Preparation and characterization of α-Fe2O3–CeO2 composite

In our previous study we attempted to see the effect of cerium doping (Ce/Fe ratio 0.015 to 0.074) on goethite matrix and conversion of doped goethite to hematite. In the present communication, nano-structured α-Fe₂O₃–CeO₂ composite with Fe/Ce weight ratio as 1.1 has been synthesized by calcination of goethite-cerium hydroxide precursor prepared by co-precipitation method. It was observed that co-precipitation of cerium along with iron in hydroxide medium resulted in hindering the formation of crystalline order as the precursor formed showed poorly crystallized goethite and almost no crystallinity in Ce(OH)₄. Calcination of the precursor at 400 °C showed the formation of hematite together with a broad peak corresponding to cerium oxide whereas at 800 °C, two distinct phases of α-Fe₂O₃ and CeO₂ were observed. The Mössbauer spectra showed the presence of a paramagnetic component both for the precursor as well as for the sample calcined at 400 °C but on raising the calcination temperature to 800 °C, the paramagnetic component disappeared and the spectrum corresponding to pure α-Fe₂O₃ phase was observed. The microstructure of the product obtained by calcining at 800 °C showed rod like structure (30 to 50 nm width and 300 to 500 nm length) of α-Fe₂O₃ having equi-dimensional CeO₂ particles on and around the surface. Besides the rods, equi-dimensional particles and agglomerates corresponding to CeO₂ were also observed. The results show that co-precipitation followed by calcinations gives nanorods hematite with CeO₂ particles bonded to its surface.     

K2S2O8-Na2S2O3引发苯乙烯磺酸钠接枝阴离子交换膜改性

通过K_2S_2O_8-Na_2S_2O_3氧化还原体系引发苯乙烯磺酸钠(SSS)接枝阴离子交换膜,用衰减全反射傅里叶变换红外光谱(ATR-FTIR)、扫描电子显微镜(SEM)、原子力显微镜(AFM)和接触角测量仪等对阴离子交换膜改性前后进行性质表征,并以十二烷基苯磺酸钠(SDBS)作为模型污染物进行污染实验,考察改性膜的抗污染性能及其稳定性.结果表明,SSS接枝后可有效改善阴离子交换膜表面的亲水性和负电荷密度,改性膜接触角由72°变为60°,表面电荷密度由0.92 mV变为-7.85 mV,表明带负电荷的磺酸基团被成功接枝到阴膜表面.通过探究改性条件对改性膜性质的影响发现,当改性温度为35℃、单体质量浓度为1.0 g/L、接枝时间为10 min时改性效果最佳.该改性条件下获得的SSS修饰阴离子交换膜抗污染能力明显提高,稳定性良好且不影响其脱盐性能.     

Mössbauer studies of α″-Fe16N2 and α′-Fe8N films

Conversion-electron Mössbauer spectra of epitaxial -Fe₁₆N₂ and -Fe₈N films have been studied and their differences are discussed in detail. The Mössbauer spectrum of -Fe₁₆N₂ can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mössbauer spectrum of -Fe₈N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for -Fe₁₆N₂ than for -Fe₈N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for -Fe₁₆N₂. The iron moments tend to locate in the film plane for -Fe₁₆N₂ and to arrange perpendicularly to the film plane for -Fe₈N.     

Polarized infrared and neutron scattering studies of α-Bi2O3

Studies on the lattice dynamics of -Bi₂O₃ have been performed including IR polarized reflectance spectra on single crystal, inelastic neutron scattering and specific heat measurements. Dispersion parameters and polarizations of IR-active phonons are presented and compared with neutron and specific heat data.     

