Evaluation of methods for calculation of the formation enthalpies of some inorganic compounds in the system CaO—BaO—Al2O3—Fe2O3—SiO2

Abstract

CaO—BaO—Al2O3—Fe2O3—SiO2 system, containing both high­melting hydraulic active compounds and phases, which are characterized by high­protection properties for x­rays and gamma­radiation, is of potential interest in the field of special binders.

To create the materials mentioned above first of all it is necessary to predict the preliminary interaction of components in the system and, consequently, the properties of products obtained. From this point of view, the thermodynamic method is preferable since it allows a calculation approach, without carrying out numerous experiments, to determine optimum synthesis conditions and composition of products. However, the absence of experimental data for standard enthalpies of formation (ΔHfº298) of some inorganic compounds does not allow us to obtain thermodynamic characteristics of all studied processes.

By using the various methods, the unknown values of standard enthalpies of formation for binary compounds Ba4SiO6, Ba3SiO5, Ba5Si8O21, Ba3Si5O13, Ba4Al2O7, Ba5Al2O8, Ba7Al2O10, Ba8Al2O11, Ва10А12О13, СaFe4O7, Ba5Fe2O8, Ba2Fe6O11 as well as ternary compounds ВаСа2Si3О9, BaCaAl4O8, CaBaFe4O8 have been calculated. An assessment of the accuracy of calculations fulfilled following the various methods is given. The possibility of using the modernized Sladkov—Morachevsky’s method for calculating the formation enthalpies of ternary compounds is shown. Also, the advantages of the technique proposed by authors for the calculation of heat formation of complex oxygen­containing inorganic compounds are presented. The given method allows to calculation of the standard heat formation for ternary compounds using the mean gram­atom heat of the formation of compounds for the specific class which is defined as the ratio of the sum of the formation enthalpies of all binary compounds of the ternary system ΔHfº298, whose have been determined experimentally, to the number of atoms which these compounds consist of.