H_2O_2处理碳包覆铁纳米颗粒的表面特性及分散行为

采用体积分数30%的H2O2处理碳包覆铁纳米粒子外层的非晶态类石墨碳层,并将其超声分散于水介质中,通过改变pH值分析测定碳包覆铁纳米粒子表面zeta电位和粒径。结果表明:碳包覆铁纳米粒子非晶碳层的特殊结构可通过双氧水化学处理使其表面产生羧基和羟基;在强碱性介质下,羟基和羧基可强化颗粒间的静电斥力,提高碳包覆铁纳米粒子在水介质中的分散性能。当pH值约为11.5时,碳包覆铁纳米粒子表面zeta电位为48 mV,水合粒子粒径可达到110 nm。     

化学处理法制备碳包铜导热纳米流体及其性能表征

氩电弧等离子体法制备碳包铜纳米粒子,采用双氧水化学处理和添加十二烷基苯磺酸钠两种方法制备碳包铜-水纳米流体,探讨了不同分散方法对碳包铜纳米流体导热性能的影响.结果表明,双氧水化学处理碳包铜纳米粒子制备水介质分散体系具有比添加分散剂制备分散体系更高的导热性能.采用化学处理法,添加质量分数为2.0%的碳包铜-水纳米流体导热...     

基于粒子吸附层的纳米流体有效导热系数模型

基于纳米粒子表面吸附层的分析,构建包含纳米粒子、分散剂层、类固相层和分散基液的导热单元,利用最小热阻法建立纳米流体的有效导热系数模型,推导出其表达式,并分别讨论纳米粒子粒径、分散剂层和类固相层对纳米流体的有效导热系数的影响。结果表明,考虑类固相层的影响得到的纳米流体的有效导热系数比不考虑其影响得到的数值大;添加分散剂后,纳米流体的有效导热系数随着分散剂导热系数的增大而增大,当纳米粒子较小时分散剂在纳米粒子表面的吸附层对纳米流体导热系数的影响更大。     

非水介质中纳米金刚石的改性、分散与应用

开展纳米金刚石在非水介质中应用的前提是其在介质中的良好分散与稳定.鉴于此,综述了非水介质中纳米金刚石改性与分散研究进展,以及相关应用现状和前景.     

SiO2-H2O纳米悬浮液的导热及其机理分析

采用"两步法"分别将50 nm、500 nm粒径的SiO2纳米颗粒加入去离子水中制备纳米悬浮液,采用稳定性分析仪测试SiO2-H2 O纳米悬浮液的分散稳定性.结果显示:SiO2-H2O纳米悬浮液的不稳定性指数低于0.37,说明SiO2纳米颗粒在去离子水中分散稳定.在此基础上,采用Hotdisk导热系数仪分别测试SiO2-H2 O纳米悬浮液在25℃、-20℃下的导热系数,就颗粒浓度和粒径的影响进行研究.结果显示:SiO2-H2 O纳米悬浮液在25℃下的液相导热系数随颗粒浓度的增大、粒径的减小而上升;在-20℃下由于冰的导热系数比SiO2纳米颗粒大,SiO2-H2 O纳米悬浮液的固相导热系数转而下降.采用Maxwell、Bruggeman、Yu and Choi和Xie提出的导热系数模型计算SiO2-H2 O纳米悬浮液的液相和固相导热系数,与测试结果对比发现:导热系数模型能相对较好地预测SiO2-H2 O纳米悬浮液的固相导热系数,但对悬浮液液相导热系数的预测存在很大偏差.分析认为,在纳米颗粒自身导热性能和其微观布朗运动对SiO2-H2 O纳米悬浮液的导热强化中,纳米颗粒的微观布朗运动起到主要作用.     

超细CeO2粉体在醇水混合介质中的超声分散行为

通过测定20nm、200nm、500nm和5μmCeO2粉体在醇水混合介质中的粒度分布、表面电性及分散稳定性,研究了不同粒径级别超细CeO2粉体在体积比为1∶1的醇水系悬浮液中的超声分散行为。实验结果表明:在一定超声功率和超声频率下,不同粒径级别醇水系CeO2悬浮液均存在最佳超声时间。不同粒径级别醇水系CeO2悬浮液的表面电性各不相同;纳米级和亚微米级CeO2在醇水中所带Zeta电位为正值,微米级CeO2的Zeta电位为负值,悬浮液中CeO2粉体的平均粒度越大,其电位绝对值越小。不同粒径级别醇水系CeO2悬浮液的分散稳定性能各不相同;从超声结束后的分散效果来看,亚微米CeO2粉体在醇水混合介质中的分散性能最好;从多个沉降时间段内的稳定性来看,纳米CeO2粉体在醇水混合介质中的稳定性能最好。     

