热氧老化对碳纤维织物增强聚合物基复合材料弯曲性能的影响

为了探索增强体结构对碳纤维增强聚合物基复合材料(CF-PMCs)热氧老化后弯曲性能的影响,对三维四向编织碳纤维/环氧复合材料(简称为三维编织复合材料)和层合平纹碳布/环氧复合材料(简称为层合复合材料)的热氧老化性能进行了研究。利用FTIR、老化失重、弯曲测试和SEM等手段分析了热氧老化前后的试样。结果表明:热氧老化导致基体树脂的氧化断链以及纤维/基体界面结合力的退化是两种复合材料弯曲强度和弯曲模量下降的原因,弯曲强度比弯曲模量更容易受热氧老化的影响。在相同的热氧老化条件下,层合复合材料的热氧老化失重大于三维编织复合材料的,而三维编织复合材料的弯曲强度和弯曲模量保留率均大于层合复合材料的。在140℃下老化1 200h后,层合复合材料的弯曲强度和弯曲模量保留率分别为74.7%和88.3%,而对应的三维编织复合材料的分别为79.4%和91.5%。因此,采用三维编织预制件作为CF-PMCs的增强体是一种有效的提高其热氧稳定性的方法。     

上浆量对碳纤维的立体织造损伤及其复合材料拉伸性能的影响

结合立体织造技术和树脂传递模塑(RTM)工艺制备了不同上浆量国产碳纤维的2.5D经向增强复合材料。使用毛羽测试法、复丝拉伸法及SEM分析了不同上浆量预制织物中经纱、衬经纱和纬纱的织造损伤情况。结果表明:碳纤维织造损伤率随着上浆量的增加而减小;2.5D经向增强复合材料中纱线的损伤率大小依次为纬纱、经纱、衬经纱。复合材料拉伸性能测试结果表明:当国产碳纤维上浆量为2.01%时,2.5D经向增强复合材料的性能最佳。     

气液两相流对气升式管式MBR膜污染的影响

采用计算流体力学(CFD)与实体模型相结合的方法,对气升式管式MBR运行中气液两相流的水力学参数进行计算和验证。CFD模拟结果显示,当单管曝气量>43 L/h时,可得到10.1 Pa以上的膜面剪切力,继续增大曝气量对提高膜面剪切力影响不明显。采用与CFD模型同尺寸的实体模型验证CFD模拟结果,两种方法所得膜面剪切力误差为10%～20%。分析膜面剪切力对气升式管式MBR中膜污染的影响可知,当单膜管曝气量为57 L/h、膜面剪切力为8.7 Pa时,能够得到3.2 kPa/d的膜污染速率,继续增大曝气量反而会加速膜污染速率。     

氟钛酸钾接枝改性羽绒纤维的阻燃性能

为获得永久性阻燃性能,采用氟钛酸钾作为阻燃剂对羽绒纤维进行改性,通过红外分析,极限氧指数,残炭率,热分析和扫描电子显微镜等分析方法对其阻燃性能和热降解行为进行分析研究。结果表明:与未经阻燃处理的羽绒纤维比较,阻燃羽绒纤维的极限氧指数明显增加,热降解温度有所降低,热降解稳定性降低,热降解范围变窄,阻燃性能明显提高。改进后测得的极限氧指数为36.7%～41.8%,远远高于未处理的羽绒纤维的23%。     

Fabrication and microstructure of porous SiC ceramics with Al2O3 and CeO2 as sintering additives

In the present study, porous silicon carbide ceramics were prepared via spark plasma sintering at relatively low temperatures using Al₂O₃ and CeO₂ as sintering additives. Sacrificial template was selected as the pore forming mechanism, and gelcasting was used to fix the slurry in a short time. The evolution process of the microstructures during different steps was observed by SEM. The influence of the sintering temperature and sintering additives on the shrinkage and porosity of the samples was studied. The microstructures of different samples were characterized, and the mechanical properties were also evaluated.     

Mechanical aspects of ceramic membrane materials

Interest in ceramic transport membrane materials has increased significantly leading also to questions with respect to mechanical reliability and robustness, hence, requiring knowledge of the mechanical properties. The current review focuses on the mechanical properties of such ceramics, emphasizing in particular relationships between mechanical properties, non-elastic effects, phase changes and materials’ stability. Room and elevated temperature application is considered with a main emphasis on elastic and creep deformation as well as fracture. Consideration is given to dense membranes as well as porous substrate materials for advanced asymmetric concepts. Properties are summarized for selected oxygen and proton conductors. Furthermore, mechanical properties of some selected porous ceramic and metallic substrate materials are given. In addition to the failure probability associated with the Weibull distribution of fracture stresses, creep rupture of dense materials and enhanced creep deformation of porous materials are aspects that need special consideration in the application of these materials in gas separation systems.     

