Silica coating on ultrafine α-alumina particles

In this study, the coating of silica on the fine α-alumina (<200 nm) surface was performed using sol-gel route. The processing conditions such as pH, solid loading, TEOS concentration, temperature, were optimized though analyzing the characteristic of coating layer. A typical successfully procedure was as follows: 20 wt.% of TEOS anhydrous ethanol solution was added to 5 wt.% α-Al2O3 ethanol/H2O suspension. The suspension was then mechanical stirred and adjusted the pH to 11, at a temperature of 50 °C for 6 h. An uniform silica layer with the thickness around 20 nm was deposited on the surfaces of α-Al2O3 particles. Both heterogeneous nucleation and homogeneous nucleation were shown in the 2 wt.% solid loading of α-Al2O3 suspension, due to the available surface area reduces, and the supersaturation of the hydrolyzed silicon species is only partially relieved. As the hydrolysis continues, homogeneous nucleation yields independent spherical silica particles.