Ceramic nanocomposites obtained by sol-gel coating of submicron powders

MgAl2O4-ZrO2 nanocomposites were fabricated by conventional sintering of co mposite powders obtained by sol-gel coating of a submicron spinel powder. I n the composite powder the zirconia grains remain narrow sized and complete ly tetragonal even after being heat treated at temperatures where a free xe rogel is completely monoclinic. The sintered material exhibits a dense, fin e and highly homogeneous microstructure. The zirconia nanoparticles are loc ated at both inter- and intragranular positions and exhibit heteroepitaxial relationships with the surrounding crystals. Tetragonal zirconia seems to be stabilised by an interface effect. Both the scale of the microstructure and the fraction of intragranular grains were controlled by adjusting the m ean grain size of spinel grains before coating and sintering conditions. (C ) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights r eserved.