Strain Engineering for the Kapitza Resistance of the ZrO2/α-Al2O3 and YSZ/α-Al2O3 Interfaces

The Kapitza resistance is of fundamental importance for the thermal stability of the interface between the ceramic top coat and the thermal growth oxide layer i...     

Synthesis of layered cathode materials Li[CoxNiyMn1−x−y]O2 from layered double hydroxide precursors

Cathode materials Li[Co_xNi_yMn_1?x?y]O₂ for lithium secondary batteries have been prepared by a new route using layered double hydroxides (LDHs) as a precursor. The resulting layered phase with the α-NaFeO₂ structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co/Ni/Mn ratio on both the structure and electrochemical properties of Li[Co_xNi_yMn_1?x?y]O₂ have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1.     

简化CH4/O2/N2基元反应模型在爆轰模拟中的应用

基于改进的全耦合TVD格式和简化的基元化学反应模型,建立了二维可燃预混合气爆轰波传播过程的模型并编制了相应的CFD程序,对CH4／O2／N2预混气爆轰波的形成和传播进行了数值模拟。使用不同的计算初始条件来考察模型的计算模拟能力,计算结果表明,该模型能够精确捕捉爆轰波及其波后的反射过程,同时,也能够预测不同计算初始条件下爆轰波的传播轨迹。计算结果与相同条件下CJ爆轰理论模型的计算结果进行了比较,两者符合较好,这表明简化的CH4／O2／N2机理能够较好地应用于可燃气爆轰过程的数值计算中。     

Two-cell detonation: losses effects on cellular structure and propagation in rich H2–NO2/N2O4–Ar mixtures

Detonation experiments in H₂–NO₂/N₂O₄–Ar mixtures (Equivalence ratio 1.2 and initial pressure lower than 0.1 MPa) confined in a tube of internal diameter 52 mm reveal two propagation regimes depending on initial pressure: (1) a quasi-CJ regime is observed along with a double cellular structure at high pressures; (2) at lower pressures, a low velocity detonation regime is observed with a single structure. Transition between this two regimes happens when the spinning detonation of the larger cell vanishes. Each detonation regime is characterized by velocity and pressure measurements and cellular structure records. Coherence between all experimental data for each experiment leads in assumption that losses are responsible for the transition between one regime to another. In a second part, we study such behaviour for a two-step mixture through numerical simulations using a global two-step chemical kinetics and a simple losses model. Numerical simulations qualitatively agree with experiments. Both detonation regimes with their own cellular structures are reproduced.     

Microstructure and mechanical properties of ZrO2 (Y2O3)–Al2O3 nanocomposites prepared by spark plasma sintering

Zirconia (yttria)–alumina ceramic nanocomposites were fabricated from different powders by spark plasma sintering (SPS). One powder was a commercially available nanocomposite powder TZP-3Y20A, consisting of 3 mol% yttria-stabilized zirconia (3-YSZ) reinforced with 20 wt% alumina, and the other, used as a comparison, was a conventional mechanically mixed powder 3YSZ-20A, a blend made of 3 mol% yttria-stabilized zirconia powder ZrO₂ (3Y) and 20 wt% α-alumina powder. The effect of the sintering temperature on the densification, the sintering behavior, the mechanical properties and the microstructure of the composites was investigated. The results showed that the density increased with increasing sintering temperature, and thus, the mechanical properties were strengthened because of the increased densification. The nanocomposite powder TZP-3Y20A was easily sintered, and good mechanical properties were achieved as compared with the powder from the conventional mechanically mixed method, the maximum flexural strength and fracture toughness of which were 967 MPa and 5.27 MPa m^1/2, respectively.     

PVC/纳米Al2O3复合材料的力学性能研究

通过熔融共混方法制备了PVC/纳米Al2O3复合材料,研究了纳米粒子对PVC的增强、增韧效果。采用细观力学方法理论上求解了纳米复合材料的有效弹性模量,比较并分析了试验值和理论计算值的偏差。     

Al2O3SiO2/ZL109 金属基复合材料的强度性能研究

介绍了硅酸铝短纤维增强ＺＬ１０９铸铝合金（Ａｌ２Ｏ３ＳｉＯ２／ＺＬ１０９ＭＭＣ）的静态实验和冲击实验结果。给出了这种复合材料的静态强度、动态屈服强度和层裂强度并对实验结果进行了分析讨论。     

