红外辐射陶瓷的导电化

本文根据单相的个体特性选择堇青石和ＴｉＣ两相复合制备出了导电型的红外辐射陶瓷材料。对体系电性能进行研究发现，体系电导率值随ＴｉＣ含量的变化呈非线性变化，ＴｉＣ含量在９％ｗｔ以下时，体系电导率在１０￣（－１）Ｓ／ｃｍ以下，而从９％ｗｔ开始，随着ＴｉＣ含量的增加，体系的电导率迅速增加，幅度达几个数量级之多。通过电子探针分析我们认为，材料的导电是由ＴｉＣ相形成的导电通路所提供的，其导通过程是一种逾渗过程。根据渗流理论对体系的导电特性进行分析，可以很好地说明电导率发生的突跃现象，由此得到了本复合体系的导电模型。利用这种模型可以从理论上预测某一给定ＴｉＣ含量时系统电导率值的大小，使体系的电导率可控可调。     

自由体积理论在聚氨酯/掺杂盐体系中的应用与矫正

利用交流阻抗谱仪，FT－IR，DSC研究了聚氨酯／盐体系的离子状态和电导率，通过自由体积理论推导了聚合物固体电解质电导率的计算公式，为使公式更符合实际离子的存在状态，用变温红外光谱首次对离子状态随温度的变化进行跟踪研究，对公式进行了改进，并从电导率数据计算出了VTF公式应用于聚氨酯／LiCF3SO4体系的各种参数，讨论了盐浓度对参数的影响。     

塑性双离子聚丙烯腈（PAN）膜的固态阻抗性能

用碳酸丙烯脂（ＰＣ）、高氯酸锂（ＬｉＣｌＯ４）与聚丙烯腈纤维（ＰＡＮ）复合，制备出较高电导率的离子复合膜（１．８×１０＾－３Ｓ／ｃｍ，２６℃）。用电化学交流阻抗谱对其进行了测试，分析了离子导电率的温度依赖性，并在非线性最小二乘拟合程序对其进行了模拟，得到了其等效电路，从而对此体系微相离子传递与转移进行探讨。     

聚氨酯/富马酸二甲酯磺酸钠复合物的离子导电性和形态研究

采用溶液聚合的方法合成了线型聚醚聚氨酯（PU），以其作为基体，与富马酸二甲酯碘酸钠（SDMFNa)复合制得了一系列新型的聚合物固体电解质。利用傅立叶变换拉曼吸收光谱法（FT－Raman)、差示扫描量热法（DSC）、原子力显微镜（AFM）和交流复阻抗谱（IA）对该体系的化学结构、微观形态和离子导电性能进行了研究。结果表明，当有机钠盐的用量为[EO]/[Na^ ]=24时，体系的相容性最好，玻璃化转变温度（Tg)达到极大值，随着盐含量的增加，SDMFNa会聚集析出，体系的Tg下降。复合物的电导率随着温度的升高而升高。在所研究的盐浓度范围内，该聚合物固体电解质的电导率存在一最大值。     

掺入碳纳米管提高聚苯乙炔的导电性研究

用AlCl3作催化剂制备了聚苯乙炔（PPA），采用共混法制备了碳纳米管（CNTs）与PPA的复合材料，并进行了导电性能测试，结果表明，当CNTs含量增加时，复合材料的电导率升高，CNTs含量为3%时是复合材料导电的临界浓度，当CNTs含量达25%时复合材料达极限电导率，比纯的PPA的电导率提高了13个数量级。CNTs/PPA复合材料的导电机理符合导电通道理论。     

K_2NbOF_5－MF_3系玻璃的结构及电性质

研制了Ｋ＿２ＮｂＯＦ＿５－ＭＦ＿３（Ｍ＝Ａｌ、Ｇａ）新体系氟化物玻璃，测定了玻璃的特征温度、Ｒａｍａｎ光谱和电导率，玻璃中Ｎｂ￣（５＋）、Ａｌ￣（３＋）、Ｇａ￣（５＋）分别以ＮｂＯＦ、ＡＩＦ、ＧａＦ八面体形式存在，玻璃的电导率随ＡｌＦ＿３含量的增加而增加，ＡｌＦ＿３含量达到３０ｍｏｌ％时，Ａｌ￣（３＋）除ＡＩＦ八面体外，还有ＡｌＦ四面体结构出现，同时电导率降低，Ｆ￣－阴离子是主要的导电离子，７５Ｋ＿２ＮｂＯＦ＿５·２５ＡｌＦ＿３玻璃的电导率在１９６℃时，σ＝１．０２×１０￣（－２）Ｓ·ｃｍ￣（－１）。     

