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- 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.
- 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.
- 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.
- 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.
- ItemCorrosion of granulated glassy blast furnace slags in aqueous solutions(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Olbrich, Eva; Frischat, Günther HeinzStructure and reactivity of several commercial and laboratory granulated glassy blast furnace slags were investigated. From the compositions NBO/T was calculated, the number of nonbridging oxygens per tetrahedron. Electron spin resonance spectrometry answered questions regarding the coordination numbers of the ions Mn2+ (Mg2+) and Ti3+. Both the hydrolytic reactivity of the slag glasses in water and their corrosion mechanisms in 0.1 mol/1 KOH model pore solution were studied. Scanning electron and atomic force microscopy showed the development of gel-like phases on the slag grains. Although distinct features could be resolved already, only the nanoscale in-depth profiles obtained by secondary neutral mass spectrometry helped to enlighten the complex reaction sequences. Thus, for example, it could be shown that first Mg2+ -rich gel phases developed by the corrosion process, however, after some hours the leach solutions became supersaturated successively with the consequence of forming a secondary calciumsilicate hydrate phase by a redeposition process. This phase showed a tobermorite-like structure. AI2O3- and TiO2-rich blast furnace slags were more stable than the CaO-rich materials and they also displayed reaction mechanisms at least partly dissimilar to the just mentioned.
- 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.
- 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.
- ItemPreparation and characterization of Na2O-Al2O3-B2O3 sol-gel glasses with aluminum lactate and formiate as precursors(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Hoyer, Lars P.; Helsch, Gundula; Frischat, Günther Heinz; Zhang, Long; Eckert, HellmutIn this work aluminum lactate and aluminum formiate have been used as precursors to obtain room temperature stable sols and gels and after annealing homogeneous glasses in the System Na2O-Al2O3-B2O3. The local environments and connectivities of boron and aluminum have been investigated by 11B and 27Al solid-state nuclear magnetic resonance (NMR). It was found that the local atomic structures of the sol-gel glasses markedly depend on the precursors and the preparation routes and are also dissimilar to those of melt quenched glasses of the same compositions. Thus, for example, the fractions of BO3/2 and BO4/2 units differ and it is interesting to note that there are no asymmetric ΒO2/2(O-) units present in the sol-gel materials. The 27Al spectra show AI in four-, five- and sixfold coordination, whose relative abundance in a given glass composition is also dependent on the preparadon route. Rotational echo double resonance (REDOR) 11B {27Al} and 27Al {11B} resuhs indicate that the extent of B-O-Al connectivity is diminished in the gel prepared glasses when compared to the melt cooled glasses. Element distributions are reported on the basis of secondary neutral mass spectrometry (SNMS) data, and the nanostructures of surfaces have been characterized by atomic force microscopy (AFM).