锂离子电池Al2O3-SiO/C负极材料的制备和电化学性能CSCD

本文首先以SiO、沥青为原料,制备了SiO/C复合材料.然后以SiO/C复合材料,硝酸铝,氨水,尿素为原料,利用水浴加热和高温热处理的方法,制备出了Al2O3-SiO/C复合材料.采用激光粒度分析、比表面积测试仪、XRD、SEM对样品进行了物相结构分析和微现形貌的表征测试.电化学测试表明:加入尿素的A12O3-SiO/C复合材料具有最佳电化学性能,首次效率高达74.81％,充电比容量为1436.4mA·h/g,表现了优异的电化学性能.     

利用莫来石陶瓷与AlSi_(12)合金制备相变储热材料的研究

以莫来石陶瓷和AlSi_(12)合金为原料,合成一种新型的相变储热材料。分析服役期间相变储热材料的物理化学性质,及其相组成、显微结构的变化规律,并探讨AlSi_(12)合金的氧化损坏对相变储热材料储热性能的影响。分析结果表明:经莫来石陶瓷封装的AlSi_(12)合金具有优良的抗氧化性,持续服役1 000 h后,AlSi_(12)合金的氧化增重率仅为3.75%;服役期间,AlSi_(12)合金中部分Al元素被氧化成Al_2O_3,导致了AlSi_(12)合金的相变温度范围变窄,储热量随之减小,从而影响了AlSi_(12)合金的储热性能;AlSi_(12)合金不会严重腐蚀莫来石陶瓷,也不会向莫来石陶瓷渗透,且部分Al_2O_3积聚在莫来石陶瓷表面,从而降低了AlSi_(12)合金在服役后期的氧化速度。研究结果为利用AlSi_(12)合金制备相变储热材料提供参考。     

基于均匀设计法的Al_2O_3纳米流体稳定性影响因素的实验研究

采用均匀设计法对利用两步法制备的氧化铝纳米流体进行了稳定分析。将悬浮液的zeta电位作为氧化铝纳米流体稳定性的衡量指标。在实验中,选择了四个因素,分别为纳米流体的浓度、分散剂的浓度、pH值、超声震荡时间,并对这四个因素都取了12个水平,这样的实验设计可以系统地反映出各个因素如何影响氧化铝纳米流体的稳定性。随后通过对实验结果进行回归分析,得到了关于这四个因素与纳米流体zeta电位的方程式,并分析得出悬浮液的pH值和超声震荡时间对纳米流体稳定性起着非常重要的作用。最后找到了在实验范围中的最佳纳米流体溶液的配方,并按此配方配制纳米流体,测得实际zeta电位值与预测值吻合较好。     

脉冲波形对脉冲反射法的电缆故障 定位影响的研究

摘要： 针对脉冲反射法在电缆故障定位中的应用进行了研究。利用电磁暂态软件建立仿真模型,对电缆的不同的故障模式、脉冲波形和脉冲宽度对测量的精度的影响进行了分析。研究结果表明：断线故障的反射波形和原始脉冲是同向的,而接地故障反射波形是反向的,脉冲反射法中,推荐使用方波作为脉冲的波形。方波的脉冲波形宽度越窄,高频分量越高,信号衰减越快,则可测范围越短,测距精度越高。对正确判断故障类型、确定脉冲波形形式和宽度等具有重要指导意义。     

活性环境空心阴极溅射特性与沉积Al2O3、ZnO掺杂和In2O3：Mo薄膜的应用（上）

研究了薄膜沉积方法,基于空心阴极金属溅射,在基材附近提供反应气体。工作气体和携带溅射原子通过一个狭长通道从阴极出来,这样,反应气体被阻止到达靶面。用Cu靶和脉冲电源激励,研究了阴极的基本运作。研究包括沉积率对电源、压强、气体流量和膜厚分布的依存关系,以及膜电阻率作为基材上的状态函数。用模型进行计算气体的速度分布和在腔内的压强,Al2O3膜是在氧的活性环境下溅射一个Al靶获得的,必须指出只要极少量氧气通过阴极就能氧化（中毒）靶,而外面大量氧气完全不会影响靶,在后者模式下实现了非常稳定的放电且易形成的Al2O3薄膜。利用该方法制备透明的ZnO导电膜,掺杂Al或B,达到了高沉积率,且在适当氧流量下得到了低的膜电阻率。同时,制备了高迁移率的In2O3：Mo透明导电膜,电阻率仅有1．9×10^-4Ω·cm。给出了空心阴极的比例关系、沉积效率,比较了磁控溅射和直线的活性环境空心阴极溅射。     

