Structure investigation results for MASHS powder Fe40Al/Al2O3 are presented. The
powder structure formation proceeds via two stages. On the first step (mechanical activation)
aluminothermal reaction takes plays in the system Fe+Al+Fe2O3, leading to formation of
nanocomposite precursor Fe-Al-Al2O3. On the second step (SHS), iron and aluminum reacts,
forming intermetallic FeAl. As-synthesized composite powder completely inherits the precursor
structural morphology in spite of the phase transformations taking place during the production
process. Such a production route provides the formation of intergrowth nanocomposite material
structure with improved interfacial strength.
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Solid state reactions taking place dming formation of differently substituted Yttrium-Iron Garnets (YIG) from the corresponding oxides were studied with high temperature X-ray powder diffraction method up to 1400°C. The measurements were carried out in a newly developed high temperature chamber PMP1600 which provided good temperature uniformity in the sample, and reduced the recrystallization caused grain size effects by spinning the samples of compacted pellets. Reaction kinetic studies were based on Rietveld refinements of ,.in situ" high temperature diffraction patterns. Different diffusion processes and thern1ochemi-cal reactions could be observed. The phase compositions at different temperatures were determined with standardless quantitative analysis, the substitution rates were concluded from both refinement of the site occupancy factors and unit cell volume changes, subtracting thermal expansions. In this way the distiibution of all cations in the numermis phases (stm1ing oxides, intermediate phases and end-products) could reasonably be tr·aced on. The reaction paths were observed to be distinctly different when samples presintered at lower temperatures were ground. The influence of the substituents on the reaction kinetics was clmi±]ed in systems with compositions con·e-sponding to gmnets Y3Fe2-xlnxFe3012. m1d Y3-xCaxFe2-xZrxFe3012 in the rm1ge x=O to 1.0 for In, m1d x=O to 2.0 for the Zr,Ca substitution resp. Zr was found to be able to substitute Fe of octahedral coordination completely, but no In substitution could be reached for x 1. The angulm· dependencies of peak broadenings have special composition dependent behaviours: GaJTiets with Zr,Ca substitution close to x=O, 1 and 2 gave shmp reflections also at high 2 8 angles, while those with substitution rates in between showed reflections highly broadening with 28 angles. An attempt was made to explain these peculimities with the phenomenon of paracrystallinity [1]. The kinetic aspect of muscovite hydroxylation in a softened glass medium is of piimmy importance in the formation of optimal technological conditions of production of mica-glass compositions. Kinetic studies of the phases formed in the process of muscovite-glass sintering were cmTied out by x-ray diffraction and UV spectroscopy. Heating of the mica-glass composition leads to the dehydroxylation of muscovite with the release of moleculm water and the formation of sanidine and sillimanite. The rate of dehydroxylation and formation of these phases depends on muscovite size, glass composition, and temperature. The dehydroxylation of muscovite occurs at a temperature 'lower than that of the formation of sanidine and sillimanite, especially, in the presence of glass. Therefore, their appemance in the sintering products at-1100 K should be considered as a result of the interaction of the glass with mica dehydroxylate rather than with the initial mica. The dehydroxylate formed seems to be a supersaturated solid solution relative to sanidine and aluminum oxide isolated as independent phases. Alumin...
Композиты на основе сверхвысокомолекулярного полиэтилена, модифицированные наночастицами карбида бора B 4 C и композита B 4 C/W, для материалов защиты от быстрых и медленных (тепловых) нейтронов и γ-излучения сформированы методом механохимического синтеза в высокоэнергетических планетарных шаровых мельницах. Фазовый состав и микроструктурные характеристики композитов изучены методами рентгенографического фазового анализа (дифрактометр D8 Advance, Bruker), электронной микроскопии (сканирующий электронный микроскоп CamScan 4) и инфракрасной Фурье-спектроскопии (Фурье-спектрометр Nikolet iS10). Совместная механическая обработка в планетарной мельнице порошков сверхвысокомолекулярного полиэтилена и карбида бора В 4 С приводит к формированию полимерных композиционных частиц чешуйчатой формы с хаотичным распределением в них частиц карбида бора и равномерным распределением нанокристаллического железа в матрице полимера (~ 9 масс. %). Кроме того, формируется структура карбида бора с меньшим содержанием углерода (В 6.5 С), а также происходит разрыв молекулярных цепочек полиэтилена и его аморфизация. Совместная обработка в планетарной мельнице сверхвысокомолекулярного полиэтилена и механокомпозита B 4 C/W приводит к формированию полимерных композиционных частиц чешуйчатой формы с равномерным распределением в полимерной матрице частиц карбида бора и вольфрама. Изменяются параметры тонкой структуры карбида бора B 4 C. В результате взаимодействия полимерной матрицы и дисперсных порошков модификатора происходит образование поперечно сшитых структур и деструкция полимера с уменьшением его молекулярной массы. Ключевые слова: механохимические реакции, сверхвысокомолекулярный полиэтилен, карбид бора B 4 C, композит B 4 C/W, рентгенографический фазовый анализ, электронная микроскопия, инфракрасная Фурье-спектроскопия. Введение На космических летательных аппаратах с ядерными энергетическими установками должны выполняться требования по радиационной без-
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