Li_2SO_4－Li_2O－P_2O_5体系非晶态Li~＋离子导体的研究

本文给出了非晶态Ｌｉ￣＋离子导体Ｌｉ＿２ＳＯ＿４－Ｌｉ＿ｂＯ－Ｐ＿２Ｏ＿５体系的制备条件、导电性以及差热分析（ＤＴＡ）结果，同时还对其晶化过程进行了研究。结果表明，首先成功地制备出了以Ｌｉ＿２ＳＯ＿４为基质的非晶态离子导电材料，并且在３５０℃时组成为Ｌｉ＿２ＳＯ＿４－０．３０Ｌｉ＿２Ｏ－０．７０Ｐ＿２Ｏ＿５样品的电导率最大（σ＝６．７８×１０￣（－３）Ω￣（－１）ｃｍ￣（－１）），这一结果与ＤＴＡ测量结果取得一致，ＳＥＭ证明是由于非晶母体部分晶化造成的。采用液氮温区急冷技术已成功的将该状态稳定到了室温，稳定后的态再重测其电导率随温度变化关系，相应的电导率提高３０％左右，如果找到某种合适的稳定剂使其一直处于微晶态，将为高电导率离子导体的制备提供一条新路。     

聚二氧戊环聚氨酯/高氯酸锂复合体系的离子导电性能研究

合成了以聚二氧戊环（PDXL）为软段的聚氨酯（PDXL－PU）以及聚乙二醇（PEG），聚二氧戊环混合软段的聚氨酯，并进一步制备了聚氨酯／高氯酸锂型聚合物固体电解质，通过红外光谱分析，DSC分析以及复阻抗谱分析等方法对体系的结构及离子导电性能进行了研究，结果发现，PDXL－PU具有很低的软段微区玻璃化转变温度，PDXL软段对高氯酸锂有较强的溶剂化能力，体系的室温电导率可以达到10^-1S／cm以上，而PEG软段的引入则提供了样品软段微区的Tg，无助于提高掺杂样品的电导率。     

轻掺杂聚乙炔的导电机制

用改进的Ｎａａｒｍａｎｎ方法合成了聚乙炔（ＣＨ）ｘ。在碘的上氯化碳和氯化铁的硝基甲烷溶液中掺杂后，分别形成［（Ｈ（Ｉ３）ｙ］ｘ和［ＣＨ（ＦｅＣｌ４）ｙ］ｘ，且掺杂浓度ｙ很小，属于轻掺杂区，测定了未掺杂、碘掺杂和氯化铁掺杂样品的电导率随温度的变化曲线。实验结果表明，电导率对温度有很强的依赖关系，与Ｋｉｒｅｌｓｏｎ的电荷通过电子在孤子间的跳跃的输运理论相吻合。     

电导法对CTAB／正丁醇／环己烷／水四组分微乳体系的研究

利用电导率（K）-增溶水量（ml）关系曲线研究了CTAB／正丁醇／环己烷／水四组分微乳体系在不同增溶水量时的3种结构，即油包水（W／O）、油水双连续（BC）、水包油（O／W）。讨论了表面活性剂CTAB与助表面活性剂正丁醇不同浓度时对微乳液稳定性的影响，得出了微乳液稳定时CTAB和正丁醇的合适配比。     

Quantitative prediction of effective material properties of heterogeneous media

Effective electrical conductivity and electrical permittivity of water-saturated natural sandstones are evaluated on the basis of local porosity theory (LPT). In contrast to earlier methods, which characterize the underlying microstructure only through the volume fraction, LPT incorporates geometric information about the stochastic microstructure in terms of local porosity distribution and local percolation probabilities. We compare the prediction of LPT and of traditional effective medium theory with the exact results. The exact results for the conductivity and permittivity are obtained by solving the microscopic mixed boundary value problem for the Maxwell equations in the quasistatic approximation. Contrary to the predictions from effective medium theory, the predictions of LPT are in better quantitative agreement with the exact results.     

