Control of hydroxyapatite crystallinity by mechanical grinding method

Crystallinity of hydroxyapatite reflecting crystal size and crystal elastic strain was controlled by the mechanical grinding (MG) technique using a se t of container and balls made of SUS304 stainless steel or agate. Variation in the crystallinity through MG was monitored by the XRD method and repres ented by the broadening of the diffraction peak. Effect of changes in cryst allite size and strain on the crystallinity was also examined using the Hal l-plot method. Crystallinity rapidly decreased with milling time. Significant crystallogra phic diffraction peaks disappeared and a broad diffraction around 2 theta = 32 degrees was observed after MG for 72 h. The broadening was dominantly du e to an increase in crystal strain in addition to fine crystallite size. Co ntamination from the container and balls during MG was more suppressed usin g agate than SUS304 stainless steel. The recovery process of crystallinity during heating between 300 degreesC a nd 1200 degreesC was examined focusing on the decrease in residual elastic strain. Low crystallinity was maintained at annealing temperatures below 80 0 degreesC but lattice defects were recovered above 1000 degreesC. (C) 2001 Kluwer Academic Publishers.