Liquid-phase flash sintering 8YSZ with alkali halide sintering aids

The properties of ZrO₂: 8 mol% Y₂O₃ (8YSZ) ceramics with LiF and KCl sintering aids for liquid phase formation during electric field-assisted sintering were studied. Sintering experiments were carried out at 650 °C under 200 V cm⁻¹ AC electric field by varying current density, current application time, as well as LiF and KCl contents. Pellets sintered with KCl addition had cavities, cracks and fractures. Pellets sintered with 15 wt.% LiF, on the other hand, were homogeneous after thermal removal of LiF upon Joule heating. Low electric current densities coupled with longer application times produced homogeneous specimens. Three different stages were identified during sintering experiments: (i) LiF melting with the electric field applied at furnace temperatures lower than its melting point, (ii) shrinkage due to liquid phase formation and LiF removal, (iii) final densification due to grain growth and pore elimination. The electrical behavior and an estimate of the porosity were carried out by electrochemical impedance spectroscopy measurements.     

航天发动机叶片电解加工流场设计和试验研究

电解加工作为整体构件制造的主要技术之一,其流场设计的合理性将严重影响电解加工过程的稳定性、加工效率和质量。针对航天发动机叶片式扩压器设计了部分阻隔式反W型流场,并开展了与侧流式和反W型流场的仿真比较。仿真结果表明,该流场方式可以保证加工区电解液的高速流动,并能有效避免进/排气边漏液现象。最后,在部分阻隔式反W型流场中开展了叶片式扩压器电解加工试验,在阴极进给速度为0.5 mm/min时加工出了扩压器叶片,验证了流场设计的合理性。     

覆岩结构类型与开采覆岩损害特征分析

煤层开采打破了上覆岩层原有的平衡,必然引起岩层的移动、破断,导致应力场和裂隙场的改变,工作面出现矿压显现。上覆岩层的岩性和组合结构对工作面开采覆岩损害特征分布影响显著,一般岩性越坚硬,上覆岩层应力集中程度越高,采动裂隙越发育,矿压显现也越明显;坚硬岩层尤其是关键层对覆岩的破断运动起控制作用,覆岩破断发展到一定层位后软弱岩层往往是抑制覆岩破断进一步向上发展的关键。当工作面上覆岩层同时存在远近场关键层时,近场关键层的周期性破断引起裂隙带范围内岩层的运动和工作面周期来压;而远场关键层的周期性破断导致地表裂缝或台阶下沉,工作面压力急剧上升,有时甚至导致煤矿动压灾害,尤其是远近场关键层同步破断时动力现象更明显。通过地面钻孔使远场关键层提前破断是防止此类动力灾害的关键。     

闸片材料参数与制动盘温度关系

闸片材料参数不仅关系到摩擦副的摩擦磨损性能,也是影响制动盘温度分布的一个重要因素。采用ADINA软件,建立列车制动盘和闸片的三维热机耦合有限元模型,在制动速度100 km/h、压力0.538 MPa和惯量23 kg·m2条件下,研究闸片材料热膨胀系数、弹性模量、热传导系数对制动盘温度和接触压力的影响。结果表明:当闸片热膨胀系数从0.5×10-5 K-1增大到2.5×10-5 K-1时,制动盘峰值温度升高8.4%,最大接触压力增大47%,闸片热膨胀系数的增大加剧接触压力分布不均匀程度而使制动盘温度变化明显;弹性模量增大9倍,接触压力的分布对弹性模量不敏感,弹性模量对盘面温度影响不明显。闸片热传导系数增大7倍,制动盘峰值温度下降4.3%,热传导系数增大,加快热量的扩散速度使制动盘峰值温度降低,该研究结论可为高速列车闸片材料的开发提供参考。     

新型除草剂精草铵膦对柑橘园杂草的田间防效

[目的]为评价新型除草剂精草铵膦对柑橘园杂草的田间防效。[方法]采用定向茎叶喷雾法,分别于2018、2019年进行了10%精草铵膦钠盐可溶液剂的田间小区试验。[结果]10%精草铵膦钠盐可溶液剂570~870 g a.i./hm^2对柑橘园阔叶杂草、禾本科杂草均具有较好的防效,药后30 d,总草株防效和鲜重防效分别为94.9%~98.8%、95.0%~98.5%,与对照药剂200 g/L草铵膦水剂1400 g a.i./hm^2处理相当。[结论]精草铵膦可作为防治柑橘园或非耕地杂草的高效低用量药剂,具有较好的推广应用前景。     

