Hydrogen in calcium alanate Ca(AlH4)2 and in hydrides of aluminum and calcium

Abstract The statistical theory of thermal decomposition of calcium alanate by stages with the release of hydrogen has been developed. The calculation of free energies of all constituent phases of chemical reactions has been performed on the basis of molecular-kinetic theory, their dependences on temperature, hydrogen atoms concentration and activity, values of energetic parameters of the system has been ascertained. The conditions of thermodynamic equilibrium of all phases, determined the temperature dependence of hydrogen concentration, have been found. The numerical values of energetic constants have been evaluated using experimental literature data. The plots of temperature dependence of hydrogen solubility in the studied phases have been constructed with the curve breaks and bends in the points of transitions between phases. The plot of temperature dependence of hydrogen extraction from the system with the temperature rise has been obtained. The comparison of numerical values of free energies of phases in the points of phase transformations has been performed that confirm the experimentally manifested phase composition of the system, i.e. the possibility of each phase realization in the certain temperature and concentration ranges on hydrogen.