共查询到20条相似文献,搜索用时 31 毫秒
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Md. Amir M. Geleri S. Güner A. Baykal H. Sözeri 《Journal of Inorganic and Organometallic Polymers and Materials》2015,25(5):1111-1119
In this study, FeBxFe2?xO4 nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µB and almost half or less with respect to 4 µB of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K eff ) are between 43.3 × 104 and 19.4 × 104 emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeBxFe2?xO4 NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe3O4 NPs in the literature. The bigger E g values are mainly attributed to B concentration and partly to quantum confinement effect. 相似文献
3.
Daniel Sastre Alfonso J. Carrillo David P. Serrano Patricia Pizarro Juan M. Coronado 《Topics in Catalysis》2017,60(15-16):1108-1118
Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La0.6Sr0.4Mn1?xAlxO3 (x?=?0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300?°C in inert atmosphere up to 0.32 mmol g?1 of O2 are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x?=?0.5, corresponding to an O2 release of 0.318 mmol g?1 (δ?=?0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO2 in the oxidation step at 900?°C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La0.6Sr0.4Mn0.6Al0.4O3, with reduction extent of 0.266 mmol?g?1, but the production of CO is in comparison significantly lower (0.114 mmol?g?1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials. 相似文献
4.
Carbon free LiFe1−x
Mn
x
PO4 (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural
and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy
(SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical
performance of LiFePO4 prepared in this manner showed to be positively affected by Mn2+-substitution. Among the Mn2+-substitution samples, the LiFe0.9Mn0.1PO4 exhibited an initial discharge capacity of 141.4 mA h g−1 at 0.1 C, and the capacity fading is only 2.7% after 50 cycles. 相似文献
5.
The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La2 ? x Sr x CuO4 lattice have been determined by the method of emission Mössbauer spectroscopy on 57Co(57m Fe), 67Cu(67Zn), 67Ga(67Zn), and 155Eu(155Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe3+, Zn2+, and Gd3+ ions. Based on the comparison of the calculated and experimental dependences of V zz on x it was shown that the holes appearing during the substitution of La3+ for Sr2+ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La2 ? x Sr x CuO4 is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy. 相似文献
6.
R. S. Bubnova E. S. Derkacheva S. K. Filatov V. L. Ugolkov 《Glass Physics and Chemistry》2010,36(1):61-69
Solid solutions K1 − x
Cs
x
BSi2O6 (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization
of glasses in the KBSi2O6-CsBSi2O6 borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching
techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I
$
\bar 4
$
\bar 4
3d and I
a
$
\bar 3
$
\bar 3
d, respectively. The cubic-cubic phase transition I
$
\bar 4
$
\bar 4
3d ai Ia
$
\bar 3
$
\bar 3
d occurs in the composition range x = 0.35−0.40 at room temperature. In the series of solid solutions with x = 0−0.30, the reversible cubic-cubic polymorphic transition I
$
\bar 4
$
\bar 4
3d ai ia
$
\bar 3
$
\bar 3
d with an increase in the temperature has been revealed, the temperature of the polymorphic transition has been determined,
and the thermal expansion in both polymorphic modifications has been studied using high-temperature X-ray diffraction and
dilatometry. The solid solutions belonging to the space group Ia
$
\bar 3
$
\bar 3
d are characterized by a lower thermal expansion than the solid solution belonging to the space group I
$
\bar 4
$
\bar 4
3d. According to the calculations, the equivalents α/γ for the space groups I
$
\bar 4
$
\bar 4
3d and Ia
$
\bar 3
$
\bar 3
d are 0.03 and 0.02 (in cesium atomic fractions per degree Celsius), respectively. 相似文献
7.
