Some Sources of Activation Energy Errors in Sintering Experiments

Abstract

The time and temperature dependent morphology changes of a sintering powder compact are quite often used to calculate properties such as mass diffusivities. The fact that non-isothermal conditions exist for a portion of most sintering experiments has prompted the development of data correction routines to aid mechanism identification. 1 However, it is generally recognized that the. simultaneous operation of multiple mechanisms gives ambiguous growth rates.2 As a result, the determination of a sintering mechanism must be substantiated with additional data, such as activation energies. Unfortunately, little attention has been given to the effects of experimental variables such as heating rate, relative sintering temperature, and isothermal hold time on the calculated activation energy. In many sintering experiments, the heating rate to an isothermal condition is reasonably slow. Despite slow heating rates, several studies have produced activation energies in close agreement with tracer determinations.3 The present note discusses some of the errors introduced into experimental activation energy determinations and suggests ways to minimize such errors. previous small step of length At. The final cumulative sintering after an isothermal hold can then be calculated from a combination of eqns. (1)-(3). By varying the isothermal temperatures for such calculations, the cumulative sintering values can be used to extract the observed process, activation energy. Comparison of the observed value with the input value Qo gives a measure of the errors resulting from the different experimental parameters. The res.ults presented here were produced using a digital computer and represent the results of 165 separate simulations, some of which were specifically designed to test for errors. The time increments for eqn. (3)were v~ried from 0·1 to 100 s. Based on such studies it was determined that a At value of 3 s provided a reliable' simulation.