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- ItemThermodynamic calculations of chemical solubilities of gases in oxide melts and glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Pelton, Arthur D.The Reddy-Blander thermodynamic model for calculating sulfide solubilities in oxide melts and glasses has been modified and extended to predict a priori solubilities of sulfide, sulfate, phosphate, carbonate and halides in multicomponent oxide melts and glasses, from a knowledge of the thermodynamic activities of the basic component oxides (SiO₂, Na₂O, K₂O, CaO, etc.), in most cases with no adjustable parameters. Agreement with measured solubilities is within or nearly within experimental uncertainties over wide ranges of composition in two-, three-, four- and five-component melts and glasses. Particularly good agreement is obtained for the dissolution of sulfur, SO₂ and SO₃ as sulfate. The oxide activities used in the computations are calculated from a database of model parameters obtained by optimizing thermodynamic and phase equilibrium data for oxide Systems. Sulfide, sulfate, phosphate, carbonate and halides as solutes have now been included in this database. Software for Gibbs energy minimization with automatic access to this and other databases permits the calculation of solubilides in multicomponent oxide melts and glasses in equilibrium with other phases such as gases, molten salts, solids and metals, and can be useful to model evaporation processes and bubble formation.
- ItemUV-VIS spectroscopic investigations of amber glass at high temperatures(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Müller, Matthias; Rüssel, Christian; Claußen, OlafThe absorption spectra of iron-containing glasses and an amber glass were recorded in the temperature ränge of 25 to 700 °C. Α shift of the UV absorption edge towards lower wave numbers with increasing temperature was found. The amount of the shift depends on the Fe³⁺ concentration. Here, the UV absorption edge may superimpose or even cover up the absorption bands of colouring ions with increasing temperatures. For an amber glass sample, with increasing temperature, the intensity of the absorption bands of the amber chromophore decreases slightly. However, above 550 °C the decomposition of the chromophore is observed. All changes are reversible when temperature is decreased again. The decomposition of the chromophore and the attributed temperature ränge are in agreement with thermodynamic calculations.
- ItemDetermination of the composition of glass, glass-ceramics and glass raw materials with Laser-ICP-MS(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Strubel, Christine; Meckel, Lothar; Effenberger, RuthΑ mass-spectrometric method with an inductively coupled plasma as an ion source (ICP-MS) is presented which uses an excimer laser for direct ablation of solid material. The oxide compositions of a television screen glass, a glass-ceramic and a quartz powder analyzed by LA-ICP-MS are given and compared with data obtained by wet chemical analysis. Fundamental processes of the technique are described and advantages and disadvantages for the analysis of glass are discussed.
- ItemAnalysis of as-prepared and corroded glass fibers by secondary neutral mass spectrometry(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Müller-Fildebrandt, Constanze; Priller, Stefan; Frischat, Günther HeinzThree types of glass fibers, differing mainly in their alumina, alkaline earth and alkali oxide contents, were investigated by secondary neutral mass spectrometry. The investigation was carried out on fibers as-prepared and after exposure to humidity and to attack in distilled water. Concentration-depth profiles of the fibers obtained by secondary neutral mass spectrometry showed that the asprepared fibers were already pre-experimentally weathered in a ≤50nm deep surface zone. The pattern of chemical change and leaching was found for each fiber to be similar after exposure to humidity and short-term attack by water, respectively, however with enhanced leaching observed in water, where the leached elements are removed from the fiber surfaces. Different leach mechanisms could be established for the different fiber types and changes of leach mechanisms with time could be observed. Altogether, the depth profiling method proved to be a powerful tool to elucidate the comphcated leach mechanisms also in the case of glass fibers.
- ItemComparison of the diffusion approximation and the discrete ordinates method for the investigation of heat transfer in glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Lee, Kong Hoon; Viskanta, RaymondHeat transfer by combined conduction and radiadon has been investigated in a one-dimensional glass layer. The layer is semitransparent to radiadon and the dependence of the absorption coefficient on wavelength is accounted for. The discrete ordinates method and the diffusion approximation are used to analyze radiative transfer. The differencing scheme for the discrete ordinates method has been investigated to obtain the constant total heat flux distribution across the glass layer as required by the energy conservation equation, and the best uniformity is obtained with the diamond scheme. The results predicted by the discrete ordinates method are in good agreement with those based on the exact (integral) equation formulation of radiative transfer. The diffusion approximation greatly underpredicts the temperature and heat flux distributions in the glass layer when the thickness or the opacity of the layer is small. The predictions of the diffusion approximation are only reasonable for thick glass layers. This approximation should be used with extreme caution to obtain quantitatively accurate results.
