Cavitation erosion of aluminas

Various aluminas were eroded in distilled water at 18 degrees C using an ultrasonic facility operating at 20 kHz and with a peak-to-peak amplitude of 50 mu m. The progress of erosion was measured by weight loss and the eroded surface was examined using a scanning electron microscope. Eight aluminas contained from 99 to 99.99% Al2O3 (considered pure) and three aluminas were debased by 4, 5 and 6% glass. The pure aluminas displayed incubation periods of about 15 to 30 min, linear erosion rates typically in the range 0.66 to 1.32 mg/h, failed in an intergranular manner, and gave linear erosion rates that were nearly independent of the grain size. The debased aluminas had incubation periods less than 15 min, linear erosion rates in the range 1.08 to 13.1 mg/h, failed mainly by intergranular fracture in the glass, and had linear erosion rates that were approximately proportional to the square of the average grain size. Steady state erosion occurred after the whole of the surface had been eroded to a depth approximately equal to that of the average grain size. The effects of porosity, purity of the alumina, and other microscopical details, are also discussed and a simple model is introduced which attempts to describe the results in terms of the fracture behaviour of the materials. (C) 1999 Elsevier Science Limited and Techna S.r.l. All rights reserved.