The effect of heat treatment on tensile properties of 2D C/SiC composites

Two-dimensional (2D) carbon fiber reinforced silicon carbide (C/SiC) composites with different initial strength were prepared by chemical vapor infiltration (CVI). After tensile property testing, results exhibited that as the heat-treatment temperature (HTT) increases to 1900°C, the tensile strength and toughness of the low strength specimen (LSS) increased by 110% and 530%, while the high strength specimen (HSS) increased by 5.4% and 550%, respectively. As observed from morphologies, the heat treatment increases the graphitization of the amorphous PyC interphase, which leads to the weakening of interfacial bonding strength (IBS). Meanwhile, the defects arising from heat treatment cause thermal residual stress relaxation. Therefore, the tensile strength and toughness of LSS with relatively high initial IBS increase significantly as HTT increases. For HSS with moderate initial IBS, the heat treatment slightly improves the tensile strength, but significantly improves the toughness. Consequently, the post-heat-treatment tensile properties of 2D C/SiC composites can be regulated by varying HTTs and different initial strength.     

Microstructural evolution and interfacial reactions between Ti and ZrO2/CaTiO3 composites

Various proportions of ZrO₂/CaTiO₃ powders were mixed and hot pressed at 1500°C/30 min for Ti casting. The hot-pressed ZrO₂/CaTiO₃ composites were reacted with pure Ti at 1700°C/10 min in Ar. The interfacial reaction between Ti and ZrO₂/CaTiO₃ composites was investigated through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The ZrO₂/CaTiO₃ composites with less than 10 vol.%, CaTiO₃, and a minor amount of residual TiO₂ were found. When the content of ZrO₂ was increased to larger than 10 vol.%, two Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ phases appeared in the composites. The amount of CaTiO₃ and CaZrTi₂O₇ in the composites gradually decreased as the amount of ZrO₂ increased. When Ti came in contact with ZrO₂/CaTiO₃ composites with less than 10 vol.% ZrO₂, the resulting eutectic reaction produced a liquid phase and induced melting. When ZrO₂ was increased to more than 30 vol.% in the composites, Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ changed completely to CaZrO₃, Ti₂O, CaO, and ZrO₂. With more than 30 vol.% ZrO₂, no other reaction phases occurred in the Ti side after contact with the ZrO₂/CaTiO₃ composites, which is conducive for producing ceramic composites for Ti casting applications.     

Effect of SiC nanowhisker addition on microstructure and mechanical properties of regenerated cemented carbides by low-pressure sintering

The hardness and toughness of regenerated cemented carbides, in general, are contradictory. Therefore, it is critical to explore regenerated cemented carbides with both high hardness and high toughness. In this study, regenerated WC-8-wt% Co cemented carbide with SiC nanowhisker were prepared by low-pressure sintering. The influence of SiCw contents on the microstructure and mechanical properties of regenerated WC-8-wt% Co cemented carbide was investigated. The results indicated that the hardness, density, flexural strength, and fracture toughness of regenerated cemented carbide first increased and then decreased with the addition of SiCw. The Vickers hardness, density, flexural strength, and fracture toughness could reach 1575 HV, 14.6 g/cm³, 2204 MPa, 16.85 MPa·m^1/2, respectively, with SiCw content 0.5 wt%, which were increased by 14.4%, 0.7%, 12.2%, and 17.3%, respectively, when compared with the regenerated cemented carbide without SiCw. The lowest friction coefficient and the best wear resistance could be also reached when 0.5-wt% SiCw was added. The fracture mechanism of the regenerated cemented carbide contained both transgranular and intergranular fracture through the microscopic observation of fracture surface via scanning electron microscope.     

Global insight into microwave stoneware firing: Macro and microstructural changes

Industrial competition and environmental concerns lead to the exploration of alternative and energy-efficient technologies for ceramic materials processing. The main objective of this work was to present microwave heating as a viable option for stoneware processing. Stoneware functional properties are presented and discussed, with emphasis on impact strength, water absorption, porosity, and color. Microstructure analyses show that microwave- and gas-fired samples have higher densifications than electrically fired samples. A relevant finding for processing conditions is that microwave firing requires temperatures approximately 100°C lower than those required by conventional firing. Microwave-fired samples’ rupture energies are approximately twice (0.57 ± 0.06 (J)) those of the reference samples (0.26 ± 0.03 (J)), and their water absorptions are approximately one-half (1.5% at 1170°C and 0.8% at 1190°C) of those of the reference samples (2.0%), whereas the water absorption of electrically fired samples at 1180°C has been estimated to be 7.5%. Color analysis also evidences a shift to lower microwave firing temperatures, what is attributed to the enhanced transformations promoted by microwave heating when comparing with the transformations promoted by conventional (gas or electric) heating.     

基于ANSYS Workbench下芯片的耦合研究

为了研究电子设备在温度较高的环境下电路板元器件散热和在温度载荷下引起的变形,通过ANSYS数值模拟的方法建立流热耦合的电路芯片散热模型,对芯片与电路板表面形成冲击压力进而导致热疲劳进行研究,分析与讨论温度对流场与静力学结构的影响.通过数值模拟分析得出:电路板为铝材质的变形很大,变形从中间凸起;而PCB材料电路板的变形不是局部变形,属于扩散式变形.     

