热残余应力对C/SiC复合材料界面剪切强度影响的有限元分析

根据C/SiC复合材料的属性,建立单纤维顶出的二维轴对称模型,采用有限元法对C/SiC复合材料的界面剪切强度进行数值研究,分析中考虑材料制备过程中的残余应力对界面剪切强度的影响,在细观力学层面上系统分析纤维顶出过程的界面剪应力及其相关影响因素。分析得出,残余应力会对界面造成损伤,降低界面脱粘载荷。材料的界面承受能力与热膨胀系数呈正相关,与固化温度呈负相关。     

Shape‐Controlled Synthesis of High‐Quality Cu7S4 Nanocrystals for Efficient Light‐Induced Water Evaporation

Copper sulfides (Cu_2–xS), are a novel kind of photothermal material exhibiting significant photothermal conversion efficiency, making them very attractive in various energy conversion related devices. Preparing high quality uniform Cu_2‐xS nanocrystals (NCs) is a top priority for further energy‐and sustainability relevant nanodevices. Here, a shape‐controlled high quality Cu₇S₄ NCs synthesis strategy is reported using sulfur in 1‐octadecene as precursor by varying the heating temperature, as well as its forming mechanism. The performance of the Cu₇S₄ NCs is further explored for light‐driven water evaporation without the need of heating the bulk liquid to the boiling point, and the results suggest that as‐synthesized highly monodisperse NCs perform higher evaporation rate than polydisperse NCs under the identical morphology. Furthermore, disk‐like NCs exhibit higher water evaporation rate than spherical NCs. The water evaporation rate can be further enhanced by assembling the organic phase Cu₇S₄ NCs into a dense film on the aqueous solution surface. The maximum photothermal conversion efficiency is as high as 77.1%.     

Interfacial microstructure and shear strength of Ti–6Al–4V/TiAl laminate composite sheet fabricated by hot packed rolling

A two layer Ti–6Al–4V(wt.%)/Ti–43Al–9V–Y(at.%) laminate composite sheet with a uniform interfacial microstructure and no discernible defects at the interfaces has been prepared by hot-pack rolling, and its interfacial microstructure and shear strength were characterized. Characterization of the interfacial microstructure shows that there was an interfacial region of uniform thickness of about 250 μm which consisted of two layers: Layer I on the TiAl side which was 80 μm thick and Layer II on the Ti–6Al–4V side which was 170 μm thick. The microstructure of Layer I consisted of massive γ phases, needlelike γ phases and B2 phase matrix, while the microstructure of Layer II consisted of α₂ phase. The microstructure of the interfacial region is the result of the interdiffusion of Ti element from Ti–6Al–4V alloy layer into the TiAl alloy layer and Al element from the TiAl alloy layer into the Ti–6Al–4V alloy layer. The shear strength measurement demonstrated that the bonding strength between the TiAl alloy and Ti–6Al–4V alloy layers in the laminate composite sheet was very high. This means that the quality of the interfacial bonding between the two layers achieved by the multi-path rolling is high, and the interface between the layers is very effective in transferring loading, causing significantly improved toughness and plasticity of the TiAl/Ti–6Al–4V laminate composite sheet.     

Study on surface and mechanical fiber characteristics and their effect on the adhesion properties to a polycarbonate matrix tuned by anodic carbon fiber oxidation

Polyacrylonitrile (PAN) based high strength carbon fibers were anodically oxidized using the galvanostatic mode in alkaline electrolyte solutions to influence the chemical surface composition. The change of chemical and physical properties was investigated using scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDX) and contact angle as well as zeta (ζ)-potential measurements.

An initially improved wettability for polar liquids, particularly water, was observed for oxidized carbon fibers. This result was confirmed by ζ-potential measurements. The chemical state of the oxygen containing surface groups changes during anodic oxidation in K₂CO₃/KOH due to further oxidation of C–OH and C=O groups to COOH groups. Therefore the surface acidity increases, which leads to a shift of the isoelectric point to lower pH values and increases the negative ζ_plateau value. The ζ–pH as well as the ζ–concentration dependence show the same tendency. During anodic oxidation of carbon fibers in KNO₃/KOH electrolyte solution beside ‘normal’ (like C–OH, C=O and COOH) surface oxides also carboxylate groups (COO⁻K⁺) were formed at the fiber surface in contrast to an oxidation in K₂CO₃/KOH which introduces ‘normal' surface oxides. No influence could be observed of such an anodic oxidation on the single fiber tensile strength. Contact angle measurements of polycarbonate melt droplets onto single carbon fibers show no dependence of the surface composition. The interfacial shear strength, measured using the microdroplet pull-off test were compared with the thermodynamic work of adhesion. The calculated as well as the measured adhesion show the same absence of any influence of fiber treatment.     

