Unusual nucleation and growth of γ′ iron nitride upon nitriding Fe–4.75 at.% Al alloy

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe₄N_{1? x} ) was investigated upon nitriding in NH₃/H₂ gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe₂N_{1? z} ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite.     

Recent progress on the frontiers of polyoxometalates structures and applications

<正>Polyoxometalates (POMs), a class of discrete anionic metal oxides in groups Ⅴ and Ⅵ, are constructed via the condensation of metal oxide polyhedral (MO_x, M=W~(Ⅵ), Mo~(Ⅵ),V~Ⅴ, Nb, Ta, etc. and x=4–7) with each other in a corner-,edge-, or rarely in a face-sharing manner [1–3]. Up to now,the broadening family of POM derivatives ranges from small     

EAST ������ICRF ���ߵ���ά��ų�����

The performance of the four strap ion cyclotron range of frequency (ICRF) antenna in EAST was studied by three dimensional electromagnetic code CST MWS. The coupling impedance with various frequencies, the distribution of current on straps and the power spectra for the three types of phases were calculated. The voltage breakdown and ICRF-related impurity were also studied. Simulation results show that the coupling impedance and power spectrum of the antenna design were reasonable, however, highest electric field, which is 3.61MV•m⁻¹ for (0, 0, 0, 0) toroidal phasing at the local area, exceeds the empirical value of breakdown. After the structure size was optimized, the maximum of E-field was below the breakdown value, the results also show that the high radio frequency (RF) potential was close to the antenna limiter, the RF potential along total B-field in front of Faraday screens 10mm for (0, π, π, 0) phasing was one-third of that for (0, 0, π, π) phasing.     

Type II hybrid structures of TiO2 nanorods conjugated with CdS quantum dots: assembly and optical properties

We developed a novel method to assemble TiO₂ nanorods conjugated with CdS quantum dots by L-cysteine molecular linker for type II semiconducting hybrid structure. The XRD patterns indicate that the CdS quantum dots perform the cubic phase structure, and TEM images show that CdS quantum dots are well dispersed on the surfaces of anatase TiO₂ nanorods with little agglomeration. The UV-vis absorption spectra reveal the bandgap alignment in type II configuration between CdS QDs and TiO₂ nanorods.     

磁性Y-MOF@SiO2@Fe3O4催化剂的制备及其在Aza-Micheal加成反应中的性能

在磁性SiO₂@Fe₃O₄纳米微球表面原位合成包覆不同含量的Y-MOF,从而制备出新型磁性Y-MOF@SiO₂@Fe₃O₄催化剂。采用XRD、TEM、FT-IR、VSM和N₂吸附-脱附测试等手段对催化剂的结构进行表征,并且评价了催化剂对苯胺和丙烯酸甲酯的Aza-Micheal加成反应性能。结果表明Y-MOF能均匀包覆在磁性SiO₂@Fe₃O₄纳米微球表面,形成具有核壳结构的磁性Y-MOF@SiO₂@Fe₃O₄催化剂,催化剂具有良好的超顺磁性。Y-MOF含量为43.3%（w/w）的Y-MOF@SiO₂@Fe₃O₄催化剂,在苯胺和丙烯酸甲酯的Aza-Micheal加成反应表现出最好的催化性能,丙烯酸甲酯的转化率为88.3%时,N-（β-甲氧碳酰乙基）苯胺的选择性可达99.8%。反应后的催化剂可以通过外磁场容易回收,并且重复使用5次其转化率和选择性没有明显下降。     

Copper-catalyzed reaction of alkyl halides with cyclopentadienylmagnesium reagent

Treatment of alkyl halides, including tertiary alkyl bromides, with cyclopentadienylmagnesium bromide in the presence of a catalytic amount of copper(II) triflate yielded the corresponding cyclopentadienylated products in high yields. The following hydrogenation of the products provided alkyl-substituted cyclopentanes.     

A fluorescent fluoride ion probe based on a self-organized ensemble of 5-hydroxyflavone-Al(III) complex

In the presence of Al(III) ions, 5-hydroxyflavone (5HF) through a complexation reaction in MeOH, shows dual fluorescence, characterized by a newly developed peak at 554nm upon excitation at 363nm. In this communication, the subsequent ligand exchange reaction of the complex with fluoride ion causing a fluorescence enhancement followed by a decrease in fluorescence intensity involving an intermediate mechanistic pathway, delivering a quantitative estimation route for fluoride ion in the concentration range from 5x10(-5) to 7x10(-4)M, has been reported. The ligand exchange reaction, without interference from other common anions, has been investigated by UV-vis and fluorescence spectroscopies combined with the AM1 semi-empirical self-consistent field quantum chemical calculations within UHF formalism in their ground state.     

An Efficient synthesis of pyrimido[4,5‐b]quinoline and indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidine derivatives via multicomponent reactions in ionic liquid

A series of pyrimido[4,5‐b]quinoline and indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidine derivatives were synthesized via the three‐component reaction of an aldehyde, 6‐aminopyrimidine‐2,4‐dione and 5,5‐dimethyl‐1,3‐cyclohexanedione or 1,3‐indanedione in ionic liquid 1‐n‐butyl‐3‐methylimidazolium bromide ([bmim]Br). This protocol has the advantages of easier work‐up, milder reaction conditions, high yields and an environmentally benign procedure compared with other methods.     

Stability and bonding of carbon(0)-iron−N2 complexes relevant to nitrogenase co-factor: EDA-NOCV analyses

The factors/structural features which are responsible for the binding, activation and reduction of N₂ to NH₃ by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N₂-binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ₆-bridge. Here, a series of [(S₃C(0))Fe(II/I/0)-N₂]^n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph₃P)₂C(0); Ph₃P→C(0)←PPh₃] and three S-donor sites (i.e. ^-S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N₂-binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N₂-binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe−N₂ bond are in the range from −42/−35 to −67 kcal/mol in their corresponding ground states. The S₃C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S₂C_ring donor, π-C donor) and stronger donor set like CP₃ (σ-C donor) ligands, respectively.