Copper ferrite superparamagnetic nanoparticles as a heterogeneous catalyst for directed phenol/formamide coupling

The copper ferrite-catalyzed, directed coupling of ortho-arylated phenols and dialkylformamides in the presence of a peroxide oxidant is described. Acyclic and cyclic amides were compatible with the reaction conditions. The copper ferrite catalyst is heterogeneous since substantial leaching was not detected and re-use of the catalyst for 9 consecutive reactions proceeded without a significant decrease in yield. To the best of our knowledge, this transformation has not been previously performed under heterogeneous catalysis conditions.     

Raman characterization of α- and β-LiFe5O8 prepared through a solid-state reaction pathway

Lithium ferrite, a mixed-inverse spinel of type A_xB_y[A_1−xB_1−y]O₄ was produced through solid state synthesis by calcining a Li₂CO₃/Fe₂O₃ mixture at 900 °C. The presence of both the ordered α-phase and disordered β-phase of LiFe₅O₈ was confirmed by XRD analysis, while formation of the latter was achieved by air quenching from high temperature. Laser Raman analysis was performed on both the α-LiFe₅O₈ and β-LiFe₅O₈ powders in order to achieve a reference set of Raman shifts for the spinel. The strongest, characteristic Raman peaks were determined to be 493, 382, 358, 300, and 263 cm⁻¹ for both phases while smaller peaks at 202 and 236 cm⁻¹ present in the α-phase were diminishing in intensity when the β-phase was present, thus providing unique identifiers for the presence of the disordered ferrite structure. SEM images taken of the synthesized LiFe₅O₈ powders showed particle sizes of less than 300 nm and an even particle size distribution.     

p-Type thermoelectric properties of the oxygen-deficient perovskite Ca2Fe2O5 in the brownmillerite structure

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion α_L) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma-Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α²σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden-Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10⁻⁶ K⁻¹) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.     

高透量 PdAu/陶瓷复合膜的表征与性能评测

 采用化学镀方法在非对称氧化铝管状载体上制备出高性能 PdAu 合金膜. 采用阶段性热处理方法通过 X 射线衍射技术监测 PdAu 膜层合金化进程, 发现在 823 K 下 H2 气氛中厚度为 2 μm, Au 含量为 17.37% 的 PdAu 双金属膜层需要 200 h 达到完全合金化; N2/H2 气氛对 PdAu 合金化速率无显著影响, 但 N2 气氛中合金化后的 PdAu 合金膜表面粒子烧结更为严重. 在 623~823 K 下, 与未进行化学镀 Au 时的纯 Pd 膜相比, PdAu 合金膜的 H2 渗透速率平均增加 1.68 倍, 透氢活化能 (Ea) 降低 38.51%; 当温度低于 573 K 时, PdAu 合金膜的 Ea 由高温时的 8.83 kJ/mol 增加到 15.75 kJ/mol, 此时 PdAu 合金膜的 H2 渗透控速步骤由体相扩散为主的 H2 传质步骤过渡到由表面扩散为主的传质步骤. 通过扫描电镜和能谱联用仪对 PdAu 合金膜的膜厚度和截面组成进行了表征. 关键词     

Microstructure and magnetic properties of CoFe_2O_4 thin films deposited on Si substrates with an Fe_3O_4 under-layer

The microstructure and magnetic properties of cobalt ferrite thin films deposited by the sputtering method on an Fe3O4 under-layer were investigated at different post-annealing temperatures.Results show that the Fe3O4 under-layer can accelerate the grain growth of cobalt ferrite films due to the phase transformation of the Fe3O4 under-layer at about 400°C-500°C.By introducing the Fe3O4 under-layer,cobalt ferrite nanocrystalline thin films with high coercivity can be obtained at lower post-annealing temperat...     

多功能磁光子晶体太赫兹可调偏振控制器件

通过对磁场控制下的二维磁光子晶体太赫兹波偏振传输特性的研究,利用铁氧体磁光材料的磁导率随外磁场改变而变化的特点,设计了具有可控起偏、偏振分束和可调谐波片功能的光子晶体太赫兹偏振控制器件.利用平面波展开法和严格耦合波分析分别计算了光子晶体带隙位置和透过率随外磁场强度变化的关系,用时域有限差分法计算了场分布和相位.结果表明,该结构可以实现高偏振消光比的偏振起偏器和分束器,以及在1 THz附近-π-π相位范围的连续可调谐波片. 关键词： 太赫兹 光子晶体 铁氧体 偏振控制     

Effects of pulsed bias duty ratio on microstructure and mechanical properties of TiN/TiAlN multilayer coatings

TiN/TiAlN multilayer coatings were deposited on M2 high speed steel by a pulsed bias arc ion plating system. The effect of pulsed bias duty ratio on the microstructure, mechanical and wear properties was investigated. The amount of macroparticles reduced with the increase of the duty ratio. The surface roughness was 0.0858 μm at duty ratio of 50%. TiN/TiAlN multilayer coatings were crystallized with orientations in the (1 1 1), (2 0 0) (2 2 2) and (3 1 1) crystallographic planes and the microstructure strengthened at (1 1 1) preferred orientation. At duty ratio of 20%, the hardness of TiN/TiAlN multilayer coatings reached a maximum of 3004 HV, which was 3.2 times that of the substrate. The adhesion strength reached a maximum of 77 N at 50% duty ratio. Friction and wear analyses were carried out by pin-on-disc tester at room temperature. Compared with the substrate, all the specimens coated with TiN/TiAlN multilayer coatings exhibited better tribological properties.     

Electrocatalysis of oxygen reduction reaction on Nafion/platinum/gas diffusion layer electrode for PEM fuel cell

In this work a new membrane electrode based on Pt-coated Nafion membrane was fabricated. Chemical deposition process was used to coat platinum on Nafion 117 membrane and then Pt-coated Nafion membrane was hot pressed on gas diffusion layer (GDL) to make new membrane electrode. The electrochemical and chemical studies of the Pt-coated Nafions were investigated by electrochemical techniques, X-ray diffraction and scanning electron microscopy. The electrochemical results indicated that as the concentration of H₂PtCl₆ increased, the oxygen reduction reaction rate increased until the concentration was reached where the reduction reaction was limited by the problem of mass transport. The electrochemical results for oxygen reduction reaction showed that the new electrode which prepared by plating Nafion membrane with 0.06 M H₂PtCl₆ in electroless plating solution, has a higher performance than other electrodes. The XRD results showed that the average platinum particle size of the best sample was about 3 nm. The loading of platinum for this electrode was 0.153 mg cm⁻².     

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10 mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40 N and 18 GPa, respectively. Thus such TiN thin films can be expected in applications.     

A corrosion resistant cerium oxide based coating on aluminum alloy 2024 prepared by brush plating

Cerium oxide based coatings were prepared on AA2024 Al alloy by brush plating. The characteristic of this technology is that hydrogen peroxide, which usually causes the plating solution to be unstable, is not necessary in the plating electrolyte. The coating showed laminated structures and good adhesive strength with the substrate. X-ray diffraction and X-ray photoelectron spectroscopy analysis showed that the coatings were composed of Ce(III) and Ce(IV) oxides. The brush plated coatings on Al alloys improved corrosion resistance. The influence of plating parameters on structure and corrosion resistance of the cerium oxide based coating was studied.