表面喷砂对有机玻璃沿面闪络性能影响

绝缘子表面粗糙处理是提升其沿面闪络性能的重要途径,表面粗糙化处理方式不当,极易带来表面结构不均匀,难以获得稳定耐压性能的绝缘材料。为提升绝缘子表面粗糙处理的均匀性,本文利用表面喷砂技术对圆柱形有机玻璃(PMMA)绝缘子进行了粗糙化处理研究,以球形二氧化硅(SiO2)颗粒为工作介质,研究了不同喷砂粒径、氢氟酸后处理等因素对绝缘材料表面形貌和组分的影响,并利用短脉冲高压测试平台对喷砂处理前后有机玻璃绝缘子样品进行了真空沿面闪络性能测试。研究结果表明,喷砂处理在有机玻璃表面形成了较为均匀的凹坑,HF酸能够有效去除表面残留的SiO2颗粒,具有表面喷砂粗糙结构的绝缘子沿面闪络电压得到了稳定提升,相较于未处理的绝缘子闪络电压提升了约80%。     

New low-cost tubular ceramic microfiltration membrane based on natural sand for tangential urban wastewater treatment

In wastewater treatment, the development of low-cost separation methods is of significant importance. Low-cost membranes based on natural materials have become a highly active research topic in recent years. Herein, using low-cost natural Moroccan sand, new ceramic supports have been developed and characterized using different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), along with scanning electron microscope (SEM). Plastic paste (average particle size ≤125 µm) was blended with organic additives and water, then the obtained paste was extruded into porous tubular supports. The support had a porosity of 43%, water permeability of 1928 L/h m² bar, excellent chemical and mechanical properties and an average pore diameter in the range of 8–15 µm after firing at 950 °C/2 h. As per SEM analysis, the tubular supports had a smooth and crack-free surface. The slip casting process was used to create a microfiltration layer from the same natural sand powder (average particle size ≤63 µm) using a mixture of powder sand, water, and polyvinyl alcohol solution. The water permeability of the microfiltration membrane sintered at 950 °C/2 h was 1052 L/h m² bar, the average pore size diameter was about 0.90 µm and 82% of pores had a diameter ≤1.00 µm. The obtained microfiltration membrane was tested for the treatment of urban wastewater. The membrane showed excellent separation performance in turbidity removal and chemical oxygen demand.     

Synthesis and characterization of TENORM-free nano zirconia from zircon sand

To avoid radiation exposure in the use of nano zirconia in the ceramics and dentistry industries, a Technologically Enhanced Natural Radioactive Materials (TENORM)-free nano zirconia was required. The purpose of this research was to obtain an environmentally friendly TENORM-free nano zirconia prototype. TENORM-free nano zirconia synthesis consists of processing zircon sand into sodium zirconate, leaching of sodium zirconate to form zirconyl chloride solution, separation of impurities (silica, ThO₂, U₃O₈, etc.), crystallization of zirconyl chloride, zirconyl-oxalate sol-gel formation, and calcination. The quality test of nano zirconia products was characterized by XRD, FT-IR, SEM, and Surveymeter, while the composition test was carried out by the XRF method. The results of this research obtained an environmentally friendly TENORM-free nano zirconia prototype, that has the chemical compound of ZrO₂, the crystal size was 15.09 nm, the average particle size was 91.33 nm, free of radiation exposure, and its composition includes ZrO₂: 96.599%, HfO₂: 2.899%, and CaO: 0.303%. This synthesis can process zircon sand containing TENORM (ThO₂: 0.070% and U₃O₈: 0.047%) into TENORM-free nano zirconia and increase the added value by increasing the zirconia content from 40.493% to 96.599%.     

