PHOSPHORUS AND BORON SPECIATION IN K2O-B2O3-SIO2-P2O5 GLASSES

Raman, B-11, and P-31 MAS NMR spectra of yP(2)O(5).(1- y) [(20 - x)% K2O.x% B2O3.80% SiO2] glasses (y = O 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 30) 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% P2O5 Homogeneous equilibria are determined from the spectral data to generalize the observed structural changes for each group of glasses with a fixed K2O/B2O3 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.