Preparation and characterization of optical spectroscopy of Lu2O3:Eu nanocrystals

Nanoscale Lu₂O₃:Eu powders were prepared by solution combustion synthesis. X-ray diffraction (XRD), high-resolution electronic microscope (HREM), Fourier transform infrared spectroscopy (FT-IR), excitation and emission spectra, as well as fluorescent decay curves were measured to characterize the structure and luminescent properties of the samples. The results show that the compound of composition Lu₂O₃ crystallizes in pure cubic structure. By changing the ratio of glycine to nitrate in the combustion process, the particle size varies from 40 nm to less than 5 nm. The emission and excitation spectra strongly depend on the particle size of the samples. Novel emission band, red-shift of charge transfer band (CTB) and shortening of lifetime were observed in nanoscale samples.     

Nanocrystalline undoped tetragonal and cubic zirconia synthesized using poly-acrylamide as gel and matrix

Nanocrystalline zirconia powders with tetragonal and cubic structure have been prepared from ZrO₂-polyacrylamide gel and precipitated zirconia in polyacrylamide matrix respectively. X-ray diffraction results of the samples annealed at high temperatures show that the tetragonal and cubic form, obtained from the gel, are fairly stable in air up to 1,173 K and partially stable in inert atmosphere, up to 1,273 K. The stability at such high temperatures is due to the presence of oxygen vacancies in zirconia sample, incorporated in the process of decomposition of polymer.     

Preparation, treatment and characterisation of nanocrystalline mesoporous ordered layers

The general approach to mesoporous ordered silica and crystalline metal oxide thin films, involving soft chemistry, liquid deposition technique, surfactant templating and tuned annealing conditions, is presented. Highly ordered cubic mesoporous structures, made of amorphous SiO₂ xerogels or nanocrystalline particles such as anatase TiO₂, γ-Al₂O₃, ilmenite CoTiO₃, or perovskite SrTiO₃ have been chosen to illustrate this article. In situ time resolved SAXS analyses, involving synchrotron high flux, were used to assess the various phenomena involved during deposition, thermal treatment and crystallisation. It will be demonstrated that the self-assembly is not only critically dependant on the structuring agent to inorganic volume fraction, but also on chemical and processing parameters such as the inorganic degree of condensation and the atmosphere applied during the deposition. A general model of self-assembly, based on a Tunable Stated State, is proposed. Concerning the crystallisation step, we will show that, depending on the heating regime, ordered mesoporous nanocrystalline framework can be obtained through a rigorous control of nucleation, growth and diffusive sintering taking successively place in the mineral matrix. Finally, the porosity and pore size distribution of these silica and non silica layers were assessed using ellipsometry porosimetry. This novel and very efficient technique provides the full characteristics of the layer porosity by measuring the variation of optical constant associated to the adsorption/desorption of a gas within the porous network.     

用于吖内酯合成的二氧化钛纳米晶体材料(英文)

Titanium dioxide nanoparticles were prepared by a electrochemical reduction method using para-meters such as current density, solvent polarity, distance between electrodes, and concentration of stabilizers to control the size of the nanoparticles. The nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microsco-py, and their catalytic performance was tested for the synthesis of a series of 4-aryldiene-2-phenyl-5(4)-oxazolones from the cyclodehydration and condensation of the respec-tive aldehyde, hippuric acid and acetic anhydride. Easy availability, reusability and eco-friendliness were some prominent features of the nanocrystalline titanium dioxide catalyst.     

Fabrication of Cu-SiC surface composite under ball collisions

A nano-grained Cu-SiC surface composite was fabricated on a Cu plate precoated with SiC particles at room temperature after 15 min treatment using ball collisions. The composite formation was the result of mechanical mixing of the plasticized Cu and the SiC particles. Ball collisions refined the grains near the surface to the nanometer scale and destroyed the initial rolling texture of the Cu plate. The surface hardness of the composite layer was almost twice that of the initial Cu plate.     

Copper catalyzed oxidative cross-coupling of aromatic amines with 2-pyrrolidinone: a facile synthesis of N-aryl-γ-amino-γ-lactams

Synthesis of N-aryl-γ-amino-γ-lactams by oxidative coupling of aromatic amines with 2-pyrrolidinone using catalytic amount of CuO nanoparticles is described. The procedure has broad substrate scope, good yields, complete regioselectivity and catalyst recyclability.     

