Abstract: The“Gibbs free energy method” was used to study the thermodynamics of CoP₃ preparation by Fe₂P or Fe₃P and Co.The Gibbs free energy of the reactions varied from 196.12kJ·mol^-1 to 146.22kJ·mol^-1 and from 442.38kJ·mol^-1 to 399.21kJ·mol^-1, respectively, when the temperature is in the range of 298K to 1600K. It is impossible to prepare cobalt triphosphate CoP₃ in the calculated temperature range. The Gibbs free energy that the reaction to prepare cobalt phosphate and formation 3CaO · 2SiO₂ added appropriate amount of CaO and SiO₂ into the ferrophosphorus varied from -42.45kJ·mol^-1 to -108.42kJ·mol^-1 under the same temperature range. At the same time, the equilibrium constant of preparation of CoP₃ by Fe₂P is from 2.73×10⁷ to 1.03×10⁴ in the temperature range of 298K to 700K. The results show that it is not only feasible but also thorough that the CoP₃ can be prepared by adding Co and CaO and SiO₂ in ferrophosphorus under the temperature of 700K and in vacuum.It provides thermodynamic parameters for experimental study.

Key words: thermodynamics, ferrophosphorus, preparation, CoP₃