Fretting wear behavior of laser-nitrided Ti–5Al–5Mo–5V–1Cr–1Fe alloy fabricated by laser melting deposition

Fretting wear behavior of laser-nitrided titanium alloy (Ti–5Al–5Mo–5V–1Cr–1Fe) fabricated by laser melting deposition (LMD) has been investigated to explore surface engineering for protection against wear damage of laser melting deposited titanium alloy. The morphology and volume of the wear scars of unmodified and laser-nitrided LMD Ti–5Al–5Mo–5V–1Cr–1Fe tested at different frequencies, 10 and 50 Hz, were studied using non-contact three-dimensional surface profilometer and scanning electron microscope. Friction coefficients measured at different frequencies or loading forces were compared for unmodified and laser-nitrided LMD specimens. Experimental results show that laser-nitrided LMD specimens have shown fretting resistance superior to unmodified LMD specimens due to the presence of hard TiN dendrites in the laser-nitrided layer. W-shaped wear scar caused by local rotation of fretting ball at the two ends of the scar was observed. Given a constant loading force of 50 N, unmodified and laser-nitrided LMD specimens exhibited similar friction coefficients and their friction coefficients increased with test frequency. The friction coefficients of both specimens increased with the reduction of normal load, which corresponds to the trend in Hertzian contact model.     

Structure selective complexation of cyclodextrins with five polyphenols investigated by capillary electrokinetic chromatography

The complexation of five polyphenols, namely trans‐resveratrol, astilbin, taxifolin, ferulic acid, and syringic acid (guest molecules) with α‐, β‐, and γ‐cyclodextrin (host molecules), was investigated by capillary electrokinetic chromatography. The binding constants were calculated based on the effective electrophoretic mobility change of guests with the addition of cyclodextrins into the background electrolyte. Because of cavity size, cyclodextrins showed structure‐selective complexation property to different guest. The stability of the trans‐resveratrol complexes was in the order of β‐ > α‐ > γ‐cyclodextrin. The cavity size of α‐cyclodextrin was too small for astilbin and taxifolin molecules, and thus they could not form complexes. The molecular size of syringic acid was too big for all cyclodextrins cavity, and no cyclodextrin could form complexes with it. Temperature studies showed that the binding constants decreased with the rise of temperature. Enthalpy and entropy values were calculated and the negative values of these parameters indicated that the complexation process was enthalpy‐controlled. Van der Waals force and release of high‐enthalpy water molecules from the cyclodextrins cavity played important roles in the process.     

新型非贵金属碳材料的开发及其氧还原性能研究

高效碳基非贵金属氧还原催化剂的开发是燃料电池突破高成本壁垒,实现商业化应用的关键.本文以金属有机框架为前驱体,采用简易的硫化-烧结处理工艺设计获得了一种新型钻/氮掺杂的多孔碳材料.通过对制备工艺进行优化,提高了材料的氧还原催化活性,分析获得了材料的微观结构与氧还原性能之间的相互影响规律,为非贵金属催化剂的开发提供了参考...     

套索冠醚固定相的气相色谱研究

用一种新合成的套索冠醚Ｎ，Ｎ′－双（乙酰苄胺）－二氮杂－１８－冠－６作为固定相，涂渍在弹性石英毛细管内，测其柱效、惰性、热稳定性、平均极性及选择性等性质。实验表明，它具有良好的色谱性能，中等极性，分离选择性高，适用于对醇、卤代烃、芳香烃等各类异构体的分离，并从分子结构和热力学参数等探讨了保留机理。     

Influence of Gas Components on the Formation of Carbonyl Sulfide over Water-Gas Shift Catalyst B303Q

Water-gas shift reaction catalyst at lower temperature (200—400℃) may improve the conversion of carbon monoxide. But carbonyl sulfide was found to be present over the sulfided cobalt-molybdenum/alumina catalyst for water-gas shift reaction. The influences of temperature, space velocity, and gas components on the formation of carbonyl sulfide over sulfided cobalt-molybdenum/alumina catalyst B303Q at 200—400℃were studied in a tubular fixed-bed quartz-glass reactor under simulated water-gas shift conditions. The experimental results showed that the yield of carbonyl sulfide over B303Q catalyst reached a maximum at 220℃with the increase in temperature, sharply decreased with the increase in space velocity and the content of water vapor, increased with the increase in the content of carbon monoxide and carbon dioxide, and its yield increased and then reached a stable value with the increase in the content of hydrogen and hydrogen sulfide. The formation mechanism of carbonyl sulfide over B303Q catalyst at 200—400℃was discussed on the basis of how these factors influence the formation of COS. The yield of carbonyl sulfide over B303Q catalyst at 200-400℃was the combined result of two reactions, that is, COS was first produced by the reaction of carbon monoxide with hydrogen sulfide, and then the as-produced COS was converted to hydrogen sulfide and carbon dioxide by hydrolysis. The mechanism of COS formation is assumed as follows: sulfur atoms in the Co9S8-MOS2/Al2O3 crystal lattice were easily removed and formed carbonyl sulfide with CO, and then hydrogen sulfide in the water-gas shift gas reacted with the crystal lattice oxygen atoms in CoO-MoO3/Al2O3 to form Co9S8-MoS2/Al2O3. This mechanism for the formation of COS over water-gas shift catalyst B303Q is in accordance with the Mars-Van Krevelen's redox mechanism over metal sulfide.     

