Diffusion and chemi-desorption rate coefficients from desorption transient measurements

Abstract The rates of gas release from a solid which is subjected to a linear temperature increase, i.e. desorption transients, have been computed assuming bulk diffusion to be the rate controlling process. The sample shapes considered are those of a sphere, a cylinder of infinite length, and a plane sheet of infinite extension. The assumed activation energies of diffusion range from 5 to 60 kcal/mole while D 0 / a 2 β lies between 10 −4 and 10 +11 (time −1 ), a being the radius of the sphere, or the cylinder, or the half-thickness of the plane sheet The results are presented in a form suitable for simplified curve fitting of experimental data. Based on this procedure, one can normally distinguish single or uncomplicated diffusion processes from simple surface desorptions; the rate controlling steps in composite processes, however, can usually be identified only if additional experimental criteria are used.