稀土(Ln=Y/Yb)掺杂对Sm2Zr2O7陶瓷材料结构及热导率的影响

利用稀土Ln=Y/Yb对Sm_2Zr_2O_7进行A位取代掺杂,通过固相合成法制得Sm1.8Ln0.2Zr2O7(Ln=Y/Yb)陶瓷材料。分别利用XRD分析材料的晶体结构,SEM观察其显微形貌,激光导热仪测试其热扩散系数并计算得到热导率。结果表明,Sm1.8Ln0.2Zr2O7(Ln=Y/Yb)陶瓷材料为立方烧绿石结构,晶粒分布均匀,Yb~(3+)/Y~(3+)的掺杂降低了陶瓷材料的热扩散系数和热导率,其中Yb的作用更为明显。     

二维碳化钛/碳纳米管负载铂钌粒子的制备及电催化性能研究

直接甲醇燃料电池因操作方便、转化效率高、操作温度低、污染少以及液体燃料易存储易运输等优势具有良好的应用前景, 但现有阳极催化剂存在催化活性低、抗CO中毒性差等缺点, 制约了其商业化应用前景。本研究采用三步法制备得到了一系列不同Pt、Ru配比的PtRu/(Ti₃C₂T_x)_0.5-(MWCNTs)_0.5阳极催化剂材料, HF腐蚀Ti₃AlC₂得到Ti₃C₂T_x, 与酸化处理的多壁碳纳米管(MWCNTs)复合后通过溶剂热法负载Pt、Ru颗粒。通过XRD、SEM、EDS、TEM、XPS等分析铂钌的协同关系。结果表明: Ru原子与Pt原子晶格混合, 形成了粒径约3.6 nm的铂钌双金属合金。电化学分析结果表明: Pt₁Ru_0.5/(Ti₃C₂T_x)_0.5-(MWCNTs)_0.5催化剂具有最佳的电化学性能, 其电化学活性面积(Electrochemical Active Area, ECSA)为139.5 m ²/g, 正向峰电流密度为36.4 mA/cm ²。     

C/C复合材料表面硬度对抗氧化性能的影响EI北大核心CSCD

C/C复合材料使用后由于氧化表面硬度有不同程度的下降。经再次防氧化处理后,测试了表面硬度及抗氧化性能。结果表明:氧化后C/C复合材料试样的表面肖氏硬度为HS70时,再次防氧化处理后,其表面硬度增至HS80,在700℃恒温静态氧化条件下,氧化失重率分别为0.44%/15h,1.2%/22h,其抗氧化性能最强。表面硬度为HS40的C/C复合材料试样,距表层1mm深度范围内其硬度均低于基底,再次防氧化处理后其硬度值从HS40增至HS60,其700℃抗氧化性能最差,氧化失重率分别为3.93%/15h,6.52%/22h。     

人类骨桥蛋白(hOPN)在细胞增殖中的功能研究

为了研究人类骨桥蛋白（hOPN)与293细胞增殖。细胞周期及与细胞周期有关基因表达的关系。并对其机制进行探讨。成功地构建了hOPN真核表达载体并获得了稳定表达hOPN的细胞系，也同时获得了稳定表达EGFP的细胞系，hOPN对293细胞具有促增殖效应，hOPN蛋白激活了293细胞细胞周期蛋白A的表达。实验结果表明：hOPN通过一定的信号通路刺激了细胞周期蛋白A的表达。加快了细胞进入通过S期，从而促进了细胞的增殖。     

单机双级滚动活塞式压缩机适宜容积比的探讨

为研究以R410A为工质的两级压缩制冷循环性能,模拟计算两级压缩制冷循环制冷系数随工况和高低压容积比的变化情况,以及不同工况下容积比与中间温度变化的关系。得出结论,在蒸发温度3~9℃,冷凝温度35~50℃范围内,相同蒸发温度和冷凝温度下,容积比越大对应的中间温度越低,当容积比ζ在3/4~4/5之间时,循环制冷系数更为接近最大制冷系数。本研究为合理选择两级压缩高低压容积比、确定最佳运行工况提供指导。     

TMCP工艺对X100管线钢M/A岛的影响

M/A岛是X100管线钢典型组织,对钢的强韧性有着重要的影响。利用热模拟和显微分析技术研究了冷却速度、变形量和等温温度对X100管线钢中M/A岛的影响规律。结果表明:随着冷速增加,M/A岛体积分数和平均尺寸都减小,由在晶界处分布的较大块状向板条间隙弥散分布的细小片层状转变;随着变形量增加,M/A岛体积分数先增加,变形量为40%达到最大,变形量达到50%时,M/A岛体积分数降低;快冷后随着等温温度升高,M/A岛平均尺寸增大,等温温度为450℃时体积分数最大,温度继续升高体积分数减小。观察到M/A岛形貌多呈棱角状、链条状、片条状和针状,分布在晶界和基体内,岛内精细结构观察到微孪晶马氏体。