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MEASUREMENT OF PARTICLE STRENGTH IN ALUMINA POWDERS USING ULTRASOUND

Coghill, P.J. and Giang, P.M.

The strength of alumina is consistently rated as one of the most important product quality parameters. Particle strength is difficult to quantify and not well understood, which leads to inadequate control of fines generation, a costly problem for industry. CSIRO is developing a method and apparatus for the measurement of particle strength in powder beds using ultrasonic velocity measurements. It is considered to have several advantages over the current method for measuring alumina strength which is a modification of the Forsythe-Hertwig attrition index (AI) method, and has the potential to be reproducible, sensitive across the range of particle strengths encountered in alumina samples, quick to perform and independent of particle size.

Tests using the ultrasonic technique have been conducted on a range of calcined and uncalcined alumina samples to demonstrate empirically the relationship between ultrasonic measurements and particle strength. Good correlations between ultrasonic measurements and strength as measured by the breakage rate method were obtained with correlation coefficients in the range 0.8-0.9. To determine if there is any chance of measuring likely product strength before calcination, a correlation was made between the calcined breakage rate and uncalcined measurements of velocity and density, reasonable correlation was obtained with correlation coefficients in the range 0.75-0.8, these correlations were heavily dependent on the bulk density measurement. The size independence and non-destructive nature of this method of particle strength measurement were also established. The results of these tests demonstrate that the strength measurement apparatus and method is sufficiently developed for a large-scale assessment on alumina samples. Modification and automation of some aspects of the ultrasonic measurement procedure are expected to provide improvements in repeatability.