1996, Müller, Ralf, Reinsch, Stefan, Pannhorst, Wolfgang

The surface nucleation of high-quartz sohd Solution crystals at fractured surfaces of glasses of the stoichiometric cordierite composition (2MgO · 2AI₂O₃ · 5SiO₂) was studied by optical microscopy. Particular attention was focused on the nucleation kinetics. Α constant nucleation density, Ν ≈ 10⁻⁴ μm⁻², was found not to be significantly influenced by the time and the temperature of nucleation treatment. Even a very fast heating of samples employing heating rates u p to 1200 K/min does not lower Ν substantially. However, for small average crystal diameters ( < 2 0 μm) a distribution of crystal size in the same order of magnitude is detectable indicating a simultaneous appearance of b o t h measurable nucleation rates and growth velocities. It can be concluded that the surface nucleation of µ-cordierite occurs during the thermal treatment from a limited number of preferred nucleation sites; these sites are "used Up" rapidly enough to cause a strong Saturation effect of nucleation, but slow enough to cause a crystal size distribution at the same time. The surface nucleation rate, Is , was calculated from the observed distribution of crystal sizes. Is progressively increases with rising temperature similar to the crystal growth velocity indicating a broad temperature ränge of essential nucleation activity. The latter must be regarded as t he main obstacle to measure or to control surface nucleation density by means of two-step nucleation and growth treatments and must therefore be claimed to be mainly responsible for the observed constancy of N.

1996, Spremulli, Paul F.

Α scale-up rule is developed to estimate the resistance for each circuit of a projected glass melter. Given all the internal sizes and contours including shapes of the electrodes as well as the power and power ratios and the resistivity of the molten glass for the proposed melter, this rule permits calculating the voltage and current for each of its circuits. Single-phase circuit-interactions, distributions of equipotential surfaces and lines of current and some safety considerations are discussed and illustrated for a multiplicity of electrodes and single-phase power supplies by using two-dimensional, isothermal, salt water models of electric melters. Phase relations that occur between currents in non-linear fluid conductors when additional transformers are used as currentbalancing means are also explored. This material is useful for understanding and designing electric melters.

1996, Yue, Yuanzheng, Brückner, Rolf

The glass melts of a non-homologous series were investigated with respect to flow behaviour and stress generadon behaviour as well as to workability by means of the cylinder compression method. The results show that the competition between the gross viscosity effect and the bonding strength of the dynamic glass melt structure extremely deterrnines the high-temperature tensile strength, σ_ts, the critical deformation rate hc, and by that the isochomal workability. The larger hc values are not always connected to a larger non-Newtonian flow effect or to a larger gross viscosity effect as it is usually the case for homologous series. However, the rule for homologous series that smaller Emax moduli, i.e. smaller stiffness and brittleness of a glass melt, are coupled to a better isochomal workability is also vahd for non-homologous series. The special connections between σ_ts, hc and deformation, Δh/h0, are analyzed.

1996, Spremulli, Paul F.

Leakage currents and their low resistance paths through refractories from the interior of glass melting furnaces to the binding steel are discussed. By defmition, a ground current flows from an electrode, through the intervening glass to ground through grounding conductors. All melters have leakage currents and may have ground currents. Current and voltage characteristics and phasor diagrams have been analyzed for some circuits that can be used in horizontal melters. The furnaces may be heated solely with electricity or in conjuncdon with fossil fuels. Phasor diagrams may be helpful in the design stage of a melter, may be useful for trouble-shoodng and to display electrical distributions for all parts in a precise form. Hence, totally unexpected voltage differences become easily understandable. Phasor diagrams can disclose wiring errors and/or undesirable voltage distributions and may suggest ways to improve electrical characteristics. For symmetrically built and cross-fired furnaces they show side-to-side symmetry and indicate that the central plane of these units can be Virtual or phantom grounds. They may also indicate the conditions minimizing voltage differences between adjacent electrodes. Voltage phasor diagrams are even more useful for longitudinally fired furnaces. For these units they also explain why ground currents occur and how to minimize them. Data from a salt water model with two cross-fired circuits connected to the same phase disclosed linear relations between the electric currents and voltages over a large range. In this ränge each line current was a hnear function of the two line voltages and vice versa and these variables could be treated as scalars. In addition, either line current could be forced to zero by appropriate voltage(s) in the other circuit. Somewhat similar results were obtained when two different phases were used but now neither current could be forced to zero by adjusting the voltage in the other circuit. Again in the linear range each hne current was a linear function of the line voltages and vice versa but the variables now had to be treated as phasors and not as scalar quantities. Salt water modelling with a longitudinally fired melt end yielded representative data showing how the applied voltages may be located on a ground current's voltage phasor in both the capped and uncapped condition.

1996, Gutmann, Roland

Solid waste residuals f r o m waste incinerator flue gas cleaning Systems consist of various oxides, alkali halogenide salts, heavy metal Compounds and traces of organic pollutants. After the Separation of the volatile components from the oxides and the complete destruction of the organics by a thermal treatment at a temperature υ > 1200°C, the remaining oxides are obtained as a homogeneous black glass ready for the direct reuse as a filling or stabilizing material, the production of glass-ceramics by a further thermal processing and/or the use as a secondary raw material for the production of technical glass products, e.g. glass wool, glass fibre or foam glass. For the determination of the reuse potential of the vitrified wastes, basic material parameters have to be determined and compared with Standard glasses. Under this aspect the chemical resistance in acids, bases and water, the density, the hardness, the elasticity, shear and compression moduli, the Poisson's ratio, the bending strength, the dielectric permittivity a nd losses, the refractive index, the optical reflectivity and absorption behaviour, the thermal expansion coefficient, the thermal conductivity and heat capacity were determined for vitrified electrostatic precipitator ash from municipal solid waste incineration plants. The results of these studies, compared with those obtained for Duran, showed a low leachability in neutral and alkaline media a nd good electrical, mechanical and thermal properties. Tests to transform the as-received glasses into glass-ceramics were carried out. Preliminary recrystallization experiments led to dark brown to black-coloured, partially recrystallized glass samples.

