Solvothermal synthesis and photocatalytic activity of Al-doped BiOBr microspheres

A series of Al-doped BiOBr microspheres with different Al contents were synthesized via a facile solvothermal method. The as-prepared samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectrometry(EDS), X-ray photoelectron spectroscopy(XPS), N₂ adsorption–desorption and UV–visible diffuse reflectance spectroscopy(UV–vis DRS). The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange in an aqueous solution under visible light irradiation. The results revealed that Al doping could greatly improve photocatalytic performance of BiOBr and different Al contents resulted in different photocatalytic activities. The highest activity was achieved by 4 at%Al-BiOBr. The enhanced photocatalytic activity was attributed to efficient separation of photogenerated electron–hole pairs and large BET surface area.     

飞机对中和偏心拦阻钩索动力学分析

研究装有尾钩飞机对中或偏心拦阻着陆后,计及弯折波在索中的传播情况下拦阻索的动力响应.计算作用在拦阻钩上的冲击载荷和飞机的减速过程.文中以美国BAK-13和E-28拦阻机为例进行计算分析,并用BAK-13拦阻机和各种机型,比较模拟计算和实测值的拦阻最大钩载.结果表明, 文中建立的模型和分析结果具有良好的精度,可为飞机-拦阻机相容性及舰载机的拦阻提供参考.     

视觉引导下的自主式捡球机器人多目标路径规划算法

文章首先简要描述了捡球机器人路径规划的目的、视觉处理的工作特点,分析了自主式捡球机器人设计时所面临的问题,然后结合滚动窗口理论提出了一种基于视觉传感器的自主式移动机器人多目标路径规划算法。该算法有效地减少了移动捡球机器人执行任务的时间,提高了其捡球效率。     

发电机程序逆功率保护回路改造

丰镇发电厂1号发电机程序逆功率保护因主汽门误关直跳发电机,增加了机组非计划停运次数,因此对1号发电机程序逆功率保护回路进行了改进。改造后,机组未因主汽门关闭接点误接通而发生停机事故,从而保证了继电保护的可靠性,确保了机组的安全稳定运行。     

Experimental study on spray cooling under reduced pressures

Spay cooling is a complicated flow and heat transfer process affected by multi-factors among which the environmental pressure is extremely important. However the influence of pressure is not investigated sufficiently, especially the reduced pressure. In the present study, spray cooling under low initial environmental partial pressures and vapor partial pressures with R21 are investigated with a closed spray and condensation system. To study the influence of initial environmental partial pressure, different amounts of nitrogen are inflated into the vacuum flash chamber, while the vapor partial pressure is kept constant. To study the influence of vapor partial pressure, a cascade refrigerator is used to condense the vapor with different condensation temperatures so that the vapor partial pressure can be maintained or adjusted, while the initial environmental partial pressure is kept constant.The experimental results show that the spray cooling power increases monotonically with the increasing spray flow rate in the experimental range, while the cooling efficiency decreases with the increasing spray flow rate. The spray cooling power and cooling efficiency vary with the initial environmental partial pressure or the vapor partial pressure non-monotonously, which indicates there is an optimal pressure for the heat transfer performance. Besides, the mechanism of the non-monotonous variation trend is discussed based on the key aspects including flash evaporation, convection and boiling. Especially, the boiling heat transfer curve is applied to explain the trend.     

罗茨转子双曲线轮廓构造的探索与分析

为挖掘和提升双曲线在罗茨转子方面的应用性能,先后从双曲线转子轮廓、参数化轮廓方程、极限取值、高形提升等四方面内容,展开双曲线在罗茨转子中的应用研究,并与常见渐开线、圆弧转子就动不平衡、轻量化、脉动等性能进行比较分析。结果表明:高形双曲线的转子质心系数为圆弧、渐开线转子的91.7%、93.4%,距轴心更近,利于提高转子泵的动不平衡性能;容积利用系数为圆弧、渐开线转子的105.3%、106.7%,结合更小的内泄漏,利于提高转子泵的轻量化性能;脉动系数为圆弧、渐开线转子的93.4%、94.9%,利于提高转子泵的流体质量;不过,极限形状系数为圆弧、渐开线转子的96.1%、96.9%。得出高形双曲线为一款适宜的非接触转子轮廓。     

Granular porous calcium carbonate particles for scalable and high-performance solar-driven thermochemical heat storage

Science China Technological Sciences - Calcium carbonate is promising thermochemical heat storage material for next-generation solar power systems due to its high energy storage density, low cost,...     

Mechanical behaviors of polycrystalline NiTi SMAs of various grain sizes under impact loading

This work presents mechanical properties of the NiTi polycrystalline superelastic shape memory alloys(SMA) of 5 different grain sizes under high-speed impacts. The amorphous, nanocrystalline(40, 80, 120 nm) and coarse grain(20 μm) sheets are manufactured with cold rolling and suitable heat treatments. A Hopkinson tensile bar is used to perform tests up to 45 m/s. Highspeed camera system and digital image correlation method are used to get the strain field and particle velocity field at a sampling frequency of 2×10~6 frames/s with a resolution of 924×768 pixels. Nominal stress-strain curves are obtained for all the sheets with a strain rate of about 1000 s~(-1) and they have a similar evolution to the quasi-static case but with much higher stress levels. The rate sensitivity is increased with the grain size and the stress level can reach up to a 70% growth for a coarse grain sheet but be totally insensitive for the amorphous sheet in the strain rate from 10~(-4) to 10~3 s~(-1). A single transformation front can be found under high-speed impact(45 m/s) at the early loading stage. The speed of the transformation front is calculated from strain time histories and the highest front speed of 811 m/s is observed which is never observed before. It also reveals that the front speed depends also on the grain size. With the same loading speed, the bigger the grain size is, the slower the transformation front speed is.     

高铬铸铁不同工艺软化热处理后的组织与性能

采用组织观察、XRD物相分析和硬度测试等实验方法,研究了不同的软化热处理工艺对抗磨高铬铸铁组织和硬度的影响。结果表明:在硬化态三种高铬铸铁均具有较高硬度,具体硬度值≥58 HRC,组织均为初析M7C3型碳化物、共晶碳化物、马氏体、奥氏体组成。KmTBCr22NiMo具有较好的软化效果,分别采用950℃×2 h炉冷至820℃×4 h炉冷至250℃出炉空冷和1 050℃×4 h炉冷至720℃×10 h炉冷到室温的两种热处理工艺软化后,KmTBCr22NiMo的硬度分别由57 HRC降低为39.9 HRC和40 HRC。KmTBCr25NiMo和KmTBCr28NiMo在采用不同热处理工艺软化后,软化效果均不理想,其最佳实验结果分别为硬度由硬化态的60 HRC下降到53.7 HRC和由硬化态的61 HRC下降到54.5 HRC。实验结果表明,随高铬铸铁中铬含量的增加,其软化难度增大。     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.