Effect of titania addition on crystallization process and some properties of calcium mica-apatite glass-ceramics

In order to obtain calcium mica-apatite glass-ceramics having high water resistance and excellent machinability, TiO2 was added to the starting materials of glass-ceramics with chemical composition of 3:7 weight ratio of fluoroapatite to calcium-mica. A large number of fine spherical particles in which mica and apatite should be included were generated uniformly. The mica and apatite were crystallized at lower temperatures and at narrower temperature ranges than those in the undoped specimen. However, the crystallization quantity ratio of apatite to mica was smaller, compared with that of apatite to mica for the undoped specimen. These results suggest that TiO2 acted as a nucleation agent of mica but impeded the crystallization of apatite. Mica in the fine spherical particles became plate-like when TiO2 was separated at greater than or equal to 900 degreesC. The plate-like mica with size of 0.5-2 mum was surrounded by apatite, TiO2 and residual glass, and formed the interlocking microstructure at 1000 degreesC. Such a microstructure resulted in high water resistance and excellent machinability. Particularly, a large number of fine TiO2 particles surrounded the mica uniformly, which was very effective in the deterrence of disintegration. (C) 2003 Elsevier Science B.V. All rights reserved.