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- 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.
- 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.
- ItemPreparation and properties of model glasses of historic enamels of the Green Vault Museum, Dresden(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Wagner, Marcel; Frischat, Günther Heinz; Hellmold, PeterMany enamelled art objects of the Green Vauk Museum, Dresden, have been suffering a severe deterioration of the enamel layers during the last 20 to 30 years. The authors obtained three splinters of about 200 mg weight each of green, blue, and opaque turquoise enamel of the Aurangzeb ensemble. Model glasses of these originals were prepared which should match them as closely as possible. The investigations showed that the simple degree of network polymerization related to the SiO2/Na2O ratio is insufficient to understand their chemical properties even if one takes components such as MgO, CaO or AI2O3 also into consideration. To understand further structural influences IR, UV/VIS, and EPR spectroscopy studies were performed on the enamels, and it could be evidenced that components such as MnO, Fe2O3, CuO, CoO, PbO and SnO2 not only act as colorants or opacifiers but also as stabilizers of these materials. Taking this into account the chemical and physical behavior of the respective enamels in the museum can be elucidated.
- ItemPreparation and properties of R₂O - CaO - SiO₂ - Si₃N₄ oxynitride glasses and melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Larson, Sandra Christiane; Frischat, Günther HeinzOxynitride glasses, or rather melts, of the molar composition (74-3x) SiO₂, xSi₃N₄, 16 R₂O, 10 CaO with R₂O = Na₂O, K₂O show a significant increase in the glass transition temperature Tg, viscosity η and density ρ with increasing nitrogen content, whereas the thermal expansion coefficient α decreases. These data confirm the assumptions of the structural model in which trivalent nitrogen Substitutes for bivalent oxygen to produce a more tightly-linked glass network and most, if not all, of the nitrogen in the glass is linked to Silicon. ²⁹Si-MAS-NMR measurements on glasses of the System Na₂O-CaO-SiO₂-Si₃N₄ prove that the number of links between the [SiO₄]⁴¯ tetrahedra increase with increasing nitrogen content. Mixed alkali glasses, or rather melts, of the molar composition (74-3x) SiO₂, xSi₃N₄, 16(R₂O + K₂O), 10 CaO with R2O = Na₂O, Li₂O and different ratios of Na₂O:K₂O or Li₂O:K₂O show a deviation from the linearity in the glass transition temperature Tg, thermal expansion α, viscosity η and density ρ, which is shown in a minimum or maximum in the curves at a molar composition of about 10 R₂O:6 K₂O.
- ItemMechanism of defect creation on sheet glass by particle impact and its influence on stray light(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Holtmann, Klaus Heinrich; Frischat, Günther Heinz; Ruppert, KarlStray light on the windshields of automotive vehicles, caused by the impact of small particles, imposes severe safety hazards during night driving. Due to reduced contrast by stray light, nonilluminated objects are perceived much later than through pristine windshields. The objective of this paper therefore is to show the dependence of stray light on impact velocity, impact angle, particle shape and the mechanical properties of the impacting particle and the target material. Single and multiple impacts of SiC (≈1 mg/particle) and quartz sand (≈ 0.7 mg/particle) on ordinary and strengthened float glass under angles of 30°, 45° and 90° and velocities between 50 and 200 km/h were investigated. Profilometer and various methods of stray light measurement, such as total integrated scattering, were used. Based on the correlation between surface roughness and stray light, it can be proved that the amount of stray light is proportional to the ratio of impact volume to the area of the undamaged surface. Caiculating the contact pressure during impact on the target for Sharp and rounded particles in dependence on velocity and impact angle and applying the fracture mechanical criteria for the formation of lateral cracks allows the modeling of the impact volume for the various combinations of particle and target contacts and thus an estimation of the stray light to be expected. Comparison of the model calculation with experimental data exhibits good agreement. Both sets of data show an increase in the amount of damage with increasing velocity and steeper impact angle. The damage caused by SiC is always more severe than the damage by quartz sand. Increasing the fracture toughness of the target material reduces the extent of the damage by about 10%. Α more pronounced reducdon of stray light and mechanical deterioration of up to 60% in comparison to normal float glass can be achieved by a newly developed composite material, consisting of a 0.2 mm thick glass, a 0.36 mm thick layer of PVB, and a float glass Substrate of 3 mm thickness.
