Thermal Desorption Spectroscopy (TDS) Of Hydrogen from Niobium

摘要

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(theta/sub o/T/sub p/ exp 2 ) vs 1/T/sub p/ (where theta/sub o/ is the initial surface coverage and T/sub P/ 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, it is argued 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 theta/sub o/ must now be replaced by the initial concentration x/sub o/, will yield a slope determined by the heat of solution. In the following experiments the functional dependence of the desorption temperature on hydrogen loading as outlined above is verified. Deviations from these theoretical predictions were observed, and numerical kinetic simulations were made to aid in understanding them.