Steady-state parameter-jump methods and relaxation methods in thermogravimetry

Abstract

We describe a technique for thermogravimetric analysis in which the magnitude of a rate-forcing variable such as temperature, pressure, gaseous flow-rate, gaseous composition, etc., is jumped by discrete steps. This method can be used to determine kinetic relationships between the rate of weight-loss and the jumped variable. The method avoids the disparate effects of separate experimental histories in methods in which two or more experiments are compared. The necessity for guessing the often complex rate vs. extent of reaction relationship in methods where the rate forcing variable is changed continuously in a single experiment is also avoided. The method is illustrated with examples from the oxidation of polystyrene. Techniques involving multiple jumps and more complex programming are proposed. The fruitful investigation of weight-loss kinetics by the measurement of relaxation times during jumps or of phase lags while the rate forcing variables are oscillated is predicted for diffusion limited reactions and reactions with gaseous atmospheres.