BaCe0.9−x
Zr
x
Y0.1O3−δ powders were synthesized by a solid-state method at 1,400 °C. Two compositions were studied (x = 0.3 and x = 0.7). Pellets were prepared and conventionally sintered in air at 1,700 °C. Then, the samples were heated at 600 °C for
3 h in different reducing atmospheres: dry hydrogen, wet hydrogen and wet deuterium. After each treatment, the proton diffusion
depth profile was obtained using Secondary Ion Mass Spectroscopy (SIMS). Protons were not incorporated in the material when
the gas was not wet, and the isotope effect suggests that protons present in the pellet come from water and not from hydrogen. 相似文献
8.
Yuhang Wang Chunmei Li Jiaojun Tan Wenbin Wang Qiuyu Zhang Hongxia Yan 《Journal of Porous Materials》2017,24(3):639-646
In this paper, the core–shell structured NiFe2O4@TiO2 nanoparticles and nanochains as photocatalysts were successfully prepared through hydrothermal and hydrolysis method. The as-prepared core–shell structure was composed of a magnetic NiFe2O4 core and photocatalytic titanium oxide coating shell. SEM and TEM images characterized the morphology of NiFe2O4@TiO2 nanoparticles. Moreover, the results of XRD patterns proved that the TiO2 coating shell consisted of anatase. The VSM measurements showed that the saturation magnetization values of NiFe2O4 and NiFe2O4@TiO2 nanoparticles was 65 and 53 emu/g, respectively. The photocatalyst of NiFe2O4@TiO2 nanoparticles exhibited the outstanding recyclable performance for RhB. And, the photo_degradation ration of maintained 69 % after the photocatalyst experienced ten photocatalysis experiments, which is better than that of Fe3O4@TiO2 photocatalysts. 相似文献
9.
E. V. Mikhaleva V. G. Vasil’ev A. P. Nosov E. V. Vladimirova B. V. Slobodin 《Glass Physics and Chemistry》2009,35(1):81-86
Single-phase finely dispersed perovskite-like manganites La1 ? x Sr x MnO3 + δ (0 ≤ x ≤ 0.33) with an average particle size of approximately 3μm were synthesized by the pyrohydrolytic method from a stoichiometric mixture of the corresponding metal nitrates at a temperature of 500°C in a water vapor atmosphere. The parameter δ was changed as a result of the subsequent heat treatment. It was established that the manganite La0.67Sr0.33MnO3 + δ synthesized by the pyrohydrolytic method is characterized by a more pronounced change in the magnetoresistance as compared to the manganite that had the same composition but was synthesized according to the conventional ceramic technique. 相似文献
10.
The absorption edge spectra of vitreous alloys in the As-S-Se system are measured in the temperature range 77–300 K. The parameters of the fundamental absorption edge and the electron-phonon interaction in As40S60 ? x Se x (x = 0–40) glasses are determined, and the influence of the compositional disorder on these parameters is investigated. The contributions of the static structural and temperature disorders to the smearing of the fundamental absorption edge of the alloys under study are evaluated. 相似文献
11.
S. Kh. Estemirova S. G. Titova V. F. Balakirev I. A. Samatov I. L. Sashin 《Glass Physics and Chemistry》2007,33(4):356-361
The specific features revealed in the behavior of the parameters of the crystal structure and the lattice dynamics of the La1 ? x Ca x MnO3 + δ manganites upon the transition to a magnetically ordered state are investigated using X-ray powder diffraction and inelastic neutron scattering. The results obtained are explained in terms of an inhomogeneous state of the samples. This state manifests itself in the form of local regions that are enriched or depleted in charge carriers, with the former regions characterized by the highest temperature of ferromagnetic ordering in the system under investigation. A comparison of the evolution of the crystal structure with variations in the temperature both in the presence and in the absence of a magnetic field has demonstrated that the inhomogeneities are eliminated by an external magnetic field and that the regions enriched in charge carriers become predominant in the system. 相似文献
12.
