Fe2+对碳钢硫酸盐还原菌腐蚀行为的影响

对比分析了Q235钢在无Fe2+的接菌培养基和Fe2浓度为30mg/L的接菌培养基中的腐蚀行为.使用光学显微镜跟踪观察Q235钢在两种介质中的表面形貌随时间的变化,用电化学阻抗谱研究Q235钢在两种培养基中的电化学行为.用聚焦离子束显微镜制作Q235钢在两种培养基中的腐蚀产物剖面,并用能谱对腐蚀产物进行成分分析.对电化学阻抗谱所得结果进行拟合,结果表明,Fe2会使Q235钢表面形成的生物膜电阻降低,电容升高,Q235钢反应电阻保持较低,从而使反应持续进行,铁不断溶解.培养基中加入30mg/L的Fe2+后,Q235钢表面附着的细菌显著增多,形成的生物膜厚而疏松,膜中混合有腐蚀产物硫化物,膜下的金属出现众多微小的点蚀.电化学阻抗谱拟合结果与形貌观察及成分分析结果吻合,Fe2+对Q235钢的SRB腐蚀反应具有催化作用.     

MHD waves in coronal flux tubes

The basic MHD waves of a coronal flux loop are investigated for the rectangular box model of a plasma with oblique magnetic field and line-tied at the ends. The waves found are completely different from those in a periodic box, representative for tokamaks. They consist of a mixture of Alfvén components with a ballooning factor, favouring minimal field line bending, and fast components without such a factor. Pure Alfvén modes are only found as singular limiting cases of cluster spectra of Alfvén-fast waves, where the fast components are localised in a photospheric boundary layer which is dictated by the requirements of line-tying. This justifies the assumption of continuous spectra in coronal loops, required for the mechanism of resonant Alfvén wave heating. The waves consist of large amplitude Alfvén components in the corona and fast components with a small but rapidly varying amplitude in the boundary layer, so that they appear to have the right signature for effective transfer of energy from the photosphere to the corona.     

火焰筒内燃气辐射的蒙特卡罗法计算

用概率统计方法计算了航空发动机燃烧室火焰筒内燃气对壁面的辐射热流, 计算中考虑了燃气的辐射及吸收特性。该计算程序适用于二维轴对称的环型燃烧室和单管燃烧室辐射热流的计算, 并对计算结果进行误差分析。介绍了算例计算结果, 为了检验该计算程序的可靠性, 对角系数进行了校核计算, 其结果是令人满意的。此外, 文中还介绍了对某环型燃烧室和一假想单管燃烧室的计算及误差分析结果。      

1/4波长驻波型热声发动机的非线性模型

为研究声波在热声系统开口端和负载构成的阻抗间断面上的声反射问题,针对一端开口的1/4波长驻波型热声发动机建立了一种基于截面平均的准一维非线性热声模型,并采用具有频散保持特性的高精度计算格式进行数值求解。在发动机开口端采用了对于系统共振频率具有一定选择自适应性的宽频时域声阻抗边界条件。宽频阻抗模型写成共轭复数对的留数和极点分式之和的形式,其时域形式可用递推卷积方法进行快速高效的求解,共轭复数系数采用优化拟合方法近似得出。模型可对一端开口的1/4波长驻波型发动机进行临界起振温度的预测,能够描述热声系统的瞬态压力波由初始小扰动经过非线性增长,最终达到饱和的全过程,计算结果与某微小型驻波热声发动机的实验结果相符。最后分析讨论了板叠的形状对热声系统的影响。     

Failure of EB-PVD Thermal Barrier Coatings Subjected to Thermo-Mechanical Loading

Thermal barrier coatings (TBCs) were developed to protect metallic blades and vanes working in turbo-engines. The two-layered structure TBCs, consisting of NiCoCrAlY bond coat and yttria stabilized zirconia (YSZ), were deposited on a cylinder of superalloy substrate by the electron beam-physical vapor deposition (EB-PVD). The failure mechanism of the TBCs was investigated with a thermo-mechanical fatigue testing system under the service condition similar to that for turbine blades. Non-destructive evaluation of the coated specimens was conducted through the impedance spectroscopy. It is found that the crack initiation mainly takes place on the top coat at the edge of the heated zones.     

