Phase Relationships and Related Microstructural Observations in the Ca‐Si‐Al‐O‐N System

Abstract

A systematic set of samples with compositions in the Ca alpha‐SiAlON (α′) system has been fabricated using pressureless sintering to evaluate the phase relationships on, and near, the Ca α′ plane. A phase behavioral diagram for the Ca α′ plane within the Jänecke prism has been determined and found to be similar to those for the Y and Sm α′ systems. However, distinct differences were also observed; two additional regions (α′+ 27R + liquid) and (α′+ 33R + liquid) have been identified. Investigation of the microstructures revealed elongated Ca α′ grains in the samples prepared by pressureless sintering. The aspect ratio of the elongated grains of α′ increased as the concentration of stabilizing cation was increased. Single crystalline phase Ca α′ samples of comparable density to hot‐pressed material were fabricated successfully using pressureless sintering.

Texturing Ca-.ALPHA.-Sialon Via Strong Magnetic Field Alignment

“…according to the starting composition. When the time increases to 60 min, both samples reach the maximum density of close to 3.19 gcm 3 , similar to the value reported by Hewett et al 4 With further increased time, both samples show a slight decrease in the density because of the promoted decomposition, as indicated by the increased weight loss.…”

“…of its weight fraction required to meet the designated composition of a-sialon. 4 Thus, the composition of the starting powder mixture was 64.69! Si 3 N 4 13.85!…”

Ca-α SiAlON hollow spheres prepared by carbothermal reduction–nitridation from different SiO2 powders

“…Calcium compounds such as CaO and CaCO 3 are cheaper than rare-earth elements. Calcium also has a higher solubility per unit cell in the a-SiAlON lattice, hence the quantity of residual glass in the grain boundary of Ca-a SiAlON ceramics can be less and the formation range of a-SiAlON single phase would be wider compared to a-SiAlONs containing rare-earth elements [2,5]. Furthermore, thermal stability in Ca-a SiAlON is superior to rare-earth stabilized aSiAlON [3].…”

“…a-SiAlON ceramics have been generally produced from powder mixture of Si 3 N 4 -AlN-M x O y at high temperatures through a liquid phase sintering process [1][2][3][4]6,7]. In order to improve the reliability of a-SiAlON ceramics, it is important to develop homogeneous and fine a-SiAlON powders.…”

“…SiAlON, a-and b-SiAlON, have been well known as representative groups in engineering ceramics because of their high hardness, excellent wear and corrosion resistance in severe environment [1][2][3][4]. a-SiAlON is a solid solution of the a-Si 3 N 4 crystal structure in which metal cations are incorporated as a stabilizer.…”