Microstru cture and oxygen storage capacity of Sr-modified Pt/CeO2 –ZrO2catalysts

Strontium was introduced into CeO2–ZrO2 mixed oxides (CZ) by doping and impreg-nation metho ds, and then Pt was impregnated on the Sr-modifie d CZ to obtain the catalysts. X-ray diffraction (XRD), X-photon spectra (XPS), high-resolution transmission electronic microscopy (HRTEM) and H2 temperature programmed reduction (TPR) were carried out to characterize the micro-structure and reducibility of catalysts. The oxygen storage capacity (OSC) was evaluated with CO serving as probe gas. The results showed that the incorporation of Sr₂₊ in the lattice of CZ could promote the OSC properties by increasing the structure defects and enhancing the diffusion rate of oxygen from bulk to surface. For the Sr-impregnated sample, the strong metal–support interaction (SMSI) between Pt and CZ was interrupted, since Sr covered parti al surface Ce species. Such interruption retarded the back-spillover effect occurring at the Pt/Ce interface at low temperature, resulting in the loss of OSC. Meanwhile, it was found that a part of impregnated Sr₂₊ could partially diffuse from the surface to the inner atomic layers of CZ and partially incorporated in the lattice during the calcination. The OSC performance of Sr-impregnated sample therefore climbed remarkably with the rise of temperature.     

Deletion analysis of oligomycin PKS genes （olmA） in Streptomyces arermitilis

Gene deletion vector pXL05(pKC1139::△olmA1 △olmA4) was used to disrupt oligomycin PKS encoding genes (olmA ) in Streptomyces avermitilis CZ8-73, the producer of anthelmintic avermectins B and the cell growth inhibitor oligomycin, olmA gene cluster in the chromosome was displaced by deletion allele on the plasmid via double crossover. Four of disruptants were confirmed by Southern blotting. Shaking flask experiments and HPLC analyses showed that the four mutants no longer produced the toxic oligomycin, but only made four components of avermectins B, which were avermectin Bla, Blb, B2a, B2b. The yields of avermectins B in these mutants were separately equal to those in CZ8-73. This revealed that olmA genes deletion did not affect the biosynthesis of avermectins. The deletion mutants were proved to be genetically stable, and thus might be promising strains in industrial production of avermectins B.     

Metallic phases of Dong Ujimqin mesosiderite: A field emission scanning electron microscope study

The microstructure of Fe-Ni metallic phases in Dong Ujimqin mesosiderite was studied using the field emission SEM. Taenite is characterized by a zoned structure, consisting of outer clear taenite and inner cloudy zone (CZ). CZ has a typical "island-honeycomb" microstructure. The average size of the island phase is about 358 nm, suggesting a cooling rate of ～ 0. 5℃/Ma at low temperature (<400℃ ). The Ni concentration profiles across kamacite and zoned taenite were also measured by electron probe microscope analysis (EPMA). Formation of the Fe-Ni metallic phases, microstructure in Dong Ujimqin mesosiderite was discussed based on the new low-temperature Fe-Ni phase diagram.     

Corrosion damage evolution and residual strength of corroded aluminum alloys

The LY12CZ aluminum alloy specimens were corroded under the conditions of different test temperatures and exposure durations. After corrosion exposure, fatigue tests were performed. Scanning electron microscopy and optical microscope analyses on corrosion damage were carried out. The definition of surface corrosion damage ratio was provided to describe the extent of surface corrosion damage. On the basis of the measured data sets of the corrosion damage ratio, the probabilistic model of corrosion damage evolution was built. The corrosion damage decreased the fatigue life by a factor of about 1.25 to 2.38 and the prediction method of residual strength of the corroded structure was presented.     

