Solid state NMR investigations of dicalcium phosphates

Important new information about the crystal structure of dicalcium phosphate (DCP) powders was obtained using the 31P NMR technique. There were two types of powders under investigation. One type includes pure DA (CaHPO4) and DH (CaHPO4· 2H2O) powders, and their mixtures in different proportions. The other includes powders from an industrial production. They were obtained by DH heating. An effective and fast method of identification of the structure of the nuclear nearest surroundings is presented. Determination of the concentration of nearest surroundings corresponding to DA or DH types for the 31P nuclei was demonstrated on examples taken from production powders. Good agreement was found in comparison with data obtained by chemical analysis. Especially interesting information is obtained by using the CP MAS NMR technique. This method allows the following conclusions about the production sample structure to be drawn: it is a powder consisting of DH-type microcrystals, but with numerous vacancies at the positions of water molecules which disappeared during heating.