Glass Science and Technology
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- ItemAnisotropic optical properties and flow behaviour of mechanically deformed single-phase glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Brückner, Rolf; Habeck, AndreasStarting from the stress-optical coefficient around and above Tg, the following effects are regarded in order to give a comprehensive picture of the structural response of various glass melts under flow conditions at various temperatures: anisotropy o f glass fibres, the flow birefringence and Maxwell constant of the melt directly and/or indirectly via frozen-in anisotropics by cooling the melt thermally stress-free under mechanical load. Some of the applied various rheological methods allow to study the Newtonian and non-Newtonian viscosity additionally to the birefringence. Four very different glass melts are investigated under these aspects: a potassium-calciumsilicate glass, a float glass, an alkali metasilicate glass and an alkali metaphosphate glass. The results show that there are significant differences in the specific birefringence and in the deviation from Newtonian flow behaviour depending on the special flow units of the glass types. The structure of these anisotropic glasses and melts extends from frozen-in deformations of the network to orientations of chain-like flow units depending on chemical composition, temperature, mechanical stress and deformation rate. Particularly, a close connection between the onset of the non-Newtonian flow behaviour and the alteration o f the specific birefringence was found at certain critical stresses.
- ItemPractical strength of glass containers. Part 2. Influence of handling(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Wagner, Jörg; Müller-Simon, Hayo; Lenhart, ArminThe practical strength of container glass depends not only on the stress distribution at the surface, but also on the type and distribution of surface defects. After the elimination of the influence of the container shape by means of finite element methods, different types of defect show a different behaviour in the Weibull plot. This behaviour can be used to compare different handling materials. The materials used at the cold end cause no measurable weakening of the strength. A special type of defect could be associated with the transfer conveyour belt. Carbon and brass were compared as deadplate materials without finding a specific influence on the container strength.
- ItemInterlaboratory comparison of solar range transmittance and reflectance of coated and uncoated flat glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Nicoletti, Fabiano; Polato, Pietro; Roucour, JeanTransmittance and reflectance measurements on glass for architectural applications using commercial spectrophotometers may be affected by errors resulting from an improperly operated instrument, an inappropriate calibration, etc. Discrepancies between the values of parameters such as light reflectance and solar factor measured on the same glass product by different laboratories can be very pronounced. In order to avoid disputes among glass producers and complaints from glass users the interlaboratory reproducibility and the accuracy of the measurements must be improved. A n intercomparison was organized by Technical Committee 10 "Optical Properties of Glass" of the International Commission on Glass among 15 laboratories and one metrological institute on transmittance and reflectance measurements on commercial coated and uncoated glasses. Good reproducibility and accuracy in transmittance measurements ( ± 0 . 6 %) have been achieved even with each laboratory using its own instrumental procedures. In the case of reflectance, a preliminary round robin performed using the same instruments gave very large discrepancies in the spectral and integrated values. Reproducibility and accuracy of the same order of magnitude as in the transmittance measurements were obtained when each laboratory used a standardized procedure and the same reference standards, the latter having optical characteristics similar to the samples.
- ItemPolysulfid im Isolierglas-Randverbund - der Umwelt zuliebe(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Lucke, Heinz; Schmidt, Rudolf[no abstract available]
- ItemLocal temperature distribution and primary melt formation in a melting batch heap(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Conrad, Reinhard; Suwannathada, Pichanon; Pimkhaokham, PreedaThe melting behavior of mass glass batches was studied in a gas-fired lab-scale furnace. Batches were adjusted to different redox numbers by additions of sulfate and coal. In each test, 4 kg of batch were charged onto a cullet melt (7 kg, 600 cm² surface area) which was pre-molten at 1200°C. The batch blankets had an initial height of approximately 5 cm. The vertical distribution of temperatures and electrical conductivides were recorded. The occurrence of primary melt was identified by a sudden increase of conductivity by three orders of magnitude. As expected, primary melt occurred latest in the inner zones of the batch. A comparison of conductivities and temperatures, however, showed that primary melt was not formed along any specific isotherm. Thus, the concept of a uniform melting temperature valid for the entire batch heap as used in several theoretical models is not confirmed. Thermal diffusivities derived from a numerical evaluation of the temperature field also displayed a sudden increase, however, at temperatures systematically higher than the temperatures of primary melt formation.
