Features of Structural and Phase Transformations in Mo–Si–B and Сr–Al–Si–B Systems During Self-Propagating High-Temperature Synthesis

This study is dedicated to investigation of the combustion mechanisms during the SHS of ceramic materials in multicomponent Mo–Si–B and Cr–Al–Si–B systems. It is concluded that the following processes are defined the SHS for Si-rich Mo–Si–B compositions: Si melting, its spreading over the surfaces of the solid Mo and B particles, followed by B dissolution in the melt, and formation of intermediate Mo3Si phase film. The subsequent diffusion of Si into Mo results in the formation of MoSi2 grains and MoB phase forms due to the diffusion of Mo into B-rich melt. The formation of MoB phase for B-rich compositions may occur via gas-phase mass transfer of MoO3 gaseous species to B particles and B2O2 to Mo particles. In Cr–Al–Si–B system firstly, the Al–Si eutectic mixture undergoes contact melting followed by formation of the reactionary surface as the eutectic melt spreads over the Cr and B particles surface. An increase in Al content increases the proportion of the Al–Si eutectic melt. The dissolution of Cr particles in this melt becomes the rate-limiting stage of the combustion process. The melt is saturated with these elements followed by crystallization of CrB and Cr(Si,Al)2 grains. In the Cr- and B-rich areas and low melt concentration, the formation of CrB may occur via gas-phase mass transfer of B2O2 gaseous species to Cr particles. Consecutive formation of chromium and molybdenum borides and silicides is established by means of dynamic X-ray diffraction analysis. Compact ceramic samples were produced using forced SHS pressing technique. Their structural investigations were conducted by XRD and SEM

Effect of Mechanical Activation on Ti3AlC2 Max Phase Formation under Self-Propagating High-Temperature Synthesis

In this study, we have investigated the effect of various mechanical activation (MA) modes on phase and structure formation in powder mixtures made up to produce Ti3AlC2 MAX phase. The optimal MA duration has been established which results in the maximum heat release under SHS due to accumulation of structural defects leading to the growth of internal energy. The effect of MA on the character and kinetics of combustion front propagation has been investigated. It was shown that following pretreatment of a powder mixture in a planetary ball mill, the combustion mode changes from stationary to a pulsating combustion and, consequently, the combustion rate decreases. The burning-out of the sample is partial and with interruptions (depressions). Force SHS-pressing technology was used for obtaining of compacted samples with homogeneous structure based on Ti3AlC2

Marigold flower-like assemblies of phosphorescent iridium-silver coordination polymers

EZ-C acknowledges the University of St Andrews and EPSRC (EP/M02105X/1) for financial support.Racemic and enantiopure phosphorescent iridium(III)-silver(I) coordination polymers are reported. The polymers rac-, Δ- and ΔΔΔΔ- IrAg were formed, respectively, by the assembly of the chiral iridium metalloligands rac-, Δ- and Δ-[Ir(mesppy)2(qpy)]PF6 (rac-, Δ- and Δ- Ir ) where mesppy is 2-phenyl-4-mesitylpyridinato and qpy is 4,4':2',2'':4'',4'''- quaterpyridine, and Ag+ ions through Npy-Ag linear coordination. The polymers have been characterized in MeNO2 solution by 1H and 1H DOSY NMR and CD spectroscopies and in the solid-state by Scanning Electron Microscopy (SEM); the crystal structures of the racemic polymer rac- IrAg has been obtained by X-ray diffraction. The polymers rac-, Δ- and Δ- IrAg exhibited orange/red emission in solution, in films and as crystals, with intensities comparable to those of the corresponding iridium metalloligands rac-, Δ- and Δ- Ir . The morphology of the enantiopure polymers in the solid-state resemble marigold flower-like nano-porous assemblies while the racemic polymer possesses an irregular morphology formation.PostprintPeer reviewe

Cyanomethylene-bis(phosphonate)-Based Lanthanide Complexes: Structural, Photophysical, and Magnetic Investigations

10 pagesInternational audienceThe syntheses, structural investigations, magnetic and photophysical properties of a series of 10 lanthanide mononuclear complexes, containing the heteroditopic ligand cyanomethylene-bis(5,5-dimethyl-2-oxo-1,3,2λ5-dioxa-phosphorinane) (L), are described. The crystallographic analyses indicate two structural types: in the first one, [LnIII(L)3(H2O)2]*H2O (Ln = La, Pr, Nd), the metal ions are eight-coordinated within a square antiprism geometry, while the second one, [LnIII(L)3(H2O)]*8H2O (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er), contains seven-coordinated LnIII ions within distorted monocapped trigonal prisms...