On the Validity of Darcy's Law for Stable High-Concentration Displacements in Granular Porous Media

Recently, it has been suggested that Darcy's Law might not be applicable for modelling miscible, density-dependent flow in porous media. To investigate this, three sets of careful laboratory column experiments were performed on coarse and medium sands, consisting of upward displacement of water by sodium chloride solutions with concentrations ranging from 5 to 200g/l. Data on salt concentrations and water pressures were collected in horizontal transects along the flow direction. Salt concentration data were also collected in the influent and exit lines. The experimental data were analysed using a simplified approach based on Darcy's Law alone, applied with the assumption of a sharp interface. Darcy's Law was used to estimate porous medium permeability by fitting predictions to experimental data. Consistent estimates of permeability were obtained for each set of experiments. The results indicate that Darcy's Law adequately describes high concentration displacements through saturated coarse- and medium-grained porous media.     

地表温度对颗粒跃移轨迹的影响

为了研究由地表温度变化引起的向上的垂向气流对沙粒跃移运动的影响,本文给出了考虑近地表温度变化和水平来流风场作用下的沙粒的跃移运动。在定量给出不同时刻的近地表温度和垂向风速的基础上,计算了由于太阳辐射所引起的近地表层垂向气流对沙粒跃移运动的影响,发现:垂向风速在午后可达到1.5m/s并使得沙粒跃移轨迹的最大高度和长度分别增加55.56%和73.68%;同时,与不考虑温度效应的情况不同的是,沙粒跃移轨道最大高度将随粒径变化。     

颗粒型砂介质的受压力学特征及屈服滑动

提出颗粒型砂介质在压实过程中的两种特征：孔隙填充状态和颗粒滑动状态；针对孔隙填充状态的力学行为特征，提出相对体积改变量(压实量)作为表征此状态的特征参量，研究了瞬时压缩模量与压实量的函数关系；针对型砂的颗粒滑动状态，提出具有强化效应的Mohr-Coulomb屈服条件，推导描述颗粒屈服滑动状态的增量本构方程、以及三轴压实过程条件下的状态本构方程，最后，就不同侧向压力下的三轴压缩试验、带模样的型砂压实试验的大量试验数据进行处理和验证。     

Experimental analysis of sand particles'' lift-off and incident velocities in wind-blown sand flux

The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the χ²-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off and incident velocities as well as their vertical components are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed. The project supported by the National Natural Science Foundation of China (10532040) and the Hundred Talents Project, the Knowledge Innovation Project of Chinese Academy of Sciences (KZCX2-304). The English text was polished by Keren Wang.     

Evolution of downsized crescent-shaped dune in wind tunnel experiment

The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution.     

Autoradiographische Untersuchungen zur Vermisechung von Baustoffkomponenten

Die Feinverteilung des Kalkes im Kalk-Quarzsand-Gemisch ist eine notwendige Bedingung fur hohe erreichbare Festigkeit der Silikatbaustoffe. Vergleiehende Untersuchungen über die Kalkverteilung an neutronenaktivierten feinkörnigen Baustoffproben mit Hilfe von Szintillationsmessungen des ⁴⁷Ca-Gehaltes und mittels autoradiographischer Darstellung der Kalkverteilung in kleinen Prüfkörpern unter Ausnützung der relativ weichen β-Strahlung des ⁴⁵Ca ergaben, daβ die autoradiographischen Aussagen über die Homogenität der Proben am besten mit den Festigkeitsiwerten der Prüfkörper korrespondieren.     

组合单元法在砂井地基有限元分析中的应用

针对砂井地基的平面应变有限元分析，本文首次将组合单元法引入到砂井地基的分析中，提出砂墙组合单元。该单元对常规等参元进行改进，在单元内部同时考虑砂井的涂抹作用和井阻作用，从而克服了常规有限元法在计算砂井地基时单元数和节点数过多的缺点。将砂墙组合单元加入USAP有限元计算软件，工程算例分析结果表明：与已有的各砂井地基的平面应变解答和荷兰的基础工程有限元分析软件PLAXIS相比，解答合理并有效地考虑砂井的涂抹作用和井阻作用；与常规有限元法相比，在保证计算精度的前提下，减少了可观的单元数和节点数，降低了计算的工作量。