Study on the densification of composite coating particles of α-Al₂O₃-SiO₂

Composite coating particles consisting of alpha alumina cores (α-Al₂O₃, average particle size 0.26 μm) with outer homogeneous amorphous silica layer were prepared by the heterogeneous nucleation-and-growth processing. Densification of composite coating particles was studied at different sintering temperatures. Density of samples sintered at different temperatures was measured by the Archimedes method. Densification procedure of samples was observed and analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Based on the density of samples, XRD and SEM, densification procedure of samples is divided into two stages: one is the transient viscous flow of amorphous silica layer below 1350 °C, the other is mullitization of composite coating particles at 1500 °C.