Anomalous behavior of aminohydroxynaphthalenesulfonic acids during diazo coupling

The effect of pH on the diazo coupling reaction of some commonly used coupling components (J-acid, Gamma acid, H-acid and S-acid) with monosubstituted diazobenzenes has been investigated. The results demonstrate that, contrary to previous reports, selective diazo coupling ortho to an amino group of an aminohydroxynaphthalenesulfonic acid does not occur in weakly acidic (pH 5–6) media. In fact, such media were found to give nearly exclusive diazo coupling ortho or para to the hydroxyl group. The desired amine coupling reactions required a pH of 3.0–3.5 and occurred only with the more reactive diazonium salts. The structures of the dyes obtained were unambiguously determined with the aid of ¹H-NMR spectroscopy.     

激光能量密度对激光熔覆NiCoCrAlY涂层组织与性能的影响

为探究激光熔覆过程中能量密度对NiCoCrAlY涂层组织与性能的影响,在304不锈钢表面制备了NiCoCrAlY涂层.利用X射线衍射仪、扫描电子显微镜分析了NiCoCrAlY涂层的相组成和微观组织.通过显微维氏硬度计和往复摩擦磨损试验机研究了NiCoCrAlY涂层的硬度和耐磨性能.结果表明:NiCoCrAlY涂层气孔数...     

Structure and mechanical properties of nanofibrous ZrO2 derived from alternating field electrospun precursors

Nanofibrous zirconia (ZrO₂) meshes were prepared from precursor fibers which were synthesized using the method of free-surface, high-yield alternating field electrospinning (AFES). The weight ratio of zirconyl chloride salt to polyvinylpyrrolidone (PVP) polymer in liquid precursors was investigated for its effect on the spinnability and formation of precursor fibers as well as on the resulting fibrous ZrO₂. The precursor fiber generation measured at a rate up to 5.6 g/h was achieved with a single flat 25-mm diameter alternating current (AC) electrode, which corresponded to production of up to 1.5 g/h of fibrous ZrO₂. The calcination process involved annealing the fibers at temperatures which ranged from 600 °C to 1000 °C and produced 0.1–0.2 mm thick fibrous ZrO₂ meshes. Individual nanofibers were found to have diameters between 50 and 350 nm and either a tetragonal (t-ZrO₂) or monoclinic (t-ZrO₂) structure depending on the calcination temperature. The annealed meshes with total porosity between 98.0 ± 0.2% and 94.6 ± 0.2% showed little deformation or cracking. Tensile strength and modulus of fibrous t-ZrO₂ meshes strongly depended on porosity and varied from 0.07 ± 0.03 MPa to 1.05 ± 0.3 MPa and from 90 ± 40 MPa to 388 ± 20 MPa, respectively. The m-ZrO₂ meshes resulted similar moduli, but much lower strengths due to their brittleness. A power-law relationship between the elastic modulus and porosity of AFES-derived nanofibrous t-ZrO₂ meshes, in comparison with other porous zirconia materials, was also investigated. The results of this study have demonstrated the feasibility of free-surface AFES in sizeable production of zirconia nanofibers and highly porous nanofibrous ceramic structures.     

A partial sulfidation approach that significantly enhance the activity of FeCo layered double hydroxide for oxygen evolution reaction

We report a partial sulfidation approach that effectively boosts the OER activity of FeCo-layered double hydroxides (LDH). It is found that the mild sulfurized FeCo-LDH nanosheets using Na₂S converted a portion of their surface metal-hydroxide bonds to metal-sulfur (-hydrosulfide) bonds without significantly altering their crystal structure. The sulfidation degree is controlled by Na₂S concentration for obtaining a moderately surface electronic configurations. Benefits from the regulated electronic configurations, the sulfurized FeCo-LDH nanosheets only require an overpotential of 281 mV to produce oxygen at 10 mA cm⁻² and their Tafel slope is 51.8 mV dec⁻¹, which are both lower than the 348 mV and 72.7 mV dec⁻¹ of pristine FeCo-LDH nanosheets. The sulfurized catalysts have sustained 12 h of operation without notable activity loss. This work can provide new insights into understanding the roles of metal-sulfur bonds for OER and offer an attractive strategy to design low cost but efficient OER catalysts.     