Functionalized TiO2@ZrO2@Y2O3 ：Eu3＋ core-multishell microspheres and their photoluminescence properties

TiO2@ZrO2@Y2O3 ：Eu3＋ composite particles with a core-multishell structure were synthesized through the combination of a layer-by-layer （LBL） self-assembly method and a sol-gel process. The obtained sam- ples were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and fluorescence spectropho- tometry. The results showed that the composite particles had a core-multishell structure, spherical morphology, and a narrow size distribution. The presence of a ZrO2 layer on the TiO2 core can effec- tively prevent the reaction between the TiO2 core and a Y203 shell; the temperature for the reaction between the TiO2 core and the Y203 shell in the TiO2@ZrO2@Y2O3 ：Eu core-multishell phosphor can be elevated by 300 ℃ compared to that for TiO2@ZrO2：Eu. Upon excitation of the core-multishell particles in the ultraviolet （254 nm）, the Eu3＋ ion in the Y2O3 ：Eu3＋ shell shows its characteristic red emission （611 nm, 5D0→7F2）, and the photoluminescence （PL） intensity of the phosphor with the core-multishell structure was obviously greater than that of the core-shell TiO2@Y2O3 ：Eu phosphor.     

Al-TiO2-B2O3反应体系中B2O3/TiO2摩尔比对热扩散反应合成铝基复合材料磨损性能的影响

利用Al-TiO2-B2O3体系热扩散反应合成(XD)法制备了铝基复合材料;采用销-盘摩擦磨损试验机考察了所制备的铝基复合材料在干摩擦条件下同GCr15钢配副时的磨损性能;采用扫描电子显微镜和光学金相显微镜观察分析了复合材料微观组织结构及其磨损表面和剖面形貌,探讨了其磨损机理.结果表明:所制备的铝基复合材料的磨损性能随Al-TiO2-B2O3反应体系中B2O3/TiO2摩尔比的增加而提高;复合材料的磨损质量损失随着滑动速度的增加而增加,当滑动速度为0.9 m/s左右时最大,随后开始减小;磨损质量损失与滑动距离基本呈线性关系.当B2O3/TiO2摩尔比为0.0时,增强相由Al2O3和Al3Ti组成,相应的复合材料的抗磨性能较差,其磨损主要表现为Al3Ti的犁沟切削、亚表层剥落、塑性基体流失导致Al2O3颗粒裸露脱落以及Al3Ti棒断裂导致的磨粒磨损;加入B2O3后,棒状Al3Ti的数量减少,有利于基体晶粒细化,提高复合材料强度和塑性,故抗磨性能提高.当B2O3/TiO2摩尔比为1.0时,复合材料中的Al3Ti基本消失,抗磨性能显著改善,主要磨损机制为粘着磨损和轻微磨粒磨损.     

Alkali-activation reactivity of chemosynthetic Al2O3–2SiO2 powders and their 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra

Pure Al₂O₃–2SiO₂ powders were prepared by sol–gel and coprecipitation methods, and their alkali-activation reactivities were compared. The alkali-activation reactivity of the powder prepared by the sol–gel method was higher than that of the powder prepared by the coprecipitation method. The powders were investigated by ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) to understand the relationship between their structure and alkali-activation reactivity. The ²⁷Al MAS NMR data showed that the five-coordinate Al content of the powder prepared by the sol–gel method was higher than that of the powder prepared by coprecipitation. The higher content of five-coordinate Al corresponded to higher alkali-activation reactivity. The ²⁹Si MAS NMR data showed that for the powder prepared by the sol–gel method, silicon was replaced by aluminum at secondary coordination sites of the central Si atoms during calcination. However, for the powder prepared by single-batch coprecipitation, the main change was from a low degree of polycondensation to a high degree of polycondensation.     

A robust formulation of the v2−f model

The elliptic relaxation approach of Durbin (Durbin, P.A., J. Theor. Comput. Fluid. Dyn. 3 (1991) 1–13), which accounts for wall blocking effects on the Reynolds stresses, is analysed herein from the numerical stability point of view, in the form of the $\bar v^2 - f$ . This model has been shown to perform very well on many challenging test cases such as separated, impinging and bluff-body flows, and including heat transfer. However, numerical convergence of the original model suggested by Durbin is quite difficult due to the boundary conditions requiring a coupling of variables at walls. A ‘code-friendly’ version of the model was suggested by Lien and Durbin (Lien, F.S. and Durbin, P.A., Non linear κ ? ε ? υ ² modelling with application to high-lift. In: Proceedings of the Summer Program 1996, Stanford University (1996), pp. 5–22) which removes the need of this coupling to allow a segregated numerical procedure, but with somewhat less accurate predictions. A robust modification of the model is developed to obtain homogeneous boundary conditions at a wall for both $\bar v^2 $ and f. The modification is based on both a change of variables and alteration of the governing equations. The new version is tested on a channel, a diffuser flow and flow over periodic hills and shown to reproduce the better results of the original model, while retaining the easier convergence properties of the ‘code-friendly’ version.     

