Li_2O-Na_2O-Al_2O_3-SiO_2系混合アルカリアルミノケイ酸塩ガラスの粘度

Viscosities of (20-x)Li2O・xNa2O・10Al2O3・7OSiO2 and (20-x)Li2O・xNa2O・20Al2O3・6OSiO2 glasses have been determined. The low temperature viscosities, that is, the high viscosities ranging from 10 7 to 10 11 poises have been measured with a penetration viscometer and the high temperature viscosities, that is, the low viscosities ranging from 10 2 to 10 5 poises with a balanced sphere viscometer. Thermal expansions of the glasses have also been determined to estimate thermal expansion coefficients and glass transition temperatures. The mixed alkali effect in viscous flow has been observed in some cases but not in other cases. That is, the plot of the low temperature viscosities versus the alkali mole ratio Na/(Na+Li) for (20-x)Li2O・xNa2O・10Al2O3・7OSiO2 glasses has indicated the presence of a marked minimum in viscosity around an alkali ratio of 0.50, whereas the plot of high temperature viscosities has indicated the viscosity change of inverted S type. The typical mixed alkali effect has not been observed in (20-x)Li2O・xNa2O・20Al2O3・6OSiO2 glasses both in low and high temperature viscosities. Thus it has been discused that the mixed alkali effect (a marked minimum in viscosity on the logη ~ alkali mole ratio curve) does not occur necessarily in all mixed alkali glasses