Processes for Desorption from LiAlO2Treated with H2as Studied by Temperature Programmed Desorption

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Abstract
The energetics and kinetics of the evolution of H2O and H2 from LiA1O2 are being studied by the temperature programmed desorption technique. The concentrations of H2, H2O, N2, and O2 in a helium stream during a temperature ramp are measured simultaneously with a mass spectrometer. Blank experiments with an empty sample tube showed that square wave spikes of H2 introduced into the helium gas stream were severely distorted by reaction with the tube walls. The tube could be stabilized, however, by sufficiently prolonged heat treatment with H2 so that H2 peaks would not be distorted up to approximately 923 K(650°C). The amount of H2 adsorption/desorption is small compared to the amount of H2O adsorption/desorption. After prolonged treatment with helium containing 990 ppm H2 at 400°C, H2O evolution into the He-H2 stream was observed during 473 to 1023 K (200 to 750°C) ramps at rates of 2 or 5.6 K/min. The different peak shapes reflecting this process were deconvoluted to show that they are composites of only 2 or 3 reproducible processes. The activation energies and pre-exponential terms were evaluated. The different behavior originates in the differences among different surface sites for adsorption. The interpretation of higher temperature peaks (above 873 K (650°C) must still consider the possibility of contributions from interactions with the steel walls. It was found that H2 enhances evolution of N2 from the steel.