- ItemDissolution of (50-x)Na₂O-xCaO-50P₂O₅ metaphosphate glasses in different saline Solutions: mechanism and kinetic control(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Delahaye, Florence; Montagne, Lionel; Palavit, Gérard; Baillif, Patrick; Touray, Jean ClaudeThe dissolution of (50-x)Na₂O-xCaO-50P₂O₅ metaphosphate glasses has been investigated at pH 3 in Solutions containing in Na⁺, Ca²⁺, Cl⁻, NO₃⁻ and (PO₃⁻)n ions. Whatever the conditions, a hydrated layer develops over a surface covered with etch pits. Na⁺ and Cl⁻ have no specific effect on the dissolution kinetics and mechanism. In Ca²⁺-containing Solutions, XPS, electrophoretic mobility and ³¹P NMR show that Na⁺ is exchanged for Ca²⁺ in the hydrated layer, resulting in a decreased dissolution rate. Polyphosphate anions, (PO₃⁻)n, act as complexing agent for Ca²⁺, and counterbalance its inhibiting effect on the dissolution rate.
- ItemOptimizing the Christiansen-Shelyubskii method and its comparison with industrial control methods for homogeneity determination of glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Heidrich, Roland Paul; Frischat, Günther HeinzThe Christiansen-Shelyubskii method used in this work was optimized experimentally. Different tests were performed with two grain fractions of standardized crushed sheet glass. Maximum transmissions, half-widths and their Standard deviations were optimized, and it was further shown that sampling, an appropriate cleaning of the granulated glass and the quality of the optical cells used are of great importance, too. Α variety of industrial glasses was investigated and the Christiansen-Shelyubskii homogeneity numbers were compared with the homogeneity data provided by the glass manufacturers using industrial homogeneity control methods for Container, tube and flat glasses, respectively. Although the physical principles of the homogeneity methods compared were dissimilar, mostly qualitatively similar trends were found. Only in the case of the Mach-Zehnder interferometry method, which is based on a similar principle as the Christiansen-Shelyubskii method, a quantitative correlation analysis was possible. Reasonable agreement between the homogeneity values from both methods was achieved. It was further shown that the Christiansen-Shelyubskii method can monitor the homogeneity during glass melting with external cullet, both in freshly prepared and in composted states.
- Itemstress distribution in thermally tempered glass panes near the edges, corners and holes : Part 1. Temperature distributions during the tempering process of glass panes(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Laufs, Wilfried; Sedlacek, GerhardWhile theoretical and experimental analyses of temper Stresses within the central areas of glass plates, i.e. for the theoretically "infinite plate", have been carried out in the past, the distributions of the induced Stresses near the edges and holes have yet to be examined in order to give a complete description of the stress field in the entire plate. The build-up of temper stresses depends on the temperature distribution as a function of time. For this reason, in part 1 of this paper the two- and three-dimensional cooling phenomena during the tempering process have been studied for all zones of a pane by means of analytical Solutions of the equation of heat conduction as well as by means of a discrete Simulation (Finite Element Method). The latter method allows for studying the temperature distributions in the vicinity of arbitrarily shaped holes. The influence of the tempering parameters (coefficient of heat transfer) and of the material constants on the temperature distribution is described, too. Part 2 of this paper deals with the induced distributions of temper stresses resulting from the thermal history of glass plates as defined in part 1.
- ItemRheological properties of calcium metaphosphate melts during extrusion(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Yue, Yuanzheng; Carl, Gunter; Rüssel, ChristianAn extrusion method to determine viscosities is described. Here, different stages of the response on the load applied are observed and the viscous heating efFect caused by the mechanical deformation work is taken into account. The method enables the determination of viscosities in the ränge of 10⁶ to 10^(8.5) dPa s. The values obtained are in good agreement with interpolated ones determined by beam bending and cylinder rotation. During extruding of calcium metaphosphate melts, the viscositiy decreases with increasing shear rate. This shear-thinning efFect (or non-Newtonian behaviour) is attributed to the orientation of flow units of the dynamic melt network. It is found that both Newtonian and non-Newtonian flow behaviour of calcium metaphosphate melts was largely influenced by adding a small amount of SiO₂. However, the introduction of a small amount of SiO₂ into calcium metaphosphate melts is beneficial to study the flow behaviour, since by that the crystallization of melts is avoided, which hinders the continuation of extruding processes.
- ItemApproximate analytical Solutions for the heat transfer in glass melting furnaces(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Kuhn, Wolf StefanTemperatures and convections in glass melts are governed by coupled partial differential equations. These equations can, in general, only be solved by numerical methods. Α considerable simplification of the partial differential equation for heat transport is possible under certain conditions. These conditions are frequently met in glass tanks. They allow the formulation of an ordinary differential equation for the heat transport with Solutions in the form of simple equations. These equations are analytical expressions of the vertical temperature profile in the glass melt. The Peclet number for the vertical flow component in the melt under the free surface appears to be the essential parameter in these expressions. It characterizes the combined heat transport by conduction and convection. However, flow velocity and thermal diffusivity vary strongly over the depth of the glass bath, thus rendering the Peclet number Position dependent. On this theoretical basis, it follows a detailed numerical and analytical study of the dependence of the vertical temperature profile on wall heat loss, primary recirculation and pull.