We report on bifurcate reactions on the surface of well-aligned Si1−x
Ge
x
nanowires that enable fabrication of two different coaxial heterostructure nanowires. The Si1−x
Ge
x
nanowires were grown in a chemical vapor transport process using SiCl4 gas and Ge powder as a source. After the growth of nanowires, SiCl4 flow was terminated while O2 gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized
into SiO2 by the O2 gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O2 pressure without any intermediate region and enables selectively fabricated Ge/Si1−x
Ge
x
or SiO2/Si1−x
Ge
x
coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion
of oxygen through the oxide layer, respectively. 相似文献
13.
M. I. Georgievskaya R. S. Bubnova S. K. Filatov V. L. Ugolkov 《Glass Physics and Chemistry》2008,34(4):436-442
Continuous solid solutions and the reversible phase transition from the I-43d cubic phase to the Ia-3d cubic phase are revealed in the borosilicate series K1 ? x Rb x BSi2O6. Samples in the KBSi2O6-RbBSi2O6 system are prepared by solid-phase synthesis and crystallization of glasses and investigated using the annealing and quenching technique, high-temperature X-ray diffraction, and dilatometry. The above polymorphic phase transition is observed in all solid solutions at temperatures in the range from 330 to 430°C depending on the composition: an increase in the rubidium content in the solid solution leads to a gradual decrease in the phase transition temperature. The linear thermal expansion coefficients α are determined for solid solutions of different crystalline modifications and glasses. The linear thermal expansion coefficients α for the I-43d low-temperature phase are equal to (20–23) × 10?6 K?1 according to the X-ray diffraction data and (21–24) × 10?6 K?1 according to the dilatometric data. The values of α for the Ia-3d high-temperature phase lie in the range (4–9) × 10?6 K?1 according to the X-ray diffraction data and in the range (6–9) × 10?6 K?1 according to the dilatometric data. The linear thermal expansion coefficients for both modifications decrease with an increase in the rubidium content in the solid solutions. The linear thermal expansion coefficients for glasses α = (10–11) × 10?6 K?1 are close to those for the high-temperature modification and virtually independent of the sample composition. The I-43d (cubic) ai I41/a (tetragonal) o Ia-3d (cubic) polymorphic phase transitions in the KBSi2O6 compound are revealed by differential scanning calorimetry (DSC) and dilatometry. Their reversibility is confirmed by the DSC data. 相似文献
14.
Kelsey A. Stoerzinger Xiao Renshaw Wang Jonathan Hwang Reshma R. Rao Wesley T. Hong C. M. Rouleau Dongwook Lee Yi Yu Ethan J. Crumlin Yang Shao-Horn 《Topics in Catalysis》2018,61(20):2161-2174
Cobalt-containing perovskite oxides are promising electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolyzers. However, a lack of fundamental understanding of oxide surfaces impedes rational catalyst design for improved activity and stability. We couple electrochemical studies of epitaxial La1?xSrxCoO3?δ films with in situ and operando ambient pressure X-ray photoelectron spectroscopy to investigate the surface stoichiometry, adsorbates, and electronic structure. In situ investigations spanning electrode compositions in a humid environment indicate that hydroxyl and carbonate affinity increase with Sr content, leading to an increase in binding energy of metal core levels and the valence band edge from the formation of a surface dipole. The maximum in hydroxylation at 40% Sr is commensurate with the highest OER activity, where activity scales with greater hole carrier concentration and mobility. Operando measurements of the 20% Sr-doped oxide in alkaline electrolyte indicate that the surface stoichiometry remains constant during OER, supporting the idea that the oxide electrocatalyst is stable and behaves as a metal, with the voltage drop confined to the electrolyte. Furthermore, hydroxyl and carbonate species are present on the electrode surface even under oxidizing conditions, and may impact the availability of active sites or the binding strength of adsorbed intermediates via adsorbate–adsorbate interactions. For covalent oxides with facile charge transfer kinetics, the accumulation of hydroxyl species with oxidative potentials suggests the rate of reaction could be limited by proton transfer kinetics. This operando insight will help guide modeling of self-consistent oxide electrocatalysts, and highlights the potential importance of carbonates in oxygen electrocatalysis. 相似文献
15.
