Kinetics of Densification and Phase Transformation at Microwave Sintering of Silicon Nitride with Alumina and Yttria or Ytterbia as Additives (特集放電焼結の基礎と応用)

概要

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Sintering of Si3N4-based ceramics using microwave power at frequencies of 28 and 30GHz has been studied. Sintering of materials with various oxide additives, 3 wt% Al2O3+5 wt% Y2O3 and 3 wt% Al2O3+5 wt% Yb2O3, and small amount of 1.5 wt% Al2O3+2.5 wt% Yb2O3 additives has been investigated. A comparison of the results obtained at different rates of heating, from 5°C/min to 90°C/min, shows that the apparent activation energy for sintering in the materials with large amount of additives decreases with an increase of the microwave power absorbed per unit volume of material. The rate of densification depends strongly on the rate of the α-to β-phase transformation at the initial stage of sintering. The results show that microwaves do not affect directly the rate of the α-to β-phase transformation. Therefore, pressureless sintering of the Si3N4 ceramics with low content of additives and low rate of phase transformation can not be enhanced by an increase in the specific microwave absorbed power.
社団法人粉体粉末冶金協会の論文
2001-06-15