ПОЛУЧЕНИЕ СПЕЧЕННОГО СПЛАВА НА ОСНОВЕ ИНТЕРМЕТАЛЛИДА TiAl Часть 1. Гидридно-кальциевая технология получения порошкового сплава Ti–47Al–2Nb–2Cr и его свойства

Alloy powder of the Ti–47Al–2Nb–2Cr composition (at.%) with the structure of TiAl (60 wt.%) and Ti3Al (40 wt.%) is prepared by the calcium-hydride method. The mode of the calcium-hydride synthesis is optimized for the Ti–50Al (at.%) model alloy. It is established that the reduction temperature should be no lower than 1100 °C, while the excess of the CaH2 reducing agent should be no lower than 15 wt.%. The main physicochemical and manufacturing properties of the synthesized Ti–47Al–2Nb–2Cr powder alloy, which provide the formation of dense compacts during its subsequent consolidation processes, are determined using modern analytical methods.Гидридно-кальциевым методом получен порошок сплава, отвечающий составу, ат.%: Ti–47Al–2Nb–2Cr, со структурой TiAl (60 мас.%) и Ti3Al (40 мас.%). Оптимизация режима гидридно-кальциевого синтеза проведена на модельном сплаве Ti–50ат.%Al. В результате исследований установлено, что температура восстановления должна быть не менее 1100 °C, а избыток восстановителя CaH2 – 15 мас.%. С использованием современных методов анализа определены основные физико-химические и технологические свойства синтезированного порошка сплава Ti–47Al–2Nb–2Cr, которые обеспечивают получение плотных компактов при последующих процессах его консолидации

ПОЛУЧЕНИЕ СПЕЧЕННОГО СПЛАВА НА ОСНОВЕ ИНТЕРМЕТАЛЛИДА TIAL ЧАСТЬ 2. ИССЛЕДОВАНИЕ ПРОЦЕССОВ ФОРМОВАНИЯ И СПЕКАНИЯ

An integrated process for producing electrodes of TiAl-based powder alloy is proposed with the following stages: powder alloy production by hydride-calcium recovery, powder treatment in a carbide ball mill with Y2O3 added as a structure modifier, workpiece hydrostatic molding and sintering. Experimental samples were used to study molding and sintering processes and examine alloy microstructure at all stages of the processing chain. An electrode for plasma centrifugal disintegration of granules was produced using this technology.Предложена комплексная технология производства электродов из порошкового сплава на основе алюминида титана TiAl, включающая следующие стадии: получение порошкового сплава методом гидридно-кальциевого восстановления, обработка порошка в шаровой твердосплавной мельнице с добавлением Y2O3 в качестве модификатора структуры, гидростатическое формование и спекание заготовки. На экспериментальных образцах изучены процессы формования и спекания, исследована микроструктура сплава на всех этапах технологической цепочки. По данной технологии получен электрод для плазменного центробежного распыления гранул

ПОЛУЧЕНИЕ ЛИТЫХ ЭЛЕКТРОДОВ ИЗ НАНОМОДИФИЦИРОВАННОГО ВЫСОКОБОРИСТОГО СПЛАВА НА ОСНОВЕ АЛЮМИНИДА НИКЕЛЯ ДЛЯ ИЗГОТОВЛЕНИЯ СФЕРИЧЕСКИХ ГРАНУЛ МЕТОДОМ ЦЕНТРОБЕЖНОГО РАСПЫЛЕНИЯ