激光闪射法对石墨烯薄膜导热性能的研究

石墨烯是目前发现的导热系数最高的材料,其理论导热系数值可达5 300 W/(m·K),成为新一代最具潜力的高导热材料。文中采用激光闪射法研究了石墨烯薄膜横向和法向的热扩散系数,并根据测试的密度和比热计算得出导热系数。研究表明:横向热扩散系数随着薄膜厚度的增加而不断减小,当MCT检测器在电压为260 V,脉冲宽度为100μs,信号高度为1 V,Inplane+各向同性计算模型下,高温烧制薄膜横向热扩散系数高达740.16 mm~2/s,是法向的238倍,导热系数为1 252.28 W·(m·K)~(-1);压片法制得的石墨烯薄膜的横向热扩散系数为7.58 mm2/s,是法向的19倍,导热系数为9.43 W·(m·K)~(-1)。     

冷却速率对钢中MnS+Al_2O_3复合夹杂物包裹率的影响研究

通过实验室试验研究钢中MnS+Al_2O_3复合夹杂物的生成以及不同冷却速率对MnS+Al_2O_3复合夹杂物包裹率的影响。结果表明:被推动到钢液凝固前沿的Al_2O_3,会为MnS析出提供异质形核质点;随着冷却速率的增加,复合夹杂物的尺寸从4μm降至2.5μm左右,MnS+Al_2O_3复合夹杂物包裹率逐渐降低。本次试验研究为得到较优包裹程度的实验条件以及进一步改善钢材性能提供一定的理论分析。     

Ca/Cu共掺杂的O3-NaFe0.5Mn0.5O2钠离子电池正极材料的电化学性能研究

层状过渡金属氧化物由于其较高的理论比容量和较低的经济成本,被视为一种具有良好应用前景的钠离子电池正极材料。采用溶胶-凝胶法和热处理的方式,制备Ca/Cu共掺杂的铁锰基层状氧化物(O3-Na_0.9Ca_0.05Fe_0.45Mn_0.45Cu_0.1O₂)。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)等对该O3型铁锰基层状氧化物正极材料进行表征分析。结果表明,在32 mA/g电流密度下该材料具有205.2 m A·h/g的高比容量,循环50圈之后仍具有67.64%的容量保持率,在160 m A/g下循环100圈后依然具有81.4 m A·h/g的放电比容量。由于Ca的掺入,引起Na⁺空位的增加,并且Cu的掺入提高了Mn的价态,从而提高了Na⁺的扩散速率,抑制了Mn³⁺的Jahn-Teller效应,缓解了晶格应力,有效提高了材料的结构稳...     

超低水泥铁沟浇注料的研究及工业化应用

高炉用Al2O3-SiC-C质铁沟浇注料的高温性能主要与水泥的加入量有关,为了探明水泥与Al2O3-SiC-C铁沟浇注料性能的相关性及如何提高Al2O3-SiC-C铁沟浇注料的高温使用性能,对水泥加入量对材料性能的影响。本文以电熔棕刚玉颗粒、碳化硅颗粒与细粉、硅微粉、α-Al2O3微粉、白刚玉微粉、Secar71水泥、Si粉、球沥青为主要原料,分别加入质量分数为0、0.4%、0.6%、1%、1.5%的水泥等量替代白刚玉微粉,外加质量分数为4.5%的水搅拌均匀,振动浇注成型,研究了水泥加入量对浇注料经各温度热处理后常温物理性能及高温抗折强度的影响。结果表明:随着水泥加入量的增加,试样110℃烘干24 h后的体积密度及抗折耐压强度逐渐增大,1 500℃保温3h后的体积密度及强度逐渐降低。其原因分析水泥的增加会形成更多的钙长石、钙黄长石等低共熔相,水泥加入少,高温下低共熔相形成少,形成较多莫来石晶相,对高温性能有利,但水化产物少,常温性能要求得不到保障。加入水泥质量分数为0.6%时,浇注料的综合性能最好。根据试验实研究结果,添加0.6%水泥的铁沟浇注料在铁沟应用中取得了较好的效果。     

