Browsing by Author "Jones, Linda E."

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    Effects of redox State and atmosphere on the surface tension of ironcontaining soda-lime-silica melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Wing, Douglas R.; Clare, Alexis G.; Jones, Linda E.
    The density and surface tension of 15Na2O 11CaO 74SiO2 glass melts (composition in mol%) containing additions of 0.5 and 1.0 mol% Fe2O3 were measured using the sessile and pendant drop techniques at various temperatures between 1200 and 1400°C. Melts of each composition were prepared under oxidizing and reducing conditions in order to study the effect of iron redox state on the surface tension. Surface tension measurements were carried out in reducing (96 %Ar/4 %Η2), inert (Ar) and oxidizing (dry air) atmospheres. The density of the melts increased with increasing iron content and decreasing melt temperature. The surface tension of the iron containing melts was found to be influenced by the atmosphere and its effect on iron coordination. It was determined that melts with high concentrations of Fe3+ are most susceptible to changes in the atmosphere, since Fe3+ can have either tetrahedral or octahedral coordination. A minimum in melt surface tension was detected between 1300 and 1350°C for the iron containing melts.
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    Influence of various atmospheres on the surface properties of silicate melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Kucuk, Ahmet; Clare, Alexis G.; Jones, Linda E.
    The surface tension of a soda-lime-silica glass melt and some commercial glass melts including an E-glass, a TV panel glass, and a soft borosilicate was measured under various atmospheres. The atmospheres included dry argon, dry air and wet air with varying amount of water vapor using the sessile drop and pendant drop arrangements. In general, the surface tension of melts decreased in the order: dry argon, dry air and wet air. OH- groups from the water vapor in the atmosphere behave as a surface-active species according to the Gibbs adsorption equation and form a monolayer on the surface with certain number of molecules according to the Langmuir adsorption theorem. The number of OH- -like molecules in the monolayer is higher for the melts containing high ionic strength ions.
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    Sodium sulfate decomposition in dry atmospheres
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Samadhi, Tjokorde W.; Elliott, Jennifer C.; Jones, Linda E.; Clare, Alexis G.
    Na2SO4 in silicate glass batches is an environmental issue, since it releases SOx upon decomposition. Decomposition of Na2SO4 in different environments is studied by mass-loss measurements combined with evolved gas analysis, and thermochemical modeling. The decomposition experiments are undertaken in dry, pure O2(g), Ar(g), N2(g), and air(g) at 95 kPa total pressure. Thermochemical calculations using the code F*A*C*T predict SO2(g), Na(g), Na2SO4(g), NaO(g), and, in some cases, NO(g) as major emission species. The concentrations of these species increase with temperature. Na2SO4 decomposition initiates at ≈1373 K. Isothermal decomposition exhibits linear behavior with respect to time in 1473 to 1673 Κ range. At 1673 K, the decomposition rate is 24 · 10^-4 mg/(mm2 min) in UHP (ultra-high purity) O2 and 69 · 10^-4 mg/(mm2 min) in UHP N2. Evolved gas analyses identify SO(g)/SO2(g) as the emitted pollutants. In O2-rich atmospheres, SO(g) is a significant product as well as SO2(g). In inert atmospheres, SO2(g) is the sole decomposition product. At 1673 Κ in UHP O2, the concentration is 55 ppm (by volume) for SO(g) and 61 ppm for SO2. At 1673 Κ in UHP N2, SO2(g) concentration is 651 ppm. The decomposition is described by a surface reaction mechanism, in which SOx is generated by surface rearrangement of sulfur-oxygen complexes on the Na2So4 melt surface. Inert atmospheres increase SOx emission by facilitating this rearrangement process. O2-rich atmospheres passivate the melt surface, which favors the emission of lighter molecules such as SO(g).
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    Surface tension of amber glass melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Wing, Douglas R.; Clare, Alexis G.; Jones, Linda E.; Luo, Shengchun
    The surface tension of 0.1 Fe2O3, 15 Na2O, 11 CaO, 73.9 SiO2 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 %H2), 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 surfaee 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 SO3 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 surfaee 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.