Browsing by Author "Matthai, Annegret"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Redox behaviour of polyvalent ions in phosphate glass melts and phosphate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Matthai, Annegret; Doris, Ehrt; Rüssel, Christian
    Glass melts and glasses with the basie composition NaPO₃ · 2Sr(PO₃)₂ doped with V₂O₅ and Fe₂O₃ were studied with the aid of square-wave voltammetry and spectroscopic methods. From the square-wave voltammetry in the glass melt, a linear dependence of the peak potentials on the temperature was obtained. The Standard enthalpy ΔH⁰, the Standard entropy ΔS⁰ and lg(C_ox/C_red) of the transitions Fe³⁺/Fe²⁺ and V⁴⁺/V³⁺ were calculated. The diffusion coefficients calculated from the peak currents measured follow Arrhenius' law. By means of electron spin resonance, the concentration of V⁴⁺ was determined. The corresponding extinction coefficients for the V⁴⁺ bands were calculated from the absorption spectra. Concerning the vanadium-containing glass, the results of square-wave voltammetry and spectroscopy were compared quantitatively. For the iron-doped glass, the comparison was only qualitative.
  • Thumbnail Image
    Item
    Thermodynamics 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, Christian
    A 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.
  • Thumbnail Image
    Item
    Voltammetric investigations of the redox behaviour of Fe, Ni, Co and Sn doped glass melts of AR® and BK7® type
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Matthai, Annegret; Ehrt, Doris; Rüssel, Christian
    The redox behaviour of iron, nickel, cobah, and tin ions was studied in glass melts with compositions near AR® and BK7® type by means of square-wave voltammetry (SWV). From the linear dependence of the peak potentials on the temperature, the standard enthalpies, ΔH°, and the standard entropies, ΔS° of the transitions Fe3+/Fe2+, Co2+/Co0, Ni2+/Ni0, Sn4+/Sn2+ and Sn2+/Sn0 were calculated. The reduced states are formed in the AR glass melt already at less reducing conditions than in the BK7 melt. The dependence of the redox ratios upon temperature is larger in the AR melt. As colouring ion Co2+ is more advantageous than Ni2+ because of its higher stability against reduction. It is possible to reduce the Fe3+/Fe2+ ratio without formation of Co0 in a disturbing concentration.