Abstract: According to the principles of simultaneous equilibrium and mass balance, a series of thermodynamic equilibrium equations of Ni(Ⅱ)-C₂O^2-₄-NH₃-NH⁺₄-H₂O system at ambient temperature are deduced theoretically and the logarithm concentration versus pH value(lg［Ni²⁺］_T—pH) diagrams at different solution compositions are drawn. The results show that when pH is above 8.0, nickel ions coordinate with ammonia, the precipitation proceeds slowly accompanying with the release of nickel ions from the multi-coordinated Ni(NH₃)²⁺_n(n=1, 2, …, 6) and the morphology of NiO powder precursor is fibrous; when pH is below 8.0, nickel ion directly reacts with C₂O^2-₄ and the morphology of NiO powder precursor is of cubic-shape. Some experiments were made to confirm the relation between the total concentration of nickel ion and pH. It is shown that the thermodynamic mathematical model is correct and the calculated values are basically accurate.

Key words: thermodynamic analysis; NiO precursor powder; fibrous shape; cubic-shape