The crystal-growth process and growth conditions of β-alumina (Na2O · Al2O3) were investigated using the Na2B4O7-Na3AlF6 flux method. β-Alumina (electric fusion brick) was used as both nutrient and seed. Weight loss of the flux varied widely for various runs: ≅ 10 wt% of flux evaporated at 100 h, ≅ 17 wt% at 150 h, and 43 wt% at 600 h. When β-alumina crystal was grown, only 20 wt% Na2B4O7 was added to the Na3AlF6 flux. The linear growth rates of the β-alumina single crystal grown by an Na3AlF6-20 wt% Na2B4O7 flux method at 1040°C and Δ t = 18°C were ≅ 1.0 × 10−3 mm/h ( a face) and ≅0.3 × 10−3 mm/h ( c face). The β-alumina single crystals grown were bounded by only c [001] and a [100] and were colorless and transparent. 相似文献
A multiple sequence alignment algorithm is described that usesa dynamic programming-based pattern construction method to aligna set of homologous sequences based on their common patternof conserved sequence elements. This pattern-induced multi-sequencealignment (PUMA) algorithm can employ secondary-structure dependentgap penalties for use in comparative modelling of new sequenceswhen the three-dimensional structure of one or more membersof the same family is known. We show that the use of secondarystructure information can significantly improve the accuracyof aligning structure boundaries in a set of homologous sequenceseven when the structure of only one member of the family isknown 相似文献
Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.
Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air. 相似文献