Multiple Law Modelling for the Oxidation of Advanced Ceramics and a Model-Independent Figure of Merit

Abstract

Advanced ceramics from complex system often show a complex oxidation behaviour with changing kinetics both in respect to time and temperature. Models describing the behaviour by simple growths laws (parabolic, linear, logarithmic) fail to adequately reproduce experimental data. The best analytical diagram for such data is a plot of an apparent k_p(=x²/t) vs. time on a log scale for a given temperature. Many actual data are well described by a multiple law model (x=k_lin.t+k_p’ √t+k_log-log(t)) accepting only positive k-values. A detailed analysis of the individual contributions of these fitted k-values gives valuable indications for the phsyico-chemical process behind the kinetics. A model-independent figure-of-merit for the oxidation kinetics is given by “TOG(x)”-numbers (time-of-gain for specified amount).