Biomimetic fabrication of α-Fe2O3 with hierarchical structures as H2S Sensor

A facile sol–gel method is developed for the fabrication of α-Fe₂O₃ with quasi-honeycomb like structures inherited from Papilio paris butterfly wings. The exquisite hierarchical architecture is faithfully maintained in α-Fe₂O₃ from the skeleton of butterfly wings at the levels from macro to nano-scales. When used as a chemical sensor, the obtained α-Fe₂O₃ replica (P-α-Fe₂O₃) showed a much higher performance than that of the compared α-Fe₂O₃ nanoparticles synthesized under the same condition without biotemplate (S-α-Fe₂O₃). The P-α-Fe₂O₃-based sensor has a sensitivity of 19.2–50 ppm H₂S, which is four times more than that of S-α-Fe₂O₃, accompanied by a rapid response/recovery time within 1/10 s even at a relatively low working temperature of 180 °C. Compare to the S-α-Fe₂O₃, surface area of which cannot be detectable, the high sensing feature of P-α-Fe₂O₃ would be attributed to the relatively high-specific surface area 24.12 m²/g thus fabricated together with the unique 3D-network structures, which provide channel for the diffusion of H₂S. This strategy is expected to be used in fabrication of other kinds of metal oxide with unique structures for the potential application in gas sensor.     

Facile solution synthesis of α-FeF3·3H2O nanowires and their conversion to α-Fe2O3 nanowires for photoelectrochemical application

We report for the first time the facile solution growth of α-FeF(3)·3H(2)O nanowires (NWs) in large quantity at a low supersaturation level and their scalable conversion to porous semiconducting α-Fe(2)O(3) (hematite) NWs of high aspect ratio via a simple thermal treatment in air. The structural characterization by transmission electron microscopy shows that thin α-FeF(3)·3H(2)O NWs (typically <100 nm in diameter) are converted to single-crystal α-Fe(2)O(3) NWs with internal pores, while thick ones (typically >100 nm in diameter) become polycrystalline porous α-Fe(2)O(3) NWs. We further demonstrated the photoelectrochemical (PEC) application of the nanostructured photoelectrodes prepared from these converted hematite NWs. The optimized photoelectrode with a ~400 nm thick hematite NW film yielded a photocurrent density of 0.54 mA/cm(2) at 1.23 V vs reversible hydrogen electrode potential after modification with cobalt catalyst under standard conditions (AM 1.5 G, 100 mW/cm(2), pH = 13.6, 1 M NaOH). The low cost, large quantity, and high aspect ratio of the converted hematite NWs, together with the resulting simpler photoelectrode preparation, can be of great benefit for hematite-based PEC water splitting. Furthermore, the ease and scalability of the conversion from hydrated fluoride NWs to oxide NWs suggest a potentially versatile and low-cost strategy to make NWs of other useful iron-based compounds that may enable their large-scale renewable energy applications.     

Electron emission measurements and the defect structure of α-Al2O3

In this article, electron emission is used to study the defect structure of alumina. The need of a direct measurement of the position of the Fermi level (or the electron concentration in the conduction band) is shown by discussing the actual electrical data on alumina. The emission has been measured over a large temperature range (1400 to 2400 K) and the emission of a technical polycrystalline alumina is reported up to the melting temperature under a controlled oxygen partial pressure. Additional results are reported for titanium- and iron-doped polycrystalline aluminas. The results are discussed from two points of view. First the quantitative data concerning the work function are taken into account and the contribution of the surface layer is discussed. Secondly, the dependency of the electron emission on the oxygen partial pressure is explained by the defect chemistry of the oxide. The absence of variation of the electron concentration in a certain range of is due to a self compensation between donor and acceptor impurities.     

Effect of cationic size in Hg(Tl/Bi)Ba2Ca2Cu3O8+δ on superconducting and microstructural characteristics

In this paper we have reported investigations on the effect of simultaneous substitution of Bi and Tl at the Hg site in the oxygen deficient HgO_δ layer of HgBa₂Ca₂Cu₃O_8+δ cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown HgBi_0.2?xTI_xBa₂Ca₂Cu₃O_8+δ (withx = 0.00, 0.05, 0.10, 0.15, 0.20) corresponds to the 1223 phase. It has been found that the T_c varies with the average cationic size < R_d > of the dopant cations. The optimumT _c of ～ 131 K has been found for the composition HgBi_0.15TI_0.05Ba₂Ca₂Cu₃O_8+δ This composition leads to the average dopant cation size of ～1.108 å which is very close to the size of Hg²⁺ (～ 111 å). The microstructure for HgBi_0.15TI_0.05Ba₂Ca₂Cu₃O_8+δ has been found to be most dense and this phase exhibits the highest stability. The J_c of the optimum material HgBi_0.15TI_0.05Ba₂Ca₂Cu₃O_8+δ is found to be ～ 1.29 × 10³ A/cm² at 77 K.     

