Monetite (CaHPO4) Synthesis in Ethanol at Room Temperature

A straightforward process was developed to synthesize monetite (CaHPO4, dicalcium phosphate anhydrous) powders at room temperature (21 degrees +/- 1 degrees C) in ethanol solutions. The process reported here constitutes an alternative to well-publicized monetite synthesis procedures based on the dehydration of brushite (CaHPO4 center dot 2H(2)O, dicalcium phosphate dihydrate) powders either in acidic, hot (70 degrees-95 degrees C) aqueous solutions or in drying ovens (200 degrees-225 degrees C). Submicrometer monetite powders were synthesized in ethanol (ethyl alcohol) solutions containing small aliquots of concentrated H3PO4 (orthophosphoric acid, 85%). Precipitated CaCO3 (calcium carbonate, calcite form) powders with submicrometer particles were simply stirred in the above solutions in glass bottles for 3 h. The starting Ca/P molar ratio in the synthesis bottles was 0.50. Monetite powders obtained with a stacked-nanosheets particle texture did not contain any unreacted CaCO3. Monetite powders were also found to have the ability to completely transform into apatitic (apatite-like) calcium phosphate powders when soaked in calcium-containing saline solutions (i.e., 142 mM Na+, 5 mM K+, and 50 mM Ca2+ in water) for 6 days at 37 degrees C.