On the effective thermal conductivity of carbon nanotube reinforced polymer composites

In this paper, a theoretical model has been developed for predicting the effective thermal conductivity of an aligned multi-walled nanotube polymer composite. This model is based on an effective medium theory that has been developed for composites containing aligned spheroidal inclusions with imperfect interfaces. To incorporate the nanotube structure into this theory, a continuum model of the nanotube geometry is developed by considering its structure and the mechanism of heat conduction through it. Results show that the overall conductivity will be much lower than expected due to the fact that in the composite, the outer nanotube layer carries the bulk of the heat flowing through the nanotube. It is also seen that the high nanotube–matrix boundary resistance does not significantly affect the overall conductivity. The effective conductivity was also found to be highly sensitive to the nanotube diameter.     

影响磁性纳米颗粒膜吸波性能的主要因素

基于Landau-Lifshitz-Gilbert方程、Bruggeman有效媒质理论及纳米颗粒膜的电输运和介电理论,通过计算磁性纳米颗粒膜的有效磁导率、有效介电常数、计算分析饱和磁化强度、各向异性场、电导率和阻尼系数对纳米颗粒膜吸波性能的影响.结果表明,饱和磁化强度、各向异性场、电导率和阻尼系数均对纳米颗粒膜的微波吸收特性产生显著影响,通过调控纳米颗粒膜的电磁特性可以有效提高其吸波性能,可以应用于薄层吸波材料的设计中.     

Effect of the pore shape on the thermal conductivity of porous media

The effect of the pore shape on the thermal conductivity of porous media is studied in this work, considering random and aligned distributions of spheroidal pores within the matrix. This is done by using the Bruggeman differential effective medium theory which is suitable for pores with different sizes, as is usually the case of practical interest. The obtained results can be applied for porous media with low as well as high porosities, and they show that: (1) the effect of the pore shape becomes stronger as the porosity increases. (2) The thermal conductivity for randomly oriented pores takes its maximum value for spherical pores and this value is the geometric average of the thermal conductivities along the three principal axes of the pores, when they are aligned. (3) In the case of aligned pores, the thermal conductivity along a principal axis increases with its length, in such a way that it is larger along the principal axis with longer dimensions. The predictions of the proposed approach are in good agreement with reported data and are expected to be useful to provide insights on the thermal behavior of porous media.     

The thermal conductivity of Al(OH)3 covered MWCNT/epoxy terminated dimethyl polysiloxane composite based on analytical Al(OH)3 covered MWCNT

Aluminum-hydroxide-covered multi-walled carbon nanotubes (A–MWCNT) were fabricated as a thermally conductive material. The thermal conductivity of A–MWCNT was estimated based on Casimir theory. The effective thermal conductivity of A–MWCNT was estimated at about ∼26 W/mK. The thermal conductivity of A–MWCNT/epoxy-terminated polydimethylsiloxane (ETDS) composite was examined as a function of A–MWCNT loading, and the results showed the maximum value at 1.5 wt% of A–MWCNT loading, above which it decreased slightly. The effective medium approximation (EMA) developed by Maxwell–Garnett (M–G) was used to analyze the thermal conducting behavior of the composite. The experimental results showed negative deviation from the expected thermal conductivity, k_e, beyond 1.5 wt% of A–MWCNT loading, because the composites containing A–MWCNT were strongly affected by interfacial resistance. The interfacial resistance value calculated from M–G approximation increased when filler loading was higher than 1.5 wt% because of the folded and partially agglomerated A–MWCNT along with insufficient interfacial interactions.     

