Hot‐Pressing of Si₃N₄ with Y₂O₃ and Li₂O as Additives

Abstract

The rates of densification and phase transformation undergone by α‐Si3N4 during hot‐pressing in the presence of Y2O3, Y2O3−2SiO2, and Li20−2Si02 as additives were studied. Although these systems behave less simply than MgO‐doped Si3N4, the data can be interpreted during the early stages of hot‐pressing as resulting from a solution‐diffusion‐reprecipitation mechanism, where the diffusion step is rate controlling and where the reprecipitation step invariably results in the formation of the β‐Si3N4 phase.

Sinter and sinter-HIP of silicon nitride ceramics with yttria and alumina additions

“…It has been reported [4,8] that the mechanism of solution-diffusion-reprecipitation which causes densification is at the same time a mechanism for the transformation. Therefore, the addition of A1203 to the Si3N4-Y203 system encourages the transformation by providing a less viscous liquid which allows rapid diffusion.…”

“…The kinetics of densification during hot-pressing and pressureless sintering has been interpreted [8] in terms of Kingery's model [9] of liquidphase sintering, and the contribution of the successive stages was observed to vary with the amount and type of additive. Among the various sintering additives investigated [1,4,10,11], the use of Y203 seems to be favoured because it aids the formation of a liquid which produces, on solidification, a more refractory intergranular phase than those formed by most oxide additions [8]. Nevertheless, the sinterability of this 0022-2461/89 $03.00 + .12 © 1989 Chapman and Hall Ltd.…”

“…Sintering and hot-pressing of silicon nitride with [1][2][3][4], and without [5,6] consolidation additives, has attracted much attention because of its wide range of potential applications as a high-temperature engineering material. Ideally the consolidation of pure Si3N4 would lead to a light high-strength material possessing excellent high-temperature properties.…”

Morphology‐Enhanced Low‐Temperature Sintering of Nanocrystalline Hydroxyapatite

“…[7] Therefore, a variety of methods have been devised over the years to achieve low-temperature sintering. These methods include high-pressure-assisted sintering, [8,9] spark plasma sintering, [10][11][12] sinter forging, [13,14] sintering with doping or sintering aids, [15][16][17] liquid-phase sintering, [18,19] nanometer-sized powder particle enhanced sintering, [9,20,21] two-step sintering without final-stage grain growth, [22] and phase-transformation-assisted sintering.[23] Here we report a new method based on morphology-enhanced diffusion and driving force to achieve low-temperature sintering. Dense hydroxyapatite (HA) bodies normally require sintering at 1100°C or higher.…”

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

“…Hence, additives such as Y203, which give a higher viscosity grain boundary phase, generally result in lower creep rates than for MgO-doped silicon nitride [20]. However, a second oxide additive, A1203, is frequently combined with ^203, to avoid problems of reduced densification rates and higher densification temperatures, produced by -T the single refractory oxide additive [21,22].…”