共查询到20条相似文献,搜索用时 31 毫秒
1.
The geometrical and topological analysis of the crystal structure of intermetallide ε-Mg23Al30 (ToposPro program) with V = 3098.0 Å3 and space group R-3 is carried out. The symmetric and topological codes of the cluster self-assembly of the crystal structure are determined: primary chain S 3 1 → microlayer S 3 2 → microframework S 3 3 . A new type of nanocluster-precursor of the crystal structure, which is formed on the internal 13-atomic cluster, which represents a template and consists of two bound ridged rings Mg–Al–Mg–Al–Mg–Al with the central Mg atom, is discovered. A quasi-spherical deltahedron shell made from 50 atoms is formed on the template. The center of a K63 cluster occupies the position with the point symmetry 3? in the unit cell. There are six neighboring K63 clusters in the local environment of the K63 cluster in the layer. The basic 3D network, which characterizes the location of the gravity centers of the K63 clusters, corresponds to a hexagonal closely packed network (HCP, Mg type) with CN = 12. The localization of two Mg atoms in the pores of the framework is determined. 相似文献
2.
The parameters of the Mössbauer spectra on 67Cu(67Zn), 67Ga(67Zn) isotopes, and the data of nuclear quadrupole resonance on an 17O isotope are anlayzed, and the lattice gradient of the electric field for the crystal lattice YBa2Cu3O7 is calculated. It is shown that these parameters correspond to the model when the hole is predominantly in the sublattice of the oxygen chain. 相似文献
3.
4.
Steroids bearing ketone functionality at carbon-7 are found commonly in nature, and the most prevalent of these are the 7-keto-Δ5-sterols. These substances have diverse biological properties and are present in biological samples and food products. For
the purpose of studying this class of oxysterols, many chemical methods, involving the chemical oxidation of Δ5-sterols to the corresponding 7-keto-Δ5-sterols derivatives have been developed to produce these compounds. We have undertaken a review and evaluation of chemical
methods for the synthesis of these compounds and have endeavored to enhance one of these procedures to yield products for
chemical and biological investigations. 相似文献
5.
Phase behaviors of two- and three-component mixtures ‘α-pinene-water’ and ‘α-pinene-ethanol-water’ were studied over a wide range of their composition, temperature, and pressure. Conditions were found that provide heteroazeotropic states of binary mixture ‘α-pinene-water’ and ternary mixture ‘α-pinene-ethanol-water’ depending on the ratio of ‘water/(α-pinene+ethanol)’ fractions at the ‘α-pinene+ethanol’ ratio of 1:1. Critical curves were calculated to demonstrate an anomalous dependence of these curves on the mixture composition, with the temperature minimum points typical of the mixtures that form heteroazeotropes. 相似文献
6.
Tsunenori Watanabe Yoshihisa Miki Yuya Miyahara Takeo Masuda Hiroshi Deguchi Hiroyoshi Kanai Saburo Hosokawa Kenji Wada Masashi Inoue 《Catalysis Letters》2011,141(9):1338-1344
Abstract
The precursor particles for γ-Ga2O3–Al2O3 solid solutions were prepared by the coprecipitation method from aqueous solutions of Ga(NO3)3 and Al(NO3)3 with (NH4)2CO3 as a precipitant. The γ-Ga2O3–Al2O3 solid solutions were obtained by calcination of the precursor at 700 °C. In this paper, the performance of the catalysts treated with NH3 was investigated for the selective catalytic reduction (SCR) of NO with methane as a reducing agent, and it was found that γ-Ga2O3–Al2O3 catalysts treated with NH3 and subsequently annealed in air showed higher activities than the γ-Ga2O3–Al2O3 catalysts without NH3 treatment. NH3 treatment of the catalyst caused partial rearrangement of Ga3+ and Al3+ ions and increased the population of tetrahedral Ga3+ ions in the defective spinel structure. 相似文献7.
