Surface tension of amber glass melts

The surface tension of 0.1 Fe 2 O 3 , 15 Na 2 O, 11 CaO, 73.9 SiO 2 glass melts (composition given in mol %) containing additions of 0.0. 0.2. 0.5, and 1.0 wt % sodium sulfate were measured using pendant drop technique at temperatures between 1200 and 1400°C. Surface tension measurements were carried out in reducing (96%Ar/4 %H 2 ), inert (Argon) oxidizing (Dry Air) and wet (Wet Air) atmospheres. The surface tension of the amber glass melts was found to decrease with increasing temperature, these increases were larger than those reported for similar glasses containing iron alone. Melt atmosphere had only a small effect on the surface tension of the sulfur containing melts at the flow rates used in this study suggesting that sulfur decomposition could be in a sulfur-rich local environment. The fact that for sulfur containing melts the surface tension in the reducing atmosphere was slightly lower than that in the oxidizing atmosphere imitates the behavior in oxidized iron melts which would be contrary to the observations of other workers. The surface tension of the melts was found to increase with increasing SO 3 content up to 0.13 to 0.31 wt%, after which it levels off or decreases. This roughly correlates with the intensity of the amber chromophore concentration in the resulting glass. The amber chromophore contains ferric iron tetrahedrally coordinated with three oxygens and a sulfide ion but the amber glass melt contains ferrous iron and an oxide of sulfur. The amber chromophore is believed to be controlled more by the sulfur content than the iron content and therefore the fact that the isothermal surface tension tracks the amber chromophore intensity suggests that the surface tension. too. is controlled by the sulfur Since the oxide of sulfur serves to decrease surface tension partitioning of that species to the surface could cause the observed tearing effect seen in amber glass melts and assist in the homogenization of those melts.