Effect of Zr Addition on the Grain Refinement Mechanism of Mg-Gd-Er AlloysEI北大核心CSCD

In recent years, Zr is widely used as an important additive element in magnesium alloys containing rare earth (RE), to improve the mechanical properties of Mg-RE alloys such as strength, ductility, creep resistance and corrosion resistance property. Heterogeneous nucleation mechanism and peritectic reaction mechanism are recognized as the main grain refining mechanisms. Whereas, during the solidification process, the melt wetting angle and nucleation energy are important factors which influence the nucleation. In this work, the effect of Zr on the solidification microstructure of the Mg-Gd-Er alloy was analyzed by using OM and EBSD; the undercooling of alloy melts was tested by using DSC; and the Mg/Zr interface relationship and interfacial energy were investigated by using HRTEM. Moreover, the effects of Zr on the wetting angle and nucleation activation energy of the Mg-11Gd-2Er and Mg-11Gd-2Er-0.4Zr alloys were investigated; the refinement mechanism of Zr on the alloys was discussed. The results indicates that the addition of Zr element can significantly refine the grain, and the grain size decreased from 1000 mm to 50 mu m. Compared with the Zr-free alloy, the nucleation wetting angle of the present alloy melt decreased from 18.3 degrees to 11.1 degrees, and the activation energy of nucleation decreased by 44.4%. The (1010) plane of Mg was completely coherent with the (1100) plane of Zr, reducing the interfacial energy between the (1010) Mg and the (1100) Zr. The grain refinement of Mg-Gd-Er alloy was ascribed to the decrease of melt wetting angle and the fully coherent interface relationship between Mg and Zr.     

土体湿化试验研究现状

土体湿化试验是研究土体湿化特性的重要手段。随着近年来土石坝建设的快速发展,土体湿化试验研究变得尤为重要。文章总结了相关文献的研究成果,从土体湿化试验的研究方法、土体湿化特性和目前存在的问题三方面阐述了土体湿化试验研究的现状。     

A类泡沫灭火剂的润湿性能研究

测试了不同质量分数A类泡沫与水成膜泡沫的润湿性能和表面张力。结果显示,对于同一种泡沫来说,随着泡沫溶液质量分数增加,表面张力逐渐降低,润湿时间快速下降;在相同的测试质量分数下,6%AFFF溶液的表面张力远低于A类泡沫,但润湿性能明显不如A类泡沫。分析研究了泡沫灭火剂的润湿机理及影响泡沫润湿性的关键因素,认为泡沫溶液的润湿性主要取决于溶液与固体的固-液界面张力大小、固体的表面性能、溶液中润湿剂的结构、性质等。     

降雨入渗下膨胀岩渠坡失稳的原位试验研究

 为研究在降雨入渗条件下的膨胀岩（土）渠坡土-水相互作用机理及滑坡成因,在河南新乡南水北调中线工程潞王坟试验段裸坡试验区对不同坡比的 2 个膨胀岩渠坡进行人工降雨试验,试验中跟踪观测渠坡下渗强度、含水率、吸力及水平位移对降雨的响应规律。对观测成果进行分析后认为,在供水强度大于渠坡下渗能力的情况下,降雨强度及坡度对下渗强度没有影响;裂隙发育深度以内土层受降雨影响最为严重,其含水率在干湿循环过程中大幅波动;不论是陡坡还是缓坡,滞水层的存在均使浅层吸力大幅下降;水分入侵只是膨胀岩（土）渠坡滑动破坏的一个诱发因素,干湿循环所引起的裂隙发育与强度衰减才是其根本原因。     

膨胀土的干湿循环性状及其在边坡稳定性分析中的应用

膨胀土的干湿循环性状在膨胀土边坡的稳定性分析中占有重要地位。通过膨胀土的干湿循环试验,得出膨胀土性状变化的基本规律:干湿循环导致膨胀土性状的衰减,在经过4~5次干湿循环之后,其性状改变趋于稳定。从土的微观结构出发,对这些基本规律给出解释;并将这些基本规律应用到膨胀土边坡的稳定分析中,得出了符合工程实际的计算结果。     

棉织物的生物酶前处理

分析了影响棉织物润湿性的因素，证明利用酶的协同效应，选用纤维素酶和果胶酶通过预处理或添加表面活性剂的方法可显著改善棉纤维的润湿性，但生物酶精练与碱煮练对棉织物润湿性改善仍有一定差异。     

基于频域介电谱法的变压器油纸绝缘套管受潮状况分析

近年来频域介电谱法(frequency domain spectrum,FDS)作为一种无损检测方法,逐渐被尝试用来检测大型变压器、套管等油纸绝缘设备的绝缘状态。采用该方法对某500 kV变电站主变压器高中压中性点套管及低压故障套管进行了现场离线测量,然后将所测结果与实验室结果进行比对,分析其故障原因,实现了对现场实测数据的定性和定量分析,确认该批次套管存在出厂时套管芯子干燥不充分问题。研究表明,频域介电谱法不仅能够定性地反映套管内部受潮状况和受潮原因,而且还可以对其受潮程度进行定量分析,从而为该方法在实际生产中的进一步应用提供了理论和实践基础。     

超疏水表面液滴的冷凝成长特性研究

利用聚二甲基硅氧烷(PDMS)为基底采用光刻技术制备了微方柱状超疏水表面,分析了冷凝条件下超疏水表面液滴的冷凝生长特征,发现液滴的生长过程可分为微液滴成核冷凝独立生长、冷凝微液滴合并生长以及大液滴生长3个阶段。超疏水表面初始合并的液滴呈Wenzel-Cassie状态和Wenzel状态,随着冷凝液滴的成长,液滴的液-固接触面积与粗糙结构表面的表观面积之比f随着冷凝液滴尺寸的增大而增大,Wenzel-Cassie状态向完全Wenzel状态转变。最后分析了超疏水性破坏的原因。     

Wetting of Al2O3-Based Oxide Ceramics by Molten Aluminum

The temperature dependence has been determined for the wetting by molten aluminum of materials based on aluminum oxide (polycor and corundum). A temperature range has been identified in which the wetting increases significantly. There is no effect on the wetting characteristics of these oxide materials from the addition to the aluminum of up to 25% silicon, 33% copper, or 6% nickel.     

Solid‐Liquid Adhesion Energies of Composite Propellant Components Determined by Solution Calorimetry

The energetic or adhesive interaction between binder matrix and solid fillers as well as plasticizers and fillers is a property determining mechanical properties as strain capacity and stress at maximum or stress at break. To know such interaction energies is therefore of interest. An isoperibolic solution calorimeter is used to measure such interaction energies or heats of immersion of the solid propellant components ammonium perchlorate (AP) and aluminium (AL) with the liquid plasticizers bis‐(2‐ethylhexyl) adipate (DEHA) and azido‐terminated oligomeric glycidylazide (GAP−A). The determined heats indicate wettability and interaction energy in units of energy per surface area of the solid component. For AP, three different grain sizes with mean diameter about 200, 90, 42 μm were used. Results indicate dependence of AP wetting on mean particle diameter: Successful wetting occurs for AP at diameters from above 90 μm. The polar interactions between the ionic AP and GAP−A greatly enhance wetting as compared to DEHA.