Dissolution mechanisms of boro-silicate glass fibres in saline solution with added dissolved silica

Experiments of dissolution of a soluble boro-silica glass were performed at 37 degrees C in a saline solution without and with 50, 75 and 100 ppm of a dded silica. After reaction silica concentration was measured by AAS and co lorimetry and fibers were investigated by SEM-EDS and XPS. The results give informations on the dissolution velocity of the glass and the factors cont rolling the formation rate of the gel layer and its composition. The dissol ution velocity measured at the unaltered glass-gel interface is not signifi cantly decreased by the silica concentration in solution whatever its origi n (leaching of the glass fibres or initial addition). Accordingly, gel form ation is controlled by the chemical reactions rate at, or near, the boundar y of the unaltered core. The composition and the stucture of the gel layer are depending on the silica concentration in solution above a threshold of about 50 ppm. The framework of the gel appears to play the more important r ole in the dissolution velocity of the glass. (C) 2000 Kluwer Academic Publ ishers.