A Method for Measuring Thermal Radiation Properties of Semi—Transparent Films

This paper presents a method(F method)for determining the optical constants and the thicknesses of semi-transparent thin films.It has the following distinctive features:high precision;rapid determination of themeasured quantities;wide range of convergence of solutions;capable of judging whether or not the results arereasonable.In order to meet the needs of application and engineering design,a family of curves designatedFig.n-F was prepared.Using it n,k,d of the films can be conveniently and accurately determined.From theoptical constants and the thicknesses of the films determined by the F method,all important thermal radiationproperties of the semi-transparent films needed in application can be obtained.     

Thermal diffusivity measurement of glass at high temperature by using flash method

A measurement of the thermal diffusivity of a semi-transparent material (glass) by means of the "Flash Method" is investigated in the present work. By taking into account the heat losses on the two faces of the sample, and using a new experimental technique design, an improvement of the determination of the thermal diffusivity of the semi-transparent material (glass) at high temperature is realized. The experimental design presented here is an original technical concept that enables a significant reduction in heat loss during the experiments. A very simple model based on the quadrupole method is used to theoretically determine the thermal diffusivity of the semi-transparent material by taking into account both conduction and radiation. Theoretical results clarify the effect of the absorption coefficient and the thickness of the sample on the heat transfer in the semi-transparent medium.     

Measurement of the thermal diffusivity of thin materials using an infrared thermal wave imaging technique

A thermal wave imaging technique was developed for the evaluation of thermal properties. In this paper we report both theoretical and experimental studies on an infrared thermal wave imaging method for thermal diffusivity measurements of thin materials in the direction parallel to the surface. © 1999 Scripta Technica, Heat Trans Asian Res, 28(2): 89–94, 1999     

Thermal diffusivity study of aged Li-ion batteries using flash method

Advanced Li-ion batteries with high energy and power density are fast approaching compatibility with automotive demands. While the mechanism of operation of these batteries is well understood, the aging mechanisms are still under investigation. Investigation of aging mechanisms in Li-ion batteries becomes very challenging, as aging does not occur due to a single process, but because of multiple physical processes occurring at the same time in a cascading manner. As the current characterization techniques such as Raman spectroscopy, X-ray diffraction, and atomic force microscopy are used independent of each other they do not provide a comprehensive understanding of material degradation at different length (nm² to m²) scales. Thus to relate the damage mechanisms of the cathode at mm length scale to micro/nanoscale, data at an intermediate length scale is needed. As such, we demonstrate here the use of thermal diffusivity analysis by flash method to bridge the gap between different length scales. In this paper we present the thermal diffusivity analysis of an unaged and aged cell. Thermal diffusivity analysis maps the damage to the cathode samples at millimeter scale lengths. Based on these maps we also propose a mechanism leading to the increase of the thermal diffusivity as the cells are aged.     

Measurements of thermal conductivity and thermal diffusivity of alternative refrigerants in liquid phase with a transient short‐hot‐wire method

A transient short‐hot‐wire method has been proposed to simultaneously measure the thermal conductivity and thermal diffusivity of liquids. The method has been applied to the refrigerant HCFC‐22, alternative refrigerants HFC‐32, HFC‐125, HFC‐134a and refrigerant mixtures HFC‐32/125 [35/65, 50/50 (HFC‐410A), 68/32 wt%], HFC‐32/125/134a [23/25/52 (HFC‐407C) wt%]. From the present study, it is shown that the measured results agree well with the literature values on thermal conductivity and those on thermal diffusivity obtained from NIST's thermophysical property database, REFPROP Ver. 6.0. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(8): 540–552, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20032     

Thermal diffusivity and porosity of solid materials by the electromagnetic ultrasonic technique. Part 3—simultaneous measurement of ultrasonic velocity and thermal diffusivity