埋地石油管道阴极防腐措施与风险预警研究

根据埋地管道阴极保护现状,总结了阴极保护原理、分类.阴极保护主要是基于电化学腐蚀原理,采用外加电流及牺牲阳极两种保护方式.分析了目前准则存在的不足,阴极保护准则没有对管道允许受到的直流干扰程度做出明确的规定且-850 mV(CSE)准则不适用交流干扰情况,另外GB/T 21448—2008准则的适用温度不能超过40℃.分析了基于数值模拟研究埋地管道阴极保护的方法,阴极保护数值模拟基于理论建立阴极保护数学模型,设置边界条件对模型加以求解即可得到管道沿线的电位分布情况.结合管道风险预警理论对埋地管道的风险预警进行了研究.对埋地管道腐蚀风险预警流程进行设计,其应遵循风险识别、风险分析及风险等级划分的流程,时刻监视防腐措施的运行效果.     

含铀多孔板的水气结合清洗实验研究

多孔板内滞留大量含铀溶液,需要清洗,清洗后多孔板可达到清洁解控水平.采用吹扫和浸泡的水气结合方式可提高清洗效率,减少废液产生量.研究了气体吹扫对多孔板内溶液滞留的影响,考察了吹扫压力、吹扫距离、吹扫次数、风嘴类型等对吹扫效果的影响,确定了满足滞留率要求的吹扫参数和清洗次数.结果表明:滞留量随吹扫距离的降低和吹扫压力的增大而减少,多孔板的吹扫滞留量可低至7.2 mg·g-1多孔板,采用多孔板等体积纯水浸泡,再经1次吹扫,滞留率可满足低于0.3％的清洗指标.     

新能源汽车电池负极材料的制备与性能研究

采用原位合成法制备了镍-氧化镍/多孔碳纳米片（Ni-NiO/PCNs）负极材料,对比分析了氯化钠模板、退火温度和退火时间对负极材料物相组成、显微形貌和电化学性能的影响。结果表明,Ni/PCNs、Ni-NiO/C和Ni-NiO/PCNs负极材料都主要含有镍和无定型C相,且后2种负极材料还含有氧化镍相;300 ℃/4 h为Ni-NiO/PCNs负极材料适宜的退火工艺,此时Ni-NiO/PCNs负极材料中Ni-NiO粒子分散性较好且保持着三维片层结构,平均尺寸约为27 nm,Ni-NiO实现了对无定型C的包裹;退火时间过长（6 h）会使得镍粒子过氧化且发生团聚,而温度过高（400 ℃）会使得粒子以团聚为主,三维片层状结构消失。电流密度为1 A/g、循环5 000圈后Ni-NiO/PCNs负极材料的放电比容量为235 mA·h/g,此时的放电比容量约为首圈放电比容量的83.93%;Ni-NiO/C和Ni/PCNs负极材料在充放电循环过程中以及循环5 000圈后的放电比容量和容量保持率都明显低于Ni-NiO/PCNs负极材料,Ni-NiO/PCNs负极材料具有更好的循环稳定性,这主要与其具有独特的多孔三维片层结构有关。     

基于改进LMD和能量相对熵的主动配电网故障定位方法

针对配电网发生单相接地故障且分布式电源（distributed generations, DGs）大量接入后,配电网结构和运行方式复杂多变、故障后电气量不明显、故障特征弱等特点,提出一种基于改进局部均值分解（improved local mean decomposition, ILMD）和能量相对熵的主动配电网故障定位方法。首先,利用镜像延拓将信号在两端延拓,消除LMD存在的端点效应,同时,在信号中加入自适应噪声,克服LMD存在的模态混叠问题,对各区段暂态零序电流进行ILMD分解;然后对分解后所有乘积函数（product function, PF）的能量相对熵进行计算,所有PF分量的相对能量熵之和即为区段间的相对能量熵,通过所设置的定位判据,对故障区段进行判断。仿真结果表明,所提算法在10 kV小电流接地系统和改进的IEEE33节点系统中,在不同的仿真条件下故障定位结果准确率高,验证了所提方法的准确性。     

Ni/W比对NiWCx催化剂加氢性能的影响

过渡金属碳化物具有类似贵金属的电子结构和加氢性能。采用等体积浸渍法制备了不同Ni/W比的NiW/γ-Al₂O₃催化剂,以程序升温碳化法转化为NiW碳化物后对芳烃模型化合物和低温煤焦油中分离所得芳烃组分进行加氢处理。催化剂的N₂吸附、XRD、H₂-TPR和SEM表征表明,Ni的添加促进了载体表面WO₃物种的分散和还原,抑制了WO₃晶体的团聚和大晶粒的生成。萘的加氢实验表明,Ni/W原子比为0.6时催化剂的活性最佳,而添加苯酚和吡啶后的模型油加氢过程中萘的转化率和十氢萘的产率均明显下降,Ni/W原子比为0.47和0.6的催化剂性能相近,煤焦油中芳烃组分加氢后Ni/W原子比为0.47的催化剂性能更优。结果表明,Ni和W均具有良好的加氢活性,但Ni耐杂原子性能较差,二者存在一个最佳的配比以使加氢性能更优。有杂原子化合物存在时,如煤基芳烃组分的加氢,Ni/W原子比为0.47的NiW碳化物催化剂具有更好的加氢性能。