Influence of TEOS and MgO addition on slurry rheological, optical, and microstructure properties of YAG transparent ceramic

Stable dispersed slurries were prepared from a mixture of commercial Al2O3 and Y2O3 powders by the ball milling process. Ammonium poly meta acrylate (Dolapix CE64) as the dispersant and different amounts of tetraethyl orthosilicate (TEOS)+0.1 wt% MgO as the sintering aids were added to the slurries. The effects of TEOS and MgO addition on the fabrication of transparent polycrystalline YAG ceramics were investigated by slip casting and vacuum sintering. The results showed that almost all slurries containing TEOS and TEOS + MgO had a near-Newtonian behavior, but the slurry containing only MgO had shear thickening with a thixotropic behavior. Also, by increasing the amounts of TEOS, due to the creation of steric repulsion, the viscosity was decreased. In comparison, TEOS + MgO slurries had lower viscosity than the TEOS ones. This was due to both the release of more ethanol and MgO action as a dispersant agent among the particles of yttria and alumina. All samples were pure YAG phase. The maximum transmittance at 1064 nm (≈83%) was obtained for the sample of 0.5 wt% TEOS+0.1 wt% MgO. A nearly pore-free microstructure with high relative final density (99.99%), a narrow grain size distribution (2.5-7.5 μm), with the average grain size of 4.5 μm, was achieved in this sample.