Controlling the crystallization of fluorapatite in apatite-mullite glass-ceramics

Recent studies have shown that by controlling material topography on the nanoscale, it may be possible to elicit a more favorable cell response. It has been reported that apatite-mullite glass-ceramics (AMGCs) can form nanostructures of accurately controlled, self-assembled arrays of apatite nanocrystals, and it is possible that AMGCs may be used to produce bioactive nanoscale topographies. This paper systematically investigates methods for producing these structures. Controlling the crystallization of fluorapatite in apatite-mullite glass-ceramics is possible through the variation in base glass composition and heat treatment regime. Results show that increased amounts of network modifier result in a decreased fluorapatite crystal size. The reduction in crystal size is caused by growth limiting factors such as impingement and the degree of phase separation prior to crystallization. It is also demonstrated that high heating rates produce a more coarsened crystal microstructure. The Scherrer equation is used to verify the increase in the average crystal size from X-ray diffraction data. The heating rate does not affect the unit cell dimensions indicating that the level of substitutions in the unit cell is not increased by higher heating rates. The results can be used to control the resultant crystal morphology to produce microstructures of varying degrees of disorder.