小功率PEMFC移动式电源的箱体结构和造型设计

小功率质子交换膜燃料电池是目前质子交换膜燃料电池的研究热点之一,通过三维实体造型设计,使箱体结构设计达到灵活、实用、可靠和便捷等目的,以小功率自行车用燃料电池为主要应用目标,对采用高压氢气瓶、小型金属氢化物储气罐等不同氢气供气方式下的小功率质子交换膜燃料电池进行箱体结构和造型设计,使其既能在通用供气方式下作为一个独立的部件进行供电,也能快速安装金属氢化物储气罐箱体进行移动电源和便携式装置的供电,实现了使用的可靠性、灵活性和便捷性。     

高性能各向同性及各向异性Nd-Fe-B/Fe复合磁体的制备

采用将Nd-Fe-B磁粉与Fe粉混合的方法,并结合真空感应热压烧结技术制得高性能的各向同性及各向异性复合磁体。研究了Fe粉含量对热压磁体磁性能的影响,以及温度和压力对磁体致密度和磁性能的影响。结果表明,适量的Fe粉添加(3%,质量分数)可提高热压磁体磁性能;升高温度或提高压力均可大幅提高磁体致密度,但过高的烧结温度使晶粒快速长大,恶化磁体磁性能,而温度过低磁体难易全致密化。在最佳热压温度及压力下制备的热压磁体具有最佳的磁性能:Br=0.852T,Hcj=798kA/m,(BH)m=131.5kJ/m3,磁体密度达7.72g/cm3;热变形后,最大磁能积达331kJ/m3。     

Comparison about as-cast microstructures and mechanical properties of Mg–4Y–1.2Mn–0.9Sc and Mg–4Y–1.2Mn–1Zn (wt%) magnesium alloys

In this article, the as-cast microstructures and mechanical properties of the Mg–4Y–1.2Mn–0.9Sc and Mg–4Y–1.2Mn–1Zn (wt%) magnesium alloys are investigated and compared. The results indicate that the Sc-containing alloy is mainly composed of α-Mg and fine particle-like Mg₂₄Y₅, Mn₁₂Y, and Mn₂Sc phases, while the Zn-containing alloy mainly consists of α-Mg and coarse Mg₁₂YZn phases with a continuous network. Furthermore, the grains of the Zn-containing alloy are relatively finer than those of the Sc-containing alloy. In addition, the Sc-containing alloy exhibits relatively higher tensile properties at room temperature and 300 °C than the Zn-containing alloy. However, the creep properties at 300 °C and 30 MPa for 100 h for the Sc-containing alloy are relatively lower than those for the Zn-containing alloy.     

Effects of zirconium addition on as-cast microstructure and mechanical properties of Mg–3Sn–2Ca magnesium alloy

At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties.     

Dynamical processes of energy transfer in red emitting phosphor CaMoO4:Sm, Eu

Upon ⁴K_11/2 excitation of Sm³⁺ at 405 nm, the performance of energy transfer from Sm³⁺ to Eu³⁺ in the red emitting phosphor CaMoO₄:Eu³⁺, Sm³⁺ significantly extends its excitation region for better matching the near-UV LED. Photoluminescence spectra indicate that the energy transfer pathway concerns the relaxation from ⁴K_11/2 to ⁴G_5/2 of Sm³⁺ and subsequent transfer to ⁵D₀ of Eu³⁺ rather than ⁵D₁ of Eu³⁺. The fluorescent decay pattern of Sm³⁺⁴G_5/2 level in CaMoO₄:0.5% Sm³⁺, 2% Eu³⁺ is studied at 77 K based on the Inokuti-Hirayama formula, revealing an electronic dipole-dipole interaction between Sm³⁺ and Eu³⁺. The coefficient for the energy transfer is obtained to be 8.5 × 10⁻⁴⁰ s⁻¹ cm⁶. The fluorescence rise and decay pattern of Eu³⁺⁵D₀ level as Sm³⁺ is only excited at 77 K is well described by the dynamical processes of the energy transfer.     

添加剂对镀硬铬溶液性能的改善

本文通过试验对比了传统镀硬铬溶液和添加某型添加剂的镀硬铬溶液在阴极电流效率、沉积速度、覆盖能力等方面的差异,以及对镀硬铬溶液电流效率的影响。说明了镀硬铬溶液加入添加剂后对镀液、镀层性能的改善,体现了镀硬铬添加剂在镀硬铬方面的优越性。     

Experimental and kinetic investigation on the effects of hydrogen additive on laminar premixed methanol–air flames

The effects of hydrogen addition on laminar premixed methanol–air flames were studied both experimentally and numerically. To achieve this, a constant volume chamber (CVC) and the premix code in CHEMKIN were used. During the experiments, the equivalence ratios (ϕ) and hydrogen mole fractions ($X_h$) were set to 0.6 to 1.8 and 0%–100%, respectively. In addition, initial environmental conditions were set to 375 K and 1 atm. The results indicate that the laminar flame speed (LFS) and burning velocity (LBV) both increase when more hydrogen is added into the methanol–air mixtures. For premixed methanol–air flames, the Markstein length ($L_b$) decreases monotonically with an increase in the equivalence ratio; however, when the hydrogen fraction is greater than 40%, an increasing trend in the Markstein length is presented as the mixtures move toward the fuel-rich side. The variation in Markstein length is non-monotonic with the hydrogen fraction. A kinetics analysis indicates that methanol is mainly consumed by the dehydrogenation reaction caused from the impact of the active free radicals (OH and H). Reactions involving active free radicals and light intermediate species have the highest sensitivity and contribute the most to the propagation of a laminar flame. Therefore, the promotion effect of hydrogen additive is due to an enhancement in the radical pooling of H, OH, and O. The chain branching reaction R5 (O₂ + H = O + OH) is essential for the geometric growth of free radicals. In addition, the amount of formaldehyde decreases owing to the hydrogen blending.     

基于FLOW-3D仿真的横浇道集渣效果研究

夹杂缺陷对铸件产生严重破坏作用．在浇注过程中，横浇道具有一定捕获夹杂物的功能，即集渣作用．为了探索横浇道的集渣作用，以含碳量为0．45％的碳钢为例，利用FLOW-3D模拟软件研究了横浇道的形式、浇注系统的类型、集渣包等对集渣效果的影响．仿真结果表明：横浇道充满可以明显提高集渣效率；横浇道横截面的变化及弯曲不利于提高集渣效果；横浇道上设置集渣包有利于提高集渣效率．     

多通道有源噪声分布控制系统的研究

在有源噪声控制领域,为减少多通道控制系统的计算载荷,一种可行的方法是使用分布式控制,即将原有系统分为多个子系统,以减少每个控制器的通道数。然而各子系统之间不可避免地存在相互干扰,使得系统收敛速度减慢,消声效果降低。针对此局限性,对经典的多通道FXLMS算法进行了修正,通过抑制各子系统之间的相互干扰,提高了算法的收敛速度,改善了系统的性能。实验结果表明此算法是可行和有效的。     

电子基板用玻璃/陶瓷复合材料的低温共烧与性能

玻璃/陶瓷低温共烧复合材料具有高导热性、快速电子信号传输性能、热膨胀系数与硅匹配、力学性能良好等优点,被广泛应用作电子基板材料。本文简要阐述了玻璃/陶瓷复合材料的烧结机理和影响因素,综述了主要的制备方法,指出了烧结过程中可能存在的关键问题,并讨论了玻璃/陶瓷复合材料的性能调控方法。最后,展望了玻璃/陶瓷复合材料在电子信息领域的发展方向和应用前景。