Viscosity and density of molten optical glasses

Abstract

The viscosities a nd densit ies of 22 op t ical glasses, representin g all ty pes produced at t he National Bureau of Standards, were measured by a co unte rbalanced-sphere method. The densities agreed with those obtained by a vo lumeter method, and t he viscosities showed good agreement with t hose obtained with a small r otation viscometer.Expansivities calulated from density res ults in t he tem peTat ure ran ge 1,000° to 1,200° C showed that flints are low, 15 to 22, barium crowns are in termed iate, 22 to 37 , a nd borosilicate crowns are high , 34 to 40 (m icrons/ meter)/oC . The expansivities showed a posit ive correlat ion with t he slope of the viscosity temperature cur ve.The superiori ty of t he theoreticall y derived Faxen correction of Stokes law over t hat of t he e mpiri cal Francis formula was established b y means of a freely falling sphe re appa ra t us.

Surface tension of molten alkali silicates

“…Recent experience [2] in measuring densities has shown that such an assumption is not valid. The comparison of different properties must be based on measurements made over the same temperature range.…”

“…These densities were determined by a counterbalanced-sphere method [2]. E xpansivities were calcul ated from the change of density with temperatur e. The upper part of figure 5 shows a plot of the surface tensions of lithia-silica liquids at 1,300° C as a function of composition.…”

“…those that form b ina-ry' gl asse~ WIth 8102, and a stud y of th ese systems was undertaken. The objectives of this investigation were to determine (1) how the surface tension varied with composition and temperature, (2) how the temperature co effiCIent of surface tension varied with composition, and (3) how th e temperature coeffi cien t of surface tension varied with expansivity.…”

“…Figure 6 shows a plot of the volume expansivity versus the temperature coefficient of surface tension. In the case of the system N a20-Si02, expansivity data were calculated from density data in the literature [12] combined with the data of the sphere method [2]. The general trend for the temperature coefficient of surface tension to become more negative as the expansivity increases is quite marked.…”

A Review on Infrared Spectroscopy of Borate Glasses with Effects of Different Additives

“…Although borate glass forms a three-dimensional network, its viscosity is substantially lower than that of silicate glass. Again, addition of alkali lowers the viscosity of the melt, but the effect is by no means as dramatic as for silicate glass [44,45]. Introduction of alkali or moisture to alkali metal borate glasses causes some of the three-coordinate boron atoms to become four coordinate [46,47].…”