A complex manufacturing method of the billets from the material based on high-boron nickel aluminide is proposed. The method includes manufacturing the semifinished alloy products using a combined method of self-propagating high-temperature synthesis and centrifugal casting from oxide feedstock and subsequent vacuum induction remelting with introducing Al-based foundry alloys containing nanosized ZrO2 and modifying the structure. The evolution of the microstructure and phase composition is investigated at all production stages. A cast ZrO2-modified cylindrical billet, which possesses high purity in regards to gas impurities (O – 0,005 wt.% and N – 0,0001 wt.%) and is suitable for the further production of powders by the plasma rotating electrode process, is fabricated according to the proposed technology.Предложена комплексная технология производства заготовок из материала на основе высокобористого алюминида никеля. Она включает в себя изготовление полуфабрикатов сплава совмещенным методом самораспространяющегося высокотем-пературного синтеза и центробежного литья из оксидного сырья и последующий вакуумный индукционный переплав с введением модифицирующих структуру лигатур на основе Al, содержащих наноразмерный ZrO2. Изучена эволюция микроструктуры и фазового состава на всех технологических переделах. По предложенной технологии получена литая цилиндрическая заготовка, модифицированная ZrO2, которая обладает высокой чистотой по газовым примесям (O – 0,005 мас.%, N – 0,0001 мас.%) и пригодна для дальнейшего получения гранул методом центробежного распыления

Sequential construction of crystalline heterometallic architectures based on 7-azaindole and dipyrrin ligands

Les polymères de coordination revêtent un grand intérêt de par leurs applications potentielles dans les domaines de la catalyse ou du stockage de gaz, par exemple. Alors que la majorité des architectures décrites sont homométalliques, l'obtention de leurs analogues hétérométalliques représente un défi synthétique. En effet, une approche one-pot)), par principe, peut mener à un mélange statistique de composés homo- et hétérométalliques. Afin de résoudre ce problème, une stratégie séquentielle a été mise au point. Elle repose sur l'utilisation de ligands portant des pôles de coordination différenciés. Celte voie a été développée à partir de ligands dérivés du 7-azaindole et de la dipyrrine. Dans une première partie, des dérivés fonctionalisés du 7-azaindole ont été synthétisés et utilisés comme ligands pour la préparation de complexes et de réseaux à base de Cu(II) . Dans une deuxième partie, des dérivés de la dipyrrine portant un groupement imidazolyle, pyrazolyle ou pyridyle périphérique ont été préparés ainsi que leurs complexes hétéroleptiques de Cu (II) et Co(III). Ces composés forment par auto-assemblage avec des sels d'argent, : AgX, des architectures hétérométalliques ' mono- et bi-dimensionnelles. L'organisation de ces réseaux est influencée la nature de l'anion X-. Dans une troisème et dernière partie, un ligand comprenant à la fois les noyaux dipyrrine et 7-azaindole a été synthétisé. Ce dernier groupement montre une récurrence d'un motif auto-complémentaire de liaison hydrogène. Ainsi, les complexes obtenus par coordination de la fonction dipyrrine à des métaux divalents tels que Ni(II), Cu(lI) et Zn(lI) forment des réseaux unidimensionnels.Coordination polymers have altracted considerable interest over the past few years owing to their potential application in gas storage or catalysis, for example. While the vast majority of these compounds are homometallic systerns, the synthesis of heterometallic architectures remains challenging. Indeed, a one-pot synthetic approach in principle leads to a statistical mixture of homo- and hetero-metallic assemblies. To circumvent this synthetic issue, a sequential approach has been developed. The lalter relies on the use of ligands bearing differentiated coordination sites hence allowing the stepwise elaboration of heterornetallic architectures. This approach has been explored by ligands based on the 7-azaindole and dipyrrin moieties. ln a first parI, functionalized 7-azaindole derivatives have been synthesized and employed as ligands for the preparation of Cu(II) discrete complexes and networks. In a second part of the work, novel dipyrrin appended with imidazolyl, pyrazolyl or pyridyl groups have been prepared and used as ligands for the synthesis of heteroleptic Cu(lI) and Co(III) complexes. These species form mono- and bi-dimensional networks upon assembly with sil ver salts, AgX. The solid state arrangement of these species is influenced by the nature of the X- anion. In a third and final parI, a ligand incorporating both a dipyrrin and a 7-azaindole has been conceived and prepared. The lalter shows a recurrent hydrogen bonding motif that leads to the formation of one-dimensional networks upon coordination of, divalent metals such as Ni(II), Zn(lI) and Cu (II) by the dipyrrins