复合固体推进剂中固体填料的安息角测试与仿真

复合固体推进剂含有固体颗粒较多，离散单元法是一种适合固体推进剂生产过程数值仿真的有效方法，颗粒物料的接触参数是保证离散单元法仿真精度的关键。本文以复合固体推进剂的主要组分铝粉和高氯酸铵固体颗粒为研究对象，通过实验测试获得了相关物料的安息角，利用专业离散元软件EDEM仿真模拟了安息角测试实验过程，建立了物料安息角与接触参数之间的联系。研究表明，滚动摩擦系数和滑动摩擦系数越大，安息角越大，物料流动性越差。对比仿真与实验结果，通过逆向反推法确定了物料的滑动摩擦系数和滚动摩擦系数两个关键接触参数。铝粉与高氯酸铵1∶2混合颗粒的滑动摩擦系数为0.2，滚动摩擦系数为0.05。为固体推进剂加工生产过程离散元数值仿真提供了关键基础数据。     

球磨过程中介质群运动区域划分方法研究

球磨过程中介质群运动状态变化对物料的破碎效率影响极大，通过对介质群运动状态进行区域划分，探究不同球磨工况下的介质群运动区域特征更能有效揭示介质群对物料的破碎方式和有效破碎区域。针对理论划分介质群运动区域过于理想、单一，试验追踪法成本过高的问题，提出了一种介质群运动区域划分的新方法-EDEM网格划分法。首先把筒体的横截面划分为若干个微元，利用数理统计的方法得到介质群位置概率分布函数，获取介质群运动速度区域分布图和碰撞特性区域分布图。然后给出了回转运动、螺旋运动及复合颤振运动三种工况下介质群运动区域的划分实例，并与试验追踪法对比，验证了EDEM网格划分法的准确性和有效性。最后通过粉磨试验中进料的破碎速率和微细颗粒产率探讨了介质群运动区域特性对颗粒的破碎方式和有效破碎区域的影响效果。本研究为优化球磨过程的影响因素和操作参数提供了一种快捷、有效的方法。     

Protection efficiencies of surface-active inhibitors in zinc-air batteries

Zinc (Zn) particles in alkaline electrolyte of a Zn-air battery (ZAB) are unstable and prone to corrosion. Zinc oxide (ZnO) generated on the surface of Zn particles affects the electrochemical reactions and reduces the battery efficiency. Thus, inhibiting the self-corrosion rate of Zn particles has become acritical issue for the development of these batteries. In this study, a research endeavor has been attempted by employing three types and concentrations of organic inhibitors in ZABs to constrain Zn anode corrosion. Significant analyses like polarization curve, constant current discharge, AC impedance, and dendrite growth are executed for in-depth understanding of the influences of these inhibitors. The experimental results reveal that the inhibiting efficiency of 10 wt% Sodium dodecyl benzene sulfonate surpassed polyethylene glycol 600 (PEG 600) and polysorbate 20 (Tween 20), with a maximum current density of 476.20 mA/cm² and voltage output of 1.4 V along with discharge capacitance of 10.31 Ah for 2 hours and 8 minutes. Zn anode surface analysis exposes significant dendrite growth and elemental Zn required for passivation suppression. Nevertheless, the results are also justified by Nyquist and Bode plots. Thus, the selected inhibitor will proficiently guarantee the enhanced performance and stability of the ZABs obtained and provide enormous opportunities for its applications.     

