Dependence of crystal structure on mechanical and thermophysical properties of magnetoplumbite-type LnMgAl11O19 ceramics with substitution of Ln3+ Ions

Lanthanum hexaaluminate is a promising candidate to establish yttria partially stabilized zirconia as a thermal barrier coating material for super alloy due to their remarkable stability and thermophysical performance. In order to understand the relationship between the structure and properties and gain new low thermal conducting materials, the LnMgAl₁₁O₁₉ (LnMA, Ln: La, Pr, Nd, Sm, Eu, Gd) materials were synthesized firstly and further used to produce the LnMA ceramics. With the increasing relative atomic mass of the replaced Ln³⁺ ions from La to Gd, the lattice parameters and grain sizes of the LnMA platelets decrease, while the mechanical properties increase, and the thermal physic properties decrease. The GdMgAl₁₁O₁₉ ceramics obtain the lowest thermal conductivity with the value of 1.91-1.78 W/m K in the range from room temperature to 800°C, which could be considered as a promising candidate for application in thermal barrier coating materials. These results could further provide reference for developing novel materials lower thermal conductivity.     

Effect of seawater constituents on the performance of thermal spray aluminum in marine environments

Thermally sprayed coatings are often used to mitigate corrosion of offshore structures. They act as a physical barrier to the aggressive marine environment and as a sacrificial distributed anode for low carbon steel. In such environments, the severity of material degradation depends on many factors. The effect of temperature, exposure time or the presence of micro‐organisms are the focus of many studies, for example, however, the effect of the different ions present in seawater remains largely unexplored. The chemical composition of the water changes considerably depending on the location; industrial, glacial, estuarine, and so forth. In addition, when thermal spray aluminum (TSA) protects steel in seawater, calcareous matter precipitates as a result of the cathodic polarization and subsequent localized increase in pH. Therefore, understanding how ions such as magnesium (II), calcium (II), or carbonates alter the coating properties in the marine environment is important. This paper reports the experimental work carried out with TSA‐coated steel samples with defects to simulate mechanical damage or erosion of the coating. The combination of electrochemical tests and surface characterization provided evidence of the efficiency of the calcareous bilayer that forms on top of steel reducing the TSA degradation.     

基于激光闪光法的立式热扩散率测量装置研究

介绍了基于激光闪光法的立式热扩散率测量装置,利用脉冲激光对样品进行均匀加热,使样品内部产生一维热流,并通过红外探测器测量样品温升信号,采用立式真空加热炉控制测量温度环境,实现室温至1600℃的热扩散率测量。用该装置测量厚度为1. 1 mm,直径为10 mm的不锈钢样品,测量结果与PTB参考数据的偏差小于1%。     

Function mechanism of Y2O3 additive in silicon powder nitridation

Effect of sole Y₂O₃ additive on the nitridation behavior of silicon powder was systematically studied using thermo gravimetry, differential thermal analysis, particle size analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscope and thermodynamic analysis in this paper. The thermo gravimetry results showed that Y₂O₃ additive can significantly decrease the initial nitriding temperature and increase the nitriding rate. This phenomenon can be attributed to the much lower reaction temperature of the silica film and Y₂O₃ additive than that of the silica film and silicon. In addition, Y₂O₃ additive has little effect on the nitridation of silicon powder at 1300°C. However, it can obviously enhance the nitridation of silicon powder and the formation of β-Si₃N₄ at 1400°C, which is evidenced by the fact that the overall conversion increases from 58.1% to 100% and the fraction of β-Si₃N₄ in generated Si₃N₄ increases from 7.9% to 68.2% with increasing the content of Y₂O₃ additive from 0 to 10 wt%.     

高炉炉缸凝铁层的组成分析与导热系数测定

摘要：高炉炉缸内衬表面形成稳定的凝铁层将保护高炉炭砖并延长高炉寿命。利用光学数码显微镜观察统计分析高炉凝铁层生产样品，探究不同焦炭体积占比对凝铁层导热系数的影响。利用元素分析（XRF）、X射线衍射分析（XRD）、扫描电镜(SEM-EDS)等手段分析凝铁层的组成，并观察其微观形貌。利用瞬态平面热源法（TPS）测定凝铁层的导热系数，进一步分析其组成与导热系数之间的关系。结果表明,凝铁层由铁、充满铁水的焦炭、石墨碳、少量渣相组成，凝铁层内部没有气隙。凝铁层生产样品的导热系数测定范围为27.21～97.38W/(m·K)，导热系数（λ）与其组成的焦炭面积比（Sc=22%～48%）之间的线性关系为：λ=-257.47Sc +157.65。模拟实验凝铁层的导热系数范围为30.54～53.95W/(m·K)，该值远大于目前数学模型中采用的凝铁层导热系数（2～4W/m·K），随着焦炭粒度的增加，凝铁层的导热系数先增加后减小。凝铁层中导热系数（λ）与焦炭体积分数Vc（Vc=39%～50%）的线性关系为：λ=-80.50Vc +78.56。研究结果进一步明确了凝铁层的物相组成及其导热系数，为高炉长寿的研究指明了方向。     