Investigation on a Sol-gel Coating Containing Inhibitors on 2024-T3 Aluminum Alloy

For a long time, chromate incorporated conversion coatings have been drawn special attention in corrosion protection of air-craft-used aluminum alloys. However,ever-increasing environmental pressures requires that non-chromate conversion coatings be developed because of the detrimental carcinogenic effects of the chromate compounds. In recent years, the sol-gel coatings doped with inhibitors were developed to replace chromate conversion coatings, and showed real promise. A sol-gel coating was prepared and its anti-corrosion behavior was investigated using the potentiodynamic scanning (PDS) and the electrochemical impedance spectroscopy (EIS). It is found that the sol-gel coating obtained by the hydrolysis and condensation of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetramethoxysilane (TMOS) is prone to form defects if cured at the room temperature, whereas if cured at a higher temperature (100 ℃), these flaws can be avoided. Furthermore, it can be seen that addition of anti-foam agents and surfactants will reduce the faults if cured at the room temperature. Effects of the corrosion inhibitors, CeCl3 and mercaptobenzothiazole (MBT), in the sol-gel coatings on 2024-T3 aluminum alloy were also investigated. Results show that the corrosion resistance of the sol-gel coatings containing CeCl3 proves to be better than that of the pure and MBT added sol-gel coatings by the electrochemical methods.     

莫来石陶瓷的制备、微波介电特性及其对材料吸波性能的影响

采用热压烧结法,用SiO₂溶胶和Al₂O₃溶胶制备的莫来石溶胶制备了莫来石陶瓷,研究了莫来石陶瓷的微波介电特性与烧结致密度之间的关系。研究表明,当莫来石陶瓷的烧结致密度从91.4%升高到97%时,其复介电常数的实部ε从3.85增加到的5.87,虚部ε″从0.04增加到0.11。当添加MgO烧结助剂后,莫来石陶瓷复介电常数的实部和虚部明显升高。将莫来石陶瓷作为吸波材料阻抗变换层,能够大幅度提高材料的吸波性能。这主要是由于采用的莫来石阻抗变换层的波阻抗较高,为156Ω,减小了空气与吸收层界面上电磁波的反射,使更多的电磁波进入了吸收层而被损耗。     

宽带变负载阻抗匹配网络的设计研究

某坦克电台采用螺旋天线以缩短天线的几何尺寸，提高安全性。由于该天线的输入阻抗随频率而变化，需要用一个宽带变负载阻抗匹配网络来实现天线与电台之间的匹配。首先从理论上分析论证了实现具有最平坦频率特性的变负载阻抗匹配网络的可能性。然后，根据实际要求进行了计算机辅助工程设计，并给出了相应的设计和仿真结果。     

GTEM传输室特性阻抗的三维有限元分析

采用有限元法对GTEM传输室的特性阻抗进行了三维分析.沿球面波的方向截取GTEM传输室的一段作为计算模型,通过分段多角度计算,求出芯板的最佳张角.考虑芯板厚度对阻抗的影响给出了芯板优化方案.在有限元分析软件ANSYS下开发了计算特性阻抗的用户模块,提高了设计效率.由于本文提出的计算方法能更好地逼近场分布的真实情况,因而具有较高的计算精度.     

超声干涉法薄层厚度测量声阻抗匹配判据及其应用

针对超声干涉法测量薄层厚度的原理,讨论了薄层及与其相邻介质声阻抗匹配分别满足界面声压反射系数|R1|＜1/2或|R1|＞1/2时回波信号的选取原则,并以薄层声压反射系数谱为依据,分析了上述两种声阻抗匹配条件下谱线分别出现次生极大或极小值的规律,在此基础上提出了薄层厚度测量时谱线极值的选择方法.以航空雷达罩蒙皮GFRP(Glass Fiber Reinforced Plastic)层板外表面复合涂层以及钢基体表面ZrO2陶瓷涂层样品为例进行了薄层厚度测量实验研究及信号分析.研究表明,超声干涉法薄层厚度实验结果与SEM(Scanning Electron Microscope)测量结果相符.由此可知,薄层及与其相邻介质声阻抗匹配判据对于超声干涉法薄层厚度测量具有很强的理论指导意义及工程应用价值.