用于高温光学实时观察的磁场装置

最近在我们实验室里建立了一套加磁场高温光学实时观察装置．作为磁场发生器的电磁铁,在发热体中心最高可产生0.14T的侧向磁场．运用这套加磁场实时观察装置,能有效地阻抑KNbO₃熔体内的重力对流,减少界面边界层厚度．     

Bi12SiO20熔体表面张力对流研究

利用高温熔体实时观察装置观察和研究了Ｂi12SiO2０熔体表面张力对流从稳态向振荡态的转变过程;稳态过程中的对流图样变化;可能与对流转变有关的两个对流区域的交叉;振荡态对流的分叉现象。     

高温氧化物熔体中表面张力对流效应研究实验

利用高温实时光学观察方法,实时地观察了高温氧化物熔体中的表面张力对流效应．稳态的热毛细对流流线呈轴对称形式,非稳态的热毛细涡流运动伴随熔液温度呈周期性变化,同时还观察到另一种由熔体自由表面的弯月面曲率的变化引起的非稳态的热毛细对流现象．最后测定了相对熔液温度下非稳态热毛细对流的振荡频率．     

La0.85Sr0.15Cr0.9Ni0.1O3-δCe0.8Sm0.2O1.9作为SOFC阳极材料的研究

较低的催化活性大大地限制了La0．85Sr0．15Cr0．9Ni0．1O3-δ-（LSCN）作为直接碳氢化合物燃料SOFC阳极材料的应用．本文尝试用Pechini法合成LSCN，并按重量比1：1向其中加入纳米Ce0.8Sm0.2O1.9（SDC）作为阳极材料．经1500℃高温烧结12h后，LSCN与SDC以及电解质YSZ仍可以保持各自独立的相结构．加入SDC没能提高阳极的电导率，但由于改善了阳极电解质界面的结合状况，扩展了电极反应的活性区域，使阳极材料的极化性能有了提高．显微结构观察品示．LSCN-SDC阳极存甲烷与氧中使用时没有碳沉积现象．     

微重力条件下晶体生长的实验研究

本文提供了在空间晶体生长观察装置上,实时观察记录了空间高温氧化物晶体生长过程的新方法．该装置具有自动光电调焦、多工位、自动图像记录等特点,通过设置不同的温控程序,利用该装置测定了高温熔体内的温度分布,同时对高温氧化物晶体材料界面形貌变化及其周围的熔体流动状态进行了分析,并首次观察到空间高温溶质的均匀扩散现象和空间高温溶液内均匀胞状结构的形成过程,最后对比空间和地面的实验结果,阐述重力对流和表面张力对流在微重力条件下对晶体生长的影响机制．     

晶体生长的边界层效应—兼论光学实时观察法晶体生长技术

晶体生长边界层模型起源于流体动力学边界层模型，但两者又不完全相同．晶体生长边界层模型有两方面的含义：（1）在固-液界面处的、垂直于界面的、由杂质和组份构成的质量流决定晶体生长速度；（2）在界面附加溶液一侧的质量浓度流，其浓度分布是决定界面稳定性的基本参数．特征扩散长度是表征垂直于界面的质量流的一个重要参数．对熔体晶体生长而言，理论估计此值在0．04～0．4cm之间．光学实时观察法晶体生长技术是一种研究晶体生长过程的新颖方法．它能有效地区分扩散-平流和扩散-对流两种不同的生长状态，其实验测得的KNbO3熔体生长的特征扩散长度值为0．01～0．1cm之间．应用此方法实时观察到胞状结构的形成和发展，也证实了界面附近的质量浓度流是决定界面稳定性的一个重要参数．     

对流边界层的水平温度场研究

本研究运用对流水槽模拟研究了均匀下垫面自由对流边界层的水平温度场结构特点．按照几何相似、运动相似和动力相似等要求设置初始条件和边界条件实施模拟。对流水槽的尺度为1．5m×1．5m×0．6m,先加入具有一定温度层结的去离子水,然后底部加热形成对流,模拟对流边界层的发生和发展．运用快速响应的温度传感器测量温度廓线和不同高度上的温度起伏：运用准直光闪烁原理获得光学湍流场．按照温度廓线和光学湍流场的结果得到对流边界层厚度和稳定度等参数．按照不同高度的水平脉动温度,运用AR谱方法研究水平温度谱峰值频率所对应的尺度,该尺度对应于对流边界层的准二维对流热泡的水平尺度。统计研究结果表明,自由对流边界层大涡的水平尺度在边界层的下部随高度的增加而增加,约在0．65倍边界层厚度处达到最大,然后随高度的增加又逐渐减小。物理模拟和数值模拟和野外观测结果一致．按照对流热泡的这种特点,提出了一个自由对流边界层的热泡模型．     

