Browsing by Author "Blum, Friedrich"

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    A La-Nb-(Al) oxide porous glass-ceramic
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1982) Res, Miroslav A.; Blum, Friedrich; Bednarik, Jaroslav F.; White, Robert W.
    The substitution of the end-member oxides in the ternary sodium-borosilicate system diagram was studied. The replacement of SiO₂ with a combination of La₂O₃ and Nb₂O₅ was found to produce glasses and ceramics, which after heat treatment decomposed to form a leachable sodium-borate phase and an insoluble glass-ceramic phase. The mode of phase decomposition is sensitive to impurities and therefore crucible selection is of great importance, e.g., use of AI₂O₃ or Pt/Rh crucibles yield differences in pore size, surface area, chemical resistance and structure of the insoluble phase for a series of La₂O₃-Nb₂O₅ and La₂O₃-Nb₂O₅-AI₂O₃ glass-ceramics. These new materials have a specific surface area of up to 265 m²/g, a pore radius of between 0,5 and > 300 nm and an improved water resistance. Verre-céramique poreux La-Nb-(Al)-oxyde On a étudié la substitution du silicium-oxyde dans le diagramme du système sodium-borosilicate ternaire. Lorsqu'on a remplacé le SiO₂ par une combinaison de La₂O₃ et Nb₂O₅ se produisaient des verres et des céramiques qui, après le traitement thermique, ont décomposé en formant une phase sodium-borate résoluble et une phase verre-céramique insoluble. La nature de décomposition de la phase est sensible aux impurités: l'importance de la choix de creuset, par exemple AI₂O₃ ou Pt/Rh, se démontre par des différences en grandeur des pores, l'étendue de surface, la résistance chimique et la structure de la phase insoluble pour un série de verre-céramiques La₂O₃-Nb₂O₅ et La₂O₃-Nb₂O₅-AI₂O₃ Ces matériaux nouveaux ont une étendue de surface spécifique de jusqu'à 265 m²/g, un rayon de pore d'entre 0,5 et > 300 nm et une résistance à l'eau plus forte. Poröse La-Nb-(Al)-Oxid-Glaskeramik Der Ersatz der Endgliedoxide im ternären System Natrium-Borosilicat wurde untersucht. Der Ersatz von SiO₂ durch eine Kombination von La₂O₃ und Nb₂O₅ ermöglichte die Bildung von Gläsern und Keramiken, die sich nach einer Wärmebehandlung in eine auslaugbare Natriumborat- und eine unlösliche Glaskeramik-Phase zersetzten. Da Verunreinigungen die Art der Phasenumwandlung beeinflussen, kommt der Tiegelauswahl große Bedeutung zu, d. h. die Verwendung von AI₂O₃- oder Pt/Rh-Tiegeln führt zu Unterschieden in der Porengröße, der spezifischen Oberfläche, der chemischen Widerstandsfähigkeit und in der Struktur der unlöslichen Phase bei einer Reihe von La₂O₃-Nb₂O₅- und La₂O₃-Nb₂O₅-AI₂O₃-Glaskeramiken. Das neue Material hat eine spezifische Oberfläche bis zu 265m²/g, einen Porenradius zwischen 0,5 und > 300 nm und eine verbesserte Wasserbeständigkeit.
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    Microstructure of porous SiO2-Ta2O5-rich glass
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Schmid, Herbert K.; Res, Miloslav Α.; Blum, Friedrich; Schönberger, Hannelore D. H.
    Glasses composed of 60 wt% sodium borate and 40 wt% (SiO2 + Ta2O5) were melted, phase-separated by heat treatment and leached. The ratio SiO2 : Ta2O5 was varied between 4 : 1 and 1 : 14.7 (by wt). The microstructure of the glasses in the various stages of development was characterized by means of x-ray diffractometry and analytical electron microscopy. Substitution of SiO2 by Ta2O5 up to a ratio SiO2 : Ta2O5 = 1 : 5 (by wt) produced clear glasses whereas higher fractions of Ta2O5 produced opaque glasses which include a crystal-like phase. The specific surface area of the porous skeleton showed a strong dependence on composition in the leached state; a maximum of 352m2g-1 was measured for a composition with the ratio SiO2: Ta2O5 = 1 : 1. Transmission electron micrographs at high resolution show phase contrasts, indicating partial structural ordering in tantalum-rich, heat-treated and leached glasses, resembling lattice fringe Images of a crystalline structure. However, electron diffraction patterns show only one single and remarkably sharp diffraction ring, indicating a one-dimensionally ordered paracrystalline state of aggregation for the insoluble phase. This observation is in contradiction with existing models of glass structures. The presence of sodium in the porous insoluble skeleton with approximate composition Na2Ta6O15Si2 is confirmed by combined EDS and EELS analyses. The development of a fully ordered crystalline phase was monitored by means of a high-temperature x-ray camera; tetragonal crystal symmetry is proposed for this phase.