Effect on drying conditions on amorphous calcium phosphate

Amorphous calcium phosphate (ACP) plays an important role in the body and can be used as an intermediate phase for forming calcium phosphates. All ACPs are thermodynamically unstable compounds unless stored in dry conditions and spontaneously undergo transformation to crystalline calcium phosphates (CaP). This work will investigate the influence of drying on the stability of ACP. ACP powders were prepared by wet synthesis where a calcium containing solution was rapidly mixed with a phosphate solution. The suspension was stirred, filtered and washed and the filter cake was dried at different conditions and with different drying agents. XRD patterns and FTIR spectra showed low crystallinity powders after drying. FTIR spectra suggested residual organic groups after drying with ethanol. The Rietveld's method and Scherrer's relationship estimated the crystallite size as about 15-20 nm. Thermogravimetry (TG) revealed a 7-25% weight loss upon drying. The drying agents have limited effect on particle characteristics. By changing the drying conditions, it is a possible to retain the amorphous calcium phosphate or adjust the particle size, level of crystallinity, moisture content and type of carbonate modification in the apatite lattice.