ALUMINA MICROSTRUCTURAL BEHAVIOR UNDER PRESSURELESS SINTERING AND HOT-PRESSING

The aim of this study is to observe the microstructural evolution of a Bayer alumina as a function of different parameters under pressureles s sintering and hot-pressing. soaking temperature, soaking time and ap plied pressure. Experiments indicate a preponderant contribution of th e temperature on the microstructure control whatever the sintering mod e may be. A semi-manual technique of digitization of the microstructur e using a digital tablet allows quantification of the size, the shape and the orientation of the grains. For both sintering modes and beyond a grain size threshold, increase of temperature leads to anisotropic grain growth of the coarser fraction at the expense of the finer fract ion. The pressure has an effect on the mobility of grain boundaries an d contributes to an elongation that is similar for all the grains. Nev ertheless the microstructures under high pressure produce a distributi on of strongly elongated grains with an orientation perpendicular to t he pressure axis.