2006 Volume 47 Issue 9 Pages 2167-2171
Effect of silica additive on the formation of lotus-type porous alumina on the unidirectional solidification was examined. Lotus-type porous alumina with 44% porosity was formed by unidirectional solidification using the optical floating zone method under a hydrogen atmosphere when low purity alumina was used as the feed rod. However, non-porous alumina was prepared in argon atmosphere. The formed pores possessed a drop-like shape and were elongated along the solidification direction in porous alumina. Gas bubbles evolved in the molten zone and was trapped by the solid/liquid interface during the unidirectional solidification. On the other hand, lotus-type porous alumina could not be obtained when high purity alumina was used as the feed rod. The porosity of the solidified porous alumina increased with increasing silica contents in the feed rods.