INTERMEDIATE PHASES IN BASIC SOLUTION PREPARATION OF ALKALINE EARTH PHOSPHATES

The first solid to appear in the precipitation of calcium phosphates from basic solutions is structurally non-crystalline. The existence, however, of a solution-prepared, non-crystalline orthophosphate salt is not unique only to the calcium phosphate system. Non-crystalline magnesium phosphates and magnesium ammonium phosphates can also be prepared under comparable conditions, but unlike the calcium salt, which converts into hydroxyapatite, these latter compounds are apparently solution stable. Preparations of strontium and barium orthophosphates from basic solution do not yield non-crystalline intermediates. For strontium, the intermediate phase is Sr3(PO4)2·4H2O, whereas the barium precipitates immediately as a stable barium hydroxyapatite. The tristrontium phosphate, however, converts autocatalytically into strontium hydroxyapatite. The analogous stoichiometry and identical kinetic behavior of the strontium intermediate with that of the amorphous calcium phosphate suggest that the latter could be a tricalcium phosphate rather than a cryptocrystalline Ca-deficient hydroxyapatite. This supports the possibility that the non-crystalline phase in bone mineral may not be an apatite but instead a distinct and separate compound. © 1968 Springer-Verlag.