1996, Matoušek, Josef, Maryška, Martin, Helebrant, Aleš

The chemical composition of the thin surface layer of float glass is not homogeneous with respect to the concentration of some cations. This inhomogeneous cation distribution significantly changes if the glass surface comes into contact with aqueous Solutions. Using ESCA significant changes in the distribution of magnesium and sodium cations were found on the " top " surface of float glass in static corrosion environment. The magnesium concentration increases in the th in surface layer, while sodium concentration decreases almost to zero. The relative amounts of calcium, Silicon and oxygen appear to be nearly the same both in the original and the corroded surface layer. The change of magnesium and sodium concentrations as well as an electron micrograph of the glass surface indicate damage and hydration of the " top " surface layer of float glass. The distribution of the Clements does not show any significant change if corrosion proceeds in Streaming water. Consequently, total dissolution of the basic glass network built by Silicon and oxygen atoms appears to be the fundamental process in this case.

1996, Brückner, Rolf, Yue, Yuanzheng

The influence of redox State and hydroxyl concentration on the pure non-Newtonian flow behaviour, on the gross non-Newtonian viscosity, on the stress generation modulus, brittleness, high-temperature tensile strength and on the critical deformation rate of an iron oxide-containing laboratory glass melt with two different melting histories, but with the same main chemical composition, is investigated by means of the cylinder compression method. The comparison of these properties between the oxidized and the reduced glass melt is made not only at equal temperatures but also at equal viscosities in order to distinguish between isothermal and isochomal workability and to examine how sensitive the applied method is. The result is that the reduced melt with a somewhat larger Fe²⁺/F_total ratio and with a larger hydroxyl content has a smaller stiffness and brittleness and therefore, a somewhat better isothermal workability than the oxidized melt. This is valid only for the comparison at equal temperatures. When the comparison is made at equal viscosities, however, the workability - or better the isochomal workability - of the two melts is the same. The reason is that a shift of the Newtonian viscosity is produced by the redox shift and hydroxyl content of the reduced melt to lower values which diminishes with increasing temperature. It is possible to construct master curves with respect to the measured properdes at four temperatures, by which a transfer to the low viscosity range is possible, i.e., one can get the isothermal workability of the glass melts over the whole working range. The measured values of the above-mentioned properties are represented by fitting with recently developed relations which give rise to interesting practical and theoretical conclusions about industrial production optimization and about some structural aspects of stressed melts.

1996, Lochegnies, Dominique, Noiret, Christophe, Thibaud, Charles, Oudin, Jérôme

Α new incremental procedure is developed for the thermal analysis in 3D glass products considering the one-dimensional analytical solutions for a semi-infmite glass wall. When coupled to a code being capable of computing large mechanical deformations, this allows to analyze efficiently the glass flow during the pressing, self-deformation and blowing processes. The forming of a reference tumbler is analyzed via finite element simulations. For each forming step, the temperature distribution is calculated from the pressing parameters; pertinent results are found for this first application.

1996, Eifler, Dietmer, Roeder, Erwin, Schlicker, Uwe, Wagner, Jochen

The joining technology of glasses and glass-ceramics with metal is growing in importance in view of the increased application possibilities of such Compound parts in the machinery and electronics industries. Α new method has recently gone into competition with the current production methods of these Compounds such as melting, soldering and glueing. This novel method is ultrasonic welding. So far this joining technology has only been applied in ultrasonic spot welding. However, it is n ow possible to manufacture Compounds with a shear strength of up to 50 MP a at low temperatures (< 400°C) in short periods of time (< 1.5 s). To extend the application of ultrasonic welding the Department of Materials Science at the University of Kaiserslautern (Germany) has constructed and put into Operation an ultrasonic roll seam welding machine for the continuous and intermittent joining of glass and glass-ceramics with metal. So far this device has, among other things, been used to join a borosilicate and a soda-lime-silica glass with several kinds of high alloyed steel, an aluminium alloy and the glass sealing alloy KOVAR (NiCo 29 17) with the addition of a thin intermediate layer of aluminium. By means of systematic studies of the parameters feed, welding force and amplitude, that significantly influence the welding process, an optimization of the Compound strength has been achieved.

1996, Aben, Hillar, Anton, Johan, Josepson, Jüri

Residual stress measurements in many bottles, tumblers and in other axisymmetric glass articles by using integrated photoelasticity have shown that the residual stress distribution often deviates from the axially Symmetrie one. Α method is developed which enables determination of nonaxisymmetric residual stress distribution. Α computer-controlled polariscope has been developed for automatic measurements. Several examples of residual stress distributions, which deviate strongly from the axisymmetric one, are given. It is shown that deviadons from axial symmetry lead to less favorable distribution of the residual Stresses; e.g., they may lead to tensile residual Stresses on the external surface of bottles.