碳纤维复合材料薄壁圆筒的轴向导热系数测试

碳纤维复合材料薄壁圆筒为各向异性导热，其轴向导热系数是筒体温度场理论计算、成型工艺优化的重要参数。碳纤维复合材料圆筒由于较小的截面面积给筒体加热、热量有效传递带来了较大困难。本文以平板材料导热系数的稳态法测试国家标准为基础，基于傅里叶一维稳态导热原理，设计了一套用于薄壁圆筒轴向导热系数测试的装置，采用双试件对称加热、辐射换热防护及热对流环境控制等实现了热量沿筒体轴向的有效传导，利用该装置对导热系数已知的铝筒进行测试，验证了该装置设计的可行性，得到了碳纤维复合材料薄壁圆筒的轴向导热系数为（4.60±0.13） W/(m•K)。     

水平方向上的大气透过率和热辐射计算模型研究

水平方向上的空气对流和复杂的地面状况会导致大气热辐射计算的不确定度增大，目标发射起始段的红外辐射特性测量有助于实现目标识别。因此，研究水平大气透过率和热辐射对目标的高精度红外辐射特性测量具有十分重要的意义。针对以上问题，首先借鉴垂直廓线理论建立了同层大气“水平温度廓线”模型，然后推导了水平方向计算大气透过率和热辐射的公式，并对其进行了实验验证。最后将MODTRAN软件计算和实验测量的大气热辐射结果进行了比较。实验结果表明，传统软件的热辐射计算精度为8.65% ，而本文方法的计算精度为4.91%。该实验说明，在水平方向上，这种算法是正确的。通过公式推导和实验验证说明了该方法的合理性，为水平方向大气透过率和热辐射的计算提供了一种新的思路。     

地下盐穴储气库盐岩热损伤机理

基于变质量热力学原理，建立盐穴储气库注采过程中的工程热力学分析数学模型，给出了单个注气和采气过程中温度和压力随时间变化的解析解，作为数值模拟的边界条件。根据金坛储气库的基本数据和盐岩实验研究参数，利用COMSOL Multiphysics有限元软件建立单腔盐穴注采过程的温度-应力耦合模型，模拟恒定注采速率下盐腔围岩的拉伸损伤、剪切损伤和膨胀损伤分布情况，研究夹层和热应力对围岩损伤的影响。基于热应力理论，结合模拟结果分析盐穴储气库注、采气过程中围岩的热损伤机理。模拟结果表明：在热应力存在的情况下，夹层的存在促进了围岩损伤的产生，无夹层时围岩无损伤发生，有夹层时围岩存在损伤；注气过程和采气过程的损伤发生位置存在差别：注气过程损伤多发生在夹层附近的盐岩中，采气过程损伤多发生在夹层中；膨胀损伤的范围最广，且损伤范围覆盖了前2种损伤，因此实际生产过程中推荐使用膨胀损伤判据，损伤评价结果更为保守。     

Modeling the thermal decomposition of friction composite systems based on yarn reinforced polymer matrices using artificial neural networks

The presented work deals with the application of artificial neural networks in the modelling of the thermal decomposition process of friction composite systems based on polymer matrices reinforced by yarns. The thermal decomposition of the automotive clutch friction composite system consisting of a polymer blend reinforced by yarns from organic, inorganic and metallic fibres impregnated with resin, as well as its individual components, was monitored by a method of non‐isothermal thermogravimetry over a wide temperature range. A supervised feed‐forward back‐propagation multi‐layer artificial neural network model, with temperature as the only input parameter, has been developed to predict the thermogravimetric curves of weight loss and time derivative of weight loss of studied friction composite system and its individual components acquired at a fixed constant heating rate under a pure dry nitrogen atmosphere at a constant flow rate. It has been proven that an optimized model with a 1‐25‐6 architecture of an artificial neural network trained by a Levenberg‐Marquardt algorithm is able to predict simultaneously all the analyzed experimental thermogravimetric curves with a high level of reliability and that it thus represents the highly effective artificial intelligence tool for the modelling of thermal stability also of relatively complicated friction composite systems.     

基于ABAQUS的变截面橡胶密封条热应力与密封性分析

研究用于发动机油气分离器的乙烯丙烯酸酯橡胶密封胶条在不同温度下的强度和密封性能。借助于大型有限元分析软件ABAQUS建立橡胶密封胶条与配合壳体的有限元模型,采用Mooney-Rivlin模型,对不同温度下的密封胶条进行热应力计算分析,得到橡胶密封胶条在不同温度下的Von Mises应力、压缩率、接触应力和接触宽度。结果表明:随着温度的升高,密封胶条的Von Mises应力和密封胶条与壳体连续接触面上的接触应力逐渐增加,接触宽度基本不变,密封条的压缩率逐渐减小;密封胶条的Von Mises应力远小于橡胶材料的拉伸强度,满足强度要求;密封胶条连续接触面上的接触应力始终大于油气分离器的工作压力且接触宽度符合要求,橡胶密封胶条满足密封条件。