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 spec tra show a shortening of the length of metaphosphate chains together w ith the formation of chain ends, when X increases. The Ca2+ cations pr obably ''cross-link'' the short phosphate chains. From B-11 NMR spectr a of the sodocalcicborophosphate glasses (R > 0), the boron atom fract ion in four-fold coordination is determined. In the phosphate rich gla sses, the borate groups, mainly under the BO4/2- form are used as bran ching between short phosphate chains. For R > 0.2 borate groups includ ing boron atoms in three- and four-fold coordination such as those fou nd in pure vitreous Na2B4O7 are considered. The phosphate units are lo cated out of the borate network. The extent of the vitreous domain and the physical and chemical properties are correlated with these differ ent structures.