Some Paradoxes Of Borate Glasses And Melts

An account is given of some of the paradoxes of borate glasses and melts and their possible explanations. These concern the inhomogeneous structure of borate glasses on the nanometer scale and include the nature of the regions of inhomogeneity in glasses such as B203-Si02. The latter are termed pseudophases, since they are not regions of metastable immiscibility, which are absent in all of the alkali borate glass systems except Li2O-B2O3. Breaks in the temperature dependence of the X-ray scattering from thermal density fluctuations in borate melts, at the liquidus temperature or above, are explained in terms of rearrangements of the superstructural units present as a function of temperature.