Decomposition Rate of Si3N4 during Microwave Sintering

Abstract

A densification temperature of a ceramic material by microwave sintering is quite lower than the temperature by conventional sintering. However, the ceramic material is self-heated by electromagnetic energy during the microwave sintering processing, so that possibility of temperature measuring error is considerably high. Then it is difficult to prove that the densification temperature by microwave sintering is lower than the temperature by conventional sintering.There is a problem of sintering Si3N4 that sintering temperature is higher than decomposition temperature in atmospheric pressure of N2 gas, and a specimen can not be high density if a powder bed is not used. The decomposition rate becomes fast at the densification temperature. Furthermore, sintering density is lowered with the rise of sintering temperature since the decomposition rate becomes faster. Because of that, Si3N4 is sintered in high pressure N2 gas, or in atmospheric pressure of N2 gas with powder bed.When a Si3N4 specimen which included 5 w% Al2O3 and 5 w% Y2O3 as sintering aids, was sintered at 1700°C by conventional heating in atmospheric pressure of N2 gas without powder bed, sintering density reached 88%. And the density is lowered when the heating temperature was higher than 1700°C. The density more than 88% was not obtained even the sintering temperature was higher.On the other hand, when the specimen was sintered by microwave treating in atmospheric pressure of N2 gas at 1600V without powder bed, the sintering density was 98.1% and 98.7% at 1650°C and reached 99.0% at 1700°C.This shows clearly that the densification temperature by microwave sintering is lower than decomposition temperature. In other words, this shows that the densification temperature by microwave sintering is lower than the temperature by conventional sintering.