Diffusion–reaction of aluminum and oxygen in thermally grown Al2O3 oxide layers

The diffusion–reaction of aluminum (Al) and oxygen (O), to form thermally grown oxide (TGO) layers in thermal barrier coatings (TBCs), is studied through an analytical model. A nonsymmetrical radial basis function approach is used to numerically solve the mass balance equations that predict the TGO growth. Correct boundary conditions for the Al and O reactions are laid out using scaling arguments. The Damköhler number shows that the O–Al reaction is several orders of magnitude faster than diffusion. In addition, a comparison between aluminum and oxygen diffusivities indicates that TGO growth is governed by aluminum diffusion. The results are compared with experimental measurements on air plasma spray-deposited TBCs treated at 1,373 K with exposure times ranging from 1 to 1700 hours. We found that, for several time decades, the thickness of the thermally grown layer has power law dependence of time with an exponent of ½, following the diffusion control mechanism. At later times, however, the presence of other oxides and additional kinetics modify the diffusive exponent.     

Morphology and magnetic properties of α-Fe2O3 particles prepared by octadecylamine-assisted hydrothermal method

α-Fe₂O₃ particles with various morphologies, including micro-doublesphere, tetrakaidecahedron and nanoparticles-aggregated micro-ellipsoid, were successfully synthesized via an octadecylamine-assisted hydrothermal method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results indicate that the presence of octadecylamine played a crucial role in morphology evolution by selective crystal adsorption. The protonated octadecylamine increased the pH value that accelerated nucleation, and the long alkyl groups of octadecylamine acted as an adsorption inhibitor to retard the growth of nanoparticles. The as-prepared α-Fe₂O₃ particles exhibited higher remanent magnetization and coercivity than other α-Fe₂O₃ particles of similar size. These properties should be attributed to the superstructure and the shape anisotropy of the synthesized particles.     

Ti_3SiC_2/PM3O4摩擦副的高温摩擦学性能

本文考察了Ti_3SiC_2/PM304摩擦副从室温到630℃范围的摩擦磨损性能,并与Nj-Cr合金/PM304摩擦副的摩擦磨损性能进行了对比.结果表明:Ti_3SiC_2/PM304摩擦副具有比Ni-Cr合金/PM304摩擦副更好的摩擦磨损性能,特别是在400～630℃的温度范围内,Ti_3SiC_2/PM304摩擦副具有优异的摩擦磨损性能.从室温到300℃,Ti3_SiC_2/PM304摩擦副的磨损机制为Ti_3SiC_2晶粒拔出、脱落后与转移的PM304形成机械混合层,随着环境温度的升高机械混合作用加强.在400～630℃范围内,摩擦界面的机械混合作用受到显著抑制,在Ti3SiC_2磨损表面形成富集银的转移润滑膜,而转移润滑膜的连续性对摩擦副的摩擦磨损性能影响较大.     

Al2O3—40%TiO2和Cr2O3等离子喷涂层的摩擦磨损特性

研究了AC4C铸铝合金表面等离子喷涂Al2O3-40%TiO2和Cr2O3陶瓷粉末涂层的滑动摩擦磨损特性;采用划痕试验方法测定了涂层与基体之间的结合强度;用扫描电子显微镜观察分析了磨痕形貌和涂层显微组织特征.研究结果表明:Cr2O3涂层的摩擦学性能优于Al2O3-40%TiO2涂层;涂层的结合强度、硬度和表面空隙对磨损影响较大;Al2O3-40%TiO2涂层的磨损机理主要表现为塑性变形和层状剥离;而Cr2O3涂层则主要为磨粒磨损     

Synthesis and characterization of BaMgAl10O17：Eu2＋ phosphor prepared by homogeneous precipitation

A homogeneous precipitation process based on urea hydrolysis reaction was exploited to synthesize BaMgAl10O17：Eu2＋ phosphor. The process parameters, such as the dosage of urea, the calcination tem- peratures and the concentration of Eu2＋, were refined in light of the characterization of the products. The experimental results revealed that pure and well-crystallized BaMgAl10O17：Eu2＋ phosphor could be obtained at 1250℃, a much lower temperature than that for traditional solid-state reaction. The as-prepared phosphor particles were small in grain size, regular in morphology, and uniform in size distribution. Because of the high homogeneity of the process, the as-prepared phosphor exhibited stronger emission intensity and higher thermal stability than the sample prepared by solid-state reaction at 1600℃.     

