喷雾干燥法制备富锂正极材料及其电化学性能

用喷雾干燥法制备Li_1.2Mn_0.54Ni_0.13Co_0.13O₂富锂正极材料并表征其结构、形貌以及电化学性能,研究了烧结温度对材料电化学性能的影响。结果表明：这种正极材料具有良好的层状结构,一次颗粒粒径为100 nm左右且分布均匀,样品的首次放电比容量为220.2 mAh/g,库伦效率为72.5%,18个循环后容量保持率为96.8%。电化学阻抗和循环伏安特性的测试结果表明,这种正极材料具有良好的电化学性能。     

TiAl合金表面TiAlCrY/YSZ涂层高温长时间服役性能

TiAl合金具有低密度、高比强度的优异性能,是一种潜在的航空发动机用结构材料。TiAl合金的服役温度范围为700～900℃,在其表面制备高温热防护涂层可以进一步提高服役温度。本研究采用等离子喷涂技术在TiAl合金表面制备了新型TiAlCrY/YSZ涂层,并与传统的NiCrAlY/YSZ热障涂层进行高温长时间服役性能对比研究。结果发现, TiAlCrY/YSZ涂层在1100℃空气环境中服役300 h保持完好,表现出良好的高温性能,而NiCrAlY/YSZ涂层在1100℃的服役寿命不足100 h。显微分析结果表明, TiAlCrY黏结层表面会形成一层连续且致密的TGO,其主要成分为Al2O3,与YSZ涂层的界面兼容性良好。并且TGO在1100℃空气环境中服役300 h后,厚度仍<8μm。以上研究表明,与传统NiCrAlY/YSZ热障涂层相比, TiAlCrY/YSZ更适合作为TiAl合金表面的高温热防护涂层。     

环境相对湿度对牛皮纸垫缓冲性能影响的研究

目的 探究环境相对湿度对新型牛皮纸垫缓冲性能的影响。方法 基于静、动态压缩试验,分析叠加层数分别为2、3、4的牛皮纸垫在环境相对湿度分别为30%、50%、70%、90%条件下的缓冲性能。结果 在静态压缩试验中,牛皮纸垫静压承载能力随着环境相对湿度的增大而减弱、叠加层数的增多而增强。不同规格纸垫存在对应的湿度应力分界值,当材料所受外力小于湿度应力分界值时,其缓冲性能随着湿度的增大而提高;当外力大于湿度应力分界值时,缓冲性能随湿度的增大而减弱。一定湿度条件下,叠加层数对牛皮纸垫缓冲性能也存在影响：相对湿度为30%时,缓冲性能随叠加层数的增多而减弱;相对湿度为50%、70%、90%时,存在层数应力分界值,当材料所受外力小于层数应力分界值时,其缓冲性能随叠加层数的增多而减弱,当外力大于层数应力分界值时,缓冲性能随叠加层数的增多而增强。在动态压缩试验中,随着环境相对湿度的增加,牛皮纸垫传递给产品的最大加速度增大,缓冲性能减弱;叠加层数的增多,使其传递给产品的最大加速度减小,缓冲性能增强。结论 研究结果对牛皮纸垫缓冲包装的设计和材料选择存在潜在的指导意义。     

纳米银-聚合物菱形剪纸薄膜应变传感特性的研究

采用银镜制备法和激光切割技术获得了纳米银颗粒/聚二甲基硅氧烷剪纸结构薄膜,并系统地研究了薄膜作为柔性应变传感器的力学及压阻特性。将数值模拟与实验相结合,测量了传感薄膜的应变比γ、压阻滞回特性、线性度及压阻敏感性,重点探讨了薄膜制备工艺、结构参数与上述薄膜传感特性的定量关系。结果表明,在给定结构下,结构薄膜整体与结构单元的应变比γ为常数,反映了结构薄膜的变形特性,是理想的力学性能表征参数。菱形剪纸结构薄膜具有量级可达200的大应变比,即在大应变下,材料的实际应变很小。这一特点极大地提升了薄膜的应变测量范围、压阻稳定性、线性度,并保持了合理的压阻灵敏度。     

基于 ResU-Net 的三维断层识别方法及应用

断层刻画了地层的边界位置,地震成像数据中反射层的不连续性可作为断层解释的主要依据。深度神经网络的强非线性性质可作为地震数据中断层不连续特征表达的有力工具,断层识别问题可视作一个像素级别的二分类问题,并使用深度学习方法对此问题进行建模求解。据此可给出一种端到端的基于深度学习网络的三维断层自动识别方法。首先利用地震子波与反射系数卷积合成多组三维地震数据,建立用于深度网络学习断层特征的样本数据,随后搭建网络进行训练,网络训练完成后应用于实际地震数据。鉴于残差模块可很好地提升网络泛化性能,所提出的将残差网络中的残差块结构引入U-Net中的方法,可用于提升通过合成数据样本训练得到的网络模型在训练数据之外,即实际地震数据上的断层识别性能。所建立网络用于断层解释时,输入为叠后三维地震数据,输出为相同维度的三维数据体,其中每一输出值代表输入三维地震数据相同位置处断层的概率。实际算例对比测试表明,此方法可对三维地震数据中的断层进行有效识别,在合成数据集上训练精度相差不大的前提下,引入残差模块的ResU-Net在实际地震数据上的断层识别泛化性能得到提升。     

Sound Absorption Performance and Mechanism of Aluminum Foams with Double Main Pore-Porous Cell Wall Structure