Microstructure and properties of Si-TaSi2 eutectic in situ composite for field emission

The Si-TaSi2 eutectic in situ composite for field emission is prepared by electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) crystal growth technique. The directional solidification microstructure and the field emission properties of the Si-TaSi2 eutectic in situ composite prepared by two kinds of crystal growth techniques have been systematically tested and compared. Researches demonstrated that the solidification microstructure of EBFZM can be fined obviously be-cause of the relatively high solidification rate and very high temperature gradient, i.e. both the diameter and inter-rod spacing of the TaSi2 fibers prepared by EBFZM technique were decreased, and the density and the volume fraction of the TaSi2 fibers prepared by EBFZM technique were increased in comparison with that of the TaSi2 fibers prepared by CZ method. Therefore the field emission property of the Si-TaSi2 eutectic in situ composite prepared by EBFZM can be improved greatly, which exhibits better field emission uniformity and straighter F-N curve.     

Corrosion fatigue behavior of fastening hole structure and virtual crack propagation tests

The fatigue crack propagation behavior of the LY12CZ aluminum alloy fastener involving a central hole in air or in 3.5wt% NaCl solution was investigated. The experimental results indicated that the corrosion fatigue crack growth rate decreased with the increasing loading frequency,and in a corrosive environment,the crack growth rate was slightly larger than that in air. Based on the experimental results,the virtual corrosion fatigue crack propagation tests were investigated and the stochastic process method and the AFGROW simulation method were presented. The normal process and lognormal process were considered for the stochastic process method based on the numerically fitted Paris equation. The distribution of crack size and the corresponding probabilistic model of crack length distribution for a given number of cycles can be found by integrating the stochastic process over time. Using the AFGROW software,the virtual simulation was carried out to analyze the corrosion fatigue crack growth behavior and the predicted crack growth curve was in good agreement with the experimental results.     

Microstructure and properties of a wear resistant Al–25Si–4Cu–1Mg coating prepared by supersonic plasma spraying

A high content silicon aluminum alloy(Al–25Si–4 Cu–1Mg) coating was prepared on a 2A12 aluminum alloy by supersonic plasma spraying. The morphology and microstructure of the coating were observed and analyzed. The hardness, elastic modulus, and bonding strength of the coating were measured. The wear resistance of the coating and 2A12 aluminum alloy was studied by friction and wear test. The results indicated that the coating was compact and the porosity was only 1.5%. The phase of the coating was mainly composed of α-Al and β-Si as well as some hard particles(Al_9Si,Al_(3.21)Si_(0.47), and CuAl_2). The average microhardness of the coating was HV 242, which was greater than that of 2 A12 aluminum alloy(HV 110). The wear resistance of the coating was superior to 2A12 aluminum alloy. The wear mechanism of the 2A12 aluminum alloy was primarily adhesive wear, while that of the coating was primarily abrasive wear. Therefore, it is possible to prepare a high content silicon aluminum alloy coating with good wear resistance on an aluminum alloy by supersonic plasma spraying.     

A new synthetic route to MgO–MgAl_2O_4–ZrO_2 highly dispersed composite material through formation of Mg_5Al_(2.4)Zr_(1.7)O_(12) metastable phase:synthesis and physical properties

Mg_5Al_(2.4)Zr_(1.7)O_(12) metastable phase was successfully synthesized from analytical-grade Mg O,α-Al_2O_3,MgAl_2O_4,and ZrO_2 under an N_2 atmosphere.The sintering temperature was varied from 1650 to 1780°C,and the highest amount of Mg_5Al_(2.4)Zr_(1.7)O_(12) appeared in the composite material when the sintering temperature was 1760°C.According to our research of the formation mechanism of Mg_5Al_(2.4)Zr_(1.7)O_(12),the formation and growth of MgAl_2O_4 dominated when the temperature was not higher than 1650°C.When the temperature was higher than 1650°C,MgO and ZrO_2 tended to diffuse into MgAl_2O_4 and the Mg_5Al_(2.4)Zr_(1.7)O_(12) solid solution was formed.When the temperature reached 1760°C,the formation of Mg_5Al_(2.4)Zr_(1.7)O_(12) was completed.The effect of Mg Al_2O_4 spinel crystals was also studied,and their introduction into the composite material promoted the formation and growth of Mg_5Al_(2.4)Zr_(1.7)O_(12).A highly dispersed MgO–Mg Al_2O_4–ZrO_2 composite material was prepared through the decomposition of the Mg_5Al_(2.4)Zr_(1.7)O_(12) metastable phase.The as-prepared composite material showed improved overall physical properties because of the good dispersion of MgO,MgAl_2O_4,and ZrO_2 phases.     

