Solid-Gas Reaction during Sintering of Si3N4 Ceramics. (Part 1). Stability of SiO2, Y2O3 and Al2O3 at High Temperature.

Abstract

The stability during sintering of SiO2, Y2O3 and Al2O3, well known as sintering aids of Si3N4 ceramics, was examined from both thermodynamical and experimental aspects. Both the heat treatment of SiO2-Y2O3 Al2O3 glass and the sintering of Si3N4 ceramics were carried out. In the thermodynamical considerations , the stability of the glass composition was discussed on the basis of known volatility diagrams for SiO2, Al2 and MgO and the thermodynamic data of Y2O3 available in the literature. The results suggest that Y2O3 is the most stable among all materials in the sintering temperature range usually selected for Si3N ceramics. SiO2-Y2O3-Al2O3 (equi-mass%) glass was heat-treated in a BN sagger at 2023K for 2h in N2 gas of 0.1 MPa. Si3N with addition of 5 mass% Y2O3 and 3 mass% Al2O3 was sintered in the BN sagger at 2023K for 0 to 16h in N2 gas of 0.1MPa. The elemental contents in the glass and ceramics before and after heat treatment and sinter ing were determined by chemical analysis. As a result, it was found that only SiO2 in the glass and SiO2 and Si3N4 in the Si3N4 ceramics vaporized. On the other hand, the Y2O3 and Al2O3 contents in both the glass and Si3N4 ceramics did not decrease under the selected temperature.

Volumetric Modification of Transparent Materials with Two-Color Laser Irradiation: Insight from Numerical Modeling

“…Indeed, the locally absorbed laser energy density, being recalculated to the local temperature, can exceed 3500 K. This implies that not only material melting but also its sublimation can take place in the zone of the maximal absorption. Indeed, fused silica melts at 2006 K, its boiling temperature is 2523 K [39], and vaporization proceeds via the following reaction [40]:…”

Effect of chemical composition of intergranular glass on superplastic compressive deformation of β-silicon nitride

“…The oxygen loss suggested that the intergranular glass evaporated during deformation at 1873 K. The evaporation of intergranular glass has been usually attributed to SiO volatilization from Y-Al-Si-O-N liquid. 23 The oxygen loss was largest in material A that had the eutectic composition. The intergranular glass is a continuous path for fast diffusion of gaseous molecules.…”

Fabrication and physicochemical properties of particulate-reinforced precursor-derived Si-C-N ceramics

“…5) Here we report processing, mechanical and thermal properties of particulate-reinforced ceramic composites (PRC) composed of oxide or non-oxide filler materials (Al2O3, Y2O3, SiC and Si3N4) and precursor-derived Si-C-N ceramic matrix. The four materials were sequentially chosen because of the low cost and well developed processing conditions, 7) high temperature stability, 8) similar coefficient of thermal expansion (CTE) with Si-C-N, 9) and exceptional high temperature stability, respectively.…”