On impurities and the internal structure in precipitates occurring during the precipitation of nanocrystalline calcium phosphate

Nanocrystalline calcium phosphate was precipitated at 20 degrees C from calcium nitrate and ammonium phosphate solutions at a pH of 9-11. The nature of the mass loss steps in thermogravimetry of the product wits revealed by in-situ mass spectrometry of released gases upon heating. Major amounts of nitrate-containing impurities like NH4NO3 and Ca(NO3)(2) were present which could only he removed by multiple washing with water. These impurities were not crystalline, but they were clearly detectable in the infrared spectrum. in conclusion, the high specific surface area of freshly precipitated calcium phosphate may Cause the adsorption of considerable amounts of foreign compounds (molecules and ions) in the percent mass range.