Low leakage current of CdSe quantum dots/Si composite structure and its performance for photodiode and solar cell

The CdSe quantum dots were deposited on p type Si(100) substrate by spin coating process. CdSe quantum dots were selected as the interlayer to reduce the reverse-bias leakage current of heterojunction. Various junction parameters were determined from the current-voltage (I–V) and capacitance-voltage (C–V) characteristics. Au/CdSe quantum dots/p-Si structure exhibits a fairly low leakage current density of 4.54×10⁻⁹ A/cm² and a high rectification ratio of 3.1×10⁶ at applied electric field of ±4 V. Furthermore, I-V characteristics under illumination show strong photovoltaic (PV) behavior. These results are attributed to the low interfacial state density and defect density due to CdSe quantum dots at the interface. It is also evaluated that the Au/CdSe quantum dots/p-Si structure can be a potential candidate for photodiode and solar cell applications.     

Effects of fiber preform structures on the mechanical properties of C/SiC nuts and bolts

Carbon fiber-reinforced silicon carbide (C/SiC) nuts and bolts (M8) with different fiber preform structures were prepared by precursor infiltration and pyrolysis. The influences of fiber preform structures on the mechanical properties of C/SiC nuts and bolts, as well as the failure behaviors of threaded joints were studied. A C/SiC nut, which was fabricated by using the preform prepared by stacking 3K carbon fiber cloth followed by stitching, had the highest shearing strength (64.5 MPa). The bolt with the preform prepared by alternatively stacking 3 K carbon fiber cloth and unidirectional layer of carbon fiber tows followed by stitching had the highest extreme tensile strength (243.2 MPa) and shearing strength (106.3 MPa), but low thread tooth bearing ability (3.5 kN) and critical thread engagement length (9 mm). It is suitable for applications emphasizing the extreme tensile or shearing strengths of threaded joints or possessing enough thread engagement length to ensure bolt rupture as the failure mode. The bolt with the perform prepared by stacking 1K carbon fiber cloth followed by stitching had the highest thread tooth bearing ability (5.0 kN) and the lowest critical thread engagement length (6 mm), as well as moderate extreme tensile strength (163.0 MPa) and shearing strength (82.1 MPa). It works effectively for applications concerning thread tooth strength or possessing limited thread engagement length. Therefore, the preform for preparing a C/SiC bolt should be selected according to its application requirements.     

退火对激光熔覆CoCrFeNiW0.6高熵合金涂层组织与性能的影响

目的 通过对激光熔覆CoCrFeNiW0.6高熵合金涂层进行退火处理,使涂层性能得到进一步提高。方法 采用RFL–C1000光纤激光器在45钢表面制备CoCrFeNiW0.6高熵合金涂层,通过SXL–1200管式电阻炉在不同温度下(600、800、1 000 ℃)对高熵合金涂层进行退火处理,保温时间为2 h,冷却方式为随炉冷却。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、显微硬度计、摩擦磨损试验机等对熔覆层的微观组织、显微硬度和摩擦磨损性能进行分析和测试。结果 CoCrFeNiW0.6高熵合金涂层由FCC相和μ相(Fe7W6)组成,经过不同温度退火处理后,涂层未析出新的相,μ相衍射峰强度呈先减小后增大的趋势;涂层组织经高温退火(800 ℃、1 000 ℃,2 h)后发生了明显的改变,经800 ℃/2 h退火处理后,枝晶间析出了大量μ相沉淀,经1 000 ℃/2 h退火处理后晶界开始出现断裂分解,晶粒内部和晶界部位析出了大量的富W颗粒相(μ 相)。经1 000 ℃/2 h退火处理后,熔覆层具有较高的平均显微硬度,为475.68HV0.3,相较于未经退火处理的熔覆层,其硬度提高了约45%;经600 ℃/2 h退火处理后,涂层的平均摩擦因数最低,约为0.226,磨损量最小,与未经退火处理的涂层相比,其磨损量降低了约28%。退火温度的升高并未使磨损机制发生明显改变,主要为磨粒磨损。结论 高温退火处理可以促进μ相的生成;经退火后,CoCrFeNiW0.6高熵合金涂层的硬度得到显著提高,改善了涂层的摩擦磨损性能,强化机制为固溶强化和第二相强化。     

A New High-Efficiency Experimental Design for Optimizing Various Flow Velocities Testing in Extremely Aggressive Formation Water

Compared to the traditional one-by-one method, a new high-efficiency method is used to characterize large numbers of regulations varying samples.Accordingly, bump-shaped electrodes are designed using the computational fluid dynamics model, and the effect of the height and placement of these electrodes is discussed.The experimental feasibility is certified by weight loss measurement.Results indicate that flow velocities of different bump-shaped electrode surfaces are significant differences.Thus, each surface can be analyzed independently; the thickness loss of each electrode surface is consistent with that using one-by-one method, which can effectively improve the experimental efficiency 12 times.