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- ItemAtomic force microscope study of the topography of float glasses and a model to explain the bloom effect(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Moseler, Doris; Heide, Gerhard; Frischat, Günther HeinzThe topography and nanostructure of several technical borofloat and soda-lime-silicate float glasses were investigated by a high-resolution atomic force microscope (AFM). The irregular ripple pattern to be seen on as-received atmosphere and tin bath side surfaces had an average diameter of ≈ 60 nm, heights < 1 nm and root mean square (rms) roughnesses on (1 × 1) µm2 images of < 0.25 nm. Topographies obtained in the mirror region of fracture surfaces displayed a somewhat coarser nanostructure. It could further be assured that there are no specific differences between the interior and the edge of the float glass sample. Inhomogeneities like precipitates, crystals, phase separation or pores are not caused by the in-diffusion of tin into the float glass. After annealing the float glasses in air, several of them showed the already long known phenomenon of bloom, a greyish haze produced by a wrinkling of the tin bath glass surface. The borofloat glasses did not produce bloom under any condition. The same was true for the Fe2O3-rich green and blue glasses. Depending on sample dimensions and annealing conditions only the Fe2O3-poor clear float glasses developed a pronounced bloom effect. It is known that annealing of the glasses in air causes an oxidation of Sn2+ to Sn4+, which acts as a network former. This causes a change in glass properties near the surface. However, the precisely measured in-depth profiles of all relevant species in the nanometer and the micrometer regions of the float glasses showed that only in the ease of the Fe2O3-poor silicate float glasses a reversed Sn2+ diffusion from the interior to the surface is caused by the air annealing, forming a very high and steep tin (Sn4+) enrichment in a superficial layer with a thickness between 50 and 150 nm. In analogy to thin film technology a simplified model was developed and a free buckling length of ≈ 2.3 µm was estimated for the bloom surface, which is in reasonable agreement with the experimental finding. It was further shown that a sol-gel derived SiO2 coating of the bloom surface could enhance the optical transmission of the glass considerably.
- 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.
- ItemCorrosion modeling of simple glasses from the systems SiO2-Na2O-CaO and SiO2-Na2O-MgO(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Jiricka, Antonin; Helebrant, Ales; Hamackova, Jana; Heide, Gerhard; Frischat, Günther H.Static corrosion tests were conducted on two model glasses with the following composition (in mol%): 75 SiO2, 15 Na2O, 10 CaO and 75 SiO2, 15 Na2O, 10 MgO. The tests were performed in deionized water at 80 °C. Glass grains were combined with a monolithic sample in one reacdon vessel to achieve sufficient elemental release and to provide a monolithic sample for analysis. Vapor hydration tests (VHT) were performed on monolithic samples at 200 °C. Solution composition was analyzed with atomic absorption spectrometry (AAS), depth profiles of all elements in the surface layers of monolithic samples were analyzed with secondary neutral mass spectrometry (SNMS), and both monolithic and crushed samples were analyzed with scanning electron microscopy with energy dispersive spectrometry (SEM/EDS). Solution compositions and saturation indexes of secondary minerals were modeled with the geochemical code PHREEQC version 2.41 using LLNL database. The results showed that the sodium diffusion profiles in the surface layers of the glasses were established during the first few hours of the test. Both glasses showed that the dissolution rate depends on the chemical affinity for dissolution between the surface gel layer and the corrosion solution. Α glass alteration model based on transition state theory taking into account solution chemistry and precipitation of secondary alteration products is presented.
- ItemMid-infrared laser absorption spectroscopy for process and emission control in the glass melting industry : Part 1. Potentials(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Wondraczek, Lothar; Heide, Gerhard; Frischat, Günther Heinz; Khorsandi, Alireza; Willer, Ulrike; Schade, WolfgangLaser spectroscopic diagnostics of combustion species at elevated temperature has shown considerable progress during the last years and decades. Particularly, techniques of mid-infrared absorption spectroscopy using fundamental rotational/vibrational transitions offer potentially great sensitivity and selectivity for combustion control. However, applications are still limited to mostly laboratoryscale investigations, which is mainly due to drawbacks of light sources and beam guidance materials. On the other band, many efforts are made to facilitate industrial application. In this context, the relevance of mid-infrared absorption spectroscopy for in situ monitoring of minor species in glass melting furnaces is obvious, too. The present paper gives a general review of available techniques and their impact on emission diagnostics in the glass industry, considering conventional as well as emerging light sources, detectors, peripheral devices and spectroscopic techniques.
- 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.
- ItemSimulation of thermally induced stresses in glass-polymer composites(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Wondraczek, Lothar; Frischat, Günther Heinz; Heide, Gerhard; Weidenfeller, Bernd; Ziegmann, GerhardDue to differenees in thermal expansion, crazing and delamination effects are observed in multiphase materials such as glasspolymer composites. For a composite consisting of spherical particles homogeneously embedded in a matrix phase, the radial and tangential stresses occurring have been simulated. Two-dimensional calculations were used as a basis for optimizing the optical transparency of the material which was found to be strongly affected by the mechanical properties of the constituents of the composite and the resulting stresses. Further, the influence of the shape and the size distribution of the particles on the emergence of scattering surfaces inside the material is described. With the Christiansen-Shelyubskii method the maximum transparency of a potential material depending on whether it is a gradient material or not can be predicted.