Significantly enhanced breakdown field in Ca1-xSrxCu3Ti4O12 ceramics by tailoring donor densities

Significantly enhanced breakdown field of 24.52 kV cm^?1 as well as noteworthy nonlinear coefficient of 8.11 and low dielectric loss of 0.077 were obtained in Ca_0.6Sr_0.4Cu₃Ti₄O₁₂ ceramic. It was proved from impedance spectra that improved breakdown field was attributed to enhanced grain boundary resistance and elevated Schottky barrier height, which was further found resulting from reduced donor densities in C-V measurements. In addition, it was found that the activation energy originated from oxygen vacancies was increased, indicating the generation of oxygen vacancies was suppressed. Since oxygen vacancies acted as donors in depletion layers, it is reasonable to deduce that the reduced donor density was mainly ascribed to the decreased oxygen vacancies. In conclusion, maximum integrated action of strong solid solution effect and weak Sr-stretching effect was achieved when Sr/Ca ratio is 40/60, leading to greatly elevated potential barrier height and enhanced breakdown field consequently.     

Zn与Mg质量比对热挤压Al-Zn-Mg-Sc显微组织及力学性能的影响

制备了Al-2Mg-0.4Sc、Al-5Mg-0.4Sc、Al-5Mg-2Zn-0.4Sc和Al-5Zn-2Mg-0.4Sc等4种合金并在350℃进行热挤压,通过光学显微镜(OM),X射线衍射(XRD),扫描电子显微镜(SEM)、室温拉伸测试,研究了Zn/Mg比对于Al-Zn-Mg-Sc合金组织与力学性能的影响。结果表明,Zn/Mg比的提高对于铸态晶粒具有细化作用,挤压后发生动态再结晶,晶粒尺寸显著减小,但挤压态晶粒尺寸并未随Zn/Mg比的提高而减小。另一方面,Zn/Mg比的提高使Mg32(Al,Zn)49第二相数量增加,且呈现更明显的网状结构。挤压态Al-Zn-Mg-Sc合金屈服强度随Zn/Mg比的提高而提升,主要由于大量Al3Sc粒子与碎化的第二相呈网状分布于晶界,使第二相强化起到主导作用。     

基于功能参数的渐进成形件表面质量表征研究

目的 以圆锥台成形件为例，基于粗糙表面的区域支承率曲线，进行了用功能参数表征表面几何形貌的研究，以全面、准确、定量地表征渐进成形件的表面质量，预测表面性能。方法 用渐进成形工艺加工成形角分别为35°、45°和55°的圆锥台件，将各圆锥台的成形面分为顶部、中部和底部三个区域，并使用三维表面轮廓仪，在上述三个区域中随机测量各4个样本。根据ISO 25178-2:2012，将各样本表面的区域支承率曲线分为峰区、核心区和谷区，选用部分功能参数——核心区高度Sk、峰区材料体积Vmp、核心区材料体积Vmc和谷区空隙体积Vvv表征表面，并与常用的高度表征参数——Sa、Sq、Ssk和Sku进行比较。结果 成形件表面的Ssk和Sku的计算值极不稳定，变异系数（标准偏差与均值之比）最高值分别可达127.67%和39.11%，Sa、Sq的最大变异系数分别为4.41%和4.26%，虽然它们的参数计算值较为稳定，但常无法体现表面形貌的实际差异。功能参数独立表征不同功能区，Sk和Vmc的最大变异系数分别为9.32%和7.73%，说明同一表面各处，在长期工作阶段具有较为一致的表面性能，Vmp和Vvv的最大变异系数分别为60.53%和31.25%，说明表面各处峰、谷区的形貌有所不同，因而在磨合时间、磨粒存储等方面会有不同的表现。结论 粗糙表面的三维本质要求用三维表征参数才能全面表征其几何形貌。高度参数虽然计算简单，但常难以解读它们的物理意义，无法定量评价表面性能；功能参数具有明确的物理意义，可为表征表面质量、预测表面性能提供定量、实用的方法。     

提高冶炼低硅含钛铁水转炉废钢比工艺攻关

废钢比是转炉生产的重要经济技术指标,其值大小直接影响转炉冶炼钢铁料消耗及热平衡,提高入炉废钢比是实现节铁增钢、降本增效的重要技术手段。然因冶炼低硅含钛铁水成渣难、脱磷难等问题,对应入炉废钢比持低不高,直接影响转炉生产成本。为此,基于低硅含钛铁水冶炼特点及难点分析,结合水钢生产实践,通过氧枪喷头优化、枪位优化、添加提温剂等工艺优化和技术开发,使入炉废钢比由优化前7.41%提高至13.48%,优化效果较为明显,为实现节铁增钢、降本增效奠定了一定基础。     

一种X射线数字成像检测缺陷尺寸的测量方法

提出了一种X射线数字成像检测缺陷尺寸的测量方法。借鉴半波高法,以半波高法下的尺寸测量误差为基准,对不同缝隙尺寸试样在相同的检测条件下进行X射线数字成像检测,计算该检测条件下的总不清晰度,总结出缺陷尺寸与总不清晰度比值同波高比例的关系,并通过试验进行了验证。结果表明,该方法简单、实用性强,可为实现缺陷尺寸的准确测量提供技术支持。     

