40Cr钢表面包埋渗Mo涂层组织及摩擦性能

热扩散渗钼(Mo)是钢材表面化学成分的改性方式之一,其可提高钢的淬透性,与碳作用形成高熔点的碳化物,能够提高钢铁材料表面的耐磨性。为探索热扩散渗钼工艺,分别采用箱式炉加热和感应加热对40Cr钢进行1 000～1 300℃不同温度下包埋扩散渗处理,利用场发射扫描电子显微镜(FEG-SEM)、X射线衍射技术(XRD)和摩擦磨损试验研究了渗Mo试样的微观组织、元素分布、物相构成以及摩擦磨损性能,并对感应加热渗Mo微观结构的演变机理进行了阐述。结果表明:在1 100℃下箱式炉加热未观察到明显的Mo渗层,而感应加热在不同温度下形成了30～70μm厚的Mo渗层;感应加热后试样截面组织由Mo渗层、过渡层、受影响层、基体组成,其中Mo渗层主要由Fe-Mo固溶体(Fe-Mo SS)和碳化物相组成,过渡层由合金珠光体组成,受影响层为贫碳区;研究表明感应加热Mo渗层的最高硬度为560 HV_(0.2),约为原始试样的两倍,IHM-1200试样的的摩擦因数为0.73,比原始试样低0.12,磨损质量略低于原始试样,Mo渗层显著提高40Cr钢的摩擦性能。     

Synthesis of Metal Oxides@C (Metal =Ni,Fe) Based Prussian Blue Analogs as a High-performance Anode Material for Lithium-ion Battery

Ni3[Fe(CN)6]2 nano-cubic precursors were prepared by chemical coprecipitation at room temperature with nickel acetate and potassium ferricyanide as raw materials.The corresponding NiFe2O4-NiO@C composites with excellent crystallization were prepared by two-stage oxidation at low temperature.The microstructure and electrochemical behavior of the materials showed that the Prussian blue analog was transformed into metal oxide while the carbon coating was maintained in the two-stage oxidation at low temperature.The existence of the carbon coating reduces the charge transfer impedance to 31.5 Ω.At the current density of 500 mA/g,the reversible capacity of 632.7 mAh/g is maintained after 500 cycles.At the same time,carbon cladding can also enhance the role of pseudocapacitance in the material.At the scanning rate of 0.1 mV/s,the pseudocapacitance account for 54.4％ of the total discharge capacity,which is significantly higher than that of uncoated materials.     

基于BP-PID的选择性激光烧结温度控制系统设计

为消除纯滞后系统的超调、改善温度因素对制件质量和强度的影响,设计一种基于BP-PID算法的选择性激光烧结温度控制系统.该系统采用层次化架构和模块化的设计方案,以STM32控制器作为主控模块,并利用BP神经网络改进传统比例-积分-微分(PID)算法,提高了控制系统的稳定性且效果显著.通过MATLAB进行仿真模拟,与传统PID控制进行对比并进行实验.结果表明:BP-PID算法能迅速整定最优参数,且超调量小,达到稳态所用时间更短;在设定预热温度为90℃且采用BP-PID算法控制时,系统稳态误差在±1℃之内,超调量小于3％.     

Fabrication of AgAu alloy-TiO2 core-shell nanoparticles and their photocatalytic properties

In this paper, for improving the photocatalytic efficiency of titania(TiO2) nanoparticles(NPs), Ag Au alloy-TiO2 core-shell NPs are fabricated via a sol-gel(SG) process in the presence of Ag Au alloy NPs with block copolymer shells as templates. The photocatalytic activities of the Ag Au-TiO2 NPs on the photodecomposition of methylene blue(MB) are investigated. The Ag Au-TiO2 composite NPs coated with 5.0% titania related to block copolymers show higher photocatalytic activity than the other samples in which the titania contents are larger than 5.0%. The results indicate that the increase of the thickness of the TiO2 shell leads to the decrease of the photocatalytic activity.     