Photoelectrochemical synergetic degradation of Acid Orange II with TiO2 modified β-PbO2 electrode

Electrochemically assisted photocatalysis is an effective approach to improve photocatalytic efficiency. In this paper, modified β-PbO2 electrode was prepared by TiO2 co-deposition and characterized by SEM and XRD. Then 2.0g TiO2 modified β-PbO2 electrode (2.0 g TiO2 involved in the 200 mL co-deposition solution) was used in electrochemically assisted photocatalytic degradation of Acid Orange II and the influence of initial pH values was investigated when the potential applied across the electrodes was 1.5 V. When the potential applied was 2.5 V, the difference of the degradation process and the final products were studied. The results indicated that 2.0 g TiO2 modified β-PbO2 electrode was different from the unmodified one in that the β-PbO2 crystals became finer and the electrode became more compact and more uniform. The synergetic effect in electrochemically assisted photocatalytic degradation of Acid Orange Ⅱ was observed and degradation efficiency and TOC removal were the highest at initial solution pH 2.0. By UV-visible spectral analysis, it was proved that photoelectrochemical synergetic degradation of Acid Orange Ⅱ went through the step of producing main product maleic acid for the solution at the initial pH 2.0 within 2 h, but the degradation was slow for the solution at the initial pH 12.0.     

超音速等离子喷涂制备的Al–25Si–4Cu–1Mg耐磨涂层的组织与性能

A high content silicon aluminum alloy (Al–25Si–4Cu–1Mg) coating was prepared on a 2A12 aluminum alloy by supersonic plasma spraying. The morphology and microstructure of the coating were observed and analyzed. The hardness, elastic modulus, and bonding strength of the coating were measured. The wear resistance of the coating and 2A12 aluminum alloy was studied by friction and wear test. The results indicated that the coating was compact and the porosity was only 1.5%. The phase of the coating was mainly composed of α-Al and β-Si as well as some hard particles (Al₉Si, Al_3.21Si_0.47, and CuAl₂). The average microhardness of the coating was HV 242, which was greater than that of 2A12 aluminum alloy (HV 110). The wear resistance of the coating was superior to 2A12 aluminum alloy. The wear mechanism of the 2A12 aluminum alloy was primarily adhesive wear, while that of the coating was primarily abrasive wear. Therefore, it is possible to prepare a high content silicon aluminum alloy coating with good wear resistance on an aluminum alloy by supersonic plasma spraying.     

Sr2Mn2CuAs2O2的第一性原理计算研究

基于第一性原理计算,研究了3种不同结构的同组分物质Sr2Mn2CuAs2O2的电子能带结构及物质总能量,并探讨了Sr2Mn2CuAs2O2可能的最稳定结构.结果表明,3种不同结构的Sr2Mn2CuAs2O2材料均表现出金属性,且主要是具有Mn原子的层状结构起导电作用.其中同时含有CuO2层面与Mn2As2四面体层,并具...     

溴代叔丁烷的合成

报道用叔丁醇和氢溴酸在浓硫酸作催化剂的条件下，合成溴代叔丁烷的实验研究，讨论了各种因素对其产率的影响。得到了其最佳合成条件：叔丁醇：氢溴酸：浓硫酸为8：14：7(体积比)时，温度控制在30℃-35℃，其产率达到67％。     

LuNi_2B_2C、YNi_2B_2C超导参量的研究

用二带G-L模型研究了非磁性超导LuNi2 B2C和Yni2B2C的相干长度ξ(T)、速率vc(T)、伦敦穿透深度λ(T)和临界电流密度j(T)在Tc附近对温度T的依赖关系.     

