2013 Volume 53 Issue 2 Pages 250-256
The Kissinger-type formula, dX/dt=A(1–X)exp(–Ed/RT), which was thought to be applicable only in detrapping-controlled desorption has proved to be applicable also in the case of diffusion-controlled desorption under certain conditions including existence of effective diffusion coefficient or assumption of Oriani's local equilibrium and pre-exposure of hydrogen before temperature ramp. Analysis indicated that the constant A depends on the specimen geometry and the pre-exponential factor of effective diffusion coefficient. Numerical verification has been carried out by comparing the simulation result of Kissinger-type formula with that using the rigid McNabb-Foster model for typical specimen geometry including plate, cylinder and sphere. The merit of using this formula lies in its simplicity in numerical simulation of the thermal desorption spectrum with an accuracy as high as that based on the M-F model. Two different derivative forms of the Kissinger-type formula, i.e. the Choo-Lee plot d[ln (φ/Tp2)]/d(1/Tp)=–Ed/R and the Lee-Lee plot d[ln(φ/Tp)]/d(1/Tp)=–Ed/R, for determination of desorption activation energy have also been discussed and the analytical result showed that the Choo-Lee plot is a proper method to determine desorption activation energy while the Lee-Lee plot is not correct. The limit of application of the formula and the Choo-Lee plot in thermal desorption analysis is discussed in a semi-quantitative manner.
