Effect of initial particle packing on submillimeter waves sintering of alumina

The effect of forming methods on properties of alumina ceramics sintered by using a high power submillimeter waves gyrotron material processing system have been investigated. Two different packing methods, un-cold isostatic pressing (un-CIP) and cold isostatic pressing (CIP) were applied for green samples. The density evaluation shows that the densification of CIP samples is much higher than un-CIP samples. The highest density of 99.1 % of theoretical density has been achieved for CIP samples. That indicates that SMMW heating is more effective on CIP samples. The mechanisms of which the CIP enhance the densification on SMMW wave sintering are not all clearly yet but the increasing grain boundary area because of increase grain contact per particle during CIP process is indicated.