The objective of this study is to evaluate simultaneously the time dependence of the thermal diffusivity of carbon-carbon composites (C/C composites) and their porosity during heat treatment using the electromagnetic ultrasonic technique. This paper describes two kinds of experiments conducted to confirm the principle for simultaneous measurement of both the ultrasonic velocity (used to evaluate the porosity) and the thermal diffusivity at room temperature. For each material, the samples used in both experiments were identical. The ultrasonic velocity of type 304 stainless steel and its thermal diffusivity were 5.85 km/s and 3.8 mm²/s with precisions of ±1.6 and ±8 percent, respectively. The ultrasonic velocity of a two-dimensional woven C/C composite and its thermal diffusivity were 2.86 km/s and 4.8 mm²/s with precisions of ±5.0 and ±8 percent, respectively. The results appear to indicate that the electromagnetic ultrasonic technique can measure the ultrasonic velocity and the thermal diffusivity simultaneously and that it is also applicable to C/C composites. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(5): 308–322, 1996     

Experimental determination of the effective thermal capacity function and other thermal properties for various phase change materials using the thermal delay method

The recently presented thermal delay method is an improved version of the well-known T-history method, which is widely used for thermal properties measurement of phase change materials (PCM). The most important difference between the thermal delay and the T-history methods is that the former is based on the use of thermal delay (i.e. temperature difference) between PCM and a reference fluid at any specified time while the latter makes use of their time delay at any specified temperature. Although the thermal delay method has been documented in our previous publication, measurements are performed of the known and indisputable values of ethyl alcohol thermal capacity and the latent heat of the double distilled water (WFI), which confirm the accuracy of the method. Additional comparisons with values provided by PCM producing companies show disagreements lower than 1.7%. The main volume of measurements of the present study includes the following thermal properties of various practically interesting PCM: (a) the temperatures at the ends of the two-phase region; (b) the liquid and solid PCM thermal capacities; (c) the phase change heat; (d) the heat storage capacity during any specified temperature range; and (e) the effective thermal capacity function, which is a very important and useful property for practical applications. The above function is provided for each one of the PCM examined in the form of diagrams, as well as in the form of analytical expressions derived by curve fitting to the processed experimental values. All measurements were repeated 20 times and the results were averaged in order to minimize errors from accidental incidents.     

Measurements of the thermal diffusivity of linear-medium-density-polyethylene/aluminium composites using a transient comparative method

Metal-powder/polymer composites are an interesting class of material because their physical properties may, within limits, be selected to match a particular application. It is therefore important to be able to measure and model the physical properties of these composites. The effective diffusivity of linear-medium-density-polyethylene/aluminium composites was measured for a range of volume fractions using a simple, transient comparative method. Effective thermal conductivity data were calculated from the effective thermal diffusivity data. The effective thermal conductivity data were modelled well by the EMT equation.     

隔热材料导热系数的数值模拟预测

对氧化锆空心球隔热材料进行合理的简化,用数值模拟方法计算氧化锆空心球隔热材料导热系数,并分析空心球半径、温度、发射率等对导热系数的影响。数值模拟结果表明,减小空心球半径,降低空心球表面发射率,抽真空等都有助于降低隔热材料导热系数。数值模拟与实验测量结果良好吻合,用数值模拟计算隔热材料导热系数是一个行之有效的方法。     

Study on the microstructures and thermal properties of SiO2@NaNO3 microcapsule thermal storage materials

In this paper a novel SiO₂@NaNO₃ microcapsule thermal storage material is successfully fabricated via water-limited sol-gel method. The effects of SiO₂ nanoparticles on the microstructures, thermal conductivity, specific heat capacity, latent heat and thermal stability are investigated. SEM and TEM investigation indicates that the spherical SiO₂ nanoparticles with an average diameters of 30 nm are coated on the surface of NaNO₃ evenly to form a homogeneous and stable core-shell structure. Microencapsulated composites are characterized by XRD and FTIR to determine the chemical compositions and structures. The thermal conductivity of SiO₂@NaNO₃ microcapsules is significantly enhanced by 62.9% (0.756 W m⁻¹ K⁻¹) compared with 0.464 W m⁻¹ K⁻¹ of that of NaNO₃. In addition, the latent heat, phase change temperature, specific heat capacity and thickness of shell of the microencapsulated NaNO₃ with 18.1 wt% SiO₂ were 310.1°C, 144.7 J g⁻¹, 1.831 J/(g·K), and 80-150 nm, respectively. Furthermore, microencapsulated NaNO₃ have excellent shape and thermal stability at working temperature range. SiO₂ nanoparticles are uniformly attached to the modified NaNO₃ by electrostatic interaction to create a physical protective SiO₂ barrier, which can effectively inhibit the leakage and cauterization of melting NaNO₃.