A Study on the Phase Separation in Glass

Abstract

Two types of liquid are possible in two component system; the one is the type of homogeneous solution and the other is essentially the type of the mixture of two liquids. Recently, phase separation has been found in many kinds of glass. This study has been made to confirm whether phase separation is found in all kinds of glass or not: that is, whether glass is the liquid of the type of homogeneous solution or the liquid of the type of heterogeneous mixture of two liquids.In this investigation, the glass in the simple CdO-B2O3 system having stable separation range (100-60mol% B2O3) and glass formation range (60-50mol% B2O3), especially 45CdO⋅55B2O3 glass, was used. Light scattering and electron micrographs of 45CdO⋅55B2O3 glass, showed that, by heat treatment at various temperature below the liquidus temperature, 2CdO⋅3B2O3 crystal was formed, but phase separation was never detected in this glass. And an additional experiment in which small amount of TiO2 was added, showed that TiO2 has no effect to cause phase separation in such a glass of homogeneous-solution type.From the aspect of free energy of two component system, there are two types of glass in which the phase separation is not observed. One type of glass forms a liquid of the solution type owing to the decrease of internal energy of the system. In this case, the phase separation is essentially impossible. The other type of glass does not appear to separate owing to the contribution of entropy terms on free energy, although the glass is essentially a liquid of the mixture type. However, our experimental results that the glass does not separate independently of the temperature and the information derived from the phase diagram of this system, suggest that the CdO-B2O3 glass on glass-formation range correspond to the liquid of solution type. Thus, it was concluded that glass is not always separated and the kind of glass exist, which forms a homogeneous solutions and can not be essentially separated.