Structural implications of water and boron dissolution in albite glass

Abstract

A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi 3O 8) to which different amounts of B 2O 3 (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO 3 groups although some tetrahedral BO 4 is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO 4 increased. The hydrous glasses contain more BO 4 groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR ( 17O, 27Al, 29Si) spectra show that B interacts with the aluminosilicate network by formation of Si–O–B and probably Al–O–B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H 2O, develop additional shoulders, suggesting that possibly B–OH complexes are formed.