融液冷却法によるＢ２Ｏ３‐Ｎａ２Ｏ２成分系ガラスの生成に対する粘度の役割

Abstract

The glass-forming region in the B2O3-Na2O system was tried to interpret on the basis of an assumption concerning the glass-forming ability of a substance that higher viscosity melts will make a glass when quenched at an appropriately rapid rate, while lower viscosity melts will not. Ten grams of B2O3-Na2O melts were water-quenched at a rate of 7°C/sec, and two glass-forming regions were determined. The upper glass region was 100∼61 mole per cent B2O3 and the lower glass region was 32∼28 mole per cent B2O3. Viscosity was measured by a counter-balanced viscometer at elevated temperatures above the liquidus temperature, and the liquidus viscosity log ηl was obtained for the compositions of 100∼25 mole per cent B2O3. The liquidus viscosity curve plotted as a function of B2O3 content for the B2O3-Na2O system exhibited two maxima and two minima in viscosity. It was found that the glass regions, 100∼61 and 32∼28 mole per cent B2O3, corresponded quite closely with the regions where the liquidus viscosity was higher than log ηl (poise)=0∼0.1. The single-bond strength BM-O and the Rawson's parameter BM-O/Tl for glass formation were calculated and were compared with the glass-forming regions of this system. These parameters were found unsatisfactory to explain the glass-forming ability of the lower glass region. But the liquidus viscosity described rather quantitatively the existence of the separate glass regions in the B2O3-Na2O system.