- ItemIndustrial experience with oxygen-fired glass furnaces(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Lauwers, Eddy; Strohberg, HorstAmong the leading industrial gases suppliers, Praxair has developed a leadership position in oxygen combustion technology and in on-site oxygen supply technology with its Vacuum Pressure Swing Adsorption process. A tailor-made solution with regard to oxygen burner technology and to oxygen supply method is provided to meet customer requirements. The latest developments show a reduction in particulate emission o f up to 30 % and in NOx emission of up to 90 % compared to air/fuel-fired operations. These results are confirmed in industrial use. Due to specific requirements in applicadon technology, different burner concepts have been developed. These concepts can be classified in two groups: Conventional burners with direct oxygen-fuel mixing create high flame temperatures and NOx formadon; recirculating burners create low flame temperatures and NOx formation due to controlled fluid dynamics to entrain furnace atmosphere into the main oxygen stream before the now diluted oxygen reacts with the fuel.
- 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.
- ItemQuasi-equilibhum in silicate glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Bocksay, ZoltánInhomogeneity in glasses detected as a composition fluctuation with a wavelength of about 0.1 to 1.0 mm is assumed to be an inherent property of common silicate glasses caused by the circumstances of glass melting. After a single-phased melt is formed from a heterogeneous system of raw materials the component diffusion decreases the inhomogeneity This process is slowed down and practically stopped when the so-called quasi-equilibrium has been reached. In this state the chemical potendal of a given i-th component is approximately constant, i.e. µi(x,y,z) ≈ const, instead of µi{x,y,z) ≈ const, for, at least, two components. While this equation is only valid for one or two (rarely more) fixed compositions, the former one allows the coexistence of all conceivable compositions within a given range. Thus, the inhomogeneity can be preserved, especially when a long wave fluctuation prevails. The effect of the inhomogeneity on the properties of glass is emphasized.
- ItemLightweight glass technology: weight reductions and surface coatings(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Meyer, Henning[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.
- ItemDetermination of the rheological properties of high-viscous glass melts by the cylinder compression method(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Brückner, Rolf; Yue, Yuanzheng; Habeck, AndreasA detailed description of the cylinder compression method and its application on the viscoelastic behaviour of glass melts is given with the help of closed solutions and equations in contrast to algorithmic methods, like e.g. the finite element method. Special attention is paid to the system deformation and system deformation rate of the testing equipment and to the dissipation of mechanical energy within the specimen and the heat flow from the specimen. The limits of this treatment are discussed with respect to the applicability of the theoretical basis (Gent and Nadai equation) and with respect to the experimental determination of the rheological properties of glass melts. On this basis the pure non-Newtonian viscosity, ηnN, can be determined. If very small differences have to be ascertained in the rheological behaviour of glass melts due to small differences in composition or in melting history (e.g. redox condition or bad/good workability), the same conditions concerning the mechanical and thermal equipment and even the same geometry of the glass specimens have to be strictly maintained. Comparison between different glass melts should be made rather on the basis of equal (Newtonian) equilibrium viscosity, η₀, (isochomal conditions) and not on equal temperature. Owing to large thermal effects, the slope of the viscosity-temperature curve at η₀ plays a certain role, particularly for the forming process.
- ItemGlass connecting elements and constructive glass applications(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Kahlert, Wolfgang[no abstract available]
- ItemStand des Altglasrecyclings - Verpackungsverordnung und Duales System(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Hoffmann, Werner[no abstract available]
- 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.