To enhance the sound absorption performance of open-cell aluminum foam, the double main pores-porous cell walls (DMP-PCW) aluminum foams via infiltration casting of preforms mixed with two sizes of NaCl particles are prepared. The pore structure, sound absorption performance, and mechanism of DMP-PCW aluminum foam are investigated. The pore structure consists of double-sized main pores similar to the NaCl particles and the cell wall pores formed by the connections between NaCl particles. It is found that the static flow resistivity of DMP-PCW aluminum foam reaches an optimum value of 28105 Pa.s m⁻² when the volume proportion of small main pores increases, the size of cell wall pores decreases, and the number of cell wall pores per unit main pore surface area (NPPA) increases. At 800–6300 Hz, the average absorption coefficient is 0.89. In addition, the Wilson model predicts the sound absorption properties of DMP-PCW aluminum foam. The predicted values agree well with the measured values. The finite-element acoustic simulations and dynamic viscous-thermal permeability calculations reveal that the improved sound absorption performance of DMP-PCW aluminum foam is correlated to the enhanced sound transmission caused by increased NPPA and increased viscous-thermal loss due to the double main pore structure.     

Three-Dimensional Analytical Modeling of Axial-Flux Permanent Magnet Drivers

In this paper, the axial-flux permanent magnet driver is modeled and analyzed in a simple and novel way under three-dimensional cylindrical coordinates. The inherent three-dimensional characteristics of the device are comprehensively considered, and the governing equations are solved by simplifying the boundary conditions. The axial magnetization of the sector-shaped permanent magnets is accurately described in an algebraic form by the parameters, which makes the physical meaning more explicit than the purely mathematical expression in general series forms. The parameters of the Bessel function are determined simply and the magnetic field distribution of permanent magnets and the air-gap is solved. Furthermore, the field solutions are completely analytical, which provides convenience and satisfactory accuracy for modeling a series of electromagnetic performance parameters, such as the axial electromagnetic force density, axial electromagnetic force, and electromagnetic torque. The correctness and accuracy of the analytical models are fully verified by three-dimensional finite element simulations and a 15 kW prototype and the results of calculations, simulations, and experiments under three methods are highly consistent. The influence of several design parameters on magnetic field distribution and performance is studied and discussed. The results indicate that the modeling method proposed in this paper can calculate the magnetic field distribution and performance accurately and rapidly, which affords an important reference for the design and optimization of axial-flux permanent magnet drivers.     

Effects of bottom profile on the circulation and classification of particles in cylindrical hydrocyclones

The cylindrical hydrocyclone has been increasingly used in coarse classification due to its reduced fine particle entrainment, but the loss of coarse particles to overflow remains an intractable problem. Based on the notion that the strong circulation flow caused by the flat bottom structure bears primary responsibility for the problem, this study designs eight unique bottom profiles to regulate the particle circulating flow and attempts to correlate particle circulation flow with classification performance. The effects of the bottom profile on flow field characteristics, particle spatial distribution, circulation flow rates, and grade efficiency are explored in detail using validated models in a Φ200 mm cylindrical hydrocyclone. The findings suggest that bottom profiles have the greatest effect on the axial velocity near the bottom and the grade efficiency of intermediate and coarse particles, while all unique designs have the potential to lower turbulence intensity. An ascending segment near the wall or a descending segment near the axis can help to mitigate the misplacement of coarse particles by reducing particle circulation flow without affecting the entrainment of fines appreciably. Additionally, two circles are found on each side of the cut plane, which is conducive to releasing coarse particles from the circulation flow. Regulation of particle circulation flow by adjusting bottom profile parameters can improve separation performance.     

Influence of alumina nanoparticles additives into biofuel (water hyacinth)-diesel mixture on diesel engine performance and emissions

The using diesel and biodiesel blends as a fuel has been a recent field of study especially with nanoparticles additives. The addition of alumina nanoparticles to biodiesel was verified to reduce emissions, while engine performance was not given great attention to evaluate the effect of blending alumina nanoparticles with the diesel and biodiesel mixture on the performance characteristics of the diesel engine. Then performance and emission tests were carried out by using different fuel samples in a single cylinder diesel engine. The brake thermal efficiency for the alumina nanoparticles (50 ppm, 100 ppm) and biodiesel blends were lower than that of biofuel (D80B20) blends, it was decreased by 2.5 %, 6.05 % respectively as compared to the blend (D80B20). The rate of carbon monoxide emissions for the two biodiesel and alumina blends were lower than that of the biodiesel blend (D80B20) and the best reduction was for the blend (D80B20N50) and was 76.3 % as compared with the biodiesel blend (D80B20). Also, the nitrogen oxides emissions for all the blends with nanoparticles were lower than that of the blend D80B20 due to shortened ignition delay and less fuel was added during the combustion which lead to reduction in nitrogen oxides emissions.     

Characterization and evaluating the mechanical performance of halloysite nanotubes reinforced acrylonitrile butadiene styrene/polycarbonate composites exposed to aggressive environmental conditions

Developing light weight polymer based composites dispersed with novel reinforcements which can function well in the presence of aggressive environments is an active research field in the materials engineering. Hence, in the current work, halloysite nanotubes (1 %, 2 %, 4 %, 6 %, 8 % and 10 % by weight) were reinforced into acrylonitrile butadiene styrene/polycarbonate blend and the role of reinforcing phases on the mechanical performance under aggressive environmental conditions has been evaluated. Hardness was measured as gradually increased in the composites with the increased content of the reinforcements. Impact strength of the composites was observed as increased in the composites up to 4 % reinforcement and further decreased. Increased strength was measured for the composite up to 2 % reinforcement. Ductility of the composites was decreased as reflected form the decreased % of elongation with the higher fraction of reinforcements due to induced brittleness. The composites were exposed to diluted sulfuric acid for 3 h and 6 h at 60 °C and then subjected to tensile loading. With the increased time of exposure, composites with 1 % and 2 % reinforcement exhibited relatively better performance.