Li₂O-B₂O₃-GeO₂系における準安定不混和域

抄録

Metastable immiscibility region in the system Li₂O-B₂O₃-GeO₂ was estimated. Due to the easiness of devitrification and hygroscopic nature of lithium-boro-germanate glasses, it was very difficult to decide experimentally their metastable immiscibility region.
Using the liquidus temperature in GeO₂ primary-phase region, free energy of mixing was calculated thermodynamically for binary systems, GeO₂-B₂O₃ and -Li₂O and pseudobinary systems, GeO₂-1/4Li₂O⋅3/4B₂O₃, -1/2Li₂O⋅1/2B₂O₃, and -3/4Li₂O⋅1/4B₂O₃. Metastable miscibility gaps were determined by the co-tangent method for these binary and pseudo-binary systems and extended to the ternary system Li₂O-B₂O₃-GeO₂. The result indicated that metastable immiscibility region existed on the GeO₂-rich side at a relatively low temperature.
The region was showed in a ternary diagram. Electron microscopic observation on a few heat treated lithium-boro-germanate glasses verified the ocurrence of liquid-liquid separation in the composition that the calculation indicated.