Epitaxial Cubic Silicon Carbide Photocathodes for Visible-Light-Driven Water Splitting

Cubic silicon carbide (3C-SiC) material feature a suitable bandgap and high resistance to photocorrosion. Thus, it has been emerged as a promising semiconductor for hydrogen evolution. Here, the relationship between the photoelectrochemical properties and the microstructures of different SiC materials is demonstrated. For visible-light-derived water splitting to hydrogen production, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are applied as the photocathodes. The epitaxial 3C-SiC film presents the highest photoelectrochemical activity for hydrogen evolution, because of its perfect (001) orientation, high phase purity, low resistance, and negative conduction band energy level. This finding offers a strategy to design SiC-based photocathodes with superior photoelectrochemical performances.     

一步水热合成Cu-SAPO-34选择性催化丙烯还原氮氧化物

采用一步法水热合成不同Cu/Al比的Cu-SAPO-34催化剂,并对其丙烯选择性催化还原NO（C₃H₆-SCR）性能进行了研究。通过N₂吸附-脱附、X射线衍射（XRD）、X射线光电子能谱（XPS）、程序升温还原（H₂-TPR）和原位漫反射傅里叶变换红外光谱（In situ DRIFTS）等研究手段对催化剂进行表征,考察Cu-SAPO-34中Cu物种含量对催化剂的物理化学性质和反应活性的影响。结果表明,当铜负载量为2.76%~4.12%（w/w）时,Cu-SAPO-34催化剂在富氧条件下300~400℃内表现出非常有吸引力的C₃H₆-SCR活性,可实现~100%的脱硝效率和~100%的N₂选择性。原位红外光谱研究表明,Cu-SAPO-34分子筛骨架上孤立的Cu²⁺离子是NO吸附和活化形成NO₂^-/NO₃^-中间物种的主要活性位,并通过C₃H₆-SCR反应过程中Cu²⁺/Cu⁺氧化还原循环来实现Cu²⁺离子的持续供给。     

高速列车车轮踏面剥离引起的轮轨冲击力学响应有限元模拟

车轮踏面剥离是轨道车辆车轮非圆化损伤的常见形式之一。轮轨滚动接触过程中,车轮踏面剥离会循环冲击钢轨,诱发异常大的轮轨动态相互作用,严重影响高速列车运行平稳性和安全性。基于三维轮轨滚动接触有限元模型,模拟了高速列车车轮踏面剥离引起的轮轨冲击力学响应,分析了轮轨冲击过程中的轮轨接触力/压力、接触斑及黏/滑特性、钢轨表面节点速度分布和应力/应变状态等响应特征,讨论了列车速度、剥离长度和剥离深度等关键参数对轮轨冲击响应的影响。结果发现,车轮踏面剥离引起的轮轨动态垂向接触力随列车速度的提高呈现出先增大后减小的变化趋势,并在列车速度为300 km/h出现最大值,约为轮轨准静态垂向接触力的1.35倍;随着剥离长度的增大,轮轨动态接触力、轮/轨von Mises应力和等效塑性应变均显著增大;随着剥离深度的增大,仅车轮von Mises应力和等效塑性应变显著增大。     

冷热循环处理对Fe基块体非晶合金摩擦磨损性能的影响

本文中采用电弧熔炼和感应熔炼后喷铸的方法制备了厚度为4 mm的Fe基块体非晶合金. 通过对Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂块体非晶合金进行30次和60次冷热循环处理,并在往复式摩擦磨损条件下,研究冷热循环工艺对其摩擦磨损性能的影响. 结果表明:冷热循环处理没有显著改变铁基非晶合金的非晶态结构. 30次冷热循环处理后,Fe基块体非晶合金发生了明显的软化,平均硬度由铸态的16.06 GPa降为14.06 GPa,平均弹性模量由241 GPa降为216 GPa. 随着冷热循环次数和载荷的增加,非晶合金的平均摩擦系数和磨损率先减小后增大. 冷热循环处理有利于降低非晶合金的平均摩擦系数和磨损量. 当冷热循环次数为30次、载荷为30 N时,铁基非晶的摩擦系数由0.77降至0.72,表现出最小的摩擦系数,同时磨损率降低13.3%,表现出最小的磨损率[1.04×10?6 mm3/(m·N)]. 铸态Fe基块体非晶合金的磨损机理以疲劳断裂为主,伴随着轻微的磨粒磨损. 随着冷热循环次数的增加,疲劳导致的脆性断裂程度降低,磨损机制向磨粒磨损和疲劳断裂的共同作用转变. 所以,冷热循环处理有望成为调控非晶态金属材料摩擦学性能的有效手段. 进一步深化对冷热循环处理的理解,必将有利于推动非晶态材料在摩擦学领域的应用.      