一款高性能时钟驱动器电路的设计

时钟器件芯片可以实现通信网定时同步、时钟产生、时钟恢复和抖动滤除、频率合成和转换、时钟分发和驱动等功能。在系统设计中,选用好的时钟驱动芯片,可以省去系统时钟树设计,既节省空间,又提高系统性能。介绍一款高性能时钟驱动器的集成电路设计方法,主要性能要求有:低传播延时、低输出偏斜、低输出抖动、抗电磁干扰能力、抗ESD能力,一一详述了达到各项要求的设计。     

双馈感应发电机Crowbar电路的投切控制策略优化研究

研究了Crowbar投入、退出时间对双馈感应风力发电机低电压穿越性能的影响,并在Matlab/Simulink仿真平台上搭建了含Crowbar保护电路的DFIG模型,验证了Crowbar投切时间对DFIG低电压穿越的影响,保证故障发生时,Crowbar电路按设定的投切时间工作,短路电流能根据电流的变化规律快速衰减,转子电阻电压不超过直流母线电压;采用阈值投入延时切出的方案,防止Crowbar保护在电网故障时多次投切。仿真结果表明,经过适当的延时切除Crowbar电路可以避免Crowbar电路多次动作和转子再次过电流,能很好地保护风电机组,提高其低电压穿越能力。结果显示,低电压穿越效果很大程度上受退出时间影响。     

Preparation of polyacrylamide grafted collagen extracted from leather wastes and their application in kaolin flocculation

This is probably the first report on the synthesis of a series of novel collagen‐based flocculants (CP11, CP12, and CP13) by grafting polyacrylamide (PAM) chains onto the collagen backbone, which was directly extracted from leather shavings via alkali hydrolysis. The results from FTIR, XRD, ¹H NMR, and TGA well supported that PAM chains had been successfully grafted onto collagen backbone. In addition, the micrographs of SEM revealed that the PAM grafted collagen possessed much more porous and looser surface structures in comparison with virgin collagen. Zeta potential measurement showed that the introduction of branched PAM chains helped to improve the positively charge density. Furthermore, CP12 performed the best in the kaolin flocculation with the highest flocculation rate about 24%·min^?1 and could induce the generation of much larger and denser floccs for the fast settling of kaolin particles. The corresponding flocculation mechanism was also presented by analyzing the collected flocs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41556.     

Color Variation Between PSL and PL in CaAl2Si2O8:Tb3+ with the Assistance of Trap Level

We reported a green photoluminescence (PL) emission associated with a blue photo‐stimulated luminescence (PSL) phenomenon in CaAl₂Si₂O₈ (CASO): Tb³⁺, Dy³⁺. With increasing concentration of Dy³⁺, a great enhancement of the blue PSL attributed to the defects and the transition of Tb³⁺ is observed. TL spectra indicates that the establishment of trap level introduced by codoping Dy³⁺ is the reason for the color variation between PSL and PL in CaAl₂Si₂O₈: Tb³⁺, Dy³⁺. The trap level not only serves as self‐excitation state but also hinders the nonradiative relaxation processes between ⁵D₃ and ⁵D₄ state of Tb³⁺. The result suggests that the introduction of appropriate trap level could provide a promising approach for controlling the color of electron trapping materials (ETMs).     

Investigations on Radiation Tolerance of Mn+1AXn Phases: Study of Ti3SiC2, Ti3AlC2, Cr2AlC,Cr2GeC,Ti2AlC,and Ti2AlN

Nanolaminated M_n+1AX_n phases as candidate materials for next generation nuclear reactor applications show great potential in tolerating radiation damage. However, different M_n+1AX_n materials behave very differently when exposed to energetic neutron and ion irradiations. Based on first‐principle calculations, the radiation tolerance of two M₃AX₂ and four M₂AX phases were studied in this work, covering all the M_n+1AX_n phases previously investigated with experiments. We have calculated the formation energies of Frenkel pairs and antisite pairs in these materials. The improved radiation tolerance from Ti₃AlC₂ to Ti₂AlC observed by experiments can be understood in terms of different Al/TiC layer ratio as the A atomic plane in the nanolaminated crystal M_n+1AX_n accommodates radiation‐induced point defects. The formation of M_A–A_M antisite pair in M_n+1AX_n materials would provide an alternative way to accommodate the defects resulted from radiation damage cascades, whereas this ideal substitution channel does not exist for Cr₂GeC due to its pronouncedly higher M_A–A_M antisite pair formation energy. To further elucidate their radiation damage tolerance mechanism, we have made a detailed analysis on their interatomic M–X, M–A, and X–A bonding characters. Criteria based on the bonding analysis are proposed to assess the radiation tolerance of the six M_n+1AX_n materials, which can be further applied to explore other M_n+1AX_n phases with respect to their performances under radiation environment.