Apparatus and method of filtering molten metal using honeycomb structure of sintered alumina as filter element

摘要

High purity alumina filters suitable for relatively high temperature molten metal filtering applications are prepared by providing a composition comprising fine grain reactive alumina and a burn out material in amounts sufficient to increase the porosity of the resulting filter structure, the composition being free of grain growth inhibitors in amounts sufficient to inhibit growth of the alumina grains during firing; forming the composition into a honeycomb structure by suitable means; and firing the structure beyond the temperature providing maximum densification of the reactive alumina employed whereby grain growth is fostered. The honeycomb structure is fired sufficiently long for significant growth of the particles (from sizes less than about 5 microns to sizes between 10 and 20 microns) and for the creation of wide grain boundaries between the resulting grains which further act as crack arrestors. A preferred composition includes 19 parts by weight reactive alumina, at least 99.5% pure Al.sub.2 O.sub.3, and 1 part artificial graphite.