Interfacial reactions between titanium film and single crystal α-Al2O3

Titanium is commonly used to join metals and ceramics by active metal brazing methods. In this work, titanium was sputter deposited on to single-crystal -Al₂O₃ substrates and the interfacial reactions between the titanium film and the Al₂O₃ substrate were studied. Al₂O₃ was reduced by titanium when samples were annealed at 973 and 1173 K for 300 s in an argon gas flow. Metallic aluminium was produced at the interface, and this diffused from the interface into the titanium film. At 1173 K, the intermetallic compound Ti₃Al and the intermediate titanium oxides, such as Ti₂O and TiO, were formed. The Al⁰ diffusion is important in stimulating interfacial reactions.     

Composition and Electrical Properties of Hg x Cd1 – x S Whiskers

Data are presented on the morphology, composition, and electrical and photoelectric properties of Hg _x Cd_{1 – x} S (x = 0.25–0.6) whiskers.     

Wetting and adhesion of Ni-Al alloys on α-Al2O3 single crystals

The effect of Al additions on the wetting and adhesion of Ni on an -Al₂O₃ single crystal was studied. Contact angles were measured by the sessile drop technique under vacuum or in He atmosphere. The morphological and chemical features of metal-vapour and metal-oxide interfaces were determined by scanning electron microscope (SEM), microprobe analysis and profilometry. The work of adhesion of Ni-Al alloys on Al₂O₃ substrates was significantly higher than for pure Ni and Al components. This result was explained by co-operative adsorption of aluminium and oxygen atoms at the Ni-Al₂O₃ interface. The influence of oxidation of the alloy on wetting and bonding is also discussed.     

Three-dimensional hierarchical flowerlike α-Fe2O3 nanostructures: synthesis and ethanol-sensing properties

The α-Fe(2)O(3) hierarchical nanostructures have been successfully synthesized via a simple solvothermal method. The as-prepared samples are loose and porous with flowerlike structure, and the subunits are irregularly shaped nanosheets. The morphology of the α-Fe(2)O(3) structures was observed to be tunable as a function of reaction time. To demonstrate the potential applications, we have fabricated a gas sensor from the as-synthesized hierarchical α-Fe(2)O(3) and investigated it for ethanol detection. Results show that the hierarchical α-Fe(2)O(3) sensor exhibits significantly improved sensor performances in comparison with the compact α-Fe(2)O(3) structures. The enhancement of sensing properties is attributed to the unique porous and well-aligned nanostructure.     

Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions

We propose a simple method for the efficient and rapid synthesis of one-dimensional hematite (α-Fe₂O₃) nanostructures based on electrical resistive heating of iron wire under ambient conditions. Typically, 1–5 μm long α-Fe₂O₃ nanowires were synthesized on a time scale of seconds at temperatures of around 700 ° ⊂. The morphology, structure, and mechanism of formation of the nanowires were studied by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman techniques. A nanowire growth mechanism based on diffusion of iron ions to the surface through grain boundaries and to the growing wire tip through stacking fault defects and due to surface diffusion is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Morphology-controllable synthesis and gas-sensing properties of α-MoO3

Different morphologies of orthorhombic molybdenum trioxide (MoO₃) were successfully synthesized through a facile hydrothermal method followed by a subsequent heat treatment. We found that the surfactants played a critical role in the formation process and the possible formation mechanism was discussed. Especially when chromic chloride hexahydrate was added as a surfactant, the unique net-like structure was prepared. Furthermore, the gas-sensing properties of the sample were tested towards the reducing ethanol gas. The results indicated that the MoO₃ with a net-like structure shows the largest response than the other structures.     

