Glass forming ability of ZBLAN glass

Abstract

A ZBLAN glass of the following composition: 53 mol.% ZrF4, 20 mol.% BaF2, 4 mol.% LaF3,3 mol.% AIF3, 20 mol.% NaF is studied for predicting its glass forming ability (GFA). The GFA of a ZBLAN glass is evaluated by estimating the Gibbs free energy difference (ΔG) between the undercooled liquid and the corresponding equilibrium solid phases. Other GFA criteria (T_rg=T_g/T_l, T_x/T_l, γ=T_x/T_g+T_l, ΔT_xg=T_x-T_g, T_g/T_m) are also calculated. Here, the approximation for ΔG considering constant specific heat difference (ΔC_P) over a wide temperature range is calculated for a ZBLAN glass. The so-calculated ΔG is compared with the result of other heoretical approaches and experimental data. We can see from the result that the expression with the consideration of constant ΔC_P works well in the entire undercooling for ZBLAN glass forming system. So we can say that the specific heat difference is being constant in the entire undercooling for ZBLAN glass.