高强镁合金点焊接头性能

采用电阻点焊方法对高强镁合金Mg₉₆Zn₂Y₂进行了焊接.通过扫描电子显微镜对接头微观组织进行了观察,分析了接头的组织,研究了焊接电流对接头熔核直径及抗剪载荷的影响.在此基础上探讨了接头组织对接头性能的影响.结果表明,接头熔核直径与抗剪载荷均随焊接电流的增大而增大,接头最大抗剪强度约为142 MPa;接头熔核区第二相呈细网状分布,其α-Mg晶粒发生了粗化,直径约为30 μm.熔核区这些组织特征被认为是接头弱化的主要原因.     

Fabrication of SiC reticulated porous ceramics with multi-layered struts for porous media combustion

Silicon carbide reticulated porous ceramics (SiC RPCs) with multi-layered struts were fabricated at 1450 °C by polymer sponge replica technique, followed by vacuum infiltration. The effect of additives (polycarboxylate, ammonium lignosulfonate and sodium carboxymethyl-cellulose) on the rheological behavior of silicon carbide slurry was firstly investigated, and then the slurry was coated on polyurethane open-cell sponge template. Furthermore, alumina slurry was adopted to fill up the hollow struts in vacuum infiltration process after the coated sponge was pre-treated at 850 °C. The results showed that the coating thickness on the struts and the microstructure in SiC RPCs were closely associated with the solid content of alumina slurry during vacuum infiltration. The typical multi-layered strut of SiC RPCs could be achieved after the infiltration of an alumina slurry containing 77 wt% solid content. The compressive strength and thermal shock resistance of the infiltrated specimens were significantly improved in comparison with those of non-infiltrated ones. The improvement was attributed to the in-situ formation of reaction-bonded multilayer struts in SiC RPCs, which were characterized by the exterior coating of aluminosilicate-corundum, middle part of mullite bonded SiC and interior zone of corundum.     

Sintering behavior and microwave dielectric properties of 0.67CaTiO3–0.33LaAlO3 ceramics modified by B2O3–Li2O–Al2O3 and CeO2

A low temperature sintering method was used to avoid the relatively high sintering temperatures typically required to prepare 0.67CaTiO₃–0.33LaAlO₃ (CTLA) ceramics. Additionally, CeO₂ was introduced into the CTLA ceramics as an oxygen-storage material to improve their microwave dielectric properties. 0.67CaTiO₃–0.33LaAlO₃ ceramics co-doped with B₂O₃–Li₂O–Al₂O₃ and CeO₂ were prepared by a conventional two-step solid-state reaction process. The sintering behavior, crystal structure, surface morphology, and microwave dielectric proprieties of the prepared ceramic samples were studied, and the reaction mechanism of CeO₂ was elucidated. CTLA+0.05 wt% BLA+3 wt% CeO₂ ceramics sintered at 1360 °C for 4 h exhibited the optimal microwave dielectric properties: dielectric constant (ε_r)=45.02, quality factor (Q×f)=43102 GHz, and temperature coefficient of resonant frequency (τ_f)=2.1 ppm/°C. The successful preparation of high-performance microwave dielectric ceramics provides a direction for the future development and commercialization of CTLA ceramics.     

核电站在大型商用客机撞击下损伤破坏研究进展

2001年9·11事件后,美国核能管理委员会、核能研究院和能源部以及我国核安全局相继出台相关规范,明确规定核电站设计必须考虑大型商用客机的意外和恐怖性撞击作用。从飞机机身的整体撞击效应、引擎局部撞击效应以及核岛厂房结构振动3方面,回顾了核电站重要基础设施在飞机撞击下损伤破坏的理论模型、原型和缩尺试验以及数值仿真研究等的工作进展,对课题组近年来在该领域的研究工作进行了简要介绍,包括4种典型飞机（F4战斗机、空客A320、A380和新舟MA600）和4类核岛设施（预应力钢筋混凝土屏蔽厂房、普通钢筋混凝土屏蔽与附属厂房、钢板混凝土屏蔽与附属厂房,普通钢筋混凝土大型冷却塔）的精细化有限元模型及其撞击全过程的数值仿真分析。此外,介绍了引擎撞击普通钢筋混凝土和超高性能混凝土靶板的缩尺试验和数值模拟分析工作,以及引擎撞击局部效应的计算方法。最后,指出了该领域已有研究在撞击力计算、整体响应、局部破坏、振动效应和多灾害作用方面的不足和进一步研究方向的建议。     

