Browsing by Author "Durán, Alicia"

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    Alumina and zirconia as inhibitors of crystallization during sintering of borosilicate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Pascual, M. Jesus; Pascual, Luis; Durán, Alicia; Wange, Peter; Rüssel, Christian
    The glass composition (in mol%) 16 Na2O ∙ 24 B2O3 ∙ 60 SiO2 has suitable viscosity and dilatometric properties to be used as sealing material for the gas manifolds of molten carbonate fuel cells (MCFC). Nevertheless, quartz crystallization takes place during sintering of the borosilicate glass powder at temperatures between 600 and 700 °C. The quartz crystallization leads to the formation of pores and a variation in the thermal expansion coefficient; both giving rise to defects and tensions in the seal. In this work, the possibility of inhibition of quartz crystallization by substituting AI2O3 or ZrO2 for 2 or 5 mol% of SiO2 is described. The thermal properties and the viscosity-temperature curve of the new compositions, especially those containing alumina do not differ much from the original glass.
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    Phase separation and crystallization of glasses in the system R2O-B2O3-SiO2 with R = Li, K, Na - Influence on thermal properties
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2002) Pascual, M. Jesus; Pascual, Luis; Durán, Alicia
    The dilatometric properties (α, ϑ, Tg) and viscosity of glasses within the systems Li2O-K2O-B2O3-SiO2 and Na2O-B2O3-SiO2 with constant ratios B2O3/R2O =1.5 and 1 (in mol%) were characterized. These compositions have suitable thermal properties to be used as sealants for molten carbonate fuel cells (MCFC). The changes in dilatometric properties and viscosity due to phase separation and crystallization processes were measured along the different stages of a thermal treatment simulating the startup and working conditions of the MCFC. Thus, the thermal and mechanical behaviour of the studied glasses can be evaluated for the whole thermal cycle of the cell. Transmission electron microscopy (TEM) was used to analyse the development of microstructure during the thermal treatment and X-ray diffraction (XRD) to determine the appearing crystalline phases.
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    Preparation and properties of nitrided phosphate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Pascual, Luis; Durán, Alicia
    Nitrided phosphate glasses with the composition (in mol%) of 25 R2O ∙ 20 BaO ∙ 3 Al2O3 ∙ 52 P2O5 (R = lithium, sodium, potassium) have been prepared by remelting at 650 to 800 °C in a flowing dry ammonia atmosphere. The chemical durability of the glasses increases strongly with the nitrogen addition, as well as the glass transition and dilatometric softening temperatures and microhardness; whereas the thermal expansion coefficient diminishes with rising nitrogen contents. The kinetics of nitridation and the structural changes produced by nitrogen incorporation are also studied in these glasses.