原位测量固体材料热导率的改进热探针方法

热导率是一个重要的热特性参数,它的测量方法包括稳态法和瞬态法。然而,各测量方法由于接触界面均存在非完美热接触,导致接触热阻无法忽略,进而降低热导率测量的准确性。于是,本研究提出了一种改进的热探针方法,即原位浇筑单针法,来降低接触热阻的影响。同时我们还采用了另外四种常用的热导率测量方法测量六种材料的热导率。并且,为了研究接触热阻对热导率测量的影响,我们采用了涂抹导热硅脂的双针法和单针法测量材料热导率。研究表明,原位浇筑单针法的测量结果与其它四种方法热导率的测量结果相一致,并且,原位浇筑单针法可以有效地减少接触热阻,从而提高热导率测量的准确度。     

HFC161气相热导率实验测量

根据瞬态热线法原理,搭建了新的热导率测量实验装置。用标准物质氮气对该实验台进行了检验,结果表明该实验台测量结果准确可靠。对HFC161气相热导率在温度范围为253~373 K、压力范围为139.9~4470.3 kPa进行了实验测量,并将实验结果拟合成温度与压力的多项式,为以后的进一步研究提供计算依据。     

用于射频谐振腔的纯铌热导率的测量

铌材料的低温热导率是反映射频超导腔热稳定性的重要参数.一套新型的低温热导率测试装置研制成功,该装置不仅可以测量纯铌材料的低温热导率,同时还能够测量铌材料的临界超导温度和铌材料的剩余电阻率(RRR).本文介绍该装置的原理以及实验结果,并对铌材料的低温热导率与剩余电阻率(RRR)进行了分析.     

利用液体夹心法测量LiF单晶高压热导率

提出了液体夹心法热导率测量技术, 采用CHBr3液体作为夹心材料实现了样品/窗口界面的理想接触, 并将动载荷作用下的夹心法高压热导率实验测量压力下限拓展至40 GPa, 为绝缘介电晶体高温高压热导率测量提供了技术支持. 实验利用平面碰撞和DPS测试技术, 结合液体夹心法实测了LiF单晶高压热导率数据, 对现有热导率理论模型进行了研究和探讨, 结果显示, 在γ/γ0=(ρ0/ρ)2时, 修正后的Roufosse理论公式与实验数据符合较好, 这一研究结果为非透明材料冲击波温度测量中的热传导修正提供了实验数据和理论模型。     

利用液体夹心法测量LiF单晶高压热导率简

提出了液体夹心法热导率测量技术,采用CHBr3液体作为夹心材料实现了样品/窗口界面的理想接触,并将动载荷作用下的夹心法高压热导率实验测量压力下限拓展至40GPa,为绝缘介电晶体高温高压热导率测量提供了技术支持.实验利用平面碰撞和DPS测试技术,结合液体夹心法实测了LiF单晶高压热导率数据,对现有热导率理论模型进行了研究和探讨,结果显示,在γ/γ0=(ρ0/ρ)2时,修正后的Roufosse理论公式与实验数据符合较好,这一研究结果为非透明材料冲击波温度测量中的热传导修正提供了实验数据和理论模型.     

新型良导体热导率测量仪的研制

分析了测量良导体热导率教学实验中现有的实验仪器存在的一些问题,对原实验装置进行了改进和创新,研制了新颖的良导体热导率实验仪器,并对新仪器的测量准确度和稳定性做了测量和讨论.     

用拉曼光谱测量GeSbSe玻璃的热导率

本文根据斯托克斯和反斯托克斯拉曼光谱散射截面的不同,测量样品表面温度,并进一步提出了一种测量材料热导率的新方法.利用该方法系统地研究了GexSb10Se90-x,GexSb15Se85-x和GexSb20Se80-x三个系列的GeSbSe玻璃的热导率,从而证明该方法的实用性和可靠性,同时分析其化学组分对材料结构和热导率的影响.该方法测量获得的热导率与文献报道的热导率基本一致,表明拉曼光谱法测试材料的热导率简单、快捷,是一种实用的测量材料热导率的方法.结果表明每个系列硫系玻璃的热导率随着Ge浓度的增加而增加,在等于或近似化学配比组分处,硫系玻璃的热导率达到最大值,然后随着Ge含量的继续增加而降低.认为GeSbSe硫系玻璃热导率表现出的阈值现象归因于GeSbSe三元网络结构分离为二元结构的结果.     

