Study of thermal desorption: The effect of a temperature gradient along the sample

Abstract

In thermal desorption techniques some difficulties may arise of a thermal gradient in the samples; the analysis of desorption spectra under this circumstance cannot be carried out by the usual methods. We give in the case of a parabolic thermal-gradient profile a procedure for analysis of a simple peak spectrum in a first-order desorption. As a first step we have evaluated the distortion of a theoretical desorption peak by the presence of a temperature gradient. This distortion was characterized by the quantities ΔTm/Tm and Δμ/μ, Tm and μ being, respectively, the maximum peak desorption temperature and the half-width of the peak at midheight. Utilizing some mathematical properties of the desorption rate equation we have shown that ΔTm/Tm and Δμ/μ can be plotted in terms of three independent parameters. The curves so obtained allow the experimental spectra to be corrected to determine the true values of the kinetic parameters: activation energy for desorption Ed and frequency factor 1/τ0.