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- ItemVoltammetric sensor for glass tanks(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Zink, Marianne; Rüssel, Christian; Müller-Simon, Hayo; Mergler, Kurt WilhelmVoltammetric methods formerly solely applied to laboratory experiments were used for measurements in a green glass tank. The applied experimental parameters had to be restricted to step times of 20 ms or more using square-wave voltammetry and frequencies of 35 s^-1 or lower using alternating current voltammetry. Within these limitations, the voltammetric sensor used was fairly suitable for these measurements. The adjustment of the electrode area, i.e. the dip-in length of the electrodes, could easily be controlled by conductivity measurements between the electrodes. The obtained voltammetric curves were fairly similar to those obtained from laboratory experiments and were predominantly affected by the iron concentration of the glass melt.
- ItemVoltammetric studies in a soda-lime-silica glass melt containing two different polyvalent ions(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1990) Rüssel, Christian; Freude, EberhardBy the aid of electrochemical methods, a quantitative determination of polyvalent ions in glass melts is possible. This paper investigates the square-wave voltammetry in soda-lime-silica glass melts doped with iron and additionally with arsenic or antimony. In principle, a simultaneous, quantitative determination of these elements is possible, but the experimental parameters should be chosen with care and the recorded current-potential curves should be carefully analyzed.
- ItemInteraction between oxygen activity of Fe2O3 doped soda-lime-silica glass melts and physically dissolved oxygen(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Rüssel, Christian; Kohl, Reiner; Schaeffer, Helmut Α.The oxidation state of molten soda-lime-silica glass was studied by an electrochemical oxygen-sensor, based on an yttria-stabilized zirconia solid electrolyte. It is shown that the iron concentration of the glass melt influences the extent of oxygen activity variation during cooling. If the iron concentration is 0.2 mol% Fe2O3 or less, the redox ratio [Fe3+]/[Fe2+] cannot be assumed to be independent of temperature because the redox equilibrium is shifted by the reactivity of physically dissolved oxygen.
- ItemVoltammetric investigations in Na2SO4-refined soda-lime-silica glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1990) Kordon, Thomas; Rüssel, Christian; Freude, EberhardThe redox behavior of sulfate-refined soda-lime-silica glass melts was investigated by the aid of voltammetric methods. Here the possibilities for a quantitative in-situ determination of sulfur and iron are predominatly treated. Measurements in technical glass melts show that a determination of iron in melts with low sulfate and high iron concentration such as amber brown or green glass melts is easily possible. In contrast, there are problems at glass melts with low iron and high sulfate concentrations, because the current-potential curves are predominantly affected by sulfur compounds.
- 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.
- ItemVoltammetric methods for determining polyvalent ions in glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Freude, Eberhard; Rüssel, ChristianVoltammetry is an in situ technique to investigate redox equilibria in glass melts. Its sensitivity and resolution have been improved by introducing the square-wave voltammetry. The results reported in this paper clearly demonstrate the superiority of this method over the cyclic voltammetry, which had been used so far in glass melts.
- ItemIron in glass melts - A voltammetric investigation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1990) Freude, Eberhard; Rüssel, ChristianBy the aid of square-wave voltammetry, a fast potentiostatic pulse method, iron oxide-doped soda-lime-silica glass melts were investigated. The iron concentration (0.1 to 2 mol% Fe2O3) and the temperature (400 to 1300 °C) were varied in a wide range. At low iron concentrations as well as at high temperatures the reduction of the Fe3+ to the Fe2+ ion is a one-step process, while at high iron concentrations and at relatively low temperatures a two-step process is observed. By comparison with thermodynamic data of solid state iron oxides, especially of Fe3O4, it is assumed that this is due to the formation of aggregated species containing Fe3+ as well as Fe2+ ions.
- ItemIron oxide-doped alkali-lime-silica glasses Part 1. EPR investigations(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Rüssel, ChristianAlkali-lime-silica glasses containing iron oxide in a concentration range of 0.1 to 2 mol% were studied by means of EPR spectroscopy. In all glasses, two paramagnetic signals at g = 2.0 and g = 4.3 were obtained. Their intensity strongly depended on the quantity of iron oxide doping and on the type but not on the quantity of alkali. In agreement with experimental results from the literature, the peak at g = 4.3 was attributed to tetrahedrally coordinated Fe^III in C2v symmetry, assuming an alkali ion being coordinated with two oxygens of the tetrahedron. The peak at g = 2.0 was attributed to the occurrence of clusters containing more than two iron atoms.
- ItemRedox reactions in Fe2O3, As2O5 and Μn2O3 doped soda-lime-silica glasses during cooling - A high-temperature ESR investigation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Gravanis, Georgios; Rüssel, ChristianRedox equilibria in glass melts and in solid glasses, containing more than one type of polyvalent element, may shift during cooling. This was investigated by the aid of ESR spectroscopy in the temperature range from 25 to 680 °C in glasses, containing iron oxide and additionally arsenic or manganese oxides. The equilibrium was frozen in at temperatures below 400 °C. Above this temperature, redox equilibria are established again and no kinetic hindrance is visible. This is in good agreement with the results from theoretical treatments.
- ItemCorrosion of molybdenum electrodes in an aluminosilicate glass melt(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Holzwarth, Stefan; Rüssel, Christian; Tomandl, GerhardThe corrosion of molybdenum electrodes in an aluminosilicate melt was studied with the aid of electrochemical methods at temperatures up to 1600 °C. The glass melt investigated contained polyvalent ions which enabled redox reactions with the electrode material. A layer of molybdenum oxide is formed on the electrode in contact with the glass melt. The layer partially dissolves in the glass melt and eventually evaporates into the furnace atmosphere. Dissolution of the oxide layer is assumed to be the step which determines the rate of the corrosion process.