PRODUCTION OF DEFECT-POOR NANOSTRUCTURED CERAMICS OF YTTRIA-ZIRCONIA

For the production of nanostructured ceramics of yttria-zirconia four powders differing in agglomerate strength, agglomerate size and crysta llite size are compared. An ultra-fine-grained ceramic with a final de nsity of 98% and a grain size of 0.18 mu m could be produced from a hy drothermally crystallized ethanol-washed powder. The remaining porosit y is caused by some residual defects which ave present due to the irre gular shape of the agglomerates and which cause improper die filling. A commercially available powder was also investigated. This powder con sists of homogeneous porous, spherical, weak agglomerates. The resulti ng ceramic has a high density (greater than or equal to 99%) but canno t be obtained with ultra-fine grain size (minimum grain size is 0.3 mu m). The air-crystallized ethanol-washed powder resulted, after sinter ing, in larger porosities. In this case the powder consists of weak an d some strong agglomerates and a few defect clusters are found in the sintered ceramic which limit the maximum attainable density to 92%. Th e air-crystallized water-washed powder consists of agglomerates which are too strong to be fractured during compaction. The sintered ceramic s contain a large amount of porosity (20%) which is attributed to the presence of inter-agglomerate pores. (C) 1997 Elsevier Science Limited .