Decomposition of α-Aluminum Hydride Powder. 2. Photolytic Decomposition

Article abstract of DOI:10.1021/j150613a021

Similarly shaped pressure vs. time curves are obtained in the temperature range from 26 to 70.6 deg C from the ultraviolet photolysis of aged α-AlH3 powder, pristine and preirradiated with60Co γ-rays.The curves consist of an initial deceleratory peiod followed by a constant rate of gas evolution.The initial-period data can be resolved into one or two exponential terms depending on the sample and/or the pretreatment conditions.At room temperature, increasing the light intensity or preirradiating the material with γ-ray doses greater than 1E6 R increases the rate constants obtained from fitting the kinetic data.Only one exponential term is found below 1E6 R and at high lamp intensities.The linear rate has an almost, but not exact, second-order dependence on the light intensity.The dependence is ascribed to a decomposition event resulting from interaction between two excited radicals, one of which forms a radical-hole pair prior the interaction.The linear rate deviates further from a second-order dependence for a 1E6 R dose.The activation energies (kJ/mol) of the initial and linear rate periods are 3.2 (+/-0.9) and 13.0 (+/-0.9), respectively.Taken together these results suggest that two processes are initiated by UV light in α-AlH3.The first process involves the interaction of the light-induced carriers with the precursor (intrinsic) defects existing in the material.This process is associated with the lower activation energy.The second process with the larger activation energy is the interaction of the light-induced carriers with each other to produce decomposition in a complex second-order relationship.Both processes are modified by irradiation in a manner consistent with a previously developed phenomenological theory.