Radial distribution study of non-crystalline tricalcium phosphate

Abstract

A radial distribution study was performed on the x-ray scattering (cobalt- and nickel-filtered copper radiation) from freeze-dried stabilized, non-crystalline tricalcium phosphate. In addition, a theoretical radial distribution function was calculated from the published atomic parameters of hydroxyapatite. Both the amorphous and crystalline phases showed peaks in the radial distribution function at about 1.6A (P-O), 2.4A (O-O, Ca-O), and 3.7A. The latter two amorphous interionic spacings were slightly larger than the comparable apatite spacings indicative of a lower density in the amorphous phase. In addition, the amorphous curve contained a peak at 4.7A not present in apatite but found in curves from condensed calcium phosphate glasses. Not present in either the apatite or the amorphous curve was a peak at 2.9A which is related to the nearest P-P distance found in such condensed phosphates as meta- and pyrophosphate. These results support the view that the amorphous tricalcium phosphate, though a precursor of hydroxyapatite, is different chemically and physically from this compound.