Cu-水纳米流体的分散行为及导热性能研究

通过测定Cu-水纳米悬浮液的Zeta电位和吸光度,采用Hotdisk热物性分析仪测量了其导热系数,探讨了不同pH值和分散剂浓度对Cu-水纳米悬浮液分散稳定性和导热性能的影响.结果表明,pH值和分散剂加入量是影响Cu-水纳米悬浮液分散稳定和导热系数的重要因素.最优化的pH值和分散剂加入量能显著提高水溶液中Cu表面Zeta电位绝对值,增大了颗粒间静电排斥力,悬浮液分散稳定性较好,导热系数较高.从分散稳定和导热系数提高两个方面来考虑,pH=9.5左右被选为最优化值,在0.1%Cu-H2O纳米流体中,0.07%SDBS被选为最优化浓度.另外,Cu-水纳米流体的导热系数随纳米粒子质量分数的增大而增大,呈非线性关系,且比现有理论(Hamilton-Crosser模型)预测值大.     

纳米镍/炭复合材料的制备与磁性表征

以废弱酸型聚丙烯酸系阳离子交换树脂为炭前驱体,经过与镍离子交换后,再经热解制备纳米镍粒子均匀分散于炭基体的纳米镍/炭(Ni/C)复合材料.以XRD、TEM为主要分析手段研究了热解条件对纳米镍粒子在Ni/C复合材料中的形貌、大小的影响.结果表明:通过热解条件可以控制Ni/C复合材料中纳米镍粒子的平均粒径;热解温度的升高和热解保温时间的增加都可使Ni/C中纳米镍粒径增大.磁性能测试结果表明: Ni/C-500表现为超顺磁特性,而Ni/C-600、Ni/C-700为铁磁性;Ni/C-600、Ni/C-700的比剩磁化强度、矫顽力都要大于微米镍粉与块体镍,但其比饱和磁化强度要小于微米镍粉和块体镍.     

用于太阳能集热介质的纳米铜制备技术与铜纳米流体性能综述

纳米流体技术的不断发展为直接吸收式太阳能集热介质的研究提供了强有力的支持。铜价格低廉、储量丰富且导热性能良好,将纳米尺度的铜粒子稳定分散于传统集热介质中制得的纳米流体悬浮液对可见光波段表现出强吸收性能。本文首先对纳米流体中常见的球形、立方体、棒状和线状铜纳米粒子添加物的水热还原制备方法进行了综述,重点讨论了表面活性剂在产物形貌控制中的作用及其对纳米粒子在基液中分散稳定性的影响。进而分别对铜纳米流体的导热系数、粘度、比热及光能辐射特性的研究现状进行了归纳总结,给出了铜纳米流体在直接吸收式太阳能集热系统中的应用现状。最后,提出了铜纳米流体应用于太阳集热器循环工质尚需解决的问题及进一步的研究方向。     

透明结晶纳米氧化锌溶胶的制备与表征

以氯化锌和氢氧化钠为原料,在乙二醇介质中制备了透明结晶纳米氧化锌溶胶,该溶胶经乙醇絮凝和清洗后,可再分散于乙二醇中形成透明分散液.利用FT-IR、UV-vis、XRD、TEM等技术对样品的结构、形貌及晶形进行了分析和表征.实验结果表明:所得纳米氧化锌溶胶在可见光区具有高透过率,在紫外区具有很强的吸收;纳米氧化锌为六方晶系球状结晶,平均粒径约5nm,其表面包覆了有机物,从而防止了粒径的进一步增大,并提高了其在乙二醇中的分散性.     

Copper carboxylate with different carbon chain lengths as metal–organic decomposition ink

The copper carboxylates with different carbon chain length (glycolate, lactate and oleate) were used to prepare the metal–organic decomposition ink. TG–MS showed that copper carboxylates underwent a two-step thermal decomposition for the conversion to elemental copper, and the organic residues after decomposition is relevant with the carbon chain length. Conductive copper films were obtained by drop coating of a copper carboxylate solution onto a glass slide followed by sintering at different temperatures. Copper carboxylates with shorter carbon chain give better conductive films. Both copper glycolate and copper lactate films begin to show conductivity after sintered at 150 °C for 60 min under nitrogen. The resistivity of the copper features with 2 μm thickness of copper glycolate and copper lactate was 23.0 ± 2 and 44.0 ± 6 μΩ cm after sintering at 250 °C for 60 min under nitrogen, respectively, with the former being about 7.4 % of the conductivity of bulk copper. X-ray photoelectron spectroscopy results showed slight surface oxidation in the sintered copper feature from these copper carboxylates. Although the conductivity of the obtained copper film needs to be improved further, the method shows some advantages over the copper nanoparticles ink, such as avoiding tedious synthesis and protection of nanoparticles, low cost, etc.     

