I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
ISJAEE: Scientific Technical Centre «TATA», 2017, #13-15


The statistical theory of phase transformations of the potassium alanate KAlH4 temperature decomposition leading to the formation of a more complex alanate K3AlH6 and potassium hydride KH and to further dehydrogenation of the latter with free hydrogen release, pure potassium and aluminum was developed on the basis of molecular-kinetic con-cepts. The free energies values of the decay phases are calculated, dependence of the decay phases and temperature, pressure, composition on metals, hydrogen concentration, activity of its atoms and energy parameters are found. Bialkaline alanates K2MAlH6 (M = Na, Li) and Na2LiAlH6 were also studied. A number of literary experimental graphs of the thermal decomposition processes for the alanates are given, from which the averaged values of the tem-peratures for the phase transformations are estimated. Plots of the free energies values of the phases at the different temperatures are plotted vs the concentration of hydrogen, the minima of which determine the equilibrium states. The possibility of two such minima appearance corresponding to the stable and metastable states of the phase is estab-lished. The temperature dependence of the equilibrium concentration for hydrogen was found, its specificity in the region of hydrogen concentration c = 0.5 was revealed. The graphs of the temperature dependence of free hydrogen releasing from each phase are obtained and such a graph for all chemical reactions of the alanate decomposition that occur also. On the latter one, fractures were found at the points of phase transitions, which can be experimentally manifested in the form of bends. Isotherms of hydrogen absorption-desorption processes and hydrogen content isoplets in phases are also constructed. The possibility of hysteresis effect is established. The results of calculations are compared with the experimental data, their qualitative correspondence is obtained.