Browsing by Author "Höhne, Diethard"
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- ItemEquilibrium constant - determination and influence on redox reactions in soda-lime-silica glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Ortmann, Lars; Höhne, Diethard; Nölle, GüntherThe iron, arsenic and chromium redox equilibrium in an oxide glass-forming melt has been studied quantitatively The equilibrium constant K(T) and the thermodynamic Standard values were determined for the redox reaction in the melt at temperatures between 1000 and 1450 °C. These values were compared with values from the literature. The equilibrium constant is dependent on the temperature and on the concentration of the polyvalent elements. This dependence applies to the polyvalent elements investigated. For each polyvalent element it is possible to find a step in the funcdon lg([R^y]/[R^x) versus R_aO_b- This seems to be explained by the concentradon dependence of the equilibrium constant of the redox reaction. Possibilities to determine the equilibrium constants of the various polyvalent elements are described.
- ItemInfluence of Al2O3, ZrO2 and TiO2 on the properties of the microporous glasses from the system Na2O-B2O3-SiO2(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Procyk, Bernadeta; Dorosz, Dominik; Bieniarz, Piotr; Zawada, Anna; Höhne, DiethardGlasses from the Na2o-B2O3-SiO2 system, doped with AI2O3, ZrO2 and TiO2, were thermally (in the temperature range of 420 to 700 °C) and chemieally treated. During thermal treatment, separation of the borate phase from the silica skeleton occurrred resulting in the formation of an interconnected microstructure. The borates were in the form of small drops joined to each other. In the course of chemical treatment the borates were leached in water and water solutions of acids or bases with the glass becoming very porous. The experiments showed that ZrO2 and TiO2 caused an increase in pore diameter at defmite leaching times. AI2O3, however, decreased it, so that glasses doped with AI2O3 have a greater specific surface. In this case a double-pore distribution occurred. Porous glasses may find application in many branches of science and engineering. The applications depend on the internal arrangement, size and shape of pores. These parameters may be in a wide range modified by a change of the chemical composition. Testing structure and properties of microporous glasses from the system Na2O-B2O3-SiO2 with different additions was the main aim of this work. The following testing methods were applied: DTA, XRD, TEM, infrared spectroscopy and sorption porosimetry.
- ItemInfluence of redox equilibrium on the properties of glasses with a high iron concentration(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Zawada, Anna; Hessenkemper, Heiko; Höhne, Diethard; Bieniarz, PiotrIn glasses of the System Na2O-CaO-SiO2-Fe2O3, Fe2+ and Fe3+ ions were found by Mössbauer spectroscopy. In samples melted in oxidizing atmosphere, both ions occurred in tetrahedral coordination, whereas they occurred in coordination number 6 in samples with high iron content and melted under reducing conditions. It is shown that a total iron concentration has a stronger influence on the glass properties than the redox state. Differences in the properties of glasses melted in oxidizing and reducing atmosphere, respectively, were observed at lower temperatures, while at higher temperatures they are very small (however, the tendency is still maintained). Density, microhardness, transition temperature and thermal expansion coefficient of the glasses studied are affected by the changes in redox equilibrium. One can conclude that after reducing treatment iron ions present in the glass structure play a similar role as a network modifier. At higher temperatures, this kind of activity is very weak, according to viscosity and liquidus temperature measurements.
- ItemMeasurement and mathematical modelling of the heat transfer in the glass forming process, in consideration of the heat transfer coefficients and radiation influences(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Höhne, Diethard; Pitschel, Bettina; Merkwitz, Markus; Löbig, RicoDuring forming, glass to mould contact temperatures are the significant factor for the final glass surface quality. For a good characterization of this contact condition the heat transfer by conduction and radiation needs to be described in detail. Α laboratory testing unit was set up to investigate the influence of radiation emitted by different glass composidons and the influence of different mould materials used during forming. To support the experimental results, heat transfer conditions and temperatures were modelled at given boundary conditions using the CFD-Code FLUENT software program applying discrete models. Measurement and modelling results show that the radiation influence on heat transfer is strongly dependent on the spectral absorption coefficient of the glass which affects heat flux densities and surface temperatures. Results show up to 15 % higher heat flux density for amber glass compared to flint glass. In addition, internal glass temperature distributions are strongly affected. If glass throughput, type of forming tools and mould cooling settings are carefully adapted to the optical characteristics of the glass, an optimal surface quality and physical strength can be achieved, which may lead to significant economic benefits. Due to the complex interactions of the parameters which influence glass to mould heat transfer mathematical modelling proves to be essential for future developments in forming technology.
- ItemModeling of the bubble population in glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Roi, Torsten; Seidel, Olaf; Nölle, Günther; Höhne, DiethardPrevious studies of refining models have mostly dealt with the mathematical description of the behavior of individual bubbles in glass melts. A further step was the modeling of the ascent and growth of groups of bubbles, including restrictions with respect to the spatial distribution of the individual bubbles. Even though no algorithm was derived in this stage which described the total bubble balance during refining, these investigations have produced important results in the field of bubble growth and ascent. In this study, a general and comprehensive mathematical description of the bubble population during refining shall be given, on the basis of the population balance equation used in chemical engineering. The general balance equation for bubbles during refining is presented together with the corresponding computer model. Several experimental investigations into bubble size distribution are described, together with an analysis of the reduction of the bubble concentration in the pot. The obtained values were used as initial parameters and estimates in computer simulations. Some special results of modeling are shown and discussed.
- ItemProcessing of molten solid residues(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Bieniarz, Piotr; Höhne, Diethard; Hessenkemper, Heiko; Zawada, AnnaAn alternative way of recovery, recycling and re-integration of solid wastes on a laboratory scale is demonstrated. The analysed synthetic slags belong to the System SiO2-Al2O3-CaO-MgO-Fe2O3-K2O-Na2O. Α polynomial model has been developed by means of a computing program in order to calculate some important technological features directly from a variable oxide concentration and to determine a processable composition. Furthermore, a concept of maximum application of the residues is suggested for slags from waste incineration and other industrial processes with relative low volatile components. Rolling has been chosen as the most suitable forming technique, because recycling melts show a short forming interval and an aggressive behaviour towards refractory materials. It is possible to form plates or tiles which afterwards can additionally be shaped e.g. to create profiles or breaking points. Because of their affmity to crystallization the glassy end-products can be devitrified at the surface (into semicrystalline products, i.e. glass-ceramics) to receive a better resistance. The present results show the possibility of using well known forming and treating processes to make high value products from low-value by-products, with a considerable economical advantage.