纳米Al2O3和Fe2O3填充尼龙PA1010的摩擦磨损行为

采用模具挤压成型方法制备了纳米Al2O3和Fe2O3填充PA1010尼龙复合材料，采用MM-200型摩擦磨损试验机考察了所制备的尼龙复合材料在干摩擦条件下同45#钢对摩时的摩擦磨损行为。研究结果表明，填充纳米Al2O3使得PA1010尼龙复合材料的摩擦系数增大，而填充纳米Fe2O3使得摩擦系数降低；纳米Al203和Fe2O3填充尼龙复合材料的耐磨性能优于尼龙；当纳米填料的质量分数从10％提高到20％时，纳米Fe2O3填充尼龙的磨损量增大，纳米Al2O3填充尼龙的磨损量无明显变化，2种填料填充尼龙复合材料的摩擦系数变化不大．纳米Fe2O3填充尼龙复合材料同45#钢对摩时主要呈现粘着磨损和轻微疲劳磨损特征，而纳米Al2O3填充尼龙复合材料呈现脆性疲劳开裂特征。纳米Fe2O3填充尼龙复合材料在偶件磨损表面形成的转移膜更加均匀和连续，故其减摩抗磨性能优于纳米Fe2O3填充尼龙复合材料。     

WC/Al2O3颗粒增强Cu基复合材料爆炸粉末烧结实验研究

利用爆炸粉末烧结工艺,探索WC /Al2O3同时作为增强基颗粒制取多种颗粒增强Cu基复合材料的可行性,同时分析了工艺参数对压实坯致密度的影响。研究了复合材料的微观组织和致密度、韧性和硬度等性能,爆炸粉末烧结法可以成功制出WC/ Al2O3/Cu多种颗粒增强金属基复合材料。     

等离子喷涂Al2O3/TiO2陶瓷涂层在液态石蜡润滑下的摩擦磨损性能研究

利用纳米和微米结构Al2O3/TiO2喂料制备出2种陶瓷涂层,考察了这2种涂层在液体石蜡润滑下与不锈钢球摩擦副的摩擦磨损性能,并探讨了2种涂层的磨损机理.结果表明:液态石蜡润滑能有效降低纳米Al2O3/TiO2涂层与不锈钢球摩擦副的摩擦系数和磨损率,但是对微米涂层的润滑效果不明显.纳米涂层的摩擦系数仪为微米涂层的1/3,而磨损率则降低了70倍以上.纳米涂层的磨损机制在低载荷下是轻微的黏着磨损,高载荷下则是摩擦抛光,而微米涂层的磨损机制是晶粒脆性断裂.     

平面波输入下海水−海床−结构动力相互作用分析

海洋工程结构的地震反应分析是保证海洋工程结构地震安全的重要环节.由于其所处的复杂环境,该问题涉及到流固耦合和土-结相互作用.本文基于海水、饱和海床、基岩流固耦合统一计算框架,采用Davidenkov模型和修正的Masing准则考虑饱和海床的非线性,在脉冲SV波垂直入射下,进行了海域场地和海洋工程结构的动力响应分析.首先,对比分析了线性自由场和非线性自由场输入情形的海域场地非线性反应,结果表明线性自由场输入时反应不合理,自由场分析和场地分析应该采用相一致的本构模型.然后,对比分析了海床分别为线性和非线性情形时,海域场地以及海水-海床-结构体系的反应特征.与线性海床情形相比,非线性对海床反应的影响主要由如下两方面因素控制:一方面,非线性导致饱和海床模量减小,饱和海床与基岩间的波阻抗比减小,由基岩到饱和海床间的反射系数和透射系数增加,导致反应增大;另一方面,非线性导致阻尼加大,使海床反应减小.对于本文算例而言,阻尼对非线性海床结果的影响占主导作用.