Browsing by Author "Jahn, C"

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    Perovskite and tiranite crystallisation from titanosilcate melts
    (Institute of Materials Engineering, Australasia Ltd, 2004-11-29) Vance, ER; Begg, BD; Jahn, C
    On cooling alkali-calcia-titania-silica melts, both perovskite (CaTiO3) and titanite (CaTiSiO5) have been to observed to form [1-4]. Further work has now been carried out on two of these compositions (wt%): (a) SiO2 (48); Al2O3 (19); CaO (17); MgO (6); TiO2 (5); K2O (5) [1] and (b) SiO2 (53.0); Al2O3 (8.1); CaO (14.3); TiO2 (18.3); Na2O (6.6) [2,3]. For the former, it has been previously argued [1] that perovskite is preferred over titanite when fcc noble metal alloys are present, due to possible epitaxial relationships between the (010) and ((101) planes of perovskite and the (100) plane of the noble metal. The addition of simulated radioactive waste (which included noble metals) to the latter glass was argued previously [4] to affect the probabilities of titanite versus perovskite on cooling from the melt, but in the present work we are checking whether the presence of noble metals alone is the main determinant to encourage perovskite formation as against titanite (noting that the addition of rare earths in composition (b) can also promote perovskite crytallisation) . The amount of noble metal added was in the range of 0.1-1 wt%. Samples were prepared from mixed oxides and carbonates which were slurried with water to which the noble metals were added as soluble salts. After drying and calcining at 750oC in air, the mixtures were melted in alumina crucibles at ~1400oC and then cooled in the furnace or by pouring onto a metal plate. X-ray diffraction and scanning electron microscopy were carried out to characterise the materials. For melt (a), the omission of Ir from the starting preparation yielded diopside only on reheating glass for 1 hour at 1050oC, in contrast to results obtained previously [1] for the same composition when it contained 0.3 wt% of added Ir. The effect of Ag and Pd additions will also be reported. For melt (b) The effects of the inclusion of Pd and Ag in the starting composition will be measured