Hydrogen storage properties of Mg98.5Gd1Zn0.5 and Mg98.5Gd0.5Y0.5Zn0.5 alloys containing LPSO phases

In this work, the as-cast Mg-rich Mg_98.5Gd₁Zn_0.5 and Mg_98.5Gd_0.5Y_0.5Zn_0.5 alloys are prepared by the semi-continuous casting method, and their hydrogen storage performance and catalytic mechanisms are investigated by experimental and first-principles calculations approaches. The results show that the LPSO phases decompose and in-situ form the RE(Gd/Y)H_x(x = 2,3) nano-hydrides upon hydrogenation. These nano-hydrides not only serve as the in-situ catalysts to promote the hydrogen ab/desorption of Mg matrix, but also present the pinning effect to inhibit the growth of Mg/MgH₂ grains during hydrogenation and dehydrogenation. Comparatively, the two alloys exhibit the similar hydrogen absorption kinetics, while the hydrogen desorption kinetics of Mg_98.5Gd₁Zn_0.5 is superior to that of Mg_98.5Gd_0.5Y_0.5Zn_0.5. The first-principles calculations reveal that the GdH₂ and YH₂ hydrides exhibit different catalytic effects on weakening the bond strength of H–H within H₂ and Mg–H within MgH₂, which interprets well the differences in the hydrogen ab/desorption kinetics between Mg_98.5Gd₁Zn_0.5 and Mg_98.5Gd_0.5Y_0.5Zn_0.5 alloys.     

压电执行器的非对称动态迟滞特性建模研究

传统Bouc-Wen模型难以精确表征压电执行器固有非对称率相关动态迟滞非线性,因此提出一种广义Bouc-Wen(GBW)迟滞模型用于精确表征压电执行器的迟滞非线性。首先,基于传统Bouc-Wen迟滞模型引入两项非对称项和二阶IIR滤波器表征压电执行器非对称迟滞及高频相位滞后特性,进一步分析了模型参数值与频率变化规律并确定了模型的率相关参数。然后,搭建了基于NI CompactRIO测控系统的压电执行器精密定位实验平台,通过粒子群优化算法完成GBW模型的参数辨识,并对提出的GBW模型进行实验验证。实验结果表明,对于变频率正弦激励信号,GBW模型的最大误差为0.190 6μm,均方根误差为0.043 1μm仅占压电执行器位移行程的0.65%,相较于传统Bouc-Wen(CBW)模型及改进Bouc-Wen(EBW)模型分别下降了82.07%和62.10%。对比CBW模型和EBW模型,所提出的GBW模型精度和宽频性能均有显著提升,并且解析逆模型存在易于控制器设计,有助于实现压电执行器在超精密仪器设备中宽频、高速精密定位。     

Investigation on hydrogen storage properties of as-cast,extruded and swaged Mg–Y–Zn alloys

In this work, three different states of Mg-9.1Y-1.8Zn alloys including as-cast, extruded and swaged were prepared by semi-continuous casting, extrusion and swaging processes, respectively. Their compositions, microstructures and hydrogen storage properties were investigated. The results show that Mg-9.1Y-1.8Zn alloys in three different states are all composed of Mg and long-period stacking ordered (LPSO) phases. The LPSO phases occurs to break and decompose after hydrogenation and in-situ forms the YH_{χ(χ = 2,3)} nano-hydrides. The nano-hydrides can be used as in-situ catalysts to improve the hydrogen storage properties of alloys. Meanwhile, many nanocrystalline grains appear in the core of alloy after swaging, and the average grain size ranges from 80 to 200 nm. The presence of nanocrystals may increase the specific surface area of alloy, facilitating the diffusion and absorption of hydrogen. Comparatively, the swaged alloy exhibits the largest hydrogen storage capacity and excellent hydrogen sorption kinetics relative to other states of alloys.     

3D打印制备各向异性超疏水功能表面的定向输送性能

目的 在光敏树脂基底上制备各向异性超疏水功能表面，实现液滴的定向输送。方法 采用光固化逐层成形3D打印法，在样品基底上制备具有不同形状和结构尺寸的超疏水结构阵列。通过扫描电子显微镜（SEM）、EDS能谱分析，对样品的表面形貌与化学成分变化进行表征。采用接触角检测系统、高速摄像机，通过液滴弹跳、各向异性润湿性与定向输送实验，分析与评价不同阵列表面的超疏水性能、各向异性润湿程度以及定向输送行为。结果 液滴弹跳实验结果表明，液滴可在正方体及交错长方体阵列表面形成饼状弹跳，且后者超疏水性能最佳。各向异性润湿性实验结果表明，在圆柱体阵列中，各向异性润湿性程度随相邻圆柱体高度差Δh的增大而趋于显著，且Δh=1 mm时，各向异性润湿性最为显著；在长方体阵列中，长方体宽度w1及相邻长方体间距sp1对各向异性润湿性程度均有一定影响，w1=0.3 mm、sp1=1 mm时，各向异性润湿性最为显著。定向输送实验结果表明，Δh=1 mm的圆柱体阵列及w2=0.7 mm、sp2=0.7 mm的长方体阵列的定向输送性能最佳，液滴可按照设计的路线精准流动。结论 3D打印所制备的光敏树脂基功能表面的超疏水性能、各向异性润湿程度以及定向输送行为由其表面形貌和结构尺寸所决定，所制备的样品可实现液滴的精准定向输送。     

Remarkable synergistic effects of Mg2NiH4 and transition metal carbides (TiC,ZrC, WC) on enhancing the hydrogen storage properties of MgH2

