Phosphoric acid treated AlN powder for aqueous processing of net-shape dense AlN and β -SiAlON parts

Abstract

Due to fast hydrolysis of AlN when in contact with water, AlN based ceramics are processed in organic solvents, which are volatile, expensive, harmful to the health and environment. The present work intends to protect AlN powder against hydrolysis in order to enable aqueous processing of AlN based ceramics. A commercial AlN powder was treated in an ethanol solution of H₃PO₄ and Al(H₂PO₄)₃ kept at 80°C for 24 h to protect it from hydrolysis. The dispersing behaviour of the treated AlN powder in water and the ability to consolidate defect free parts of AlN and β-Si₄Al₂O₂N₆ ceramics from aqueous suspensions by slip casting and gelcasting techniques were studied. The consolidated parts were then sintered in a graphite furnace and the sintered bodies exhibited properties [bulk density (BD), apparent porosity (AP), crystalline phase composition and microstructural features] similar to those reported in literature for the same materials processed from organic media.