Interconversion of Brucite-like and Hydrotalcite-like Phases in Cobalt Hydroxide Compounds

Formation and interconversion of cobalt hydroxides have been investigated with XRD, FTIR, and compositional analysis. Effects of addition time, aging time, and preparative atmosphere on phase transformation and materials synthesis in ammoniacal solution have been systematically examined. A new precursor phase with hydrotalcite-like characteristics has been identified. While α-Co(OH)2 is prepared with short-aging in nitrogen atmosphere, this divalent metal (Co2+) hydrotalcite-like phase transforms into brucite-like β-Co(OH)2 under prolonged aging in nitrogen. The β-Co(OH)2 can be formed readily in air but later is converted into a new hydrotalcite-like phase which is stable and contains both Co2+ and Co3+ due to redox reactions. Interconversions among the four structural phases have been investigated and correlated.