有机磺酸掺杂聚苯胺电导热稳定性的研究

制备了十二烷基苯磺酸,樟脑磺酸掺杂和这两种有机磺酸共掺杂的3种导电聚苯胺,并研究了聚苯胺的电导率在高温环境中的稳定性。发现氧气的存在是导致聚苯胺电导率剧烈衰减的重要因素,在稀氧环境中能有效抑制聚苯胺电导率的衰减速度。进一步利用X射线衍射分析了聚苯胺的有序化程度,结果表明,十二烷基苯磺酸与樟脑磺酸的共掺杂不利于聚苯胺分子链的有序排列,使其电导的热稳定性最差。与十二烷基苯磺酸不同,极性樟脑磺酸与强极性聚苯胺相容性好,在高温时相分离较不明显,对提高聚苯胺的电导热稳定性是有利的。

用电导热散法研究可变电荷土壤粘粒与离子的相互作用

本工作选用二种可变电荷土壤粘粒(<2μ),分别含有0.35×10^(-4)-1.3×10^(-4)mol/L的不同电解质,在不同含水量下,在5—50℃范围内测量其直流电导率的变化。试验结果表明,电导热散法是研究土壤粘粒与离子相互作用的有用手段;电导率-温度曲线上的折点温度是随含水量、电解质种类和土壤类型而不同。在相同含水量下,含有不同电解质的红壤体系的折点温度具有如下的变化顺序:CaCl_2>Na_2SO_4>KCl>Ca(NO_3)_2>NaNO_3;砖红壤体系的折点温度明显高于红壤体系。折点温度的高低是土壤粘粒与离子相互作用强度的反映。

介电体导热系数λ的微观定义式

导热系数是物质的一个重要热物性参数，从物理学的微观观点出发，经过推导得到介电体导热系数λ的微观定义表达式，对深刻理解介电体导热系数的本质具有一定的指导意义。

氧化石墨烯复掺纤维水泥基复合材料研究综述

氧化石墨烯(GO)作为石墨烯(G)的衍生物有着与石墨烯相类似的力学性能和导热性能等优异性能,并且其亲水性官能团使其相比于石墨烯来说更容易在水中分散从而更容易与水泥基相结合。大量研究已表明GO掺入水泥基中不但可以增强水泥基的力学性能和耐久性能还可以增强水泥基的电磁屏蔽性能、导热性能等性能,为多功能型、智能型混凝土的开发提供了可能。以GO复掺其他功能纤维材料在水泥基中的应用为中心,简述了GO的性能特点、结构特质从而表明GO在水泥基材料中应用的广度和范围,并重点综述了GO的分散性研究和GO复掺纤维水泥基的工作性能、水化过程、力学性能、耐久性能、功能性能的研究,并对未来GO复掺纤维水泥基材料研究的方向进行了展望。

Preparation and electromagnetic shielding properties of PET/rGO/SWCNT composite fabric

Graphene oxide(GO)with excellent dispersion ability can assist the dispersion of single-walled carbon nanotube(SWCNT)and promote the formation of uniform and stable GO/SWCNT coating liquid.The highly conductive polyethylene terephthalate/reduced graphene oxide/SWCNT(PET/rGO/SWCNT)electromagnetic shielding composite fabric was successfully prepared by anchoring rGO/SWCNT on PET fabric via dip-coating piror to low-temperature thermal reduction.The results showed that the carboxyl groups and hydroxyl groups formed of hydrophilic-treated PET were conducive to the formation of hydrogen bonds with that of GO,which enhanced the interaction between PET fabric and GO/SWCNT coating;the loading of GO/SWCNT increased with the number of dip-coating,the unit area loading of rGO/SWCNT in the final composite fabric was 2.7 mg/cm^(2) after 10 dip-coating cycles and thermal reduction;the PET/rGO/SWCNT composite fabric had a continuous and dense conductive network,with a conductivity of up to 41.6 S/m and the average electromagnetic interference shielding effectiveness in X-band was 22 dB;the flexible PET/rGO/SWCNT composite fabric was not only easy to process,but also exhibited excellent conductivity and shielding efficiency,showing great potential in the application of electromagnetic shielding fabrics.