- ItemSpectroscopic investigations of glasses with semiconductor microcrystals at higher temperatures(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Kritz, Antje; Müller, MatthiasGlasses containing microcrystals of CuBr or CuCl show two characteristic absorption peaks caused by excitonic transitions. If temperature is increased the peaks become wider and flatter, whereas the complete disappearance o f the excitonic peaks takes place in a narrow temperature range of 30 to 50 K. Absorption intensity in the UV region (at about 30 000 cm⁻¹) increases simultaneously. The reason for these reversible changes is the melting of the microcrystals about 200 K below the melting point of the corresponding bulk crystals. The melting point depends on size and composition of the microcrystals.
- ItemIsolierglas ohne Reflexionsverzerrungen(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Küffner jr., Peter[no abstract available]
- ItemHomogenization of glass melts by bubbling on a laboratory scale(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Högerl, Klaus; Frischat, Günther HeinzIn a typical melter, the molten glass tends to be inhomogeneous due to the heterogeneity of the raw materials. One means of yielding more homogeneous glass is bubbling air through the glass melt through nozzles at the base of the melter. The induced fluid flow dissolves cords and homogenizes the glass melt. This bubbling process was investigated on a laboratory scale both from an experimental and a theoretical point of view. A standard soda-lime-silica glass was bubbled with argon in a platinum crucible at 1400 C. The samples treated were tested with regard to their optical homogeneity, using an improved version of the Christiansen-Shelyubskii method. The corresponding fluid flow phenomena were simulated by a suitable mathematical model. Due to the axial symmetry of the bubbling equipment and the high viscosity of the glass melt (creeping flow), the problem can be reduced to the solution of a differential equation of the fourth order with the stream function as independent variable. The numerical treatment superposes Gegenbauer functions matching the given boundary values for the velocity and tension, respectively. The homogeneity strongly increased with bubbling time and its local variation showed good correlation with the calculated flow pattern in the crucible.
- ItemModeling of the bubble population in glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Roi, Torsten; Seidel, Olaf; Nölle, Günther; Höhne, DiethardPrevious studies of refining models have mostly dealt with the mathematical description of the behavior of individual bubbles in glass melts. A further step was the modeling of the ascent and growth of groups of bubbles, including restrictions with respect to the spatial distribution of the individual bubbles. Even though no algorithm was derived in this stage which described the total bubble balance during refining, these investigations have produced important results in the field of bubble growth and ascent. In this study, a general and comprehensive mathematical description of the bubble population during refining shall be given, on the basis of the population balance equation used in chemical engineering. The general balance equation for bubbles during refining is presented together with the corresponding computer model. Several experimental investigations into bubble size distribution are described, together with an analysis of the reduction of the bubble concentration in the pot. The obtained values were used as initial parameters and estimates in computer simulations. Some special results of modeling are shown and discussed.
- ItemStatistical analysis of viscosity-composition data in glassmaking(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Öksoy, Dolun; Pye, L. David; Boulos, Edward N.The objective of this work is to revisit and expand the methods for calculating viscosities of glass with changes in composition that was pioneered by Lakatos, Johansson, and Simmingsköld. Using the data provided by these authors, an empirical statistical model will be presented. This will illustrate the effect of composition change on viscosity that can be expected in a typical glassmaking process.
- ItemDiopside marble-like sintered glass-ceramics(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Karamanov, Alexander; Gutsow, Ivan; Penkov, Ivan; Andreev, Julian; Bogdanov, BogdanExperimental results on the synthesis of a new marble-like glass-ceramic material to be used for wall covering are given. The material is prepared by sintering and surface-induced crystallizadon of a precursor frit. In contrast to usual glass-ceramic materials similar to natural marbles and granites, where the major crystalline phase is β-wollastonite (CaO * Si0₂ ) , in the new material diopside (CaO * MgO * 2Si0₂ ) is formed. Due to the enhanced crystallization ability of the initial glasses, the duration of the heat treatment needed for the synthesis of the new materials can be considerably reduced.