对氧化物熔体浮区中重力对流的数值模拟

利用有限元分析方法数值模拟了界面形状对氧化物高温熔体碟形浮区中的温度分布和重力对流速率的影响，发现界面形状对重力对流速率有较大的影响，对于凸面，相对于炉圈平面5％的偏离使重力对流速率增大25％，偏离越大，重力对流速度越大，对于凹面，5％的偏离使重力对流速率减小15．7％，偏离越大，重力对流速度越小。     

重力对流效应与晶体生长

本文应用高温实时观察法显示了二种对流状态：扩散一平流状态和扩散-重力对流状态,并测出它们的特征扩散长度为0.01～0.1cm．通过晶体旋转生长,计算了质量、热量和动量变换区厚度,数值分别为7．5×10^-3Cm;86×10^－2cm和44×10^－1.     

Bi_(12)SiO_20熔体表面张力对流研究

利用高温熔体实时观察装置观察和研究了Ｂｉ１２ＳｉＯ２０熔体中表面张力对流从稳态向振荡态的转变过程;稳态过程中的对流图样变化;可能与对流转变有关的两个对流区域的交叉;振荡态对流的分叉现象．     

Heat transfer enhancement by Marangoni convection in the NH3–H2O absorption process

The objectives of this paper are to quantify the effect of Marangini convection on the absorption performance for the ammonia–water absorption process, and to visualize Marangoni convection that is induced by adding a heat transfer additive, n-octanol. A real-time single-wavelength holographic interferometer is used for the visualization using a He–Ne gas laser. The interface temperature is always the highest due to the absorption heat release near the interface. It was found that the thermal boundary layer (TBL) increased faster than the diffusion boundary layer (DBL), and the DBL thickness increased by adding the heat transfer additive. At 5 s after absorption started, the DBL thickness for 5 mass% NH₃ without and with the heat transfer additive was 3.0 and 4.5 mm, respectively. Marangoni convection was observed near the interface only in the cases with heat transfer additive. The Marangoni convection was very strong just after the absorption started and it weakened as time elapsed. It was concluded that the absorption performance could be improved by increasing the absorption driving potential (x_vb−x_vi) and by increasing the heat transfer additive concentration. The absorption heat transfer was enhanced as high as 3.0–4.6 times by adding the heat transfer additive that generated Marangoni convection.     

TiO2/SnO2复合薄膜的低温制备及其光催化性能

采用溶胶-凝胶法合成了TiO2溶胶和SnO2溶胶，使用浸渍提拉法在低温下制备出底层为金红石型SnO2，表层为锐钛矿型TiO2的复合膜．考察了不同SnO2薄膜层数对TiO2／SnO2复合膜光催化活性的影响，并对其光催化活性提高的机理进行了探讨．结果表明，SnO2层的加入能有效提高TiO2薄膜的光催化活性，随着SnO2薄膜层数的增加，光催化活性先增大后减小，但始终高于单一的TiO2薄膜．这是由于SnO2的导带电位低于TiO2的导带电位，SnO2的价带电位高于TiO2的价带电位，紫外光照下，TiO2中产生的光生电子注入到SnO2层，SnO2中空穴注入到TiO2层，有效抑制了薄膜内电子-空穴对的复合，增加了复合薄膜表面空穴的浓度，因而光催化活性得到了显著的提高．     

ZrO2-Ti系材料的热力学分析与显微结构研究

通过热力学数据的预报与计算,对ＺｒＯ２－Ｔｉ体系的相间热力学稳定性进行了分析,并确定了材料民折和学条件。在此基础上常压烧结合不同组分配比的ＺｒＯ２－Ｔｉ系复合材料,并采用ＸＲＤ,ＳＥＭ,ＴＥＭ等方法对材料的显微结构进行了表征,ＺｒＯ２－Ｔｉ系均质复合材料由α－Ｔｉ相,四方ＺｒＯ２相和少量的单斜ＺｒＯ２相组成,ＸＲＤ和ＴＥＭ分析表明,组元Ｔｉ、ＺｒＯ２之间没有发生明显的化学反应,上有良好的化学相窝性     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