Magnetostrictive behaviour of Fe73.5Si13.5B9Nb3−xMoxCu1 alloys

Magnetostriction, dilatation and calorimetric measurements were performed on FINEMET type as-quenched and heat treated ribbons. Nb was gradually replaced by Mo in order to study the influence of the refractory elements exchange on several magnetostriction parameters. The results could be correlated with magnetic and structural transformations throughout thermal treatments and assured that the whole series is suitable for technical applications.     

Recent progress in nanocrystalline Sm–Co based magnets

Sm–Co alloys are the most promising candidates for high temperature applications in advanced power systems owing to their high Curie temperature and high thermal stability of the magnetic performance. The recently developed nanocrystalline Sm–Co based magnets exhibit great potentials for magnetic performance enhancement and are expected to enlarge applications to services under extreme conditions. However, there have been few comprehensive reviews on the development of the nanocrystalline Sm–Co magnets so far. The efforts in this article are paid to review the recent progress in both experimental and modeling studies on the nanocrystalline Sm–Co magnets. Particularly, the latest advances in nanostructuring technologies, doping modulation, data-driven composition design and strategies for enhancement of magnetic properties have been introduced and evaluated. Finally, new challenges and opportunities regarding the future development of high-performance nanocrystalline Sm–Co based magnets are proposed.     

Crystallisation progress in Si-rich ultra-soft nanocomposite alloy fabricated by melt spinning

The crystallisation process and the ultras-soft magnetic properties of amorphous/nanocomposite alloy Fe_73.5Si_17.5B₅Nb₃Cu₁ fabricated by conventional melt-spinning technique are systematically investigated in terms of thermal analysis and in-situ measurement of magnetisation dynamics. The thermal analysis using differential scanning calorimetry showed that crystallisation from Fe-based amorphous state to α-Fe(Si) started at . Further heating the sample leads to a transformation from the α-Fe(Si) to Fe-B phases at . Crystallisation activation energies were determined using two models: Kissinger and John-Mehl-Avrami (JMA), which were consistent to each other with a value of . High resolution transmission electron microscopy investigation revealed an ultrafine structure of α-Fe(Si) nanocrystallite with mean size of 12.5 nm embedded in an amorphous matrix. At a volume fraction of 86% of α-Fe(Si) phase, optimum soft magnetic properties were obtained with very high permeability of 110,000 and a very low coercivity of 0.015 Oe by annealing the amorphous alloy at in 40 min.     

Nanocrystalline magnetic PrFeCrB alloys

Ribbons of Pr₅Fe_77−xCr_xB₁₈ (x=0$x=0$, 1, 2, 2.5, 3, 4, 5) were produced by melt spinning and then annealed to develop an enhanced-remanence nanocrystalline magnetic material. These nanocomposites with Cr present a coercive field at least 50% higher than the Cr-free ones, which makes them promising materials for bonded magnets. Four different types of annealing were used in order to develop the nanocrystalline state and to optimize the magnetic properties of these alloys. The first was a conventional annealing, where the ribbons were wrapped in a tantalum foil and annealed in an argon atmosphere, but not encapsulated. The second was a flash annealing, where the ribbons were annealed by passing a current through them. The third was a conventional annealing in an external magnetic field. Finally, the fourth was a conventional annealing, where the ribbons were wrapped in a tantalum foil and encapsulated in quartz tubes with argon gas and then annealed. The annealed samples were studied by magnetic measurements, X-ray diffraction, scanning and transmission electron microscopy and atomic force microscopy. The best magnetic properties are found for Pr₅Fe₇₄Cr₃B₁₈, annealed by the fourth method, which resulted in the lowest oxygen content in the annealed nanocrystalline material as confirmed by scanning electron microscopy. The value for the coercive field for this composition is at least 50% higher than for the material without Cr (≈560 vs. ≈320 kA/m) and 40% higher than for the Nd₂Fe₁₄B/Fe₃B nanocomposite with Cr. Curie temperature measurements and X-ray diffraction data showed that the main phases present in all the samples are Pr₂Fe₁₄B, Fe₃B and α-Fe, Pr₂Fe₁₄B being the majoritary phase. From Curie temperature measurements it was also found that Cr atoms preferentially dissolve in the Fe₃B phase.