红外热成像法测量薄膜热物理参数

研究了一种利用稳态红外热成像法实现自悬浮薄膜面内热导率测量的方法。从一维热传导方程出发,建立了稳态时薄膜表面温度分布的理论模型,利用稳态理论模型,只需测量薄膜边缘温度及厚度,便可同时得到面内热导率、发射率及热流,无需测量薄膜对可见光的吸收率。仿真表明,当薄膜的温升不超过5K时,可以保证拟合得到的面内热导率与理论值的误差低于3%,薄膜样品x方向的最小尺寸为6mm。对厚度为900nm的自悬浮聚酰亚胺薄膜进行实验测量,拟合得到的面内热导率为2.04W/mK、红外发射率为0.92、x=0处的热流为1.77×10~4W/m~2。实验结果与查阅文献的测量值一致,证明方法可以用来测量自悬浮薄膜的面内热导率。     

良导体热导率不同测量法的比较

维德曼-弗兰兹定律指出金属的热导率和电导率的比值是常数,本文先测量了一定温度下的材料的电阻率,再由电阻率计算出材料的热导率,并与利用热波法得到的热导率进行比较,其结果相近.     

介孔二氧化硅基导电聚合物复合材料热导率的实验研究

本文首先制备并表征了介孔二氧化硅SBA-15、 填充导电聚合物的复合材料PANI/SBA-15和复合材料PPy/SBA-15, 并建立双流计实验台开展了材料压片情况下的热导率研究. 在测量得到复合材料热导率的基础上, 引入当量孔径, 结合测量孔径对 PANI/SBA-15和PPy/SBA-15复合材料热导率随填充量的变化进行了定性分析. 分析表明: PANI/SBA-15和PPy/SBA-15复合材料的热导率比基材SBA-15的热导率大得多; 在相同的测量孔径和当量孔径情况下, PANI/SBA-15复合材料的热导率比PPy/SBA-15复合材料的热导率大; 导电聚合物填充到复合材料孔道内和孔道外都有助于热导率的提高, 填充到孔道内比填充到孔道外对热导率提高的贡献更大.     

Phonon thermal transport of URu2Si2: broken translational symmetry and strong-coupling of the "hidden order" to the lattice

A dramatic increase in the total thermal conductivity (kappa) is observed in the hidden order (HO) state of single crystal URu2Si2. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to kappa is extremely small, so that this large increase in kappa is dominated by phonon conduction. An itinerant BCS or mean-field model describes this behavior well: the increase in kappa is associated with the opening of a large energy gap at the Fermi surface, thereby decreasing electron-phonon scattering. Our analysis implies that the "hidden order" parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom.     

High-temperature thermal transport in heavily doped small-grain-size lead telluride

An improved theoretical model has been used to analyse the high-temperature thermal conductivity of dopedn-type lead telluride in terms of the separate contributions from electrons and phonons. At high carrier concentrations the electronic thermal conductivity is significant and the non-parabolic nature of the energy bands must be included to obtain a reasonable agreement with experimental thermal conductivity data. Although acoustic phonon scattering is the dominant carrier scattering mechanism, the inclusion of polar optical mode scattering further improves the agreement between the theoretical results and experimental data. The improved model is employed to estimate the effect of grain-boundary scattering in reducing the thermal conductivity of small-grain-size material. At optimum doping the thermal conductivity of 1 m grain size unalloyed lead telluride would be reduced by approximately 5% compared with the single-crystal data.On leave from the University of Allahabad, India     

应力对石墨烯热输运性质影响的分子动力学模拟

本文建立了低维薄膜材料导热模型,运用非平衡分子动力学模拟的方法,利用lanmmps软件对单层石墨烯纳米带的导热特性进行仿真分析,根据Fourier定律计算热导率,再对石墨烯纳米带的原子施加一定耦合应力场,把应力耦合作用下的石墨烯热导率与正常的石墨烯纳米带进行了对比研究,模拟数据结果表明:在石墨烯纳米带上施加耦合应力时,会导致石墨烯纳米带热导率升高,且随应力增加而增大,模拟范围内热导率升高2.61倍,并且应力方向会对热导率变化产生一定影响,这个研究为纳米尺度上石墨烯相关研究和进一步提升热导率提供了新思路.     

