Theoretical and experimental studies on the solubility of magnetite

Abstract

The reduction of magnetite by hydrogen to soluble ferrous ions is an important factor in the corrosion behavior of steels in high temperature water and the maintenance of solubility equilibrium removes any tendency for deposition of oxide within the pores and thus explains the continued growth of the oxide. The variations of the solubility as a function of temperature, pH-value, and hydrogen pressure can be calculated. To find the exact method of calculation for the solubility of magnetite and the thermodynamic data, solubility measurements were made in an autoclave containing the mixture of boric acid plus dilute hydrogenated lithium hydroxide solution by a static method. Also, theoretical calculations have been made from thermodynamic data relating to magnetite and ferrous species by using "Criss-Cobble Correspondence Principle" in the case of ionic species. The experimental data were compared with the theoretical results to refine the method of calculation. On the basis of these studies the following conclusions are drawn. The experimental results are in reasonable agreement with the calculations involving formation of $Fe^{2+}$, $FeOH^+$, $HFeO^-_2$, and $FeO^{2-}_2$ with a pressure dependence S = constant × $P^{1/3}_{H_2}$. Besides, theoretical approach in this thesis can be applied to the calculation for the solubility of other oxides by using appropriate input data. Furthermore, necessary future improvement for the basic thermodynamic data.