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- ItemPreparation of coloured silica glasses made by sintering of particulate gels(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Clasen, RolfLarge pieces of silica glass can be easily made by sintering particulate gels prepared from fumed silica powders. These compacts can be doped by soaking with alcoholic solutions of salts of a large variety of colouring ions of the transition and rare earth elements. As the sintering of the compacts in a zone furnace with a silica glass tube inside is not restricted with respect to the atmospheres, higher states of valence of the dopants with additional colours can be achieved under oxidizing conditions in contrast to the conventional melting of silica glass in crucibles of molybdenum or tungsten which have to be operated under reducing conditions. In reducing sintering atmospheres red copper and gold ruby glasses can be prepared. Therefore, it is favourable to prepare compacts with smaller particles which show also smaller pores.The mechanism of the formation of the colloidal metal particles is not yet clear and needs further investigations.
- ItemExperimental measurements of the phonic diffusivity of semitransparent materials up to 800 K(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) André, Stéphane; Degiovanni, AlainA new flash equipment has been developed which enables the true thermal diffusivity of semitransparent materials to be measured in the temperature range from 300 to 800 K. A theoretical study of the coupled conduction-radiation mechanism of transient heat transfer that occurs in a plate sample during a flash experiment has proved that, with the heat pulse method, it is possible to experimentally determine the diffusivity of phonic origin, that is the diffusivity defined with the true conductivity of Fourier's law. The originality of this method over others is due to the fact that any calculations of the radiative contribution to heat transfer are unnecessary: The phonic diffusivity (conductivity) is directly extracted from the measured parameter in an identification process for opaque materials. Experimental results on various semitransparent materials are presented and discussed in relation with data available in the literature. For vitreous silica it is shown that the temperature dependence of the phonic conductivity is not linear, but similar to the variation of the specific heat content.
- ItemSensor for oxygen activity measurements in glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Müller-Simon, Hayo; Mergler, Kurt W.Traditional oxygen activity measurement in glass melts is based on Y2O3-stabilized ZrO2 which, in continuous use in the glassworks, is subjected to considerable wear. The present paper describes an oxygen sensor that is not equipped with wear parts. The new sensor is far less sensitive to temperature gradients in the surrounding area than ZrO2 sensors; the oxygen measurement, however, is greatly disturbed at direct flame irradiation.
- ItemIron oxide-doped alkali-lime-silica glasses Part 2. Voltammetric studies(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Rüssel, ChristianAlkali-lime-silica glass melts doped with different quantities of Fe2O3 in the range of 0.1 to 2 mol% were studied by means of square-wave voltammetry. At low iron concentrations a one-step reduction of Fe^III to Fe^II was observed. The shift of the standard potential with the alkali concentration is explained using a structural model where FeIII occurs as a tetrahedrally coordinated complex which forms an ion pair with an alkali cation. At higher Fe2O3 quantities a two-step reduction was observed. This means that FeIII-containing compounds occur as two thermodynamically different species. In agreement with the EPR-spectroscopic behaviour, this was explained by the formation of iron-containing clusters.
- ItemContribution to comparability of in-vitro and in-vivo man-made mineral fibre (MMMF) durability experiments(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Förster, Hansgeorg; Tiesler, HartmutToxicologists discuss three major conditions which must be met in order to prevent adverse health effects of dust with regard to three necessary fibre properties: the fibre has to be thin, long, and durable. First definitions concerning the geometric properties thin and long were made already in 1972; however, the criterion durability has not yet been defined. The durability of man-made siliceous fibres has been tested with experimental animals (in-vivo) as well as with purely chemical methods (in-vitro). A reaction of first order was deduced from in-vivo experiments. On the other hand, in-vitro experiments in different setups proved all to follow zeroth-order kinetics. From that, it was postulated sometimes that in-vitro experiments are unsuited to determine the persistence of man-made siliceous fibres. The present study will show that correct mathematical treatment of in-vivo data leads to the same results as obtained from in-vitro experiments. The lg-normal distribution in fine fibrous dust is responsible for the seemingly first-order pattern for mass and fibre number. If the time intervals are chosen to be rather long - as in published in-vivo studies - it is impossible to demonstrate the deviation from the dissolution process at the beginning and at the end. This means the solution of the apparent discrepancy between in-vivo and in-vitro experiments. The mathematical model allows to estimate the lifetime of inhaled fibrous particles from known dissolution velocity and fibre size distribution for the worst case, since the chemical process of dissolution of siliceous fibres is superimposed by accelerating effects as fragmentation or clearance. The validity of the model is shown by comparison with data from an inhalation study [1 to 3]. Also, the model allows the calculation of the accumulated fibre number from dose and duration of exposure.
