INFLUENCE OF CALCIUM-HYDROXYAPATITE ON SODIUM BOROPHOSPHATE GLASSES - P-31 AND B-11 NMR INVESTIGATIONS

P-31 MAS and B-11 NMR are used for structural investigations on glass samples with chemical composition (1 - X) [NaPO3-R Na2B4O7]-X Ca5(PO4)3OH. For the sodocalciphosphate glasses (R = 0), the P-31 MAS NMR spectra show a shortening of the length of metaphosphate chains together with the formation of chain ends, when X increases. The Ca2+ cations probably ''cross-link'' the short phosphate chains. From B-11 NMR spectra of the sodocalcicborophosphate glasses (R > 0), the boron atom fraction in four-fold coordination is determined. In the phosphate rich glasses, the borate groups, mainly under the BO4/2- form are used as branching between short phosphate chains. For R > 0.2 borate groups including boron atoms in three- and four-fold coordination such as those found in pure vitreous Na2B4O7 are considered. The phosphate units are located out of the borate network. The extent of the vitreous domain and the physical and chemical properties are correlated with these different structures.