Thermal Desorption Spectroscopy (TDS) of Hydrogen from Niobium
Thermal desorption spectroscopy is often used to determine the activation energy of desorption of an adsorbate on a substrate as well as the order of the kinetics. In the case of flash desorption of an adsorbate from a surface obeying second order kinetics, a plot of Log(θ oT p 2 ) vs. 1/Tp (where θ o is the initial surface coverage and Tp is the temperature of the maximum desorption rate, i.e., the “desorption temperature”) will yield a straight line, the slope of which is determined by the chemisorption energy. However, Davenport et al.l argued on the basis of a simple theoretical model that in the case of a system with hydrogen absorbed into the bulk in quasiequilibrium with adsorption sites on the surface, a similar plot, where the coverage θ o must now be replaced by the initial concentration xo, will yield a slope determined by the heat of solution. In the following experiments we have tried to verify the functional dependence of the desorption temperature on hydrogen loading as outlined above. Deviations from these theoretical predictions were observed, and numerical kinetic simulations were made to aid in understanding them.
KeywordsTungsten Recrystallization Diene Chemisorption
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