Characteristics of flow and liquid distribution in a gas–liquid vortex separator with multi spiral arms

Fischer–Tropsch (F–T) synthesis is an important route to achieve the clean fuel production. The performance of gas–liquid separation equipment involving in the progressive condensation and separation of light and heavy hydrocarbons in the oil-gas products has become a bottleneck restricting the smooth operation of the F–T process. In order to remove the bottleneck, a gas–liquid vortex separator with simple structure, low pressure drop and big separation capacity was designed to achieve the efficient separation between gas and droplets for a long period. The RSM (Reynolds Stress Model) and DPM (Discrete Phase Method) are employed to simulate the flow characteristics and liquid distribution in the separator. The results show that the separation efficiency is influenced by the flow field and liquid phase concentration in the annular zone. The transverse vortex at the top of spiral arm entrains the droplets with small diameter into the upper annular zone. The entrained droplets rotate upward at an angle of about 37.4°. The screw pitch between neighbor liquid threads is about 0.3 m. There is a top liquid ring in the top of annular zone, where the higher is the liquid phase concentration, the lower is the separation efficiency. It is found that by changing the operating condition and the annular zone height the vortex can be strengthened but not enlarged by the inlet velocity. The screw pitch is not affected by both inlet velocity and annular zone height. The liquid phase concentration in the top liquid ring decreases with both the increases of inlet velocity and annular zone height. The total pressure drop is almost not affected by the annular zone height but is obviously affected by the inlet velocity. When the height of annular zone is more than 940 mm, the separation efficiency is not changed. Therefore, the annular zone height of 940 mm is thought to be the most economical design.     

Fast and Efficient Removal of Cationic Dye Using Graphite Oxide,Adsorption, and Kinetics Studies

Dye adsorption on graphite oxides, which were prepared by different methods, was compared for the first time. The adsorption process was followed using ultraviolet-visible spectroscopy, while the adsorbents before and after adsorption were characterized using physicochemical and spectroscopic techniques. Surprisingly, we found that higher oxidation degree of graphite oxide resulted in higher adsorption efficiency for methylene blue (MB), while the ultrasonic exfoliation of graphite oxide impaired the adsorption efficiency. Among all samples investigated, graphite oxide prepared by modified Hummers' method (HmGO) before ultrasonic exfoliation exhibited the best adsorption capacity of MB. It is pretty high compared with other reported absorbents for MB. The experiment conditions such as pH, adsorbent dosage, stirring speed and adsorption time on adsorption of MB on graphite oxide, as well as adsorption kinetics and isotherms, were also investigated. The maximum adsorption capacity of graphite oxide is 751.9 mg · g^?1 based on the Langmuir model. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Dispersion Science and Technology to view the free supplemental file.]     

Nucleophilic Attack of α‐Aminoalkyl Radicals on Carbon?Nitrogen Triple Bonds to Construct α‐Amino Nitriles: An Experimental and Computational Study

A new reactivity pattern of α‐aminoalkyl radicals, involving nucleophilic attack on C?N triple bonds under thermal conditions, has been developed to construct α‐amino nitriles. In contrast to previous C? H functionalization of tertiary amines involving α‐aminoalkyl radicals, this methodology does not require the use of photocatalytic conditions or a transition‐metal catalyst. Inexpensive and nontoxic phenylacetonitrile was chosen as cyano source for this α‐aminonitrile forming reaction. A plausible mechanism is proposed based upon experimental and computational results. An α‐aminoalkyl radical intermediate and benzoyl cyanide have been shown to be key intermediates in this green and mild radical process. Nucleophilic attack of the α‐aminoalkyl radical on the C?N bond of PhCOCN followed by an elimination step forms the desired α‐aminonitrile and an acyl radical.     

Calculation of the contribution of scattering effects to X-ray fluorescence intensity for coating samples

Theoretical equations to calculate fluorescence intensity enhanced by scattering effects for coating samples were developed based on fundamental parameter models. The secondary enhancement by scattering radiation from the same layer or between layer and substrate and the primary fluorescence that was scattered into the direction of detector by atoms in layer and substrate were included in calculations. The contributions of different scattering effects to fluorescence intensity were calculated for a hypothetical Zn coating on infinite Fe substrate sample. The results show that the contributions of scattering effects to fluorescence intensity are related to the thickness of coating and are up to several percents of primary fluorescence intensity.     

用纠缠态表象讨论对双模压缩真空态作正交振幅分量的测量

对文献[4]的结果作了进一步推导,用纠缠态表象方法计算了对双模压缩真空态第一个模场作正交振幅分量测量的结果,发现第二个模塌缩到一个压缩态,其显式被导出。