Preparation and characterization of boron oxysulfide glasses

Stable, homogeneous xB2O3+(1−x)B2S3 glasses were prepared between 0⩽x⩽0.80. It was not possible to prepare homogeneous, stable glasses of compositions 0.85⩽x⩽0.95 due to a strong exothermic enthalpy of mixing between the B2S3 and B2O3 phases. Raman and 11B NMR spectroscopies, used to characterize the structure of the glasses, show that the boron oxide structures of B2O3 especially the six-membered (thioboroxol) rings, quickly diminish with increasing sulfide content, whereas the corresponding sulfide structures in B2S3 remain relatively intense as the oxide content is increased. Differential scanning calorimetry and density measurements, used to characterize the physical properties of the glasses, show that the physical properties of these boron oxysulfide glasses heavily favor the B2S3 properties regardless of the amount of B2O3 added to the system. It is hypothesized that the stability of the thioboroxol ring group relative to that of the BS3/2 trigonal group is a possible source of this behavior. The large heat of mixing for B2O3 rich glasses is associated with the formation of new mixed boron oxysulfide structures of composition BSiO3−i where 0<i<3.