Effect Of Calcia On The Densification And Mechanical Properties Of Sol-Gel Alumina

Boehmite sol was prepared by hot water hydrolysis of aluminium iso-propoxide using nitic acid as the catalyst. Calcium nitrate to yield 5 to 20 vol% of calcium oxide was added to the boehmite sol. The sol was precipitated in ammonia, dried at 120 degrees C and calcined at 500 degrees C for 3 h. The calcined powder was milled at 230 rpm for 6 h. The powder was compacted into cylindrical pellets using a uni-axial press at 180 MPa and sintered at temperatures ranging from 1400 degrees to 1600 degrees C for 6 h. Mechanical properties such as hardness, fracture toughness and diametrical tensile strength for compacts containing variable amounts of calcium oxide were studied. There was a slight decrease in the density and hardness with increase in calcia content. Increase in the mechanical properties such as fracture toughness, flexural strength and diametrical tensile strength was observed with increase in calcia content.