Effect of particle size distribution upon specific surface area and ultrasonic velocity in sintered ceramic powders

The changes in ultrasonic sound wave velocity and specific surface area which occur as a result of sintering have been correlated for several zinc oxide and alumina powder systems. Particle size distribution is shown to have a significant effect upon the nature of this correlation. Powders with narrow particle size distributions exhibit a nearly linear relationship between the surface area reduction and the longitudinal wave velocity over much of the initial and intermediate stages of sintering. In contrast, powders with broad particle size distributions exhibit a significant reduction in the specific surface area, with little increase in the ultrasonic velocity, during the early stages of sintering. This behavior is attributed to the differences in the thermodynamic driving forces for sintering of the different sized particles. These data also indicate that in powder compacts containing broad particle size distributions, the apparent elastic moduli, as manifested in the ultrasonic velocity, are dominated by the larger particles. The present work contributes to the understanding of the dynamic behavior of sintering powder compacts in terms of the ultrasonic velocity, which may be determined non-intrusively during processing. This understanding may facilitate the use of ultrasonic techniques for real-time monitoring and controlling of the sintering process in ceramic power compacts.