S. I. Niftaliev I. V. Kuznetsova M. V. Chislov L. V. Lygina I. A. Zvereva 《Glass Physics and Chemistry》2017,43(4):363-367
This work is devoted to the preparation of zirconium oxide nanopowders stabilized by lanthanum oxide using the method of codeposition in the presence of hydrogen peroxide. Nanopowders composed of 0.97ZrO2 · 0.03La2O3 with particles of 10–20 nm are obtained. It is found that in the temperature interval of 500–1100°C the tetragonal and monoclinic points of the zirconium oxide phase crystallize at the same time. 相似文献
8.
Huali Liu Ruijuan Yang Yinghui Wang Shiquan Liu 《Journal of Inorganic and Organometallic Polymers and Materials》2011,21(4):950-953
Lithium–iron-phosphate (LIP) glasses with different amounts of zirconia were prepared by conventional melting and annealing
process. The influence of the nucleation agent, zirconia, on the crystallization behavior of LIP glasses has been studied
using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) techniques. The
results show that addition of 2 wt% of zirconia results in increases in the glass transition and crystallization temperatures
and a decrease in the activation energy of crystallization. However, both temperatures decrease with increased addition of
zirconia while the activation energy increases. The zirconia-free LIP glass only shows surface crystallization with crystals
of LiFeP2O7. The glass containing 2 wt% of zirconia also has surface crystallization; however, mixed ZrP2O7 and LiFeP2O7 are crystallized. The addition of 5 and 8 wt% of zirconia leads to bulk crystallization and increasing formation of ZrP2O7 crystals besides the LiFeP2O7 phase. 相似文献
9.
L. P. Mezentseva A. V. Osipov V. L. Ugolkov V. F. Popova T. P. Maslennikova S. K. Kuchaeva A. V. Yakovlev 《Glass Physics and Chemistry》2018,44(5):423-427
Nanosized La1–xDyxPO4 · nH2O powders are synthesized by the sol-gel method using direct and reverse precipitation. The formation of a continuous series of hexagonal solid solutions based on LaPO4 · nH2O is confirmed by the XRD and DSC/TG methods. A continuous series of monoclinic solid solutions based on LaPO4 is formed at temperatures higher than 600°C. A reflex corresponding to a tetragonal form of DyPO4 is formed during the calcination of DyPO4 powder at 850°C. Two types of solid solutions are observed at temperatures of 1000–1200°C, namely, monoclinic solutions based on LaPO4 (to x ≈ 0.7) and tetragonal solutions based on DyPO4 (0.90 ≤ x ≤ 1.0). The results are compared depending on the methods of nanopowder synthesis. 相似文献
10.
G. A. Sycheva 《Glass Physics and Chemistry》2009,35(6):602-612
The crystal nucleation in the glass of composition (mol %) 26Li2O · 74SiO2 has been investigated in the cases of homogeneous and heterogeneous nucleation. Parameters of homogeneous nucleation, such
as the stationary nucleation rate I
st, the time of nonstationary nucleation τ, and the crystal growth rate U, have been determined. The temperature dependences of these parameters have been constructed. The surface energy σ at the
nucleus-glass melt interface has been determined, and its temperature dependence has been obtained. The surface energy σ has
been evaluated using the graphical method for solving the transcendental equation derived by transforming the relationships
for the stationary crystal nucleation rate and the time of nonstationary crystal nucleation. The critical nucleus sizes r* and the free energy of formation of the critical nucleus Φ* have been determined. The heterogeneous nucleation on bubbles
specially produced in the glass has been studied. It has been demonstrated that the presence of bubbles in the initial glass
does not affect the crystal growth rate and substantially changes the nonstationary nucleation rate. The largest contribution
to the change in the nucleation rate is made by “active” bubbles (filled by water vapor) formed in the glasses synthesized
with the use of hydrated silicon dioxide. 相似文献
11.
