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The influence of K2O/(MgO + K2O) on some melt properties, including crystallization during cooling of melts and glass-forming ability, was investigated in the Li2O–Al2O3–SiO2 system with low Al2O3 content. The dependence of viscosity on K2O/(MgO + K2O) above 1000 °C showed a monotonic decrease due to the reduction of [MgO4] concentration and the conductivity also decreased due to the larger ion radius of K. The temperature dependence of conductivity for all melts showed an abrupt change at one temperature due to crystallization in which temperature of crystallization decreases with increase of K2O. The crystallization behavior near liquidus temperature was studied quantitatively by calculating the crystal volume fraction from apparent viscosity value. The glass-forming ability of the melts was discussed by using data related with viscosity and crystallization. Finally, it was suggested that the melts with K2O/(MgO + K2O) ⩾ 0.75 have a good glass-forming ability.

The redox behavior of various elements (Fe, Sb, Ce, Ti, Zn) was investigated in alkali–alkaline earth-silica CRT (Cathode ray tube: TV panel) model glass melts using the square-wave voltammetry (SWV). The current–potential curve, so called voltammogram, was produced at temperature range of 1000–1400 °C under the scanned potential between 0 and –800 mV at 100 Hz. The Fe, Ti and Zn doped melts exhibited one peak due to reduction reaction. In the case of the Sb doped melts, two traces doubted as peak were found in the voltammogram at low temperature while only one peak existed at high temperature. The peak potential was shifted to the negative direction with decrease of temperature, however, its temperature dependence showed linearity. On the other hand, no peak was found in voltammogram of the melts doped with Ce. Based on the temperature dependence of the peak potential, standard enthalpy (ΔH0) and standard entropy (ΔS0) for the reduction of Fe3+ to Fe2+, Sb3+ to Sb0 and Zn2+ to Zn0 in CRT model glass melts were calculated.

The crystal nucleation effect in lithium aluminosilicate glasses was investigated by the viscosity measurement with aid of the fiber elongation method. The abrupt increase of viscosity due to the crystallization of glass was observed in viscosity–temperature curve but the minimum viscosity temperature (Tη) related with crystallization showed a strong dependence on the nucleation state such as nucleation temperature, nucleation time and heating rate. The results by viscosity agreed well with those of DTA. The nucleation effect on the microstructure of glass-ceramics was also discussed. Finally, the nucleation effect on the crystallization kinetics was approached quantitatively by calculating the crystal volume from viscosity value.

Gel powders in a binary glass-forming SiO 2 TiO 2 system with compositions of 2–8 mol% TiO 2 were synthesized by hydrolysis of metal alkoxides in a sol-gel process. The sintering behavior of calcined gel powders was investigated with a dilatometer. Their sintering stage could be divided into three by two characteristic temperatures ( T sin and T cry ) on the shrinkage curve. It was found that the sintering temperature, T sin , in the second stage decreases with increase of TiO 2 content. Considering the effect of viscous flow on the sintering of glass powders, these results mean that the addition of TiO 2 into silica glass reduces the viscosity of this glass. On the basis of these results, it was concluded that the formation of [TiO 4 ] units in the SiO 2 network makes the whole glass network rather weaker than stronger. The correlation between sintering temperature and thermal expansion coefficient of these compositions was also discussed.