Water-based Si3N4 suspensions:: Part II.: Effect of wet mixing/milling processes on the addition of the sintering aids

Three mixing processes were used to introduce lanthanum oxide and yttrium oxide in silicon nitride suspensions. X-ray photoelectron spectroscopy (XPS) analysis was used to identify the surface composition and investigate the surface coverage by the added oxides. XPS results evidenced the protective effect against hydrolysis and oxidation of the coated layer. Electroacoustic measurements showed that the milling/mixing process and solids loading contents had a great influence on the isoelectric point (IEP) and on the dispersing degree for suspensions with sintering aids. With the change of solids load content and mixing energy, the IEP of mixed powders suspensions reflected a surface behavior dominated by the additives oxides. The attrition mixing and the ultrasonication resulted in the more efficient processing routes to distribute the sintering aids on the starting Si3N4 powders, especially at high solids volume fraction.