A facile synthetic route for preparing silver-doped maghemite (Ag–γ-Fe2O3) nanocomposite via a modified co-precipitation method was developed. The prepared magnetic nanocomposite was characterized by means of thermal analysis, transmission electron microscope, X-Ray diffraction, vibrating sample magnetometer and Fourier transform infrared techniques. The characterization results showed that the prepared Ag–γ-Fe2O3 nanocomposite is nanocrystalline and 6–8 nm in size with superparamagnetic behavior. The synthesized Ag–γ-Fe2O3 nanocomposite showed exceptional catalytic activities towards reduction of nitroaromatic compounds with specific activities parameters of 1441.7 and 904.2 s??1 gAg?1 for both 4-nitrophenol and 2-nitroaniline, respectively. Besides, it shows a superior activity for catalytic degradation of methyl orange. All the three catalytic reactions were carried out in aqueous medium at room temperature and in the presence of reducing agent NaBH4. The magnetic behavior of the synthesized Ag–γ-Fe2O3 enables the ease of separation of the nanocomposite from the reaction medium for further reuse. 相似文献
Graphical Abstract
12.
The glass composition 55 SiO2-10 K2O-(35-x) CaO-(x) MgO (0 ≤ x ≤ 30) is prepared by the melt quenched technique. The as prepared samples are characterized by X-ray diffraction, Fourier Transform-Infrared Spectroscopy (FT-IR) and UV-Visible reflectance spectroscopy. The MgO containing glasses show better polymerization (cross-linking) and have a compact glass network as compared to CaO containing glass. Interestingly, some weak bonds are observed around 1393, 1461 and 1530 cm-1 in FT-IR spectra related to Ca/Mg-O-H. The optical band gap of the series varies from 3.42 eV to 3.72 eV, indicating wide-band gap materials that could be used in non-linear optical applications. 相似文献
13.
Vitrification in the Ga2S3–GeS2–PbF2 system is considered. The physicochemical properties of glasses, such as density, microhardness, electroconductivity, refraction index, and transmission percentage of specimens in visible and IR ranges of spectrum are studied; differential thermal analysis is carried out; and Raman and electron paramagnetic resonance spectra are investigated. 相似文献
14.
Marco Ocsachoque Jose Bengoa Delia Gazzoli María Gloria González 《Catalysis Letters》2011,141(11):1643-1650
Abstract
The Rh/α-Al2O3 catalyst was modified by CeO2 in order to improve the thermal stability and the carbon deposition resistance during the CO2 reforming of methane The carbon formation was determined by TPO, TEM and Raman spectroscopy. Characterization results showed that the incorporation of Ce in the support inhibits the carbon deposition, increasing the useful life and the stability of the Rh base catalysts. 相似文献15.
Xia Li Junsheng Yuan Zhiyong Ji Jianxin Chen 《Frontiers of Chemical Science and Engineering》2010,4(1):75-77
The equilibrium data on the ternary system of NH4Cl—CaCl2—H2O at 50°C were investigated using the wet-residue method. The experimental results show that there are three pure phase crystal areas of NH4Cl, 2NH4Cl·CaCl2·3H2O and CaCl·2H2O, two mixture phase crystal areas of NH4Cl and 2NH4Cl·CaCl·3H2O, and 2NH4Cl ·CaCl2·3H2O and CaCl·2H2O in the system. A new hydration double salt (2NH4Cl·CaCl·3H2O) was found in the ternary equilibrium system for the first time. 相似文献
16.
