Reaction process and densification process of mixed [formula omitted] ceramics

Abstract

The sintering behavior of mixed α′ β′ - sialon ceramics, fabricated from α-Si 3N 4, AlN and Ln 2O 3 (Y 2O 3, Er 2O 3 and Yb 2O 3), was examined by high-temperature dilatometry, and the densification process was discussed through the consideration of chemical reactions to form α′- and β′-sialon and kinetical analysis of shrinkage. The formation of α′-sialon and melilite caused temporary retardation of the densification rate, while during the formation of β′-sialon the densification proceeded remarkably. The densification accompanied by precipitation of β′-sialon is ascribed to dissolution of residual α-Si 3N 4, α′-sialon with low solid solubility and melilite into a liquid, which may result in an increase of liquid volume and in a decrease of liquid viscosity. These phenomena are considered to induce the solution-precipitation process, particle disintegration process and cooperative flow process of the particle-liquid mixture, yielding to rapid shrinkage. The densification at the initial and middle stages and the reactions from α′-sialon and α-Si 3N 4 to β′-sialon accelerated in the order of Y 2O 3 > Er 2O 3 > Yb 2O 3 addition, because the liquidus temperature and viscosity of liquid formed decreased in the order of Y 2O 3 < Er 2O 3 < Yb 2O 3 addition.