Preparation of alumina–high zirconia microcomposite by combined gel-precipitation

Abstract

Microcomposites of alumina and zirconia containing equal volume fractions of the two are prepared by a combined gel-precipitation route using aluminium chloride and zirconium oxychloride as precursors. Dried gel powders calcined between 375 and 800 °C show cubic phase as the only crystalline phase. Zirconia gets converted to tetragonal phase above 900 °C and is retained mostly in this form upto 1000 °C. At the higher temperatures, it converts to the monoclinic phase. Alumina starts to crystallize into -form at 900 °C and is converted to -form at 1250 °C. Pressed pellets sintered at 1400 °C achieve densities close to theoretical in 4 h. Microstructures show evidence of segregation and coarsening in a composite matrix of alumina and zirconia mixed at a submicron level.