Abstract
An effective heterogeneous catalyst, CaxMg2−xO2, was prepared and tested for soybean oil transesterification with methanol. The catalysts were characterized by using X-ray diffraction , Fourier transform infrared spectra, thermo gravimetric and differential thermal analysis , and Hammett indicator method. The catalyst with Ca/Mg ratio of 1.0 and calcined at 800 °C exhibited high catalytic activities. Under the suitable transesterification conditions (methanol/oil ratio 12:1, catalyst loading 6 wt%, reaction time 5 h, at reflux of methanol), the oil conversion of 91.3% could be achieved. The catalyst can be easily recovered and reused without significant deactivation. 相似文献16.
The phase relationships in the Na2ZnP2O7–LiKZnP2O7 system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP2O7. The phase formation of this system is compared with the previously studied NaKZnP2O7–LiKZnP2O7 system. It is shown that a structural factor affects the geometry of the state diagrams. 相似文献
17.
J. E. Anderson R. S. Bubnova S. K. Filatov V. L. Ugolkov S. N. Britvin 《Glass Physics and Chemistry》2009,35(2):191-198
The thermal behavior of ammonioborite (NH4)3[B15O20(OH)8] · 4H2O is investigated using thermal X-ray diffraction, differential thermal analysis (DTA) in air and vacuum, and thermogravimetry. It is shown that the decomposition of the mineral (dehydration, dehydroxylation, deammoniation) proceeds in several stages, and the dehydration is accompanied by the amorphization. The thermal expansion of ammonioborite is sharply anisotropic. As in the case of other hydrous pentaborates, the thermal expansion is maximum in the direction in which pentaborate groups alternate with ammonium cations. 相似文献
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19.
Liang Chen Junhua Li Wijdan Ablikim Jun Wang Huazhen Chang Lei Ma Jiayu Xu Maofa Ge Hamidreza Arandiyan 《Catalysis Letters》2011,141(12):1859-1864
Abstract
A series of cerium-tungsten oxide catalysts was prepared by the co-precipitation method and was evaluated for the selective catalytic reduction of NO x by ammonia (NH3-SCR) over a wide temperature range. These catalysts were characterized by BET, XRD, XPS and H2-TPR analyses. The experimental studies demonstrated that, among cerium-tungsten oxides, CeO2–WO3 with a Ce/W molar ratio of 3/2 exhibited the best activity toward NH3-SCR reactions, N2 selectivity and SO2 durability over a broad temperature range of 175–500 °C at a space velocity of 47,000 h−1. The strong interaction between Ce and W could be the main factor leading to the high activity of the CeO2–WO3 mixed oxide catalyst. 相似文献20.
L. P. Mezentseva A. V. Osipov V. L. Ugolkov A. A. Akatov V. A. Doilnitsyn T. P. Maslennikova A. V. Yakovlev 《Glass Physics and Chemistry》2018,44(5):440-449
Nanosized powders of orthophosphates in the LaPO4–HoPO4–H2O system have been synthesized to determine the mutual solubility of LaPO4 · nH2O and HoPO4 · nH2O initial components and to obtain ceramic matrices by sintering them. Formation of hexagonal, monoclinic or tetragonal solid solutions was revealed, and their limits and thermal stability were determined. A series of limited hexagonal LaPO4 · nH2O-based solid solutions was observed within the 0 ≤ x ≤ 0.6 concentration range up to 600°C. Further they transformed to monoclinic LaPO4-based form within the 0 ≤ x ≤ 0.3 concentration range. Solubility of LaPO4 · nH2O and LaPO4 in tetragonal HoPO4(· nH2O) is lower (≤10 mol %). Specific surface area of La1–xHoxPO4 · nH2O powders was in the range of 90.5–165.0 m2/g depending on x. Leaching rate of La3+ and Ho3+ from La1–xHoxPO4 matrices in nitric acid solution (pH 1–2) was determined to be 10–5–10–2 g/(cm2 day) for both ions. 相似文献