Effect of adsorbed water on the ultrasonic velocity in alumina powder compacts

The presence of surface adsorbed water has been found to significantly increase the apparent elastic properties of unsintered alumina powder compacts. It is proposed that the increase in the elastic moduli results from the formation of `interparticle bridgesʹ between adjacent particles and, thus, increased effective interparticle contact area. The effects upon the elastic moduli in the unsintered powder compacts were monitored by measurement of the changes in the ultrasonic velocity. The ultrasonic data are consistent with thermogravimetric analysis and mass spectrometry results which indicate the presence of multiple adsorbed water species. Understanding the effect of adsorbed water on the processing characteristics of ceramic powders may lead to better process control during green state consolidation and ultimately to higher quality sintered products.