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- Itemstress generation modulus as a counterpart of the stress relaxation modulus(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Brückner, Rolf; Hessenkemper, Heiko; Habeck, Andreas; Yue, YuanzhengIn order to measure the time dependence of the stress relaxation modulus, E, a stress-strain deformation has to precede which induces a stress within the viscoelastic sample from which the sample relaxes. The generation of stress is characterized by a strain rate-dependent and relaxation rate-dependent portion which exhibits a maximum value, E_max, which is called "stress generation modulus". E_max was called the "maximum stress relaxation modulus" in earlier papers. Meanwhile, however, it turned out that a better verbal distinction should be made in future by the new term "stress generation modulus" because E_max is about one order of magnitude larger than E.
- ItemEinsatz von Recyclingglas in der Hohlglasschmelze(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Beutinger, Markus[no abstract available]
- ItemThermodynamic approach to viscosity in the glass transition(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Conradt, ReinhardThe glass transition is re-investigated by means of the formahsm of linear nonequilibrium thermodynamics. The process is treated for melts cooled down below their liquidus temperatures in terms of three events. These events are, in the order of decreasing temperature: by-passing of crystallization, freezing-in of stress relaxation, and freezing-in o f near-range structural relaxation. Conditions for the viscosity levels are derived at which each of these events is accomplished. The model is tested against data of five one-component, three simple binary and ternary, and three multicomponent systems. Within the scope of this test, it is confirmed that the model correctly describes the viscosity levels typical of the glass transition, as well as their dependence on the cooling rate. An explanation for the 10¹³dPa*s rule at Tg is included.
- ItemBorosilicate glass matrix composites reinforced with short metal fibres(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Boccaccini, Aldo R.; Ondracek, Gerhard; Syhre, ClaudiaThe reinforcement of a borosihcate glass with Hastelloy X short fibres is discussed. A fabrication process consisting of wet mixing of the glass powder and the metallic fibres and hot pressing of the mixtures was developed. Composites containing 15 vol.% fibres homogeneously distributed in a near fully dense glass matrix were obtained. Both Young's modulus and fracture strength increased with increasing volume fraction of fibres. The experimental values for the Young's modulus are in agreement with theoretical predictions. No fibre pull-out during fracture was detected and there is a good interfacial bond. By means of a rule-of-mixture calculation for the fracture energy, a five-fold increase in fracture toughness for composites containing 15 vol.% fibres can be predicted.
- ItemNucleation at cordierite glass surfaces: Kinetic aspects(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Müller, Ralf; Reinsch, Stefan; Pannhorst, WolfgangThe 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.
- ItemThe mixed alkali effect revisited - A new look at an old problem(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Ingramm, Malcom D.Progress is reported in resolving the long-standing problem of the mixed alkali effect. Previously theories have failed to encompass all aspects of this phenomenon which involves both a loosening up of glass structure and the reduction of ionic diffusivities. The recently proposed "dynamic structural model", however, reconciles the electrical and structural anomalies by recoupling ion hopping processes to localized site relaxations in glass. The appearance of a mismatch energy and site memory effects leads to successful prediction of the diffusivity "crossover". This could be the first step towards establishing a consensus on the mixed alkah effect which is reflected in several recent publications on this subject.
- ItemThermal technologies to convert solid waste residuals into technical glass products(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Gutmann, RolandSolid 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.
- ItemComputation procedure for the temperature in hot glass application to the finite element Simulation of hollow glass forming(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Lochegnies, Dominique; Noiret, Christophe; Thibaud, Charles; Oudin, JérômeΑ 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.
- ItemFormation and behaviour of bubble curtains in glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Roi, Torsten; Seidel, Olaf; Nolle, Günther; Höhne, DiethartIt is widely assumed that bubbles form in melts when their composition and/or gas-dissolving capacity is changed by the dissolution of refractories or sand. This phenomenon is shown by photographs of dissolving sand. In experimental invesdgadons, it was not possible to explain bubble curtains in the vicinity of refractory materials by changes in composition. Computer simulations show that such bubble curtains can be formed even at a relatively low extent of bubble growth in the glass melt. By convective flows, these bubble curtains can be distributed so that they appear to be the result of a boundary layer reaction. At a constant temperature distribution, such bubble curtains maintain their position for a very long time. In the case of heating, the bubbles are distributed over a large volume of the melt. This may suddenly cause the formation of bubbles especially in tank furnaces.
- ItemElectrical modelling and scale-up rules for glass melters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 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.