Thermal conductivity of wood-derived graphite and copper–graphite composites produced via electrodeposition

The thermal conductivity of wood-derived graphite and graphite/copper composites was studied both experimentally and using finite element analysis. The unique, naturally-derived, anisotropic porosity inherent to wood-derived carbon makes standard porosity-based approximations for thermal conductivity poor estimators. For this reason, a finite element technique which uses sample microstructure as model input was utilized to determine the conductivity of the carbon phase independent of porosity. Similar modeling techniques were also applied to carbon/copper composite microstructures and predicted conductivities compared well to those determined via experiment.     

Enhanced thermoelectric performance of CuAlS2 by adding multi-walled carbon nanotubes

In this paper, we report the first-ever study on a relatively uniform dispersion of multi-walled carbon nanotubes (MWCNTs) in CuAlS₂ nanoparticles, synthesized by high-energy ball-milling, and study the thermoelectric properties of the bulk materials. A vortex mixer and bath sonicator are used to achieve well dispersion of nanotubes in the matrix, and then the powder is hot-pressed. Carbon nanotubes dispersed in the matrix improve electrical conductivity and Seebeck coefficient. The addition of MWCNT causes an increase in the grain boundary and facilitates phonon scattering, resulting in a reduction in the lattice thermal conductivity and finally total thermal conductivity. The optimum amount of carbon nanotubes is effective for reducing thermal conductivity and increasing electrical conductivity, thereby elevating the figure-of-merit of the nanocomposites. Finally, the figure-of-merit is highly influenced by total thermal conductivity, and the maximum figure-of-merit was obtained for CuAlS₂/0.5 wt% MWCNT composite, which indicated about 20% improvement.     

碳纤维含量对短碳纤维－铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料，测定了复合材料的力学性能和物理性能，表明在碳纤维与铜基体之间存在界面结合，碳纤维含量对复合材料性能影响极大。     

三水醋酸钠导热性能改善实验研究

为了提高以三水醋酸钠为基质的复合相变储热材料（PCM）的导热性能,选用铜粉、碳粉、膨胀石墨作为导热系数改善剂,并进行对比实验,结果表明铜粉、碳粉与复合PCM混合后分层明显,而膨胀石墨的混合效果较好,且当膨胀石墨体的积分率约为10%时,利用其多孔吸附特性和较好的导热性能,对复合PCM（含增稠剂和成核剂）的导热性能改善明显。     

Cement-based composites containing functionalized carbon fibers

Carbon fibers can be used to improve both mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. To guarantee both a good dispersion in water and a strong interaction with cement, surface functionalization of carbon fiber surface by reaction with acid was preferred to the use of a dispersing agent. The best oxidation conditions were chosen by using a Taguchi approach, and the samples contained the treated fibers were subjected to both mechanical and electrical tests, to determine flexural strength, toughness, compressive strength and electrical conductivity. It was shown that a not-too-strong oxidation by piranha solution was very effective to obtain well-dispersed fibers and a cement-composite with improved mechanical properties (in particular toughness) and electrical conductivity.     

Thermal conductivity of unidirectional copper matrix carbon fibre composites

The thermal conductivity of the unidirectional copper matrix–carbon fibre composite is characterised and analysed in directions parallel and transverse to the carbon fibre orientation. Unidirectional samples with different fibre content were produced by diffusion bonding of continuous copper-coated carbon fibre tows. The thermal diffusivity was measured in two main orientations to the fibre direction by the laser-flash technique. The longitudinal and transverse thermal conductivity was then calculated and results were compared with simple analytical models. Measurements revealed decreasing thermal conductivity as the fibre volume content in the composite increased and the transverse thermal conductivity of the unidirectional samples presented much lower values in comparison to the longitudinal one.     

碳纤维含量对短碳纤维-铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料,测定了复合材料的力学性能和物理性能,表明在碳纤维与铜基体之间存在界面结合,碳纤维含量对复合材料性能影响极大。     

短碳纤维-铜复合材料的研制

研究了用粉未冶金方法制造短碳纤维-铜复合材料,对这种复合材料的力学性能及物理性能进行了测试,证明该复合材料中,碳纤维与铜基体间存在着界面结合。