双盘式磁力耦合器振动噪声分析与实验研究

为了在双盘式磁力耦合器设计阶段分析振动噪声特性,优化双盘式磁力耦合器设计,提出了一种利用模态叠加原理来分析其振动噪声的方法。双盘式磁力耦合器具有高转矩密度与高效率等优势,因此逐渐发展成为煤矿机械柔性传动装置。由于双盘式磁力耦合内部的转子磁场非正弦分布以及涡电流谐波等因素影响,双盘式磁力耦合器输出转矩中不可避免的存在波动。若根据计算得出的双盘式磁力耦合器的电磁振动噪声特点,在设计时选取振动噪声小的参数进行优化组合,可在实际中降低其电磁振动及噪声,有利于减少制造成本。本文结合双盘式磁力耦合器的结构特征,提出了一种模态叠加响应法计算电磁振动噪声,建立了其电磁径向力的解析模型,并在多物理场耦合作用下分析主要电磁径向力波在工作频率内的谐波响应,最后在额定功率为55 kW双盘式磁力耦合器实验台上进行试验验证。基于麦克斯韦张量法,建立了双盘式磁力耦合器的径向电磁力解析模型,并得出0阶与10阶电磁径向力波是产生振动噪声的最主要原因;利用多物理场耦合分析法进行谐波响应NVH特性分析,结果显示0阶力波的振动加速度与形变量均大于10阶力波的振动加速度与形变量,因此双盘式磁力耦合器的电磁振动主要来源于0阶力波;在额定功率为55 kW,最高转速为1 500 r/min的双盘式磁力耦合器实验台进行振动测试,试验结果显示在1 500 r/min时,试验得出的最大振动峰值及频率约为35 m/s^2和4 950 Hz,与有限元仿真结果的误差对应为6.3%和1.1%;而当变频电机的输入转速依次增大时,振动加速度的理论值、仿真值与试验值的曲线形态较为接近,误差较小;噪声估计值与实测值的最大误差仅为8.9%,基本验证了本文所提出模态叠加法的正确性。     

矿用无人卡车国内外研究现状及关键技术

分析了国内外露天矿山用卡车无人驾驶技术发展现状,详细介绍了露天矿山卡车无人驾驶关键技术;通过分析对比前装线控和后装线控两种技术路线的优缺点以及超声波雷达、毫米波雷达、激光雷达、4D光场智能感知系统、红外传感器、视觉传感器等环境感知技术的优缺点;提出多传感器高度融合将是露天矿山卡车实现全天候环境感知的发展方向。通过分析对比惯性导航系统、GNSS差分定位技术、车联网定位技术、电子地图定位技术、视觉传感器等定位导航技术的差异,指出多定位技术融合是露天矿山无人驾驶卡车定位方式的必然选择。结合露天煤矿的生产实际,提出将现有的无人驾驶各种技术算法与露天矿山标准作业流程有机融合是实现卡车无人驾驶的必由之路。最后指出无人驾驶卡车应用5G技术是露天矿山安全生产的关键和核心,是无人驾驶的必备技术。     

Immobilization of surface non-affinitive protein onto a metal surface by an external electric field

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Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field.     

Leakage mechanisms of partially self-polarized BiFeO3 film

Partially self-polarized BiFeO₃ (BFO) film was fabricated on Pt(111)/Ti/SiO₂/Si substrate by a metal organic decomposition process at 480?°C. The influence of soaking times on leakage properties was discussed. The soaking times considered were those that could keep the leakage currents being measured in a steady state condition during the leakage tests. The length of soaking time during leakage measurement should be greater than or equal to 500?ms to rule out the contribution of backswitching to leakage properties. Different leakage characteristics induced by the built-in negative field occurred under positive and negative fields. The "flat-band" feature of the leakage current curves may result from competition between domain switching and the switching of defect complexes. It is suggested that the "unswitched" mode should be adopted during leakage measurement in BFO films. Additionally, negative bias should be adopted in negatively polarized BFO films and positive bias should be adopted in positively polarized BFO films.