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 are a which occur as a result of sintering have been correlated for severa l zinc oxide and alumina powder systems. Particle size distribution is shown to have a significant effect upon the nature of this correlatio n. Powders with narrow particle size distributions exhibit a nearly li near relationship between the surface area reduction and the longitudi nal 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 li ttle increase in the ultrasonic velocity, during the early stages of s intering. This behavior is attributed to the differences in the thermo dynamic driving forces for sintering of the different sized particles. These data also indicate that in powder compacts containing broad par ticle size distributions, the apparent elastic moduli, as manifested i n 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, whic h may be determined non-intrusively during processing. This understand ing may facilitate the use of ultrasonic techniques for real-time moni toring and controlling of the sintering process in ceramic power compa cts. (C) 1998 Elsevier Science B.V. All rights reserved.