Critical verification of the Kissinger theory to evaluate thermal desorption spectra

Multiple types of hydrogen trapping sites in advanced high-strength steels (AHSS) are often experimentally characterized by means of thermal desorption spectroscopy (TDS). The evaluation is regularly based on the peak deconvolution procedure combined with Kissinger's theory, which provides distinctive desorption energies of hydrogen trapping sites at microstructural defects. However, the desorption energies published in literature are often non-conclusive and from time to time contradictive in nature. Therefore, it is of utmost importance to verify the evaluation procedures according to Kissinger's theory for multiple types of hydrogen trapping sites. For that purpose, theoretical TDS spectra were simulated using a bulk diffusion model according to Oriani's theory. Binding energies and trap densities were chosen for providing TDS spectra with clearly separated as well as overlapping TDS peaks. Finally, the desorption energies according to Kissinger's theory were compared with the theoretical trapping energies used in the models. Based on this theoretical work, it is strongly recommended to apply the Kissinger theory only for the evaluation of single or well separated TDS peaks. If peaks overlap, complementary microstructural variation and characterization are a perquisite to correctly evaluate the TDS spectra.