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1.
Nanosized metal aluminates, MAl2O4 (M = Ni, Co), have been prepared following a nonpolluting, low temperature, and self-sustaining starch single-fuel combustion synthesis. The mixed fuel-coordinating actions of starch have given rise to an intermediary precursor which afforded monodisperse metal aluminate nanoparticles. The thermal analysis of the [M(II), Al(III)]-starch precursors indicates a similar thermochemical reactivity for the two compounds, displaying a sequence of well-defined decomposition stages associated with three endothermic effects and three/four (nickel/cobalt) exothermic ones. The XRD data confirm the formation of spinelic phase and a continuous growth of particle sizes with the increase of calcination temperatures. The mechanisms proposed for the formation of metal aluminates essentially consist in a combination of solid-state reactions of amorphous NiO/Co3O4 and Al2O3 simple oxides. The evaluation criterion of Ni(II) cations into the spinelic lattice is original and is based on the distinct occupancy degree of tetrahedral and octahedral sites in NiAl2O4 and γ-Al2O3. TEM/HRTEM investigations performed on the cobalt(II) and nickel(II) aluminate oxide powders resulted after calcination at 800 and 900 °C, respectively, for 1 h show the formation of irregular and isolated plate-like particles for Co(II)-based spinelic oxides (the average particle size is 16.6 nm) and submicron aggregates of small, bimodal, and almost uniform (as shape and size) of NiAl2O4 mixed oxide (the mean particle size is 33.6 nm). The NIR–UV–Vis spectra for the resulted MAl2O4 (M = Co, Ni) mixed oxides reveal a massive presence of tetrahedral divalent cations both for short- and long-time calcined samples. NiO impurities are detected using FTIR and electronic spectra for all NiAl2O4 samples.  相似文献   

2.
Submicron-sized NiAl2+X O4 fragments and nanocondensates of Ni-doped γ-Al2O3, Al-doped NiO and β-Ni(OH)2 were synthesized simultaneously by pulsed laser ablation of NiAl2O4 powder in water and characterized using X-ray/electron diffraction and optical spectroscopy. The NiAl2+X O4 is Al-enriched spinel with dislocations and subgrains. The Ni-doped γ-Al2O3 spinel has paracrystalline distribution (i.e., with fair constant longitudinal spacing, but variable relative lateral translations) of defect clusters and intimate intergrowth of θ-Al2O3 and 2x( \( \overline{1} \) 3 \( \overline{1} \) ) commensurate superstructure. The Al-doped NiO has perfect cubo-octahedron shape and as small as 5 nm in size. The β-Ni(OH)2 and 1-D turbostratic hydroxide lamellae occurred as a matrix of these oxide nanoparticles. The colloidal suspension containing the composite phases has a minimum band gap of 5.3 eV for potential photocatalytic applications.  相似文献   

3.
Nearly monodisperse nanoparticles were synthesized by an environmentally benign low-temperature (140-180 °C) method involving pressure-induced decomposition of metal oleates in alcohol. XRD and TEM were employed in the characterization of the samples. In this study, Fe3O4, CoO, MnO, CoFe2O4, MnFe2O4, and a mixture of Ni, NiO, Ni2O3 nanoparticles, exhibiting various shapes and assemblies, were obtained.  相似文献   

4.
We have studied the surface chemistry of the nickel-oxygen system using both temperature changes and ion bombardment as techniques for elucidating the surface structure. The spectra of metallic Ni, NiO and Ni2O3 were characterized from samples prepared directly in the spectrometer. The Ni2O3 species could be distinguished from an authentic Ni(OH)2 sample from both the X-ray photoelectron lines and the Auger transitions. The oxides of NiO and Ni2O3 could be prepared by bombardment with low energy (400eV) O2+ ions as well as by exposure of Ni to oxygen at reduced pressure (~ 100 torr). The Ni2O3 was found to be present on most nickel-oxygen surfaces except those prepared by exposing Ni to air for many hours at high temperature (> 600°C), indicating that the stability of Ni2O3 decreased as the temperature increased. Exposure of both NiO and Ni2O3 to 400 eV Ar+ ion bombardment caused reduction to metallic Ni. This observation has also been noted for several other oxides and a prediction of whether or not reduction should be observed is presented by examining the free energy of formation of the molecule.  相似文献   

