Results 1 - 10 of 41019
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[en] [Rh_6Te_8(PPh_3)_6].4C_6H_6, the first compound with a molecular Chevrel-type [Rh_6Te_8] cluster core has been synthesized and structurally characterized. By means of quantum chemical calculation, the close relationship of its electronic configuration to that of the lighter homologue has been demonstrated. The different crystal solvent content prevents an isostructural crystallization.
[en] Dependence of atoms covalent radii on oxidation state (valence state) was determined by accounting of orbitals hybridization and influence of uncoupled electrons. The results obtained agree well with empirical data. A system of recommended values of covalent radii of transition metal atoms, including V, Nb, Ta, Mo, W, Ru, in different oxidation state, which are used for calculating geometric electronegativities, is presented
[ru]На основе учета гибридизации орбиталей и влияния неспаренных электронов установлена зависимость ковалентных радиусов атомов от степени окисления (валентного состояния). Полученные результаты хорошо согласуются с эмпирическими данными. Предложена система рекомендованных значений ковалентных радиусов атомов переходных металлов, в том числе V, No, Ta, Mo, W, Ru, в разных степенях окисления, которые использованы для вычисления геометрических электоотрицательностей
[en] The state-of-the-art and prospects of the development of chemistry of chalcogenide clusters of Group 5-7 metals of the Periodic Table are discussed. The main structural types, methods of synthesis, the reactivity and possible applications of vanadium, niobium, tantalum, chromium, molybdenum, tungsten and rhenium chalcogenide clusters with nuclearity of three and larger are considered.
[en] Highlights: • Novel ideas to control cooling rate during different phase transformation are proposed. • Cooling rates induced microstructure evolutions during the whole phase transformation are investigated. • Phase transformation texture and the characteristics of lamellar structures are related to cooling rate. - Abstract: Microstructure evolution of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy (at.%) resulted from different cooling rates during the whole phase transformation process has been thoroughly investigated. The results show that the cooling rate during β → α transformation plays a crucial role in the modification of the crystallographic orientation relationship between the α grains and their parent β phase. The decrease of cooling rate can reduce the volume fraction of Burgers α grains and avoid the preferential distribution of lamellar interface traces. This could be attributed to the different nucleation and growth kinetics of α phase affected by the cooling rate. Moreover, the lamellar structure characteristics are closely related to the cooling rate during α → α2 + γ transformation and their responses to stabilization treatment shall vary accordingly. A fast cooling rate retains a high quantity of high temperature α/α2 phase. These α/α2 phase could decompose into ultrafine lamellar structure during subsequent stabilization treatment. While the average lamellar spacing of the slow cooled microstructure has a small increase by limited continuous growth of the pre-existing γ lamellae during stabilization treatment.
[en] The magnetism of bimetallic CoxM1-x (M: Ru and Rh) clusters has been investigated on systems of nanoparticles with diameters smaller than 2 nm embedded in a polymer obtained by means of organometallic synthesis. Whatever the composition (up to x=0.75), the investigation of magnetism evidence a ferromagnetic behavior. As a consequence of size reduction, both CoRh and CoRu systems display enhanced magnetic moments and anisotropy compared to bulk values
[en] Nb3Sn is the superconductor most used in the R and D of high field accelerator magnets by either the wind and react or the react and wind technique. In order to program the low temperature steps of the heat treatment, the growth kinetics of Cu-Sn intermetallics was investigated as a function of duration and temperature. The diffusion constants of η, (varepsilon) and (delta) phases between 150 and 550 C were evaluated using Cu-Sn model samples. Statistical and systematic errors were thoroughly evaluated for an accurate data analysis. Next the behavior of Internal Tin and Modified Jelly Roll Nb3Sn composites was compared with the model predictions