- ItemDevelopment of an ultrasonic method to determine the residual thickness of refractory blocks(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Fleischmann, Bernhard; Faber, Anne J.; Breeuwer, RenéAn ultrasonic method was developed to measure the residual thickness of refractory blocks at an operating glass melting furnace. This ultrasonic measuring method was used to determine the thickness of zirconia-based refractories on a small laboratory glass melting furnace. Two ultrasonic transducers with a silica delay and a coupling media were used to measure the transition time, that the ultrasonic signal needs with the applied echo method. The results of the thickness measurements at cold and hot refractory blocks were compared. The investigations prove the possibility to employ the ultrasonic device for determining the residual thickness of refractory blocks.
- ItemMolecular dynamics of the oxynitride glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Macháček, J.; Liška, M.; Gedeon, O.Parameterisations of pair-potential functions were developed by means of ab-initio energy hyper-surface mapping of AI₂O₃, SiO₂*Si₃N₄, and AIN crystals. Molecular dynamics simulation was then performed for the 19.1Si₃N₄*80.9Al₂O₃ melt. The poor glass forming ability was confirmed by the phase separation, observed in simulated structure.
- ItemReactions and Interactions between Tank Refractory and Glass Melt(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Beerkens, Ruud; van Dijk, Frans; Dunkl, MichaelThis presentation gives an overview and summary of the present knowledge on refractory-glass melt interaction phenomena. Different mechanisms, governing the wear of the refractory materials applied in glass melting tanks are presented. The interaction between the glass melts and refractory materials, leading to glass faults such as bubbles and knots are shortly discussed and some examples are given. Mass transfer processes, mainly diffusion of refractory components in to the glassmelt, determine the kinetics of refractory dissolution in the glass melt. The formation of a protective high viscous reaction-product layer between the refractory and the melt acts as a diffusion barrier. However, some refractory types in contact with a molten glass hardly show the formation of such aboundary layer: As far as solubility concentrations of refractory components in molten glasses are low, the refractory dissolution rate will be low, but then a highly viscous boundary layer will hardly be present. The stability and thickness of the protective boundary layer is determined by local convection flows caused by density differences in the melt, by external forces or caused by surface tension gradients. The process parameters, which govern the mass transfer processes and boundary layer thickness levels will be presented and some measures to reduce refractory wear will be given. The boundary layer, containing the viscous reaction product of the interaction between the melt and refractory material, can lead to glass faults such as cords, ream, cat scratches or knots. Refractory materials with a very low solubility in the molten glass can be applied to avoid the formation of the viscous boundary layers, lowering the potential for glass faults. However, the absence of a high viscous boundary layer may lead to increased diffusion rates and may cause an increased dissolution of the refractory. Α boundary layer containing a high concentration of dissolved aluminium oxide will decrease the solubility of zirconium oxide. Therefore Al₂O₃-ZrO₂ based refractory materials show a high resistance against ZrO₂ dissolution in glass melts. During the casting procedure of the refractory, the zirconia phase will crystallize into a strong structure, subsequently the alumina crystals and glassy (silicate) phase will fill the pores and voids. The glass phase contains alkali oxides in order to avoid formation of mullite phases from this phase. Bubbles can be formed in the boundary layer or in the silicate phase of a refractory material, due to electrochemical processes. These bubbles detach frequently from the refractory material, often pushing a small part of the highly viscous Silicate phase or refractory grains from there fractory into the glass melt. This mechanism will also influence the glass fault potential (bubbles, highviscous knots and stones) of refractory materials.
- ItemOptical Structuring by Laser Induced Formation of Metallic Nanoparticles(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Rainer, T.; Berg, K.-J.; Berg, G.[no abstract available]
- ItemThree-dimensional optical data communication in glass(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Jahns, Jürgen; Gruber, Matthias; Jarczynski, ManfredFor data communication over long and medium distances, optical transmission based on silica optical fiber has become the dominant technology over the past decade. For short and very short distances (on the order of meters down to millimeters), however, physical advantages of optical communications have for a long time been offset until now by technological problems. However, as the communications bottleneck in computers turns into a ser ious limitation of the processing capabilities, optical interconnection technology becomes an Interesting alternative to electrical wires. Unlike electrical signals, light beams do not suffer from electromagnetic interference and signal-frequency dependent attenuation. Both, waveguide-optical and free-space optical solutions are being considered. Freespace optics offers the chance to use the third dimension, thereby solving one of the major limitations of a 2 D wiring technology. In order to tap the potential of freespace optics for data communications inside a computer, suitable Integration techniques need to be developed. Here, we present a specific approach, calied „planar integrated free-space optics" (PIFSO). It is based on the use of lithographic fabrication in glass to build miniaturized optical systems. The fabrication approach is suitable for batch processing in a similar fashion as electronic chips are fabricated. In combination with suitable hybrid Integration techniques, the PIFSO-concept Is a viable approach to the practical realization of an optoelectronic systems technology. Here. we describe the concept of planar integrated free-space optics and describe some of the demonstration experiments for optical Interconnection.