Nanostructuring and catalyzing are effective methods for improving the hydrogen storage properties of MgH₂. In this work, transition-metal-carbides (TiC, ZrC and WC) are introduced into Mg–Ni alloy to enhance its hydrogen storage performance. 5 wt% transition-metal-carbide containing Mg₉₅Ni₅ (atomic ratio) nanocomposites are prepared by mechanical milling pretreatment followed by hydriding combustion synthesis and mechanical milling process, and the synergetic enhancement effects of Mg₂NiH₄ and transition-metal-carbides are investigated systematically. Due to the inductive effect of Mg₂NiH₄ and charge transfer effect between Mg/MgH₂ and transition-metal-carbides, Mg₉₅Ni₅-5 wt.% transition-metal-carbide samples all exhibit excellent hydrogen storage kinetic at moderate temperature and start to release hydrogen around 216 °C. Among them, 2.5 wt% H₂ (220 °C) and 4.7 wt% H₂ (250 °C) can be released from the Mg₉₅Ni₅-5 wt.% TiC sample within 1800 s. The unique mosaic structure endows the Mg₉₅Ni₅-5 wt.% TiC with excellent structural stability, thus can reach 95% of saturated hydrogen capacity within 120 s even after 10 cycles of de-/hydrogenation at 275 °C. And the probable synergistic enhancement mechanism for hydrogenation and dehydrogenation is proposed.     

Unraveling the Voltage Failure Mechanism in Metal Sulfide Anodes for Sodium Storage and Improving Their Long Cycle Life by Sulfur-Doped Carbon Protection

Metal sulfides are emerging as a promising anode material for sodium-ion batteries with high reversible capacities and fast reaction kinetics, but achieving long-cycling-life remains a great challenge. Here, taking cobalt sulfide as an example, its electrochemical sodium-ion storage failure phenomenon is first reported, which indicates that the battery cannot reach the cut-off voltage during charging. Detailed analyses demonstrate that such failure may originate from the dissolution and escape of polysulfide intermediates, further reacting with the released copper-ions from the current collector and inducing the occurrence of the shuttle effect. Based on the explored failure mechanism, a sulfur-doped carbon matrix with polar carbon sulfur bonds, which can firmly immobilize the dissolved polysulfides, is deliberately introduced into the Co_1−xS active particles (Co_1−xS/s-C) to improve their cycle stability. Consequently, the cycle life of the Co_1−xS/s-C anode for sodium-ion storage is extended from the original 125 to present 2000 cycles, even at high-rate current densities. Moreover, utilizing the carbon current collector instead of traditional copper can effectively delay the occurrence of the failure phenomenon. The present work promotes better fundamental understanding of the structural evolution of metal sulfide anodes during cycles, and the solution strategy can be extended to apply in other metal sulfides (ZnS, NiS).     

Enhanced hydrogen sorption properties of MgH2 when doped with mechanically alloyed amorphous Zr0·67Ni0.33 particles

In the present study, the effect of amorphous Zr_0·67Ni_0.33 additive containing nano-ZrO₂ on the hydrogen sorption kinetics and thermodynamics of Mg/MgH₂ was investigated. The amorphous Zr_0·67Ni_0.33 particles prepared by mechanical alloying of stoichiometric elements were introduced into MgH₂ powder through high-energy milling to produce a MgH₂/Zr_0·67Ni_0.33 composite. Structural and morphological analyses revealed that the nanostructuring effect of the ZrO₂ containing amorphous Zr_0·67Ni_0.33 has led to significant grain-size refinement of MgH₂ to the nanometric scale. As a result, the MgH₂/Zr_0·67Ni_0.33 composite demonstrates enhanced hydrogenation and dehydrogenation kinetics (4.0 wt%/50 s/250 °C and 5.0 wt%/4 min/325 °C, respectively). Meantime, substantially lowered enthalpies (−63.40 and 67.06 kJ/mol H₂ obtained through pressure-composition-isotherm measurements) and reduced desorption temperature (~270 °C) were observed in the composite as compared to the pure MgH₂, possibly due to the dissolution of Ni into MgH₂ lattice during ball milling.     

小口径非球面硫系玻璃镜片的非等温热压成型仿真与实验

为提高小口径非球面硫系玻璃镜片热压成型质量，避免成型缺陷，通过热压过程的有限元分析，提出了一种新的非等温热压成型法。在上模仁和上加热板之间设置加热间隙，对上、下加热板设置不同的加热温度，以实现玻璃预形体的非等温加热。首先，根据硫系玻璃高温粘弹性本构模型和热传递模型，结合相关参数建立了镜片热压过程的有限元模型；接着，采用所建立的模型，分析了非等温温差对玻璃预形体内部的温度分布、成型镜片最大残余应力分布及轮廓偏移量的影响，以确定最佳的温差值；最后，进行了镜片的非等温热压成型实验，并将仿真和实验结果进行了对比研究，以验证仿真模型和结果的有效性。仿真与实验结果均表明，最佳的非等温温差值为10℃。该条件下，仿真获得的玻璃预形体内部温度差仅为2.6℃，成型镜片最大残余应力可减至3.375 MPa，成型镜片ASP1和ASP2的轮廓偏移量最大值分别为0.562 m和0.615 m；实验获得的成型镜片ASP1和ASP2的PV值分别为118.2、194.0 nm，Ra值分别为17.0、37.8 nm，轮廓偏移量最大值分别为0.583、0.644 m，均满足精度要求。仿真与实验结果具有较好的一致性，采用合理的温差值进行镜片的非等温热压成型，可有效降低玻璃预形体内部温度差及成型镜片最大残余应力，避免粘连、气泡等成型缺陷，提高成型镜片的精度。