Gradual mechanochemical reaction to produce carbonate doped fluorapatite-titania composite nanopowder

Carbonated fluorapatite-titania composite nanopowders were successfully synthesized by a facile room-temperature mechanochemical process. Mixtures of calcium carbonate, phosphorous pentoxide and calcium fluoride with different amounts of titania (0, 3, 6, and 9 wt%) were milled using a high-energy planetary ball mill for 10 h. Results showed that a gradual transformation occurred during the mechanical activation. In the absence of titania, nanosized B-type carbonated fluorapatite with crystallite size of 69±3 nm was formed. In the presence of 3-9 wt% titania, mechanochemical reaction caused the formation of carbonated fluorapatite-titania composite nanopowders. The crystallite size declined drastically and reached 12±1 nm when the titania content was increased to 9 wt%. In contrast, the lattice strain and volume fraction of grain boundary increased notably from 0.0045±0.0002 to 0.0084±0.0004 and from 4±0.21% to 21±1.07%, respectively, while the titania content rose from 0 to 9 wt%. From the data obtained, the unit cell volume of carbonated fluorapatite was influenced strongly by the titania content, whereby the sharp increase in unit cell volume from 524.42 to 530.40 Å3 was due to the increase of the titania content from 0 to 9 wt%, respectively. Microscopic observations indicated that the product had a cluster-like structure with an average particle size of about 75 nm.