Solubility and film formation of phosphate and alumina containing silicateglasses

Dissolution, surface film formation and the stabilising effect of alumina w as studied for glasses in or near the bioactive composition region. Tris(hy droxylmethyl-aminomethane) buffers at pH 7.4, which contained chloride or c itrate were used as test solutions. Solution analysis showed that the silic on-release was higher in the chloride than in the citrate solution. Analysi s of glass surfaces with X-ray photoemission spectroscopy (XPS) showed that the citrate inhibited calcium phosphate film formation, but allowed alumin osilicate formation. Thus, by adding citrate to the test solution the stabi lizing effect of calcium phosphate film formation is excluded and the effec t of alumina is consequently more easily observed. The stabilising effect o f alumina was due to both stabilization of the glass structure and to alumi nosilicate film formation. Analysis showed that glasses with calcium phosph ate film formation in Tris, also accumulated berate at their surfaces. This can be explained by partial substitution of the phosphate by berate in the developing hydroxylapatite surface layer. (C) 1999 Elsevier Science B.V. A ll rights reserved.