Oxidation, densification and properties of extruded aluminium boehmite reaction-bonding mixtures

Abstract

The feasibility of preparing a plastically formed reduced shrinkage alumina component was examined. Extrudable boehmite aluminium mixtures were prepared by mixing attrition milled aluminium powder with hydrothermally produced boehmite. Extruded rods were then heat treated up to 1700 °C in air. Oxidation and densification behaviour was studied. There was no microscopic evidence for the large-scale migration of molten aluminium into voids and at higher aluminium concentration the volume expansion due to oxidation resulted in expansion of the solid rather than filling of interstitial spaces. High concentrations of aluminium caused a vermicular grain structure to develop, typical of an unseeded boehmite. The development of this microstructure in the relatively coarse aluminium particles is significant for the application of this technology. Samples with an average flexural strength of 272 MPa were manufactured with reduced shrinkage over an equivalent seeded boehmite gel, although properties of the sintered solids in general reflected the low-density achieved relative to the theoretical maximum value.