25℃-200℃ 間の水酸化コバルトの沈殿反応について

高温水溶液に関する基礎的研究 (第2報)

抄録

Hydrolysis reaction in Co (II)-H₂O system have been investigated thermodynamically and experimentally, at temperaturesbetween 25°and 200°C. The results are summerized as follows:
(1) The chemical potentials of relating substances at 25°to 250°C were derived by several thermodynamic ways.(2) The hydrolysis equilibrium was discussed thermodynamically, and it was predicted that CoOH⁺would not be predominantunder the conditions considered.(3) The pH dependences of solubility of Co (OH) ₂were measured at temperatures between 25°and 200°C. pH values were measured directly at equilibrating temperatures below 100°C, but were measuredat 25°C for quenched solutions in the experiments above 100°C.(4) Correspondence of pH values between 25°and t°C based on eq.(23) in this paper was confirmed by experiment.(5) Red Co (OH) ₂were precipitated in the experiments at above 90°C and thermodynamic behavior agreed well with the theoretical predicitions (Fig. 10).(6) A bluish active Co (OH) ₂was precipitated at 25°C as a metaslable form, and for this active hydroxide K_sp=7.8·10^-15, μ°₂₉₈=-107.7 kcal/mol were derived