Phosphorus and boron speciation in K 2O-B 2O 3-SiO 2-P 2O 5 glasses

Abstract

Raman, 11B and 31P MAS NMR spectra of yP 2 O 5 · (1 − y) [(20 − x)% K 2 O · x% B 2 O 3 · 80% SiO 2] glasses ( y = 0 to 0.03 and x = 5 to 13) show that dimers (P 1) and chains (P 2) are the dominant structural units for phosphate species; six-member rings (3B and 3O) and SiOB(IV) bonds are the major bonding types for boron-bearing species. Some of the B(IV)'s in the silicate network may be in structural sites similar to danburite. The coordination of B is strongly controlled by P in the glasses. The relative proportion of B(IV) to total B decreases significantly after adding less than 3 mol% P 2O 5. Homogeneous equilibria are determined from the spectral data to generalize the observed structural changes for each group of glasses with a fixed K 2O B 2O 3 ratio. The Dell and Bray (1983) model for B coordination is partially revised to meet the new data of B speciation derived from 11B MAS NMR spectra.