First‐order Raman scattering of the MAX phases Ta4AlC3, Nb4AlC3, Ti4AlN3, and Ta2AlC

Herein, we report on the Raman spectra of the following ternary hexagonal carbides and nitrides (MAX phases): Ta₄AlC₃, Ta₂AlC and Ti₄AlN₃. We also present the Raman‐active modes of α‐ and β‐Ta₄AlC₃, Nb₄AlC₃ and Ti₄AlN₃, – also referred to as the 413 MAX phases – as predicted from first principles calculations using density functional theory. We compare the obtained experimental and calculated results with previous studies on Ta₂AlC and Ti₄AlN₃. The vibrational behavior associated with the Raman‐active modes for the 413 phases has been identified for the first time. In general, the agreement is good between theory and experiment. The experimental and calculated results indicate that the modes at low wavenumbers ‐ dominated by the Al atoms ‐ are a weak function of chemistry and the differences in energy can be traced to variations in the reduced mass. The modes at higher wavenumbers are dominated by the C and N atoms and show a strong dependence on the unit cell chemistry, with the Ta–C bond being stiffer than the Nb–C bond, which is in turn stiffer than Ti–N. Copyright © 2011 John Wiley & Sons, Ltd.     

利用3D MAX模拟微型6脚机器昆虫动态行走过程的方法

通过模拟微型6脚机器昆虫的动态行走动画,可以将所设计的微型6脚机器昆虫的结构细节表现无遗．该文介绍了使用3D Studio MAX作为设计绘图工具,面向对象进行参数设计,实现所设计的微型6脚机器昆虫的虚拟现实的动态行走过程．     

三元层状化合物MAX相的研究进展

三元层状化合物MAX相是一种新型结构功能材料,兼具金属和陶瓷的优良性能。本文综述了MAX相及其复合材料的合成方法、组织结构及相关物理特性与机械性能,并预测了MAX相今后的发展趋势。     

基于3D和VIRTOOLS的煤矿安全行为模拟

把虚拟实现技术与煤炭安全生产相结合,建立煤矿工人安全行为仿真系统。通过电脑软硬件设备,根据煤矿地层数据、巷道数据和图像模拟出包括煤矿各种自然实体和人工实体在内的三维空间,使用户在其中可以自然地与各种虚拟实体进行交互,通过三维可视化的操作,可使工人熟悉井下环境、了解危险源、掌握安全行为,最终实现行为的规范化。开发使用的虚拟现实技术是一个最新交互虚拟平台。开发人员通过直觉式图形开发界面,可以建构出复杂的互动应用程序,可同时满足无程序背景的设计人员以及高阶程序设计师的需要,与建模软件3DS MAX结合,在计算机上实现煤矿工人安全行为的模拟。     

Theoretical investigation on radiation tolerance of M_(n+1)AX_n phases

Ternary M_(n+1)AX_n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, M_(n+1)AX_n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M_(n+1)AX_n(MAX) phases in terms of electronic structure, including the density of states(DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between M_(n+1)AC_n and M_(n+1)AN_n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti_3AlC_2 to Ti_2AlC (Ti_3AlC_2 and Ti_2AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M_(n+1)AX_n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.     

MC与$lt;i$gt;M$lt;/i$gt;$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;+1$lt;/sub$gt;$lt;i$gt;AC$lt;/i$gt;$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;$lt;/sub$gt;稳定性与电子特征的第一性原理研究

研究MC与M_n+1AC_n(M=Sc, Ti, V, Cr, Mn; A=Al, Si, P, S; n=1, 2, 3)结构的稳定性与电子特征有利于探究三元层状结构M_n+1AC_n稳定性的内在原因和设计新型M_n+1AC_n结构. 第一性原理计算研究表明, M-3d与C-2p轨道间的电子转移对MC与M_n+1AC_n 的形成焓有较大影响. 供电子能力较强的前过渡金属可以形成稳定的MC结构. 计算结果显示, MC结构是缺电子体系, 其趋向于与具有一定供电子能力的MA结构结合形成M_n+1AC_n. 与M₂PC和M₂SC 相比, M₂AlC和M₂SiC可以更为容易地被分离成二维 M₂C结构. 关键词： MAX相结构 第一性原理 电子结构 过渡金属碳化物     

熔盐法制备三元层状MAX相陶瓷的研究进展

MAX相是一种兼具金属和陶瓷性能的新型三元层状过渡金属碳氮化物。传统合成MAX相的方法都有一定的局限性,如反应温度较高、合成时间过长、合成样品较少,且大部分无法直接一步制备所需MAX相。近些年来,采用熔盐法合成MAX相的报道越来越多,并且工艺持续改进。本文从传统熔盐法合成MAX相出发,分析并阐述了新熔盐法合成MAX相的研究进展。传统熔盐法利用较低熔点的熔盐作为反应溶剂,提高了反应效率;熔盐屏蔽法以熔盐作为反应溶剂的同时还可防止氧化,使得反应可以在空气中进行;路易斯酸盐法则是将熔盐作为反应原料来合成MAX新相;熔盐电化学法以电脱氧的方式,将合成原料由纯金属改为金属氧化物,降低了生产成本。熔盐法所合成MAX相产物较传统方法所合成产物的产量及纯度更高,所需要的温度、能耗以及成本更低。因此,熔盐合成法是未来大批量合成MAX相以及MAX新相合成的一个重要方法。     

Evaluation of mixed mode solid phase extraction cartridges for the preconcentration of beta-lactam antibiotics in wastewater using liquid chromatography with UV-DAD detection

A novel and simple method has been developed for the simultaneous determination of beta-lactam antibiotics (BLAs) (penicillin G, amoxicillin, ampicillin, penicillin V, oxacillin, cloxacillin, dicloxacillin and nafcillin) in wastewater. The method is based on solid-phase extraction (SPE) and high performance liquid chromatography with UV-diode array detection (UV-DAD). Two SPE cartridges have been compared for sample clean up and preconcentration: a reversed-phase silica-based cartridge (Bond Elut C₁₈, Varian Inc.) and a strong polymeric mixed mode anion exchanger (Oasis MAX, Waters). The penicillins have been separated using a LUNA™ C₁₈ (2) (150 mm × 4.6 mm, 5 μm) HPLC column and gradient elution with mobile phases consisting of aqueous trifluoroacetic acid and acetonitrile. The analytical wavelength was set at 220 nm. Under optimised conditions it was possible to preconcentrate up to 1000 mL of Milli-Q water in the Oasis MAX cartridges with recoveries in the range 82-97% (R.S.D. 2-9%) for all the antibiotic tested, except amoxicillin (52%, R.S.D. 8%), and limits of detection in the range of 8-24 ng L⁻¹. The matrix components in industrial and urban wastewater samples reduce the preconcentration efficiency in both sorbents, especially for the Bond Elut C₁₈. The use of the Oasis MAX allowed detection limits between 2.9-25.6, 2.5-12.4 and 2.2-12.7 μg L⁻¹, when processing 250 mL of industrial, influent and effluent sewage treatment plant (STP) samples. Recoveries ranged between 46-91, 28-91 and 39-114% (industrial, influent and effluent STP, respectively) for samples spiked with all the antibiotics at 25 and 75 μg L⁻¹ (n = 3 for each level).