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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 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.
- ItemAtomic force microscope study of silicate glass fracture surfaces in air and in water environment(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Goß, Annette; Rädlein, Edda; Frischat, Günther HeinzIn the present work changes in the topography of less resistant K2O-CaO-SiO2 and more stable Na2O-CaO-Al2O3-SiO2 glasses were studied in-situ by using a high-resolution atomic force microscope (AFM) in contact mode. The images were taken in air and in water, using a special liquid cell in the latter case. Fresh fracture surfaces were prepared in the corresponding media and the samples were transferred immediately into the AFM. The freshly fractured K2O-containing glasses displayed an irregular ripple pattern in air with ripple diameters of (80 ± 20) nm, heights < 1.2 nm and root mean square (rms) roughnesses < 0.8 nm. With ongoing exposure time, these glasses form a gel layer, isolated droplets and larger drops which can even coalesce. Also partially crystalline secondary reaction products can be observed in the drops. The large drops themselves displayed topographies with a ripple pattern similar to that found on the gel layer-coated surfaces. The drops and the gel layers are soft and may be penetrated and moved by the scanning tip. The in-situ investigation of these glasses in water revealed topographies with a ripple pattern similar to freshly prepared surfaces. This pattern did not change with exposure time, obviously because the water in excess rinsed away possible reaction products. The more resistant Al2O3-containing glasses show a dissimilar behaviour. The ripple pattern on the fracture surfaces is smaller and does not change even after days. Due to the absence of capillary forces and lower van der Waals forces the ripple diameters are smaller in water than in air. Glasses with a high degree of network polymerization also show smaller ripples than glasses with more nonbridging oxygens.
- ItemWeathering of tin oxide coated glass with low IR emissivity(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Rädlein, Edda; Buksak, Anna; Heide, Gerhard; Gläser, Hans Joachim; Frischat, Günther HeinzThe weathering of K-glass has been studied by measuring transmission and reflection in the visible (VIS), near infrared (NIR) and infrared (IR) wavelength ranges, by chemical depth profiling with secondary neutral mass spectrometry (SNMS) and by atomic force microscopy (AFM) imaging. K-glass is a commercial tin oxide coated glass with low IR emissivity. The SnO2:F-coated side has been exposed to atmospheric conditions for up to 32 weeks and for up to two years. It could be shown that the optical properties are only affected in the VIS range, but the visible contamination does not influence the high IR reflection. This means that the heat-insulating properties of window glazings with the K-glass coating on the surface do not degrade under atmospheric conditions. Chemical depth profiles did not reveal major changes, except for an increase in the signals of minor elements on the surface, namely sodium, carbon and silicon. AFM showed that after 32 weeks the deep valleys of the rather rough crystalline SnO2:F are partially filled up. The high transmission of new K-glass can be regained since contamination or corrosion products can be removed by washing. The coating itself is chemically stable.