Scattering of Thermal Waves and Non-steady Effective Thermal Conductivity of Unidirectional Fibrous Composites with Functionally Graded Interface

In this paper, a thermal wave method is applied to investigate the non-steady effective thermal conductivity of unidirectional fibrous composites with a functionally graded interface, and the analytical solution of the problem is obtained. The Fourier heat conduction law is applied to analyze the propagation of thermal waves in the fibrous composite. The scattering and refraction of thermal waves by a cylindrical fiber with an inhomogeneous interface layer in the matrix are analyzed, and the results of the single scattering problem are applied to the composite medium. The wave fields in different material layers are expressed by using the wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary conditions of the layers. The theory of Waterman and Truell is employed to obtain the effective propagating wave number and the non-steady effective thermal conductivity of composites. As an example, the effects of a graded interface on the effective thermal conductivity of composites are graphically illustrated and analyzed. Analysis shows that the non-steady effective thermal conductivity under higher frequencies is quite different from the steady thermal conductivity. In the region of intermediate and high frequencies, the effect of the properties of the interface on the effective thermal conductivity is greater. Comparisons with the steady thermal conductivity obtained from other methods are also presented.     

Effective thermal conductivity of Cu/diamond composites containing connected particles

An analytical model for the thermal conductivity of Cu/diamond composites with connected particles is presented by replacement of a cluster of connected particles with an equivalent polycrystal subsequently using a multiple effective medium approach. By applying this model to the measured thermal conductivity of Cu/diamond composites prepared by high pressure high temperature sintering technique reported in the literature, we show that it quite well describes the observed thermal conductivity enhancement induced by the connected particles. We estimate the value of connected particle loading in real composites and show that large particles are easier to form the bonding contact than small particles. The present work also demonstrates that the sensitivity of thermal conductivity contribution from the connected particles strongly depends on the particle size, and their pronounced thermal conductivity enhancement should lie within the certain particle size range.     

Effective Heat Conductivity and Relaxation Processes in Superfluid Mixtures of 3He-4He

The effective thermal conductivity coefficient'ceff in superfluid ³He-⁴He mixtures with concentration of 9.8% ³He has been studied experimentally between 100 and 500 mK, where the main contribution to the kinetic processes is made only by phonons and ³He impurity excitations. In this case the effective thermal conductivity is a combination of diffusivity, thermal conductivity and thermal diffusion. The κ _eff value was found from stationary measurements of the temperature gradients caused by the thermal flow and from the temperature relaxation kinetics. Both the methods provide consistent resugts which also agree with those on effective thermal conductivity calculated in terms of the kinetic theory of phonon-impuriton system.     

Ultrasonic waveguide applicator arrays for interstitial heating: a model study

In this paper we describe an ultrasonic waveguide multiapplicator array for interstitial heating. We first discuss the heat generation term common for this type of applicator and show that the radius of the applicator is the limiting factor in the pattern of heat deposition. We carry out finite element analysis simulations of temperature profiles for three- and four-applicator array, and we test the simulations by measurements in a large volume tissue phantom. With the positive result of this test, we use the simulations to evaluate the size of the heated volume for several applicators (three to six) and for various geometries of their positioning. We do the simulations for a range of the effective thermal conductivity and for two applicator diameters. The volume of the medium with temperatures above 42 degrees C was in the 25 to 73 cm(5 ) range. This volume increased linearly with the diameter of the boundary at the basal temperature. Power required to produce preselected temperature elevation increased monotonically with the effective thermal conductivity. With the 24 mm between the applicators, the array could elevate the temperature to the required value up to the 0.030 W/cm/K effective thermal conductivity.     

Electrical conduction in thick film paste resistors

A formalism presented recently to describe the conductivity in particulate systems by effective medium theory is shown to be applicable to all families of thick film resistors. The thick film resistor is considered as being a mixture of relatively large glass particles and smaller conductive particles which are surrounded by a variably thin glass layer. The large variation in the resistance of the contact between particles that is expected to occur, combined with the particle size difference, is shown to result in the type of resistivity dependence on composition that is observed experimentally. The temperature dependence of the conductivity is predicted within the same formalism using data on extracted conductive particles and expected forms of the conductivity of the thin glass layers. The resulting behaviour is shown to be at least qualitatively correct.