电磁飞板的运动特性研究

基于电路与动力过程耦合作用的方法和发射过程中发射线圈与飞板的互感变化原理,对电磁飞板发射物理过程进行了理论分析,建立飞板发射阶段的运动模型,得到飞板发射阶段的运动特性规律,并对发射线圈的结构进行了初步优化。研究结果表明:发射线圈的特性参数对于飞板速度的影响较为明显,减小整个回路自感,增加互感,可以有效提高飞板速度,而飞板的加速度总体呈现线性特征。研究结果在军事、宇航等具有较大的应用价值。     

Phase evolution and thermal stability of novel high-entropy (Mo0.2Nb0.2Ta0.2V0.2W0.2)Si2 ceramics

Owing to the high melting points and high-temperature stability, transition-metal disilicides are potential components for aerospace, automotive, and industrial engineering applications. However, unwanted oxidation known as PEST oxidation severely limits their application owing to the formation of volatile transition metal oxides, especially in the temperature range of 500–1000 °C. To overcome this problem, a new class of high-entropy disilicides, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂, was selected by first-principles calculations and then successfully fabricated using a hot-pressing sintering technique. Furthermore, the phase evolution, thermal expansion behavior, thermal conductivity, and oxidation behavior were systematically investigated. Compared with MoSi₂, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂ possessed a lower thermal conductivity (10.9–14.7 W·m^?1·K^?1) at 25–1000 °C, higher thermal expansion coefficients (8.6 ± 1.3^–6 K^–1) at 50–1200 °C, and especially an excellent thermal stability at 500–1000 °C owing to slow diffusion and selective oxidation. This work provides a strong foundation for the synthesis and application of high-entropy disilicides.     

The oxidation resistance mechanism of SiC-B4C-xAl2O3 ceramics at 1400 ℃ in air atmosphere

The oxidation property of SiC-B₄C-xAl₂O₃ (x ranges from 0 wt% to 30 wt%) ceramics was studied in air at 1400 ℃. Results show that the porous oxide layer becomes dense and smooth with addition of Al₂O₃. When the content of Al₂O₃ is proper, the DOP (degree of polymerization) of borosilicate network can be improved with increase of Al₂O₃ content, inhibiting the migration of atoms and molecular groups. With that, the crystallization of SiO₂ and volatilization of B₂O₃ can be restrained. When the content of Al₂O₃ is excessive, the DOP of borosilicate network will be decreased, deteriorating the oxide layer morphology. It is believed that the damage of borosilicate network by excess Al₂O₃ should be responsible for this phenomenon. In this research, the SiC-B₄C ceramic with optimal oxidation resistant can be obtained when the content of Al₂O₃ is 15 wt%.     

混凝-Fenton法对中晚期垃圾渗滤液预处理研究

利用混凝-Fenton法对中晚期垃圾渗滤液进行预处理研究。首先以PAC为混凝剂,PAM为助凝剂对垃圾渗滤液进行混凝处理,然后对混凝后渗滤液进行Fenton氧化。考察混凝剂用量,起始pH值,H2O2/FeSO4·7H2O投加比,Fenton试剂投药量和搅拌速度对垃圾渗滤液COD去除的影响,并进行正交试验分析。结果表明:混凝法的最佳投药量为1 L渗滤液投加1.5 g PAC和5 mg PAM;Fenton法的最佳条件为:起始pH值为3,H2O2/FeSO4·7H2O投加比为8∶1,Fenton试剂投药量为135 g/L,搅拌速度为150 r/min;各因素对Fenton试验影响大小为:起始pH值Fenton试剂投药量搅拌速度。在最佳条件下,混凝-Fenton法对垃圾渗滤液COD去除率可达91.41%。     

ICP—OES法测定钛合金中A1元素含量的不确定度评定

将钛合金样品用10mL1：1硫酸溶解后,用ICP—OES法对其中A1元素含量进行测定,测得样品中W（A1）=6．91％。对测定过程中的不确定度来源进行了分析,依据不确定度评定的步骤,计算得到了各分量标准不确定度及合成标准不确定度,W（A1）测定结果的扩展不确定度为U=0．17％,K=2。     

Synthesis of chemically controllable and electrically tunable graphene films by simultaneously fluorinating and reducing graphene oxide

Fluorine and oxygen co-doped graphene with controllable element coverage was effectively synthesized through simultaneously fluorinating and reducing graphene oxide by pyrolysis of fluorinated graphite. Morphology investigation indicates that the doped graphene is of few-layered thickness, and the prepared films exhibit layered structure through cross-section. Chemical composition analysis confirms that fluorine has been grafted onto graphene scaffold through CF covalent bond, and the doping level can be readily manipulated just by adjusting the reaction temperature. The structural changes of graphene induced by the controllable doping thus facilitate the tunable electrical property, which can be tuned over several orders of magnitude. These results indicate our method is not only potentially useful to tailor the chemical surface and electronic structure of graphene, but also can find applications in novel electronic devices based on graphene co-doped with different dopants.