Degradation of bond coat strength under thermal cycling—technical note

Degradation in bond strength of plasma-sprayed thermal barrier coatings under thermal cycling was evaluated by tensile adhesion tests. The bond strength and failure mode for two types of bond coat materials were examined. Two bond coats having the same substrate and top ceramic coat behaved differently due to differences in the thermal mismatch stress at an interface between the metallic bond coat and the ceramic top coat.     

电极连接部位松动与CTE的关系

电极在使用过程中,有无松动非常关键。尤其在通电后,随着温度的升高电极发生热膨胀,如果接头与电极的CTE能够平衡,电极连接部位便不会松动,可以防止折断的发生。本文介绍了石墨电极连接部位松动与CTE的关系。     

Microstructure and thermal & mechanical properties of La2Zr2O7@YSZ composite ceramic

La₂Zr₂O₇ used as a top coat material has low thermal conductivity and high stability at high temperature, but it also has a low fracture toughness, which limits its application. To improve the fracture toughness of La₂Zr₂O₇, a La₂Zr₂O₇@YSZ core–shell structured composite ceramic was designed and prepared. The morphology of the La₂Zr₂O₇@YSZ composite ceramic was investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The resulting images show that the YSZ is coated on the surface of the La₂Zr₂O₇. The phases were analyzed by X-ray diffraction (XRD), and the XRD patterns show that pyrochlore and fluorite structures coexist in the La₂Zr₂O₇@YSZ composite material without any chemical reaction. Differential scanning calorimetry (DSC) was used to detect the heat change of the composite ceramic during heat treatment. The properties of the La₂Zr₂O₇@YSZ composite ceramic, such as the thermal conductivity, coefficient of thermal expansion (CTE), and mechanical properties were investigated using a laser flash method, high-temperature dilatometer, and nano-hardness tests, respectively. The thermal conductivity of the composite ceramic is in the range of 1.7745–2.3076 W m⁻¹ K⁻¹ in the temperature regime of 200–1000 °C. The maximum CTE of the composite ceramic is 10.3 × 10⁻⁶/°C. Owing to the thin YSZ coating on the La₂Zr₂O₇ surface, the hardness and Young's modulus of the composite ceramic are 8.17 GPa and 168.3 GPa, respectively. The nucleation and propagation of micro-cracks are investigated using a micro-hardness tester. Compared to La₂Zr₂O₇, the micro-cracks in the composite ceramic are shorter and more tortuous. The weak interface between the YSZ and La₂Zr₂O₇ results in the nucleation and tortuous propagation of micro-cracks, which depletes part of the energy and improves the fracture toughness of the composite ceramic. The results reveal that the La₂Zr₂O₇@YSZ composite ceramic has good mechanical and thermophysical properties.     

硅相形态及含量对Al-Si合金线膨胀系数的影响

利用金相显微镜、DIL402C高温膨胀仪等对Al-Si合金的线膨胀进行了研究。结果表明：对于Al-Si合金,硅含量越高,其线膨胀系数越小,随温度变化幅度减小;随着温度升高,磷变质比锶变质的线膨胀系数变化幅度小,合金更加稳定;此外,T6热处理也显著降低Al-Si合金的线膨胀系数。通过对合金线膨胀系数和微观组织的对比观察发现：硅相的形态和体积分数对Al-Si合金的线膨胀系数产生重要影响。初晶硅体积分数的增加和初晶硅的析出能够显著降低Al-Si合金的线膨胀系数,共晶硅的形态对合金线膨胀系数也有一定的影响,共晶硅为短棒状、颗粒状时（尤其经热处理后）,合金的线膨胀系数也显著降低。     

塑封IC翘曲问题

为分析封装材料及模塑过程参数对塑封IC翘曲的影响,本文先介绍塑料四边引线扁平封装(PQFP)使用的环氧模塑化合物(EMC)的热特性。并对不同模塑样品的聚合程度(DOC)、热膨胀系数(CTE)、玻璃转变温度Tg、剪切模量G等,运用各种热分析技术进行测量。结合不同封装过程参数,运用三维有限元分析法进行封装翘曲预测。最后对塑料四边引线扁平封装(PQFP)IC翘曲的测量值与预测值进行比较。     

Effect of structural geometry and crack location on crack driving forces for cracks in welds

