Методы расчета термодинамических потенциалов при оценке состава оксидного слоя на поверхности металлов

Abstract

To select proper water chemistry at fossil and nuclear power plants, data on the composition of oxide film formed on the metal surface contacting with aqueous coolant are necessary. By using these data, the processes occurring on the metal surface can be estimated. Calculation of Pourbaix diagrams is one of the methods using which the processes that take place on metal surface depending on the redox potential and pH can be established. To calculate these diagrams, it is necessary to have a certain set of thermodynamic data based on which it is possible to estimate the possibility of various chemical reactions to occur in the “aqueous coolant – metal” system. However, not all thermodynamic data are available from the literature, especially at high parameters. The article discusses two new methods for calculating the thermodynamic potentials of metal oxides and hydroxides. The first one, called the relative deviation method, is used for carrying out calculations in the coolant temperature range 25–327°C, and the second method, called the relative variation method, is used for carrying out calculations in the coolant temperature range 327–827°C and can also be used for more exactly determining the data obtained using the first method. Both methods can be used for estimating the most probable region for forming protective oxide films on structural material surfaces contacting with aqueous coolant.