O_2-O_2,O_2-N_2和O-N_2分子相互作用势模型

利用Tang Toennies(TT)势模型,计算了O2-O2,O2-N2,和O-N2相互作用势,得到了重要的的相互作用势的参数Rm和ε,并在此基础上计算了O2-O2系统的输运系数.其结果与文献值符合较好,说明TT势模型对于计算氧分子系统是可行的.     

SnCl2·2H2O催化下H2O2对2-金刚烷酮的Baeyer-Villiger氧化

以SnCl2.2H2O为催化剂,质量分数为30%的H2O2为氧化剂,催化氧化2-金刚烷酮得到相应的内酯,选择性高达100%,通过柱层析分离产物,并进行NMR表征.考察了溶剂、反应温度、催化剂用量、反应时间对催化剂催化活性及产物选择性的影响,简单探讨了该催化氧化体系的反应机理.     

NiP2,Ni2P2,Ni 3P2,Ni4P2团簇的量子化学研究

根据化学键理论和非晶态结构的短程有序,设计了晶态团簇NNiP2,Ni2P2,Ni 3P2,Ni4P2的四种构型,并用DFT方法对他们的几何结构型进行高水平的量子化学计算.结果表明,模型体系中P原子供给Ni原子电子这与非晶态合金Ni81.5,5p18.5的实验结构一致,说明NiP2,Ni2P2,Ni 3P2,Ni4P2原子簇模型能反映非晶态Nig1.5 P18.5的结构特点.     

团簇Co2FeB2和CoFe2B2稳定性的研究

为深入了解非晶态Co-Fe-B合金的性质,本文从能量学视角,对团簇Co2FeB2和CoFe2B2各构型所占比例定量分析,探究其稳定性,发现团簇Co2FeB2的结合能和吉布斯自由能变化量随构型能量增加出现剧变点,临界能量约为463.061a.u,主要存在构型为能量低于临界值的两种戴帽三角锥和一种四角锥构型。团簇CoFe2B2的结合能和吉布斯自由能变不存在剧变点,有多种异构体共存。高Co含量的团簇有较小的结合能和吉布斯自由能变化量,稳定性弱,此结论符合相关文献报道。     

钐、铕、镱无水二氯化物的合成与性质

改进锌还原法制备了SmCl_2,EuCl_2和YbCl_2(mp 832,827,704℃)。测定了产品的组成、晶胞参数及粉末X-衍射图谱。结果表明:SmCl_2(黑色)Pnma,a=4.5175±0.0017A,b=7.5490±0.0016A,c=8.9923±0.0018A; EuCl_2(白色)Pnma,a=4.5065±0.0013A,b=7.5341±0.0020±,c=8.9599±0.0018A,YbCl_2(浅绿色)Pbca,a=6.7001±0.0008A,b=13.1429±0.0017A,c=6.9502±0.0010A,SmCl_2,EuCl_2的晶相转变点分别为754,738℃.     

Na2O2与CO2反应的研究

文章通过实验和热力学计算探讨No2O2与CO2反应的条件。     

低温高效催化分解过氧化氢的Co-SiO_2催化剂

H2O2常在工业和实验室过程中用作绿色氧化剂,但其残留量需要分解处理,否则会对环境造成一定的污染.采用溶胶凝胶法合成M-SiO2(M=Ni、Zn、Fe、Bi、Cu、Al、Cd、Co)催化剂.考察了催化剂在低温条件下(5~20℃)对H2O2的催化分解性能,结果表明Co-SiO2催化剂对H2O2表现出优异的催化分解作用.当Co质量分数为8.0%时,Co-SiO2催化效果达到最佳.在5~20℃范围内,0.05 g 8.0%Co-SiO2催化剂对H2O2均表现出优异的催化分解性能.5℃下反应40 min时,10 mL 1.0 mol/L H2O2分解率为71.7%,20℃下分解率几乎达到100%.并以XRD对代表性的Co-SiO2催化剂进行表征,结果表明Co在SiO2中可能处于高分散状态.