5.
NiFe2O4/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al2O3 substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe2O4/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe2O4/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.  相似文献   

6.
7.
The atomic arrangement and distribution of oxides (Cr2O3, NiCr2O4 and NiO) on the sprayed-NiCoCrAlY coating after oxidation are analyzed. The formation and the growth model of Ni-Cr oxide phases are discussed according to the matching relationship between atoms. The outline character and a scale of spinel NiCr2O4 are discussed. The results show that Cr atoms can form two close-packed arrangements in the crystal plane of Cr2O3 perpendicular to 〈0 0 1〉 orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni3Al in {1 1 1} crystal face. This suggests that Ni/Ni3Al is the substrate for Cr2O3 to grow along 〈0 0 1〉 direction. The lattice mismatch between Cr2O3 and Ni/Ni3Al is less than that of Al2O3, which indicates that Cr2O3 is easier to form than Al2O3 during the oxidation process. The atomic spacing in another close-packed arrangement of Cr2O3 perpendicular to 〈0 0 1〉 orientation is approximately equal to that of Ni or Cr in the plane of NiCr2O4 and NiO perpendicular to 〈1 1 1〉 orientation. So Cr2O3 can be the substrate for NiCr2O4 and NiO to grow in the 〈0 0 1〉 direction. NiCr2O4 and NiO can grow directly along the 〈1 1 1〉 orientation on each other. NiCr2O4 can grow outward in the planes of Cr2O3 perpendicular to 〈0 0 1〉 and grow inward along 〈1 1 1〉 orientation of NiO.  相似文献   

8.
The redox reaction of Ce4+-Ce3+ promoted by the catalytic function of nickel ions in a (1−x)CeO2-xNiO solid solution was investigated for solar H2 production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O2-releasing reaction with (1−x)CeO2-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H2 gas evolved by the reduced form were 1.2-2.5 cm3/g and the evolved gases amounts ratio of H2/O2 was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H2O=H2+1/2O2). The maximum amounts of evolved H2 and O2 gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO2-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O2-releasing and H2-generation reactions with (1−x)CeO2-xNiO solid solution were repeatable with the redox system of Ce4+-Ce3+, which was enhanced by the catalytic function of Ni2+-Ni0.  相似文献   

9.
Exchange bias (EB) and magnetic properties of ferrimagnetic (FI) NiFe2O4 and antiferromagnetic (AFM) NiO bulk composites, prepared by a chemical co-precipitation and post-thermal decomposition method from Fe-doped NiO matrix, have been investigated. Enhanced coercivities and shifted hysteresis loops are still observed for these samples after field cooling. But the vertical magnetization shifts are not observed. In comparison with the bulk samples, a NiO/10% NiFe2O4 nanocomposite was also prepared via direct mixture, in which both the horizontal and vertical shift in the hysteresis loops are observed at 10 K. The observed phenomena are explained in terms of interfacial exchange interaction between the two phases and the finite-size effect, respectively.  相似文献   

10.
To obtain direct evidence of the formation of the Ni–Mo–S phase on NiMo/Al2O3 catalysts under high‐pressure hydrodesulfurization conditions, a high‐pressure EXAFS chamber has been constructed and used to investigate the coordination structure of Ni and Mo species on the catalysts sulfided at high pressure. The high‐pressure chamber was designed to have a low dead volume and was equipped with polybenzimidazole X‐ray windows. Ni K‐edge k3χ(k) spectra with high signal‐to‐noise ratio were obtained using this high‐pressure chamber for the NiMo/Al2O3 catalyst sulfided at 613 K and 1.1 MPa over a wide k range (39.5–146 nm?1). The formation of Ni–Mo and Mo–Ni coordination shells was successfully proved by Ni and Mo K‐edge EXAFS measurement using this chamber. Interatomic distances of these coordination shells were almost identical to those calculated from Ni K‐edge EXAFS of NiMo/C catalysts sulfided at atmospheric pressure. These results support the hypothesis that the Ni–Mo–S phase is formed on the Al2O3‐supported NiMo catalyst sulfided under high‐pressure hydrodesulfurization conditions.  相似文献   

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