This paper quantifies the effect of geometry (planar or cylindrical) and crack location (internal or edge cracks; weld center or interface cracks) on crack driving force for welded joints, via systematic elastic-creep and elastic-plastic finite element (FE) analyses for welded joints. For engineering estimates of crack driving forces for mismatched welded joints, the equivalent material approach is employed. It is found that the equivalent material concept works very well only for a planar geometry with an internal crack, such as the middle cracked tension specimen. For a planar geometry with an edge crack, it works reasonably well, but tends to provide conservative results for under-matching and for interface cracks. For a cylindrical geometry with an edge crack, the results are similar to those for a planar geometry with an edge crack, but caution should be exercised for over-matching, as non-conservative estimates are possible due to gross-section yielding. For a cylindrical geometry with an internal crack, excessively conservative estimates for under-matching are found, and thus an improved estimation method is desired.     

Mismatch between antimicrobial resistance phenotype and genotype of pathogenic Vibrio parahaemolyticus isolated from seafood

Antimicrobial resistance phenotypes (18 antimicrobials; disk diffusion method) and genotypes (38 antimicrobial resistance genes; PCR) of 20 pathogenic Vibrio parahaemolyticus strains isolated from seafood in Shanghai wholesale markets between 2009 and 2013 were evaluated. Seventeen isolates (85%) were resistant to one or more antimicrobials, and highest resistance was observed to ampicillin (85%) and cephazolin (30%). And the isolates with tdh displayed higher resistant rates than isolates with trh. Eight antimicrobial resistance genes (strB, aadA2, strA, tetA, floR, sulI, sulII, and sulIII) were detected in these isolates. Surprisingly, the antimicrobial resistance phenotypes and genotypes of these isolates were not consistent: some isolates were resistant to β-lactam or aminoglycoside, whereas the corresponding genes were negative. Comparatively, aminoglycoside, tetracycline and chloramphenicol resistance genes occurred in susceptibility isolates. This research reveals the mismatch phenomenon between the antimicrobial resistance phenotype and genotype of seafood-derived pathogenic V. parahaemolyticus, and that susceptibility isolates might be a potential risk source for storage and transmission of resistance genes.     

Solution‐processable colorless polyimides with ultralow coefficients of thermal expansion for optoelectronic applications

This work reports colorless polyimides (PIs) that are applicable as plastic substrates in image display devices, which produce an ultralow coefficient of thermal expansion (CTE) by solution casting without thermal imidization and mechanical stretching. An effective monomer molecular design is proposed for this purpose. Chemical imidization (CI) process compatibility is the key factor in attaining the target properties. We focused on a PI system derived from 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CBDA) and a novel para‐amide‐linked diamine (AB‐TFMB) with CF₃ groups as it has great potential as an ultralow CTE material, although it offers no CI process compatibility because of its poor solubility. The CBDA/AB‐TFMB system was modified by copolymerizing with 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride. This approach drastically improved CI process compatibility. The CTE of the PI films linearly decreased with increasing CBDA content. At a CBDA content of 70 mol%, the PI achieved an ultralow CTE of 7.3 ppm K^?1, non‐coloration/non‐turbidity, a very high glass transition temperature of 329 °C and sufficient ductility. The ultralow CTE results from the highly oriented main chains along the X–Y direction during the casting process as supported by the very high birefringence exceeding 0.1. Thus, our materials almost achieved the target properties required for novel coating‐type high‐temperature plastic substrate materials. © 2016 Society of Chemical Industry     

职住分离的行业差异及其影响因素——以北京都市区为例

本文以北京都市区为例,利用各街道就业数据和人口数据,通过计算18个行业门类的空间错位指数及各行业人口居住与就业空间分布特征,分析不同行业间职住分离的差异,并探讨造成这些差异的主要原因.研究发现,不同行业间职住分离状况存在明显不同,其中第二产业要明显比第三产业严重,同时第三产业内部各行业间也存在十分明显的差异.不同行业就业的郊区化进程及其集聚状况,成为行业间职住分离差异的最主要影响因素.     

HDI产品埋孔处理工艺技术研究

文章是就如何保证HDI产品良好的热性能对埋孔处理工艺进行研究,从材料匹配性、产品结构、塞孔工艺等几个关键点入手,分别论述这几个环节对产品热性能的影响及其之间的交互作用,并根据大量的实验和科学的分析确定HDI产品埋孔处理的工艺技术。