导模法生长Al2O3单晶温场的理论计算

用光线导向模型建立了描述Ａｌ２Ｏ３单晶内部热量交换的二维方程,用有限元法计算了Ａｌ２Ｏ３单晶的温度场,分析了片状Ａｌ２Ｏ３单晶温场及其变化规律,结果表明,对流换热系数影响晶体的温度分布,固液界面越远,影响效果越显著,地流换 增大使 本温度降低,晶体生长速率增大使结晶前洞的温度梯度增大,晶体较长时,距固液界面较近的晶体的温场可以认为是准稳态温场。     

Numerical Simulation of Thermocapillary Convection in a Shallow Rectangular Cavity Under the Action of Combining Horizontal Temperature Gradient with Vertical Heat Flux

In order to understand the influence of the vertical heat flux on thermocapillary convection, we conducted a series of unsteady two-dimensional numerical simulations of thermocapillary convection in a differently heated shallow rectangular cavity with vertical heat flux on the bottom by means of the finite volume method. The cavity was filled with the 1cSt silicone oil (Prandtl number Pr = 13.9) and aspect ratio is 30. It is found that a small vertical heat flux has slightly influence on the flow pattern of stable or unstable thermocapillary convection. However, the critical Marangoni number increases first, and then decreases with the increase of the heat flux. And the flow pattern of the oscillatory thermocapillary convection transits from a series of the rolls rotating clockwise and moving from the cold wall to the hot wall to the single roll near the hot wall and a series of rolls near the cold wall, further, two series of rolls moving from the hot wall and cold wall towards the hot spot with the maximum temperature. With the increase of the Marangoni number, the period and the wavelength of the oscillatory thermocapillary convection increase, but the wave speed decreases.     

Visualization and model development of Marangoni convection in NH3–H2O systemVisualization et développement d'un modèle de convection de Marangoni dans un système à NH3–H2O

The objectives of this paper are to obtain experimental data of surface tension and interfacial tension, and to develop a new model of Marangoni convection for the best selection of heat transfer additive in ammonia–water absorption systems. The basic mechanism of Marangoni convection in absorption systems was reviewed from the viewpoints of the surface tension and the interfacial tension gradients. Marangoni convection was successfully visualized using a shadow graphic method. The solubility limits of the additives in ammonia–water solution ranged from 500 to 3000 ppm depending on the heat transfer additives. These values are much higher than those in LiBr–H₂O solution in which the solubility ranged from 70 to 400 ppm. The temperature gradient of the surface tension should not be a criterion for Marangoni convection inducement in NH₃–H₂O system. The concentration and temperature gradients of the interfacial tension should not be a criterion for Marangoni convection inducement in NH₃–H₂O system. The magnitude of the interfacial tension did not affect the occurrence of Marangoni convection either. It was found that addition of the heat transfer additive beyond the solubility limit assisted Marangoni convection occurrence, but should not be a criterion for Marangoni convection inducement. It was proposed that the radical-out model should be a criterion for Marangoni convection inducement within the solubility limit in NH₃–H₂O system.     

Gravitational effects on evaporative convection at microscale

Thermocapillary convection induced by phase change (evaporation) has been investigated in confined environment. This paper introduces some insight into the physics of evaporatively-driven thermocapillary convection and emphasizes on the interaction between the observed convection and gravity. Non-equilibrium interfacial conditions lead to temperature/surface tension gradients which drive convective patterns. The latent heat of evaporation leads to an important cooling effect near the triple contact line. Evaporation of volatile liquids in capillary tubes is experimentally investigated to demonstrate the above effects. The size of the capillaries is found to be an important factor in the effect that gravity could have on thermocapillary convection. The oscillatory behaviour observed when buoyancy affects thermocapillary convection could be explained through the coupling between interfacial temperature and the flow within the liquid. The three dimensional nature of the flow structure is found to extend the effect of gravity to the horizontal section of the flow.     

BaTiO3基PTCR陶瓷的复阻抗谱研究

采用复阻抗方法,系统地研究了ＢａＴｉＯ３基ＰＴＣＲ陶瓷的电性能,通过Ｃｏｌｅ－Ｃｏｌｅｘ图,计算了样品的晶粒、晶界电阻值和弛豫时间常数,同时利用Ｈｅｙｗａｎｇ模型估算了势垒高度。Ｃｏｌｅ－Ｃｏｌｅ图分析表明,随阒测试温度的提高,Ｃｏｌｅ－Ｃｏｌｅ圆将从单半圆向双扭线过渡,表明在居里温度附近,由于热激活出现了不同的缺陷类型实验结果表明了ＰＴＣ效应是一种晶界效应,晶粒电阻随温度的变化呈ＮＴＣ特性,而晶