A:Al2O3（A=Cr,Fe,Ni）晶体生长及其缺陷研究

报道了A:Al2O3(A=Cr,Fe,Ni)晶体光学浮区法生长工艺,研究了旋转速率、生长速率对晶体质量的影响,制备出了φ6~8 mm、长度为60~80 mm的A:Al2O3晶体.A:Al2O3晶体的生长方向为<001>方向,X射线双晶摇摆曲线表明A:Al2O3晶体具有良好的晶体质量.通过X射线衍射、扫描电镜、偏光显微镜对晶体中的生长缺陷进行了研究,结果表明,A:Al2O3晶体的主要缺陷为小角度晶界、包裹体和溶质尾迹.研究了A:Al2O3晶体的光谱性能,并对A:Al2O3晶体的介电性能进行了测量,室温下1000 kHz时A:Al2O3晶体表现出较高的介电系数εr(12.1~15.7)和较小的介电损耗tanδ(0.0020~0.0002).     

The effects of processing variables on stress development in ultraviolet-cured coatings

A cantilever deflection technique was used to monitor stress development during ultraviolet photo-cure of acrylate coatings to the glassy state. Two coating systems were studied: a trifunctional monomer (trimethylol propane triacrylate, TMPTA) and a tetrafunctional monomer (pentaerythritol tetraacrylate, PETA). Both were photoinitiated with 2,2-dimethoxy-2-phenylacetophenone (DMPA). Average in-plane stresses of up to 30 MPa were measured upon curing at room temperature. The rate and magnitude of stress development rose with the photoinitiator concentration and with light intensity. Curing with more strongly absorbed light had similar effects. Light absorption caused decreased stress magnitudes in thicker coatings. Somewhat unexpectedly, the rate and magnitude of stress development increased with monomer functionality even though the conversion fell. Moreover, curing thick coatings with high radical concentrations (strongly absorbing light and large photoinitiator concentrations) caused ripple defects to form. With the appearance of these defects, stress ceased to rise with the photoinitiator concentration. Fourier transform infrared spectroscopy was employed to monitor conversion and to help understand these stress development trends. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1267–1277, 1997     

Understanding heterogeneous catalysis on an atomic scale: a combined surface science and reactivity investigation for the dehydrogenation of ethylbenzene over iron oxide catalysts

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), -Fe₂O₃(0001) and KFe _x O _y (111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of -Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.     

Defects in offsite construction: timber module prefabrication

The construction industry is based on craftsmanship. Quality control and assurance procedures applied in manufacturing cannot usually be readily applied in construction, where there are higher degrees of uniqueness in each project. One category of companies, industrialized housebuilders, is attempting to bridge some of the gaps between construction and manufacturing. These companies prefabricate building modules for later assembly at the building site. Since they are wholly responsible for large parts of the building process, these companies have greater opportunities to control and improve quality in a more consistent way than ordinary construction companies. Thus, it could be hypothesized that the frequency and severity of defects should be lower in industrialized housing than in ordinary construction. The aim of the study presented here is to examine this hypothesis by measuring and characterizing defects in industrialized housing. The design and manufacturing processes at two Swedish timber module prefabrication firms has been analysed through interviews, site visits and document reviews. Quality audits from three phases of the building process were compiled, analysed and categorized to provide statistical measures of defects in industrialized housing. The results show that the case study companies are better in terms of product quality than conventional housing.     