TA18钛合金管材织构对环向拉伸性能的影响

利用织构增强原理,开发出了TA18(Ti-3Al-2.5V)钛合金860 MPa级高强度管材,保证了管材的工艺性能,同时又具有优异的力学服役性能。标准规定反映径向织构的管材收缩应变比(CSR)大于1.3,但对上限值未作规定。本研究设计出小管径的环向拉伸夹具,测试了不同CSR管材的环向拉伸力学性能,分析织构对环向抗拉强度的影响,发现存在一个最有利的CSR值为1.75,大于或小于该CSR值时都会导致管材环向屈服强度下降。进一步测定了对应管材的极图和ODF图,从微观结构上可以解释这一规律和本质。环向抗拉强度下降会引起液压系统工作时疲劳强度降低,CSR值的上限在工艺设计时应当加以控制。本研究对发展安全可靠的航空液压系统具有十分重要的理论意义和工程应用价值。     

Poisson’s ratio of porous and cellular materials with randomly distributed isometric pores or cells

The porosity dependence of Poisson's ratio of materials with random microstructure is investigated via analytical and numerical modeling. It is shown that all analytical models predict porosity independence if the solid Poisson ratio is 0.2 and for low porosities a converging trend toward this value with increasing porosity. From all theory-based relations, only power-law and exponential relations allow for auxetic behavior. Numerical calculations on computer-generated digital microstructures (overlapping and isolated spherical pores, pores between overlapping spherical grains, wall-based cellular materials/closed-cell foams, and strut-based cellular materials/open-cell foams) confirm the general qualitative trends of the analytical models, although a closer look reveals significant quantitative differences. Cellular materials and foams exhibit similar features as porous materials in general, but lack their converging trend toward values around 0.2. Comparison of our results with the classical Roberts-Garboczi results shows good agreement, with subtle differences due to the different microstructures generated.     

Oxidative Stability of Chia (Salvia hispanica L.) and Sesame (Sesamum indicum L.) Oil Blends

Chia and sesame oils are important sources of essential fatty acids; however, their ω-3:ω-6 proportions do not comply with nutritional recommendation. A feasible approach to improve the ratio is to blend different oils, but only after understanding physical and chemical changes of the new matrix. Objective of the investigation was to determine the physico-chemical characteristics and the oxidative stability index (OSI), using the Rancimat method, of chia-sesame oil blends. The four ω-3:ω-6 blends tested (1:4, 1:6, 1:8, and 1:10) were exposed to temperatures of 110, 120, and 130 °C. The OSI values of the mixtures varied between 6.24–8.08, 3.07–4.00, and 1.62–2.01 hours for each temperature, respectively. In addition, their mean activation energy, enthalpy, entropy, and Q₁₀ were 88.4 kJ/mol, 85.2 kJ/mol, −41.1 J/mol K, and 2.0. Finally, a shelf life prediction performed at 25 °C indicated stability times between 80 and 123 days. Therefore, combining chia and sesame oils produced blends with a good balance of essential fatty acids.     

Effects of electrical parameters and their interactions on plasma electrolytic oxidation coatings on aluminum substrates

Based on orthogonal experiments, the effects of voltage, frequency, duty ratio and their interactions on the thickness and corrosion resistance of coatings prepared by plasma electrolytic oxidation (PEO) on aluminum in an alkaline silicate-containing electrolyte were investigated. The thicknesses of these coatings were obtained by measuring their cross-section using Image J software. Their corrosion resistances were evaluated in HCl and NaCl media through spot test and electrochemical test. The results show that the experimental design of this study is the key to investigate the interactions among these electrical parameters. Additionally, not only each independent factor, but also their interactions exhibit a remarkable influence on the coatings. The combination of high voltage, low frequency and large duty ratio significantly increases the coating thickness and content of the corrosion resistance phase, and thus improves the corrosion resistance of the coating in HNO₃ medium. Conversely, the coating possessing the densest microstructure and best corrosion resistance in NaCl medium is obtained when low voltage and high frequency match with a small duty ratio.     

Experimental study and CFD numerical simulation of an innovative vapor splitter in dividing wall column

The vapor split ratio (R_V) adjustment plays an important role on energy efficiency during dividing wall column (DWC) operation. In order to achieve active control of R_V, this aticle presents an innovative vapor splitter driven by hydraulics. The vapor flows into main tower from prefractionation section through the rectangle hole located at the end of the partition. Vapor splitting is implemented by the change of flow resistance at the rectangular hole caused by adjusting the liquid level on the bottom plate. This design makes full use of the hydraulic properties in DWC, employing simpler construction with single tunable parameter. Numerical simulations and laboratory tests were both carried out to validate its performance in the DWC with a diameter of 600 mm. The results demonstrate that the desired R_V can be handled effectively in the approximate range from 0.5 to 2, basically satisfying the industrial demand for the gas distribution.