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。     

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.     

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。     

连铸用耐火材料对洁净钢的影响及其发展

分析了连铸用耐火材料对洁净钢的影响,并针对连铸用耐火材料对钢水洁净度的影响如增碳等,就其发展进行了评述,认为采用钙质等碱性材料和无碳无硅或低碳低硅材质有利于洁净钢的生产.     

Synthesis of aluminum borate nanorods by a low-heating-temperature solid-state precursor method

Well-crystalline Al₄B₂O₉ nanorods were synthesized by a low-heating-temperature solid-state precursor method. This process does not involve the use of metal catalyst or protective gas. The products were characterized by thermogravimetry and differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed the products to possess a single phase, large surface area, narrow size distribution of 20-30 nm and lengths up to several micrometers. A self-catalytic growth mechanism of the aluminum borate nanorods is proposed.     

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm² in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient (D_Li) calculated from the CV measurements was about ∼10⁻¹³ cm²/s. The Si thin film anode was also successfully coupled with LiCoO₂ thin film cathode. The a-Si/LiCoO₂ full cell showed stable cycle performance between 1 and 4 V.     

非平衡气动加热条件下的材料热响应差异研究

针对风洞烧蚀试验中碳/碳与超高温陶瓷两种复合材料存在热响应差异的问题,本文从材料壁面催化与非平衡流场气动加热的机理出发,基于两种风洞设备设计了3个烧蚀试验状态,并对可能影响材料热响应的重要因素进行了分析.结果表明:在不同试验设备条件下,碳/碳端头驻点温度差异主要是由试验状态调试偏差和温度测量偏差造成的,而超高温陶瓷端头驻点温度的差异主要是由不同条件气流非平衡度不同、试件表面实际接受的热流不同造成;对碳/碳材料而言,由于其壁面催化特性接近完全催化壁面,在试验设备选择或状态调试时,可以不必考虑流场非平衡度的影响;而对于超高温陶瓷材料,在试验设备的选择上,则需要结合风洞非平衡流场特点,对试验考核的有效性做充分评估.相关结论可为碳/碳、超高温陶瓷复合材料防热性能的考核与评价提供参考与借鉴.     

过渡金属离子掺杂对磷酸铁锂性能的影响

以碳酸锂、草酸亚铁、磷酸二氢铵、葡萄糖为原料,添加不同的过渡金属乙酸盐(乙酸锰、乙酸钴、乙酸镍、乙酸锌),在氩气保护下采用高温固相法制备LiFePO4/C复合材料.采用X射线衍射、扫描电子显微镜、同步热分析、恒电流充放电、电化学阻抗、循环伏安等方法研究掺杂金属离子及掺杂量对LiFePO4/C晶体结构和电化学性能的影响.结果表明,LiFe0.9M0.1PO4/C(M=Mn、Co、Ni、Zn)样品的晶体结构均与橄榄石型LiFePO4相同.掺杂过渡金属阳离子可以提高LiFeP04/C的还原电位,降低氧化电位,缩小氧化还原峰间距,提高化学反应的可逆性.掺杂后的样品在5C下的放电性能较好,以LiFe0.9Ni0.1PO4/C的放电容量最高,达到89 mAh/g.     

Phase formation mechanism and kinetics in solid-state synthesis of undoped and calcium-doped lanthanum manganite

LaMnO_3+δ and La_0.7Ca_0.3MnO₃ were synthesized from La₂O₃(La(OH)₃), CaCO₃ and MnO₂ powder mixture with solid-state reaction technique. X-ray diffraction and thermal analysis were employed in the present study on the process of synthesizing of the two compound powders. The kinetic study on solid-state reaction between La₂O₃ and MnO₂ in the powder mixture was isothermally carried out for LaMnO_3+δ formation. The result showed that the reaction process was controlled by three-dimensional solid-ionic diffusion. Both Jander and Ginstling-Brounstein model can be used to describe the reaction kinetics satisfactorily. The relevant apparent activation energy values obtained were as great as 205 ± 11 and 189 ± 8 kJ/mol. The reaction process of La_0.7Ca_0.3MnO₃ preparation from La₂O₃, SrCO₃ and MnO₂ powder mixture was also studied using X-ray diffraction and thermal analysis. The result indicated that the following steps composed the overall reaction: the decomposition of the reactant; the formation of La_1−xCa_xMnO_3+δ; La₂O₃ and Mn₃O₄ reacted with La_1−xCa_xMnO₃ to form final La_0.7Ca_0.3MnO₃ phase. The latest step was the most time-consuming one among others in the overall reaction.