H. Hayashi, S. Yoshizawa, Y. Ito
Oct 1, 1983
Abstract Thermodynamic behaviour of copper in molten NaOH at 623K (350°C) has been studied. The solubility product of cupric oxide, Ksp−2, was determined to be 2.5 × 10−12 by chemical analysis. The standard potential of the Cu Cu + couple was found to be 1.97 V vs Na Na + and that of the Cu + Cu 2 couple was 1.87 V vs Na Na + , respectively. Moreover, the standard potential of the Cu Cu 2 O and Cu 2 O CuO couples were determined by the use of stabilized zirconia and compared with the values derived from published thermochemical data. Finally Ksp−1, the solubility product of cuprous oxide, was evaluated to be 3.0 × 10−15. From the experiment, the following conclusions were obtained. 1. In this system, copper can be oxidized to its divalent state, such as cupric oxide or cupric ion, through its univalent state, such as cuprous ion or cuprous oxide, in the presence of oxygen. 2. Solubility products of the oxides of copper are much larger than that of nickel oxide, which behaves as a protective film. Thus, copper is not suitable for materials to be used in this media.