Sinterability of spinel (MgAl 2O 4)-Zirconia composite powder prepared by double nozzle ultrasonic spray pyrolysis

Two kinds of spinel (MgAl 2O 4)-zirconia (ZrO 2) composite powders were prepared by double nozzle ultrasonic spray pyrolysis; the aqueous solutions in the Mg(NO 3) 2-Al(NO 3) 3 and ZrOCl 2-YCl 3 systems were spray-pyrolysed in a hot zone of an electric furnace heated at 900 °C, using two ultrasonic vibrators. The compositions of the composite powders were as follows: (1) Sample No.1: MgAl 2O 4 93.36 mol% and yttria-stabilized tetragonal ZrO 2 polycrystals (Y-TZP) 6.64 mol% and (2) Sample No. 2: MgAl 2O 4 75.51 mol% and Y-TZP 24.49 mol%. While MgAl 2O 4 and Y-TZP were present in both powders, MgO was additionally detected from Sample No. 2; such MgO disappeared when it was heated up to 1100 °C or higher. The composite powders contained spherical particles with diameters of below μm and, in part, acicular particles with long axis lengths of 1 to 2μm. The wet-milled powder of Sample No.1 showed an excellent sinterability; when the composite powder compact was fired at 1700 °C for h, the relative density attained 97.6%.