios less than or equal to 30/70 indicating the presence of t he 'surface spinel', ZnCo2O4. Co2+ was detected at higher Co loadings.