Fabrication of a fine grained alumina ceramic

Abstract

Alumina is one of the most important and most widely studied oxide ceramics because of its usefulness as a structural, electrical and optical material (1). However, the pure material requires a sinterin tem erature greater than l700°C, because of its covalent nature, to densify to greater than 95% of theoretical (% TD). Such high temperature sintering produces a porous, coarse grained (> l0 μm) ceramic with poor mechanical properties.

Sintering aids (2-4) and exotic fabrication techniques, such as hot pressing and hot-isostatic (2,5,6). have been used to improve the sintering kinetics and to control non-uniform grain growth. A small amount of MgO (typically 250 to 300 ppm) has been reported to increase the sintering kinetics, allowing dense aluminas with uniform microstructures to be fabricated (2,3). However, a sintering temperature >1600°C is still necessary and a homogeneous distribution of the required amount (depending upon the sintering temperature) of MgO is essential for producing alumina with good mechanical properties.

In an effort to reduce the sintering temperature further and to fabricate alumina with an optimum, uniform microstructre (dense alumina with small grains and narrow grain size distribution), a number of wet chemical methods for powder production (7-9), and alternative processing (10-12) and fabrication techniques (12- 14) have been developed in recent years.

In this paper, the sintering characteristics of an alumina powder which has been prepared by a precipitation method is reported and the results are compared with AKP-50) a commercially available, ne alumina (Sumitomo powder. In addition, the colloidal processing of ne powders, and its effect on subsequent fabrication operations, is discussed.