In situ optical dilatometric measurements of the initial stages of sintering of alumina Original Research Article

The initial stage of shrinkage of a series of alumina powder compacts containing different proportions of small and large particles was measured using an in situ optical dilatometry technique. The effect of sample radiance, leading to overestimation of sample dimensions, was determined by comparing the volume change of a fully dense alumina body with that predicted by thermal expansion data. Using this technique, it was possible to produce a calibration curve to eliminate the effect of sample radiance at elevated temperatures. Results showed that with increased levels of large particles the degree of densification decreased. Shrinkage data were then compared with a model that predicted parallel straight lines for plots of ln[1−(ρi/ρ)1/3] against ln[t/R4L] where ρ and ρi are current and initial density, t is time and RL is the size of the large particles. The experimental results obtained were shown to be parallel with changes in the slopes of the lines occurring at identical times irrespective of compact composition. This behaviour was attributed to the range of the particle sizes present—beyond the bounds of the model—giving rise to changes in the densification rate with time. The analysis has shown that it is necessary to consider the range of particle sizes that occur in real powder systems when attempting to model the sintering behaviour of powders.