基于螺旋折流板的有机热载体加热器流动与传热研究

文章针对螺旋折流板热油锅炉内入口折流板导致的导热油在电加热器内分布不均和传统的弓形折流板容易在折流板后方形成流动死区,引起换热系数较低、导热油温度过高、增大导热油结焦风险等问题,提出梅花折流板、四分开口折流板、四分梅花折流板结构的入口折流板与轴向分离四分螺旋折流板的复合折流板结构。采用Fluent软件对四分螺旋折流板电加热器进行模拟优化,拟合出四分螺旋折流板电加热器的Nu方程和油膜温度关系式,通过PEC指标和相对标准偏差CV评价方法,得到综合性能和流体分布均匀度最优的复合折流板参数。

自发热针织手套的结构与性能

为满足低温环境工作及热舒适性的要求,针对人体手部易冷问题,采用镀银导电纤维作为发热元件,在全自动手套编织机上通过添纱、衬垫、衬纬的方式,将镀银导电纤维织入手套手掌部位,并配以适当的电池组成闭合电路,进行导电发热。测试不同组织结构手套的发热性能。结果表明,衬纬编织方式便于形成电路,且并联衬纬方式优于串联方式;实验初期手套温度与输入功率呈线性增加,之后达到稳定状态,表面温度分布较为均匀,从而起到保暖及改善人体手部温度的作用。

Effective thermal and electrical conductivity of graphite nanoplatelet composites

The relationship between the thermal/electrical conductivity enhancement in graphite nanoplatelets （GNPs） composites and the properties of filling graphite nanoplatelets is studied. The effective thermal and electrical conductivity enhancements of GNP-oil nanofluids and GNP-polyimide composites are measured. By taking into account the particle shape, the volume fraction, the thermal conductivity of filling particles and the base fluids, the thermal and electrical conductivity enhancements of GNP nanofluids are theoretically predicted by the generalized effective medium theory. Both the nonlinear dependence of effective thermal conductivity on the GNP volume fraction in nanofhiids and the very low percolation threshold for GNP-polyimide composites are well predicted. The theoretical predications are found to be in reasonably good agreement with the experimental data. The generalized effective medium theory can be used for predicting the thermal and electrical properties of GNP composites and it is still available for most of the thermal/electrical modifications in two-phase composites.

Microstructure and properties of SiC_p/Al electronic packaging shell produced by liquid-solid separation

The electronic packaging shell of high silicon carbide （54%SiC, volume fraction） aluminum-based composites was produced by liquid-solid separation technique. The characteristics of distribution and morphology of SiC as well as the shell’s fracture surface were examined by optical microscopy and scanning electron microscopy, and the thermo-physical and mechanical properties of the shell were also tested. The results show that Al matrix has a net-like structure while SiC is uniformly distributed in the Al matrix. The SiCp/Al composites have a low density of 2.93 g/cm^3, and its relative density is 98.7%. Thermal conductivity of the composites is 175 W/（·K）, coefficient of thermal expansion （CTE） is 10.3×10^-6 K-1 （25-400 ℃）, compressive strength is 496 MPa, bending strength is 404.5 MPa, and the main fracture mode is brittle fracture of SiC particles accompanied by ductile fracture of Al matrix.Its thermal conductivity is higher than that of Si/Al alloy, and its CTE matches with that of the chip material.

On-Resistance Degradations Under Different Stress Conditions in High Voltage pLEDMOS Transistors and an Improved Method

The on-resistance degradations of the p-type lateral extended drain MOS transistor （pLEDMOS） with thick gate oxide under different hot carrier stress conditions are different, which has been experimentally investigated. This difference results from the interface trap generation and the hot electron injection, and trapping into the thick gate oxide and field oxide of the pLEDMOS transistor. An improved method to reduce the on-resistance degradations is also presented, which uses the field oxide as the gate oxide instead of the thick gate oxide. The effects are analyzed with a MEDICI simulator.

Properties and microstructure of Cu/diamond composites prepared by spark plasma sintering method

Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond were successfully prepared by spark plasma sintering（SPS） method. The sintering temperatures and volume fractions（50%, 60% and 70%） of diamond were changed to investigate their effects on the relative density, homogeneity of the microstructure and thermal conductivity of the composites. The results show that the relative density, homogeneity of the microstructure and thermal conductivity of the composites increase with decreasing the diamond volume fraction; the relative density and thermal conductivity of the composites increase with increasing the sintering temperature. The thermal conductivity of the composites is a result of the combined effect of the volume fraction of diamond, the homogeneity and relative density of the composites.

Effects of carbonaceous conductive fillers on electrical and thermal properties of asphalt-matrix conductive composites

The relationship between thermal/electrical conductivity enhancement in asphalt-matrix mixtures and the properties of filling conductive particles is studied. The thermal properties with filling the carbon fiber, graphite conductive particles in asphalt-matrix mixtures are investigated. Based on the generalized effective medium theory （ EMT ）, the effective thermal and electrical conductivity of carbon fiber/asphalt and graphite/asphalt composites are theoretically elucidated. The theoretical results are found to be in reasonably well agreement with the experimental data. Moreover, the theoretical and experimental results show that the large-aspect-ratio shape of particles can help to achieve a large enhancement of effective conductivity, and the use of disk-like high conductivity particles can limit the additive contents for preserving the volumetric properties and mechanical properties of asphalt composites. The generalized effective medium theory model can be used for predicting the thermal and electrical properties of asphaltmatrix composites, which is still available for most of the thermal/electrical modifications in two-phase composites.