Thermal conductivity of bismuth tellurite

This paper reports on the results of investigations of the thermal conductivity along the three crystallographic directions in bismuth tellurite crystals. It is found that bismuth tellurite exhibits a low thermal conductivity inherent in glasses and disordered solid solutions. At temperatures below the Debye temperature, the thermal conductivity coefficients depend on the temperature as \(\sqrt T \), which is characteristic of disordered solid solutions. The temperature dependence of the thermal conductivity of bismuth tellurite is calculated in the framework of the Debye model.     

Determination of thermal conductivity of silica dioxide Tarkosil T-50 nanopowder by laser flash technique

Results of measuring the thermal conductivity coefficient of silica dioxide Tarkosil T-50 nanopowder by a laser flash technique are reported. Experimental data on thermal conductivity of nanopowder in vacuum, in different gas media, and at different temperatures were obtained. Comparative analysis of thermal conductivity was performed for the T-50 nanopowder and materials with close density values. Based on the experimental data, we obtained a mathematical model to determine the thermal conductivity coefficient of T-50 nanopowder in different gas media.     

"Ω"形微槽热管传热性能的实验研究

本文对一定型"Ω"形轴向槽道热管传热性能进行了实验研究,着重分析了该型热管在水平工况下的轴向温度分布、当量导热系数和总热阻、蒸发/凝结传热系数和最大传热能力.研究表明,该型热管元件具有良好的等温特性和导热性能,可实现高热流、长距离、低温差的热量传输;热管的最大传热能力受其工作温度影响较大,在工作温度较低时具有良好的传热能力,但在高温工况下,传热能力受到削弱.     

Bistability and "negative" viscosity for a suspension of insulating particles in an electric field

It is shown that a suspension of insulating particles in a liquid with low conductivity possesses bistability and has a "negative" effective viscosity effect in the electric field due to internal rotations. By Brownian dynamics simulation it has been found that thermal fluctuations of the angular velocity of particles in this bistable system can have a large effect on the viscosity of the suspension.     

Ba/Ag双掺杂对Ca3Co4O9基热电氧化物热传输性能的影响

采用溶胶-凝胶结合放电等离子烧结的方法制备了Ba, Ag双掺杂的Ba_xAg_yCa_2.8Co₄O₉块体热电氧化物材料, 利用X射线衍射仪, 扫描电子显微镜和热参数测试仪分析了所得样品的物相、微观组织结构和热输运性能. 结果表明, 通过Ba, Ag双掺杂有效调制了Ca₃Co₄O₉的热传输性能, 增加Ba掺杂量能有效降低其热导率. 分析结果表明, Ba, Ag双掺杂对热导率的调制来源于对晶格热导率的调制, 其中Ba, Ag等量掺杂所得样品热导率最低, 其总热导率和晶格热导率在973 K时分别达到了1.43 W/mK和1.10 W/mK. 关键词： 3Co₄O₉')" href="#">Ca₃Co₄O₉ 双掺杂 热导率     

Shape,size and phonon scattering effect on the thermal conductivity of nanostructures

A phenomological model is described here to study the effect of size, shape and phonon scattering on the thermal conductivity of nanostructures. Using the classical model proposed by Guisbiers et al (Phys. Chem. Chem. Phys. 12, 7203 (2010), J. Phys. Chem. C 112, 4097 (2008)) in terms of the melting temperature of nanostructures, the expression for variation of thermal conductivity is obtained in terms of shape and size parameter. An additional term is included in the expression of thermal conductivity to consider the impact of phonon scattering due to the surface roughness with a decrease in size. The expression of thermal conductivity is obtained for spherical nanosolids, nanowires and nanofilms. The thermal conductivity is found to decrease in nanostructures in comparison with the counterpart bulk material. The values of thermal conductivity obtained from the present model are found to be close to the available experimental data for different values of roughness parameter which verifies the suitability of the model.     

Effect of pit formation and surface roughness on size-dependent thermal conductivity of nanometer-thick semiconducting films

In this work, the thermal conductivity variation due to pit formation and surface roughness in nanometer-thick semiconducting films has been studied. It is shown that the thermal conductivity of thin films is reduced due to the presence of these effects in the films. This reduction in thermal conductivity is dependent on film thickness. The present analysis has been done on GaAs nanometer-thick films using the available experimental data.