Synthesis and thermophysical properties of RETa3O9 (RE = Ce,Nd, Sm,Eu, Gd,Dy, Er) as promising thermal barrier coatings

Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa₃O₉ compounds have a defect‐perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa₃O₉ bulk ceramics were fabricated via solid‐state reaction. The crystal structure was characterized by X‐ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermophysical properties of RETa₃O₉ were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients, and high‐temperature phase stability. The thermal conductivities of RETa₃O₉ are very low (1.33‐2.37 W/m·K, 373‐1073 K), which are much lower than YSZ and La₂Zr₂O₇; and the thermal expansion coefficients range from 4.0 × 10^?6 K^?1 to 10.2×10^?6 K^?1 (1273 K), which is close to La₂Zr₂O₇ and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high‐temperature phase stability with these oxides, RETa₃O₉ ceramics were promising candidate materials for TBCs.     

Investigation on La3+ and Dy3+ co-doped ceria ceramics with an optimized average atomic number of dopants for electrolytes in IT-SOFCs

In the present study, we investigate the fundamental properties of CeO₂ by selecting La³⁺ (57), and Dy³⁺ (66) as dopants with optimized average atomic number of 61.5, which lies in between Pm³⁺ (62) and Sm³⁺ (62) in accordance with the criteria for optimum doping. A system of co-doped ceria ceramics Ce_1–x–yLa_xDy_yO_2-δ ((x, y) = (0.00, 0.00), (0.025, 0.025), (0.05, 0.05), (0.075, 0.075), (0.10, 0.10), (0.00, 0.20) and (0.20, 0.00)) as electrolytes for intermediate temperature solid oxide fuel cells were successfully prepared by a well-known sol-gel auto-combustion route. In order to obtain dense samples, the prepared pellets were sintered in air at 1300 °C for 4 h using conventional furnace and relative densities of all the samples were found to be higher than 95%. Single phase cubic structure, microstructural density and elemental composition analysis of all the samples were studied by powder X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy techniques, respectively. Raman spectroscopy analysis confirmed the formation of concentrated O^2-–vacancies in the co-doped ceria system. Impedance spectroscopy measurements revealed the high value of total ionic conductivity and low activation energy for the composition Ce_0.85La_0.075Dy_0.075O_2?δ i.e., 2.08 × 10^–2 S cm^–1 and 0.58 eV, respectively. Linear thermal expansion analyses of all the samples revealed the matched thermal expansion coefficients. Finally, these results recommend that the Ce_0.85La_0.075Dy_0.075O_2?δ sample can be useful as a solid electrolyte in IT-SOFC applications.     

数值模拟法在膨胀套管修复套损井技术中的应用

为了分析膨胀套管在套损井修复过程中的应力、应变及残余应力情况,剖析膨胀过程中管材内部变化规律,利用ANSYS软件建立了膨胀套管在套损井修复应用中的有限元模型,优选模型的边界条件,进行模型的数值模拟分析.数值模拟结果直观地反映了管材膨胀过程中的应力一应变情况,结合实验室台架试验及现场施工,总结出可在制管、套管膨胀和后处理3个阶段采取有效措施消减残余应力;膨胀套管在高压液体作用下发生二次形变后.内径尺寸比膨胀锥的外径单边增加0.9～1.3 mm,据此修正了膨胀锥、膨胀套管和原套管尺寸间的经验公式.在华北油田京708井采用膨胀套管技术修复套损井,施工完成后,产油量增加,含水率降低,达到施工要求,表明膨胀套管补贴套损井技术的有限元数值模拟分析符合油田现场施工的需求.     

连铸钢包用铝镁尖晶石-炭砖的研制及应用

针对铝镁炭砖在使用过程中残余膨胀过大、热导率较高等问题,从基质组成、鳞片石墨的粒度及加入量和生产工艺等方面进行了研究试验,在铝镁炭砖基础上研制开发出了综合性能优良的铝镁尖晶石-炭砖。     

Negative thermal expansion properties of Cu1.5Mg0.5V2O7

Cu_1.5Mg_0.5V₂O₇ was prepared by a solid state method. Its phase, microstructure, thermal expansion property, and Raman spectra were analyzed in detail. Results show that Cu_1.5Mg_0.5V₂O₇ maintains a monoclinic crystal structure and exhibits an excellent linear negative thermal-expansion property with coefficient of thermal expansion of ?8.72?×?10^?6?K^?1 over a wide temperature range of 153–673?K. The mechanism underlying the negative thermal expansion of Cu_1.5Mg_0.5V₂O₇ involves the coupling effect of the tetrahedron caused by the lateral vibration of the bridge oxygen atom and the tensile effect of the tetrahedron, The partial collapse caused by the loss of the oxygen atoms also plays an important role in the mechanism.     

基于Abaqus的双裂纹不同间距对裂纹扩展速率的研究

扩展有限元法是近年经过大量运用的,在传统有限元的范围中求解不连续问题一种有效计算方法,它是基于单位分解的思想,在计算不连续问题时加入跳跃函数。以ABAQUS为平台,基于扩展有限元方法 (XFEM),以含双穿透型裂纹的有限宽板受横向拉伸载荷为力学模型,建立相应的裂纹尖端应力的有限元模型,研究焊接接头区域不同间距双裂纹相互作用对裂纹扩展速率的影响。结果表明:双裂纹间距的的大小并没有对裂纹的扩展速率产生影响。     

Valid Edgeworth Expansions of Some Estimators and Bootstrap Confidence Intervals in First-order Autoregression

We derive the third-order valid Edgeworth expansions for the standardized and the Studentized versions of some estimators in first-order autoregression without Gaussianity. As a special case of a Gaussian process, the validity of the expansion obtained by Ochi (Asymptotic expansions for the distribution of an estimator in the first-order autoregressive process. Journal of Time Ser. Anal. 4 (1983), 57–67) is demonstrated. By applying the second-order Edgeworth expansion to the bootstrap procedure, we construct the confidence intervals for the autoregressive coefficient.     

热膨胀石墨水洗温度与膨胀倍数关系的研究

研究了水洗温度对热膨胀石墨膨胀倍数的影响,并对其内部机理进行了探讨。得出了生产工艺中的最佳水洗温度。     

钢管膨胀混凝土力学性能及其膨胀模式的研究

配制出了强度性能和工作性能良好的膨胀混凝土,研究了该种钢管膨胀混凝土的力学性能,分析了钢管限制条件下核心混凝土的膨胀模式。研究结果表明,掺加适量膨胀剂的钢管膨胀混凝土具有较优良的力学性能,其极限承载力比普通钢管混凝土可提高8％左右。     

静压桩承载力分析

结合东营某工程的静力压桩资料、静载试验资料及静力触探资料,计算模拟了压桩力,分析了沉桩的可能性,预估了单桩承载力并与静载试验结果进行对比,其结果令人满意,为设计和施工提供了很有价值的依据．