Improvement of structural and mechanical properties of alumina coatings by incorporation of TiO2 and α-Al2O3 nanoadditives

Abstract

Alumina coatings embedded with different nanoadditives were fabricated on aluminium alloy by microarc oxidation (MAO). Incorporation of nanograins into the prepared coatings was accomplished by dispersing nanoadditives into different electrolytes during the MAO process. Our results show that nanograins are successfully embedded in the ceramic coatings, and the embedded coatings are compact and have lower porosity. The mechanical properties of the nanograin embedded coatings such as hardness, adhesion and wear resistance are consequently improved, and the samples prepared in aluminate electrolyte with α-Al₂O₃ nanoadditive have better mechanical properties than those prepared in other electrolytes. Our results also show that the mechanical properties of MAO coatings are closely related to the surface structure. The introduction mechanism of nanograins into the ceramic coatings resulted from the reactions occurring in the microarc discharge channels such as diffusion and electrophoresis, which is believed to improve the structure of the prepared coatings.     

Phase equilibria in the reciprocal system 3Tl2S + Bi2Te3 ↔ 3Tl2Te + Bi2S3

Phase equilibria in the reciprocal system 3Tl₂S + Bi₂Te₃ ? 3Tl₂Te + Bi₂S₃ (A) have been studied by differential thermal analysis, X-ray diffraction, microhardness tests, and emf measurements using thallium concentration cells, and a number of vertical sections, the 300-K isothermal section of its phase diagram, and the liquidus projection have been mapped out. The system is shown to be reversibly reciprocal, with broad solid solution regions in the Tl₂S-Tl₂Te-Tl₉BiTe₆ subsystem and along the TlBiS₂-TlBiTe₂ join. We have determined the homogeneity ranges and primary crystallization fields of the phases and identified the nature and coordinates of invariant equilibria in system A.     

Controlled synthesis of mesoporous α-Fe2O3 nanorods and visible light photocatalytic property

Porous α-Fe₂O₃ nanorods with typical pore size of 2–4 nm were controlled prepared by a facile hydrothermal process of Fe(NO₃)₃·9H₂O aqueous solution in the presence of NaOH, followed by a calcination treatment. Contrast experiments indicate that the morphology and crystalline structure of the hydrothermal products depend greatly on the quantity of NaOH. Hematite nanoparticles and microplates were respectively obtained under conditions without or with excess NaOH. The porous α-Fe₂O₃ nanorods exhibit a high BET surface area of 105.1 m² g^?1 and a pore volume of 0.13 m³ g^?1. UV–vis measurement shows wide absorption to visible light and an obvious blue-shift of the adsorption edge due to the quantum size effect. The visible-light photocatalytic performances of the as-prepared samples were evaluated by photocatalytic decolorization of methylene blue at ambient temperature. The results indicate that the photocatalytic activity of the porous α-Fe₂O₃ nanorods is superior to hematite nanoparticles and platelets and exhibit good reusable feature. The photocatalytic process of porous structure is determined to be pseudo-first-order reaction with apparent reaction rate constant of 1.04 × 10^?2 min^?1. And the optimum photocatalyst dosage is 20 mg per 100 mL of dye solution. The porous α-Fe₂O₃ nanorods are considered potential photocatalyst for practical application due to the excellent photocatalytic behavior and good reusability.     

Thermal Conductivity, Thermal Expansion, and Microhardness of CaLa2S4–La2S3 Solid Solutions

The thermal conductivity, thermal expansion, and microhardness of CaLa₂S₄–La₂S₃ solid solutions were measured. The increase in thermal expansion in going from La₂S₃ to CaLa₂S₄ was shown to correlate with the variation in bond strength. The thermal conductivity and microhardness were found to vary nonmonotonically, which was interpreted in terms of the defect structure of the solid solutions. The estimated thermal shock resistance of the solid solutions passes through a maximum around 70 mol % La₂S₃.     

Electrical and optical properties of single crystalline α-Al2O3 doped with nickel

Nickel, substituting for aluminium in α-Al₂O₃ acts as an acceptor with a level ∼2.46 eV above the conduction band if a large polaron model applies, ≅ 2.57eV−H(μ _h) above the band if a small polaron model applies. It is present as Ni³⁺ at high, and as Ni²⁺ at low, oxygen pressures, the concentration of Ni³⁺ being reduced to one-half of its high value at =1 Pa. Analysis of the data provides proof that the native defect compensating the charge of Ni²⁺ (=ni _al ^′ ) is V _O ^2. , Al _i ^3. being a minority species; H _F,Al−1/2H _s=121 kJ mol⁻¹.