Self-assembled cubic-hexagonal perovskite nanocomposite as intermediate-temperature solid oxide fuel cell cathode

Self-assembly is an emerging strategy for preparing composite cathodes with good oxygen electrochemical reduction activity and congenital chemical compatibility for intermediate-temperature solid oxide fuel cell (IT-SOFC). Here we report that a self-assembled BaCo_0.6Zr_0.4O_3-δ (BZC-BC) nanocomposite is prepared through one-pot glycine-nitrate process and exhibits high cathode performance. The BZC-BC nanocomposite is composed of 62 mol% cubic perovskite BaZr_0.82Co_0.18O_3-δ (BZC) as an ionic conductor and 38 mol% hexagonal perovskite BaCo_0.96Zr_0.04O_2.6+δ (12H-BC) as a mixed ionic and electronic conductor. The BZC-BC nanocomposite has the pomegranate-like particles aggregated with a larger number of nanoparticles (50-100 nm) which greatly enlarge the three-phase boundary sites. The BZC-BC nanocomposite exhibits a thermal expansion coefficient of 12.89 × 10⁻⁶ K⁻¹ well-matched with that of Ce_0.8Gd_0.2O_3-δ (12.84 × 10⁻⁶ K⁻¹) electrolyte. The high electro-catalytic activity of BZC-BC nanocomposite cathode for oxygen reduction is reflected by the low polarization resistances of oxygen ions incorporation at cathode/electrolyte interface (0.02823 Ω cm²), oxygen species diffusion (0.03702 Ω cm²) and oxygen adsorptive dissociation (0.07609 Ω cm²) at 700 °C. The single cell with BZC-BC nanocomposite cathode achieves the maximum power density of 1094 mW cm⁻² at 650 °C and shows good stability under 25 h run.     

Influence of zinc and cadmium co-doping on optical and magnetic properties of cobalt ferrites

Zinc and cadmium based cobalt ferrites Zn_xCd_0.375-xCo_0.625Fe₂O₄ (where x = 0, 0.075, 0.125, 0.25) were successfully synthesized by a facile co-precipitation technique. Structural, optical and magnetic characteristics of the doped ferrites were systematically analyzed. X-ray Diffraction (XRD) pattern confirmed the formation of cubic spinel structure in all samples. Scanning electron microscopic analysis of surface morphology revealed cubic and spherical shaped ferrite particles. Fourier transform infrared (FTIR) spectroscopy confirmed the existence of metal oxygen (M − O) bonding in the prepared samples. Moreover, the prepared samples exhibited two frequency bands corresponding to phonon vibrational stretching in both octahedral and tetrahedral lattice positions. The optical properties were investigated in detail through photoluminescence (PL) spectroscopy and Raman spectroscopy. The PL spectrum confirmed the strong emission peaks in the ultraviolet to visible region of all the samples. Further, four active Raman modes, associated with cubic spinel structure are identified in all prepared samples. Finally, the magnetic characteristics are evaluated by using vibrating sample magnetometer (VSM) revealing ferrimagnetic and soft magnetic behavior of the samples. As the Zn and Cd co-doping in Co was increased, the H_c was decreased. The magnetic studies show the maximum H_c of 576 Oe for Cd doped cobalt ferrite, and maximum saturation magnetization (M_s) for Zn–Cd doped cobalt ferrite. It is envisaged that the newly prepared Zn–Cd co-doped cobalt ferrite would be appropriate for a number of important applications, for example, magnetic recording devices, sensors, actuators, high-density data storage devices, and biomedical equipments.     

Origin of stress overshoot in amorphous solids

Based on the shear-transformation-zone (STZ) theory, we propose a constitutive model for describing homogeneous elastoplastic deformation of amorphous solids where the interaction of shear transformations and free volume dynamics is incorporated. This theoretical model can reproduce the stress overshoot behavior that shows the dependence of strain rate, temperature, STZ population and dilatancy of systems. It reveals that the stress overshoots its steady state value due to the delayed activation of shear transformations that results from the insufficient free volume in the system. However, the subsequent strain softening (stress drop) is attributed to the shear-induced dilatation that is a result of the positive interplay between shear transformations and free volume creation, the latter playing the dominant role. Our analysis also demonstrates that the STZs, as basic carriers of amorphous plasticity, govern the yielding of the system, whereas the free volume dynamics significantly affects the post-yielding behaviors.