Sol-gel synthesis of Fe-containing silica glasses

Fe-doped glasses and composites were prepared by hybrid sol-gel process, modified in the part of doping technique. The UV-VIS spectra and XRD-investigation show both the presence of oxide and fluoridecomplexes in the glass matrices

ОСОБЕННОСТИ ОКИСЛЕНИЯ ДИСПЕРСНОГО АЛЮМИНИЯ В УСЛОВИЯХ ВЫСОКИХ ТЕМПЕРАТУР И ДАВЛЕНИЙ

In recent times, researchers are interested in ultra and nanopowders of oxide ceramics and functional materials based on them. This article describes the results of obtaining an aluminum hydroxide powder – boehmite produced by the method of hydrothermal oxidation of aluminum. Boehmite obtained by this technology is characterized by high phase purity (according to the XRD-analysis there is well-crystallized boehmite). It is found that the hydrothermal synthesis, carried out by combustion in pre- and supercritical water, can be considered as an effective method of obtaining extra pure nanocrystalline hydroxides (boehmite) and oxides of aluminum (corrundum). In the case of realization of oxides and hydroxides of aluminum and also the technology of obtaining hydrogen and heat energy, this process can be considered to be highly profitable.В последние годы все больший интерес проявляется к исследованиям ультра- и нанодисперсных систем на основе оксидокерамических порошков и функциональных материалов на их основе. В представленной работе приводятся результаты получения порошка гидроксида алюминия – бемита, полученного по технологии гидротермального окисления, который характеризуется высокой фазовой чистотой (по данным рентгенофазного анализа присутствует хорошо закристаллизованный бемит). Установлено, что гидротермальный синтез, осуществляемый путем сжигания в до- и сверхкритических водных средах, можно рассматривать как эффективный способ получения особо чистых нанокристаллических гидроксидов (бемит) и оксидов (корунд) алюминия. При условии реализации оксидов и гидроксидов алюминия как товарных продуктов, а также технологии получения водорода и тепловой энергии, представленный процесс может относится к высокорентабельным.

УДАРНО-ВОЛНОВОЕ КОМПАКТИРОВАНИЕ ПОРОШКОВ

Materials based on MAX phases have a unique combination of properties. They combine the best properties of metals and ceramics. Such a set of useful operational parameters allows for wide technical application in various industries. However, despite the large number of research works carried out in this area, obtaining a dense, uniform MAX material remains an unresolved issue. The possibilities of the pulsed compacting method with blasting explosives for obtaining products from MAX phase powders were investigated. As a model material for the research, powders of MAX phases based on Ti2AlC and Ti3AlC2 synthesized by free sintering in vacuum were used. It was shown that double pulse compacting powders based Ti2AlC Ti3AlC2 and reducing compacts porosity from 22 % to 9 %, is practically unchanged while the phase composition of the material. Test samples obtained by pulsed compaction in oxidation resistance showed that the method of the shock-wave loading applicable for competitive materials realizing potential properties of MAX phases. It is noted that to increase the heat resistance it is necessary to minimize the porosity of the material. Significant reduction in porosity can be achieved due to repeated shock-wave loading of the material. Материалы на основе МАХ-фаз имеют уникальную комбинацию свойств. Они объединяют лучшие свойства металлов и керамики. Такой набор полезных эксплуатационных параметров дает возможность широкого технического применения в различных отраслях промышленности. Однако несмотря на большое количество исследовательских работ, проведенных в данной области, получение плотного, однородного МАХ-материала остается нерешенным вопросом. Изучались возможности метода импульсного компактирования бризантными взрывчатыми веществами для получения изделий из порошков МАХ-фаз. В качестве модельного материала для проведения исследований были использованы порошки МАХ-фаз на основе Ti2AlC и Ti3AlC2, синтезированные свободным спеканием в вакууме. Показано, что двукратное импульсное компактирование порошков на основе Ti2AlC и Ti3AlC2 позволяет снизить пористость прессовок с 22 % до 9 %, при этом фазовый состав материала практически не изменяется. Испытание образцов, полученных методом импульсного компактирования, на стойкость к окислению показало, что метод ударно-волнового нагружения применим для получения конкурентоспособных материалов, реализующих потенциальные свойства МАХ-фаз. Отмечено, что для повышения жаростойкости необходимо стремиться к минимизации пористости материала. Существенное снижение пористости может быть достигнуто за счет многократного ударно-волнового нагружения материала

Upconversion Luminescence of Er3+ Ions from Barium Titanate Xerogel Powder and Target Fabricated by Explosive Compaction Method

Photo- and cathodoluminescence in the visible range from erbium-doped barium titanate xerogels obtained in the form of a powder and a target pressed from it by explosive compaction are investigated. The powder and target exhibit upconversion luminescence of erbium ions excited at wavelengths in the regions 950–1000 and 1450–1550 nm that is characterized by strong bands at 650 and 520–560 nm and a weak band at ~820 nm that correspond to the 4F9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4I9/2 → 4I15/2 transitions of Er3+. The target also demonstrates cathodoluminescence at room temperature and liquid nitrogen temperature with the strongest bands at 650, 520, and 538 nm

X-Shooting ULLYSES: Massive stars at low metallicity: I. Project description

Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational wave events involving spectacular black hole mergers indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observing ∼250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES programme. The complementary X-Shooting ULLYSES (XShootU) project provides an enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESOa's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates as a function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of astrophysics, the data and modelling of the XShootU project is expected to be a game changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope spectra of the first stellar generations, the individual spectra of low-Z stars need to be understood, which is exactly where XShootU can deliver

Spectropolarimetry of stars across the H-R diagram

The growing sample of magnetic stars shows a remarkable diversity in the properties of their magnetic fields. The overall goal of current studies is to understand the origin, evolution, and structure of stellar magnetic fields in stars of different mass at different evolutionary stages. In this chapter we discuss recent measurements together with the underlying assumptions in the interpretation of data and the requirements, both observational and theoretical, for obtaining a realistic overview of the role of magnetic fields in various types of stars.Comment: 23 pages, 3 figures, chapter 7 of "Astronomical Polarisation from the Infrared to Gamma Rays", published in Astrophysics and Space Science Library 46