Origin of extrinsic dielectric loss in 1:2 ordered,single-phase BaMg1/3Ta2/3O3

Among the family of temperature-compensated microwave dielectric ceramics, BaMg_1/3Ta_2/3O₃ shows the lowest dielectric loss and remains a material of choice for state-of-the-art airborne and land-based communication systems. We report on the compositional stability range, microwave dielectric properties, and the degree of atomic order of the title compound within the BaO–MgO–Ta₂O₅ ternary diagram. In most cases an atomic order is robust to the deviation from stoichiometry with an exception of Ba-rich and/or Ta-deficient samples which favor (partial) disorder. We further demonstrate that the dense, atomically ordered BaMg_1/3Ta_2/3O₃ ceramic shows large variation of dielectric loss within a single phase composition region – a clear message that the dielectric loss in practical ceramics is dominated by extrinsic sources and that the cation order alone is insufficient to achieve a minimum dielectric loss in BaMg_1/3Ta_2/3O₃. The low-temperature dielectric relaxation studies suggest that the extrinsic dielectric loss in the title compound is due to the ‘rattling’ of the off-centered Mg²⁺ ions misplaced at the Ba sites. Controlled deviation from the BaMg_1/3Ta_2/3O₃ stoichiometry toward the Mg-deficient region leads to suppression of the extrinsic dielectric loss as a result of the reduced chemical activity of Mg ion.     

内燃机车传动轴焊接缺陷的有限元力学分析

针对内燃机车传动轴的断裂故障,利用有限元对其焊接处的焊接缺陷进行力学研究。以子模型为研究对象,对传动轴的焊接处的缺陷进行应力集中系数的计算,为更好地解决传动轴的断裂问题提供了理论依据。     

含缺陷压力管道模糊失效概率的分析计算方法

应用模糊随机概率理论,在同时考虑压力管道评定参数的随机性和失效模式模糊性的基础上,指出含缺陷压力管道的失效概率实际上是一个模糊随机概率,进而提出了计算含缺陷压力管道模糊失效概率的方法。这种方法与仅考虑参数的随机性相比,更科学合理、更符合工程实际。     

Defect-Chemical Aspects in the Synthesis of Metallic Conductors La1–xBaxCuO3 (x= 0.0 to 0.5)

Compositions of La_{1- x} Ba _x CuO₃, where x ranges from 0.0 to 0.5, were fired in air, oxygen-enriched air, and oxygen. Studies show that BaO cannot make a solid solution with LaCuO₃ without changing the basic structure. The resulting phases, in all attempts, were the binary compounds La₂CuO₄, La_{1- x} Ba _x CuO_3-δ ( x = 0.2 to 0.5), or their mixtures. All samples showed metallic conductivity. Extra oxygen in the reaction atmosphere appeared to encourage the formation of the LaCuO₃-based phases of La_{1- x} Ba _x CuO_3-δ ( x = 0.2 or 0.5). We provide a defect-chemical and thermodynamical explanation for this observation.     

TiAl金属间化合物的淬火缺陷研究

采用自电子寿命谱技术研究了ＴｉＡｌ以下Ｔｉ３Ａｌ金属间化合物的淬火缺陷及其回复行为，结果表明，充分退火ＴｉＡｌ试样中有一定数量的晶界存在的ＴｉＡｌ合金高温淬火过程中在产生大量空位的同时也产生了一定数量的空位团和空位－杂质原子复合体等二次缺陷，在３００－６００℃的温度范围内，由于这些复合缺陷的分解和迁移，使空位团进一步聚集长大。     

高压高温处理条件下钻石中晶格缺陷的演化与呈色

实验室的高压高温条件为褐黄色钻石中的晶格缺陷提供了足够的均向压力和势能,有助于Ⅰa,型,Ⅱa型褐黄色钻石中的位错发生攀移,重组,湮灭,增殖和滑移,最终转变成无色,黄绿色及蓝色钻石。研究表明,由两组细密,微波状,明暗相间,断续排列且边界渐变的变形带组成的似格状应力图案属修复型滑移面（线）系,代表了IIa型钻石中位错的攀移,重组合和湮灭,沿钻石四方生长环带方向相间有序排列的位错壁和边界突变似聚片双晶的强度形带属增强型滑移面（线）系,代表了Ia型钻石中位错的增殖和运动,3760cm^-1（低温状态下为3738cm^-1)拉曼谱峰与2087,796cm^-1拉曼谱带一道归属钻石中晶格缺陷心所致。证实晶格缺陷的形成与演化共同制约了钻石的呈色和发光。