- ItemApplication of the Christiansen-Shelyubskii method to determine homogeneity and refractive index of industrial glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Tenzler, Thomas; Frischat, Günther HeinzThe Christiansen-Shelyubskii method has been applied to determine the homogeneity of both colorless and colored technical glasses. It could be confirmed that this method is sufficiently sensitive to changes by the melting process of flat, container and special glasses. The homogeneity factor, which essentially is the standard deviation of the refractive index, can be obtained with a precision of about ±5 %. The measurement simultaneously delivers the mean refractive index with high accuracy. This property possibly could be used to substitute density measurements to control the constancy of glass composition. The Christiansen-Shelyubskii method can be standardized and highly automated. About 15 samples can be measured per day. Thus it shows all features of a method to be used for industrial quality control.
- ItemDepth profiling analysis of lithium and barium disilicate coatings on silica glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Schmitz, Regine; Frischat, Günther HeinzThe electron gas secondary neutral mass spectrometry, operated in the high-frequency mode, is especially suitable for the analysis of electrically insulating materials. This is demonstrated for the sol-gel coating Systems Li₂O · 2 SiO₂ and BaO · 2 SiO₂ on silica glass Substrates as examples. The Li₂O · 2 SiO₂ coating is crystalline and displays fluctuations in composition and/or phases. This heterogeneity is confirmed on atomic force microscope Images. Depending on heat treatment the BaO · 2 SiO₂ coatings are glassy and crystalline, respectively. They do not show any fluctuations; however, the depth profiles display some AI₂O₃ having diffused from the silica Substrates into the films during sol-gel consolidadon. Atomic force microscope Images reveal grooves in the Substrate surfaces in which AI₂O₃ remnants of the grinding process have been captured. The depth of the AI₂O₃ profile from the SNMS measurement corresponds to the depth of Channels found using the atomic force microscope. It is assumed that AI₂O₃ originates from remnants of the grinding material used to produce the silica Substrates.
- ItemImproved homogeneity of various glasses by gas film levitation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Janke, Achim; Frischat, Günther HeinzHeavy-metal fluoride glasses of the system ZrF₄-BaF₂-LaF₃-AlF₃-NaF and soda-lime-silica glasses both from industrial and laboratory crucible production were processed by the gas film levitation technique. In this process the glass melt is suspended contactlessly on a thin gas film, avoiding any reaction with the crucible material. This prevents chemical contamination, surface defects and heterogeneous nucleation, which is especially advantageous for the preparation of specialty glasses. The overall homogeneity of the glasses was strongly improved, too, which was characterized quantitatively by the Christiansen-Shelyubskii method.
- 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.
- ItemMid-infrared laser absorption spectroscopy for process and emission control in the glass melting industry : Part 2. Difference frequency generation based MIR laser spectrometer for glass melting furnaces(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Wondraczek, Lothar; Heide, Gerhard; Frischat, Günther Heinz; Khorsandi, Alireza; Willer, Ulrike; Schade, WolfgangEmerging techniques of mid-infrared absorption spectroscopy offer potentially great sensitivity and selectivity for combustion control and emission monitoring. Beeause of that, a differenee frequency based mid-infrared absorption spectrometer has been considered for application in the glass industry. Based on preliminary tests within laboratory conditions, a spectrometer which operates at wavelengths around 5 μm was applied to online monitoring of the atmosphere of a gas fired glass melting furnace. The CO concentration was measured in order to demonstrate the feasibility of a mid-infrared absorption spectrometer for process control in the glass industry. Α series of measurements was performed in situ as well as crossing the recuperator entry, resulting in general advice on the construction of a prototype device.