Uniform-sized molecularly imprinted polymer for metsulfuron-methyl by one-step swelling and polymerization method

Uniform-sized molecularly imprinted polymer (MIP) beads for metsulfuron-methyl (MSM) were firstly prepared by one-step swelling and polymerization method using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. The preparation was optimized by varying the ratio of MSM to 4-VPY. The chromatographic behaviors of MSM and other structurally related sulfonylureas (SUs) on the resultant MIP column were evaluated. The imprinted polymer revealed specific affinity to the template and the fair resolution of SUs was also obtained. Furthermore, the uniform-sized MSM-MIP was used as the solid phase extraction (SPE) material to enrich MSM in real water samples before reversed-phase HPLC (RP-HPLC) analysis. The recovery of MSM from 100 mL of drinking water at a 50 ng/L spike level was 99.59% with R.S.D. of 1.13%. The detection limit was about 6.0 ng/L of MSM when enriching a 100 mL water sample.     

β—（酚酯基）乙基锗倍半氧化物的合成及对体外培养细胞的作用

β-羧基乙基锗倍半氧化物(即Ge-132)是一种无毒和具较强抗癌活性的有机锗化合物。为了进一步提高其抗癌活性。已对Ge-132进行了化学结构修饰。本文介绍8种未见报导的Ge-132衍生物,β-酚酯基乙基锗倍半氧化物的合成和体外培养细胞实验结果。     

Effects of chain entanglement on liquid-liquid phase separation behavior of LCST-type polymer blends: Cloud point and decomposition rate

By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly(methyl methacrylate)/poly(styrene-comaleic anhydride)(PMMA/SMA) blends presenting a typical lower critical solution temperature(LCST) behavior. The meltmixed PMMA/SMA blends with a higher chain entanglement density present a lower cloud point(Tc) and shorter delay time, but lower phase separation rate at the given temperature than solution-cast ones, suggesting that for the polymer blends with different condensed state structure, thermodynamically more facilitation to phase separation(lower Tc) is not necessarily equivalent to faster kinetics(decomposition rate). The experimental results indicate that the lower Tc of melt-mixed sample is ascribed to smaller concentration fluctuation wavelength(Λm) induced by higher entanglement degree, while higher entanglement degree in melt-mixed sample leads to a confined segmental dynamics and consequently a slower kinetics(decomposition rate) dominated by macromolecular diffusion at a comparable quench depth. These results reveal that the chain packing in polymer blends can remarkably influence the liquid-liquid phase separation behavior, which is a significant difference from decomposition of small molecular mixtures.     

Direct Electron Transfer and Electrocatalysis of Myoglobin Based on its Direct Immobilization on Carbon Ionic Liquid Electrode

Direct electron transfer of myoglobin (Mb) was achieved by its direct immobilization on carbon ionic liquid electrode (CILE) with a conductive hydrophobic ionic liquid, 1‐butyl pyridinium hexaflourophosphate ([BuPy][PF₆]) as binder for the first time. A pair of well‐defined, quasi‐reversible redox peaks was observed for Mb/CILE resulting from Mb redox of heme Fe(III)/Fe(II) redox couple in 0.1 M phosphate buffer solution (pH 7.0) with oxidation potential of ?0.277 V, reduction potential of ?0.388 V, the formal potential E°′ (E°′=(E_pa+E_pc)/2) at ?0.332 V and the peak‐to‐peak potential separation of 0.111 V at 0.5 V/s. The average surface coverage of the electroactive Mb immobilized on the electrode surface was calculated as 1.06±0.03×10^?9 mol cm^?2. Mb retained its bioactivity on modified electrode and showed excellent electrocatalytic activity towards the reduction of H₂O₂. The cathodic peak current of Mb was linear to H₂O₂ concentration in the range from 6.0 μM to 160 μM with a detection limit of 2.0 μM (S/N=3). The apparent Michaelis–Menten constant (K and the electron transfer rate constant (k_s) were estimated to be 140±1 μM and 2.8±0.1 s^?1, respectively. The biosensor achieved the direct electrochemistry of Mb on CILE without the help of any supporting film or any electron mediator.