Browsing by Author "Rudolph, Thomas"

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    Electrochemical study on the corrosion of molybdenum electrodes in lead glass melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Rudolph, Thomas; Balazs, G. Bryan; Rüssel, Christian; Tomandl, Gerhard
    The corrosion of molybdenum in lead glass melts is a two step process. In the cathodic part of the ac heating cycle lead ions of the glass melt are reduced to metallic lead. During the anodic part molybdenum is oxidized. Cyclic voltammetry revealed Mo3+ ions as the intermediate state in the oxidation process. During corrosion experiments a porous layer of Mo(VI) Compounds and MoO2 were detected. A drastic reduction of the corrosion rate was obtained when a small anodic dc potential was superimposed on the ac heating current. Slow voltammetric scans showed passivation of the molybdenum at potentials higher than -300 mV. The protection layer consists most likely of molten K2Pb(MoO4)2.
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    Microstructural development of a P2O5-modified cordierite glass ceramic during sintering Part 1. Microscopic characterization
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Rudolph, Thomas; Szabó, Dorothée V.; Pannhorst, Wolfgang; Weisskopf, Karl-L.; Petzow, Günter
    The crystallization sequence of a P2O5-modified cordierite glass was investigated using conventional and analytical transmission electron microscopy, as well as transmission optical microscopy. The experiments show surface nucleation for both bulk and powdered glass specimens. The crystallization process leads to a preferred orientation of high-cordierite crystals via a metastable high-quartz solid solution. The hexagonal crystal lamellaes grow with their c axis perpendicular to the surface. A distinct dependence of the cordierite lamellae size on the crystallization temperature is observed. The residual glassy phase between the cordierite lamellae develops via a phase-separation process into a SiO2-rich amorphous phase and a polycrystalline matrix with magnesium orthophosphate as the major phase.
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    Microstructural development of a P2O5-modified cordierite glass ceramic during sintering Part 2. Densification experiments
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Rudolph, Thomas; Weisskopf, Karl-L.; Pannhorst, Wolfgang; Petzow, Günter
    The non-isothermal sintering of a P2O5-modified cordierite glass powder was investigated using sintering dilatometry, DTA and x-ray diffractometry. A typical densification curve as obtained by dilatometry with a constant heating rate is discussed. To clarify the dependence of the final degree of porosity on the heating rate additional porosity measurements were carried out on selected specimens using a stereological image processing system. The porosity exhibits a distinct minimum for a heating rate of 15 K/min. This effect is discussed based on a variation of the effective sintering interval which ranges from Tg of the glass to the onset temperature of crystallization. Together with the crystallization behaviour, as given in part 1 of this paper, a schematic description of the microstructural development is presented.