Enhanced thermal and electrical properties of poly (D,L-lactide)/ multi-walled carbon nanotubes composites by in-situ polymerization

Biodegradable poly （D,L-lactide） （PLA）/carboxyl-functionalized multi-walled carbon nanotubes （c-MWCNTs） composites were achieved via in-situ polymerization. These as-prepared composite materials were characterized with FT-IR, XRD, TG, DSC, SEM, and high insulation resistance meter. The results demonstrate that the multi-walled carbon nanotube was carboxyl functionalized, which improved the collection between c-MWCNTs and PLA, and further realized the graft copolymerization of c-MWCNTs and PLA. There is a higher glass transition temperature and a lower pyrolysis temperature of PLA/c-MWCNTs composites than pure PLA. The c-MWCNTs gave a better dispersion than unmodified MWCNTs in the PLA matrix, and an even coating of PLA on the surface of c-MWCNTs was obtained, which increased the interfacial interaction. High insulation resistance analysis showed that the addition of c-MWCNTs increased the electric conductivity, and c-MWCNTs performed against the large dielectric coefficient and electrostatic state of PLA. These results demonstrated that c-MWCNTs modified PLA composites were beneficial for potential application in the development of heat-resisting and conductivity plastic engineering.

Microstructure and thermophysical properties of Mg-2Zn-xCu alloys

The microstructure and thermophysical properties of Mg-2 Zn-x Cu alloys(x=0.5, 1.0 and 1.5, at.%) were investigated through microstructural and thermophysical characterization, heat treatment, and first-principles calculations. It was found that the addition of Cu had influence on the microstructure and thermophysical properties of the alloy. As the Cu content increased, the content of the MgCuZn phase increased in the as-cast alloys along with the electrical and thermal conductivities. After solution treatment, the eutectic structure partially decomposed and Zn atoms dissolved into the matrix, leading to the decrease in both the electrical and thermal conductivities of the alloy. During the early stages of the aging treatment, solute atoms precipitated from the matrix, thus increasing the electrical conductivity of the alloy. After aging for 24 h, the thermal conductivity of Mg-2 Zn-1.5 Cu alloy reached the maximum of 147.1 W/(m·K). The thermostable MgCuZn phases were responsible for increasing the electrical and thermal conductivities. Smaller amounts of Zn atoms dissolved in the matrix resulted in smaller lattice distortion and higher conductivities. The first-principles calculations findings also proved that the MgCuZn phases had very high conductance.

Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

Thermal coupled photoconductivity as a tool to understand the photothermal catalytic reduction of CO2

Photocatalysis shows great promise in the field of solar energy conversion.One of the reasons for this is because it promotes the development of multi-field-coupled catalysis.In order to explore the principles of multi-field-coupled catalytic reactions,an in situ multi-field-coupled characterization technique is required.In this study,we obtained hydrogenated ST-01 TiO2 and observed enhanced catalytic activity by thermal coupled photocatalysis.In situ photoconductivity was employed to understand the activity enhancement.The effects of the reaction temperature,reaction atmosphere,and oxygen vacancy(Ov)on the photoconductivity of TiO2 were studied.After coupling thermal into photoconductivity measurement,highly active Ov-TiO2 displayed rapid decay of photoconductivity in a CO2 atmosphere and slow decay of photoconductivity in a N2 atmosphere.These phenomena revealed that photothermal coupling assisted the detrapping of electrons at the Ov surface and promoted electron transfer to CO2,which clearly explained the high photothermal catalytic activity of Ov-TiO2.This study demonstrated that photoconductivity is a useful tool to help understand photothermal catalytic phenomena.

High-Thermal Conductive Coating Used on Metal Heat Exchanger

Based on modified silicon polyester resin in addition to several functional fillers such as corrosion-resistant fillers, heat-resistant fillers and thermal conductive fillers, a high thermal conductive coating can be made. On the basis of boronnitride(BN) and aluminum nitride(AIN) used as thermal conductive fillers and by means of the testing system of hot disk and heat transfer experiment, researches on the varieties of thermal conductive fillers and the effects of the contents of high-thermal conductive coating have been done, which shows that the thermal conductivity of coating increases with the increase of the quality fraction and the coefficient of thermal conductivity of the thermal conductive fillers of coating. With guaranteeing better heat resistance, stronger corrosion resistance and adhesive force, the coefficient of coating can reach a level as high as 3 W·m-1·K-1.

Heat Resisting Mechanism of Heat-Resisting Aluminum Alloy Conductor and Its Application in Transmission Line

In this paper the heat withstanding mechanism of heat-resisting aluminum alloy conductor is discussed, the types and performance of the conductor and its application on transmission lines are analyzed and introduced, and suggestions on accelerating exploitation and application of the conductor are put forward.