Nonstoichiometric Heating Loss of CaHPO4

The relationship between heating loss and structure of CaHPO4 prepared by wet process was studied by means of thermogravimetric analysis, differential thermal analysis, X-ray diffractometry and optical microscopic analysis. The reaction products, precipitated from aqueous solutions of various pH (2-5) at the temperatures between 70 and 100° C, contained about 0.4-1.7% H2O, although their X-ray diffraction patterns identified the materials as CaHPO4. From the analysis of heating loss of products and precipitation temperature, it is presumed that CaHPO4 was a metastable phase and contained some stepwise times of (1/30), (1/60) or (1/120) mol. H20, and that an abnormal weight loss by heating was based on such bound water. The samples canbedivided intotwo groups. One group showed asingle X-raydiffraction peak at d=3.37A, (020) and another one showed double peaks at d=3.37Aand d=3.35A. The double peak altered to a single one by grinding, and the X-ray intensity became to approximately twice. This phenomenon might be caused due to the slip along (020) effect.