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- ItemUV-VIS spectroscopic investigations of amber glass at high temperatures(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Müller, Matthias; Rüssel, Christian; Claußen, OlafThe absorption spectra of iron-containing glasses and an amber glass were recorded in the temperature ränge of 25 to 700 °C. Α shift of the UV absorption edge towards lower wave numbers with increasing temperature was found. The amount of the shift depends on the Fe³⁺ concentration. Here, the UV absorption edge may superimpose or even cover up the absorption bands of colouring ions with increasing temperatures. For an amber glass sample, with increasing temperature, the intensity of the absorption bands of the amber chromophore decreases slightly. However, above 550 °C the decomposition of the chromophore is observed. All changes are reversible when temperature is decreased again. The decomposition of the chromophore and the attributed temperature ränge are in agreement with thermodynamic calculations.
- ItemQuantitative in-situ determination of iron in a soda-lime-silica glass melt with the aid of square-wave voltammetry(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Claußen, Olaf; Rüssel, ChristianSquare-wave voltammetric measurements are fairly convenient to determine thermodynamic data and diffusion coefficients o f polyvalent elements in glass melts. In principle, these methods also allow the quantitative in-situ determination of the total concentrations of polyvalent ions. For the in-situ determination of small quantities, however, improvements of the measuring and analyzing procedures were necessary This was achieved by approximating background currents using polynoms and describing Faradaic currents using theoretically derived equations. Simulations using least Square approximations then allow a much more detailed analysis of the current potential curve. Further improvements were possible by preelectrolyzing the melt at negative potentials and then shifting the potential to zero while recording the square-wave voltammogram. Using both procedures, a quantitative determination of iron concentrations as low a s 0.004 mol% Fe₂O₃ is possible.
- ItemVoltammetry in a sulfur and iron-containing soda-lime-silica glass melt(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Claußen, Olaf; Rüssel, ChristianWith the aid of square-wave voltammetry soda-lime-silica melts with sulfate fining were investigated in order to enable a quantitative in-situ determination of sulfur and iron. In this study, glass melts with low iron and high sulfate contents, typical for technical white glasses, were examined. The current-potential curves are predominantly influenced by sulfur and not solely controlled by diffusion. This behavior is supposedly caused by deposition of a sulfur layer on the surface of the working electrode. However, a simultaneous quantitative in-situ determination of iron and sulfur in melts of white glasses is possible.
- ItemThermodynamics of redox equilibria and diffusion of polyvalent ions in a phosphate glass melt(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Matthai, Annegret; Claußen, Olaf; Ehrt, Doris; Rüssel, ChristianΑ phosphate glass melt with the basie composition of NaPO₃ · 2Sr(PO₃)₂ doped with various oxides of polyvalent elements (Fe₂O₃, AS₂O₃, Sb₂O₃, CuO and SO₄²¯) was studied with the aid of Square-wave voltammetry. The Standard potentials depended linearly on temperature. The Standard enthalpy ΔH⁰ and the Standard entropy ΔS⁰ of the attributed redox reactions were calculated from the Standard potentials measured. The diffusion coefficients were determined from current densities obtained and fulfilled the Arrhenius' law. Both thermodynamics of the redox equilibria and diffusion coefficients are compared with those measured in soda-lime-silica glasses.