The use of a carbonized phenolic formaldehyde resin coated Ni foam as an interlayer to increase the high-temperature strength of C/C composite-Nb brazed joints

A novel carbonized phenolic formaldehyde resin (PF) resin-coated Ni foam was used as an interlayer for brazing carbon fiber reinforced carbon composites (C/C) and Nb using a Ti–Ni filler. At first, uniformly distributed carbonaceous laminae with different mass fractions on the Ni foam surface were acquired after the carbonization process by controlling the concentration of the PF solution. Afterwards, the obtained carbonaceous laminae covered Ni foam composite (C-Ni_f) was applied as an interlayer for brazing C/C and Nb via an assembly of C/C/Ti foil/Ni foil/C-Ni_f interlayer/Ti foil/Nb. The morphologies and microstructures of the carbonization product and the interfacial microstructures of the joints were investigated. The brazing mechanism has been elaborated in detail. With the help of the interconnected porous structure of the Ni foam, the distribution of the in-situ formed (Ti,Nb)₂Ni particles, (Ti,Nb)C ring reinforcements as well as the Nb solid solution were uniformly obtained throughout the brazing seam. As a result, the joint residual stress was effectively released and consequently, the joint shear strength at elevated temperature (1000 °C) reached up to 33 MPa, which is 4.5 times higher than the directly brazed joint without an interlayer.     

Improvement the electrochemical performance of Cr doped layered-spinel composite cathode material Li1.1Ni0.235Mn0.735Cr0.03O2.3 with Li4Ti5O12 coating

The Cr doped layered-spinel composite cathode material Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 was synthesized and coated with different content of Li₄Ti₅O₁₂ by a sol–gel method. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of Li₄Ti₅O₁₂ coatings on the electrochemical performance of the pristine material was evaluated from charge/discharge cycles, rate performance, and electrochemical impedance spectroscopy (EIS). The XRD results show that the lattice crystal and the content of spinel phase have been increased in the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials after Li₄Ti₅O₁₂ coating. The results from TEM and selected area electron diffraction (SAED) indicate that the Li₄Ti₅O₁₂ coating assumes a spinel structure on the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3. The discharge capacities, cycling and rate performances of the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials in the first cycle are improved with the addition of Li₄Ti₅O₁₂. Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 coated with 3 wt% Li₄Ti₅O₁₂ shows the highest discharge capacity (271.7 mA h g⁻¹), highest capacity retention (99.4% for 100 cycles), and best rate capability (132 mA h g⁻¹ at 10 C). EIS result indicates that the resistance of Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 electrode decreases with the addition of Li₄Ti₅O₁₂. The enhanced electrochemical performance can be ascribed to the increased spinel content, lower resistance and the enhanced lithium-ion diffusion kinetics.     

Effect of cooling parameters on the microstructure and properties of Mobearing and Cr-bearing steels

To develop low-cost low carbon bainitic steel,Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory.As the cooling rate increases from 0.2 to 50℃/s,the transformation temperatures of two steels lie between 650 and 400℃,and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite.Compared with cooling in air or by interrupted cooling,Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness,for large-size islands are responsible for the poor mechanical properties.Compared to Mo,Cr is effective to isolate the bainitic reaction in low carbon steel,and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.     

17-4PH不锈钢时效析出相的形成过程

对17-4PH(0Cr17Ni4Cu4Nb)马氏体不锈钢进行了3种不同条件下的时效处理。利用透射电子显微镜(TEM)技术详细分析了17-4PH不锈钢时效处理后析出相的形成过程。实验结果表明,时效条件为442℃,8h空冷时,在马氏体内部析出弥散的、尺寸小于10nm的ε-Cu、Nb6C(N)5和Nb2C(N)型亚稳相颗粒;时效条件为465℃,4h空冷时,析出尺寸为10～15nmε-Cu和稳定的NbC(N)相;时效条件为480℃,1h空冷时,析出尺寸为20～25mm的ε-Cu+NbC(N)相,且析出相NbC(N)与马氏体为共格析出,取向关系为NbC[001]//α-Fe[001]。     

修饰剂对1,2-丙二醇体系中制备纳米镍的影响

用有机醇液相还原制备不同形貌、粒径的纳米镍,通过X射线衍射、透射电子显微镜、选区电子衍射和傅里叶红外光谱对其进行了表征。讨论了吐温系列(Tween-20、Tween-40和Tween-80)和十二烷基硫酸钠(SDS)单独或两者复配为修饰剂时,对所制备纳米镍的形貌、粒径及粒径分布的影响。结果表明,Tween-20为修饰剂时易形成粒径较小的以十二面体和三角形薄片为主的规则晶体;Tween-80为修饰剂易形成粒径较大的雪花状晶体;Tween-40和SDS复配易形成粒径较大的十二面体和八面体为主的规则晶体。初步解释了修饰剂的作用机理为静电效应和位阻效应。