Investigations on the effect of added nuclei on the manufacture of conversion-reinforced ceramics by a sol-gel process

It is well-known that the ZrO2 phase conversion from the tetragonal to the monocline phase can be used to improve the toughness at fracture of Al2O3 ceramics. The most important problems here are the control of the metastable tetragonal state of the ZrO2 and an homogeneous distribution of the ZrO2 at the wedges of the Al2O3 matrix. The ZrO2 grain size must be less than a critical size (0.5-1.0 μm) for control of the tetragonal ZrO2. As the Al2O3-ZrO2 ceramic requires a high temperature for compression, a coarsening of a growth of the ZrO2 grains beyond the critical size results from this. In order to meet these requirements, one has recently used the sol-gel process for manufacturing Al2O3-ZrO2 ceramic. (orig.)