The influence of the electrode manufacturing procedure on surface and electrocatalytic properties for oxygen and ozone evolution at electrodes of nominal composition Ti/[IrO2–Nb2O5] (45:55 mol%) was investigated. Thermal decomposition at 450 °C (1 h, air stream) was adopted as standard procedure. Metal support pretreatment, solvent mixture, method of applying the precursor mixture and calcination procedure were all investigated. X-ray diffraction, scanning electronic microscopy, voltammetric and differential capacity analysis show the use of HCl 1:1 as solvent and applying the mixture by brush led to fragile rugged/porous oxide coatings. However, for the same conditions, but controlled calcination (heating/cooling rates), the coating becomes more compact. Using isopropanol as solvent results in a more homogeneous coating, presenting the lowest morphology factor. Kinetic investigation shows the rugged/porous coating presents the lowest Tafel slopes and the highest global electrocatalytic activity for OER. The more compact the coating the lower the electrochemically active surface area and the global OER activity. Ozone efficiency depends on the electrochemically active area while support pretreatment strongly influences the lifetime of the electrode. Application of a Pt interlayer between the oxide and Ti base improves the service life. 相似文献
17.
The possibility of increasing the laminar flame velocity in a hydrogen-air mixture by excitation of O2 molecules into the a
1Δ
g
singlet state. The presence of 10% of O2(a
1Δ
g
) molecules in oxygen is demonstrated to result in noticeable (up to 50%) enhancement of mixture burning. The temperature
of combustion products and also the concentrations of H2O, NO, and other constituents increase. The greatest effect of O2(a
1Δ
g
) molecules is manifested in combustion of lean mixtures; the least pronounced effect is observed in rich mixtures. These
effects are caused by intensification of the chain mechanism in the presence of a super-equilibrium amount of excited O2(a
1Δ
g
) molecules in a hydrogen-air mixture.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 3–12, July–August, 2008. 相似文献
18.
L. V. Morozova M. V. Kalinina T. I. Panova M. Yu. Arsent’ev T. V. Khamova I. A. Drozdova O. A. Shilova 《Glass Physics and Chemistry》2016,42(3):277-283
The—technology of the liquid-phase synthesis of metastable phases in the ZrO2–Y2O3 system has been developed. Mesoporous xerogels with the specific surface area of ~350 m2/g and monophase nanopowders (5–10 nm) of the tetragonal solid solution (ZrO2)0.97(Y2O3)0.03 have been obtained and their structural peculiarities have been revealed. The efficiency of the suggested technology and good prospects of the synthesized ZrO2-based precursors in creating catalysts’ substrates have been demonstrated. 相似文献
19.
Interest in the combustion chemistry of multifuel blends is motivated by the need to study the combustion of natural gas, which is known to be a mixture of alkanes. The present study performed using molecular beam mass spectrometry and numerical modeling has shown that the width of the zones of hydrogen and methane consumption in the H2/CH4/C3H8/O2/Ar flame and the width of the zones of methane and propane consumption in the CH4/C3H8/C4H10/O2/Ar flame differ significantly from each other. The causes of this phenomenon were determined by analyzing the modeling results. It has been found that in the presence of heavier compounds, lighter fuels, such as H2 and CH4, are formed, which reduces the total rate of their consumption and, hence expands the zone of their consumption in the flame. The influence of the presence of hydrogen in the fuel mixture on the concentration of C2 hydrocarbons has also been studied. It has been established that the addition of hydrogen reduces the maximum concentration of ethane, ethylene, and acetylene in the flame, and the fraction of unsaturated C2 hydrocarbons with respect to saturated ones also decreases. 相似文献
20.
L. A. Angolenko G. D. Semchenko V. V. Povshuk S. V. Tishchenko M. A. Kushchenko E. E. Starolat 《Refractories and Industrial Ceramics》2010,51(2):99-103
Results are given for a study of the dependence of apparent density and ultimate strength in compression on the quantity of
silica and form of modifying addition (Al, Si, B and mixtures of them) for materials of the composition Al2O3 – SiC – C based on high-alumina cement and aluminochromium phosphate binder after low-temperature (400°C) heat treatment.
It is established that the most efficient form the point of view of compaction and strengthening of raw material of corundum-graphite
refractory is addition of aluminum powder. 相似文献