(Ti/Zr)B_2填充环氧树脂基复合材料热导性能的实验和数值分析研究

采用原位聚合的方法制备了高导热硼化物陶瓷颗粒(Zr/Ti)B_2填充的环氧树脂基复合材料,通过激光脉冲方法对复合材料的热导率进行测试,并利用有限元方法对其热导率进行模拟分析.实验结果表明,TiB_2/ZrB_22种陶瓷颗粒的加入均能有效地提高环氧树脂基复合材料的热导率,且随着陶瓷颗粒填充量的增加,复合材料的热导率在一定的范围内均呈上升的趋势,相对于纯的环氧树脂,其复合材料热导的提升可分别高达100.7%和126.8%;相比之下,ZrB_2填充环氧树脂复合材料较TiB_2具有更高的热导值,分析认为这主要由于ZrB_2颗粒与环氧基体具有较低的界面热阻所致.有限元分析表明,2种复合材料热导的试验值与预测值基本吻合,且在较高体积分数下,ZrB_2复合材料热导两值的偏差较TiB_2的更小.     

碳纳米管改性环氧树脂的导热和阻燃性能

以双酚A二缩水甘油醚(DGEBA)环氧树脂(Epoxy Resin,EP)为基体、甲基六氢苯酐(MHHPA)为固化剂、以多壁碳纳米管(MWCNTs)为添加剂制备了环氧树脂/碳纳米管纳米复合材料。通过对微观结构、玻璃化转变温度(Tg)、热失重、热导率和锥形量热测试结果分析,研究了质量分数少于1.5%的MWCNTs对环氧树脂的导热和阻燃性能影响,结果表明,MWCNTs质量分数为1.5%时,复合材料发生团聚;纳米复合材料随着MWCNTs质量分数的增加Tg值先增加后降低;失重5%时,对应的温度先增加后降低,残炭量增加;样品的热导率呈现先升高后降低的趋势,当MWCNTs质量分数为1%时,复合材料的热导率最大;MWCNTs加入后环氧树脂的总释热量减少,释烟量增加,阻燃性得到一定程度的提高。     

参杂缺陷石墨烯的高分子复合材料导热特性分子动力学模拟（英文）

传统高分子材料由于内部分子链无规则缠绕的特点,导致其热导率较小。近年来,拥有高导热特性的新型高分子材料在众多领域都显示出了极大的发展潜力。随着研究的不断深入,具有优秀导热能力的石墨烯等低维碳材料引起越来越多人的关注。引入石墨烯制作的高分子复合材料具有较高的导热性能,在热管理方面具有很大的应用前景。本文使用非平衡态分子动力学方法计算了石墨烯点缺陷对石墨烯-高分子复合材料界面热导和整体热导率的影响。石墨烯层的界面热导受点缺陷密度的影响较大。当石墨烯缺陷密度由0%增大到20%时,其界面热导由75.6 MW·m~(-2)·K~(-1)增加为85.9 MW·m~(-2)·K~(-1)。石墨烯点缺陷造成sp~2共价键断裂、结构刚性下降,导致其振动态密度的低频分量增加,增强了与高分子基质间的低频能量耦合,进而提高了界面热导。而点缺陷密度的增大对复合材料整体热导率也具有相似的提升效果(从40.8 MW·m~(-2)·K~(-1)增加为45.6 MW·m~(-2)·K~(-1))。此外,高分子基体在石墨烯界面处会造成局部密度提高,但石墨烯点缺陷对高分子材料局部密度提升并无显著影响。这些计算结果加深了对石墨烯与高分子基体间导热机理的理解,并有助于开发和设计具有优异热学性能的高分子复合材料。     

钒基/稀土-镁-镍系A_2B_7型合金复合储氢材料的微观组织和电化学性能

以钒基合金(TiCr)0.497V0.42Fe0.083为基体,通过掺入稀土-镁-镍系A2B7型合金(MlMg)2(NiCoAl)7作为电催化活性物,采用机械球磨改性方法制备了储氢合金复合电极材料(TiCr)0.497V0.42Fe0.083+x(%,质量分数)(MlMg)2(NiCoAl)7(x=5～50),系统研究了电催化活性物含量对球磨复合材料微观组织和电化学性能的影响规律。XRD和SEM分析结果表明,随x值的增加,球磨后A2B7型合金颗粒细化后分散并包覆在钒基合金表面上;与铸态钒基合金相比,复合材料中BCC固溶体相结构的晶胞参数a和晶胞体积V均明显减小。电化学性能测试结果表明,球磨复合材料电极的最大放电容量随着x值的增加呈先增加后减小的变化规律,当x?5时,复合材料电极的放电容量为280～433.2mAh.g-1,其100次充放电循环后的电极容量保持率S100为92%～98.9%,表现出良好的电极循环稳定性,其中x=30时的复合材料的综合电化学性能较佳,A2B7型合金的抗腐蚀性能及其包覆效果以及V元素的溶出行为对球磨复合储氢合金电极的电化学循环稳定性具有重要的影响。随A2B7型合金含量x的增加,球磨复...     

铽β-二酮配合物复合离子凝胶的合成及其发光性质的研究

离子凝胶是一种将离子液体固定在Si-O基质凝胶材料中的新型离子液体固态材料。首先通过溶胶-凝胶法合成均匀透明的离子凝胶材料,然后利用离子液体这一良好溶剂及其在凝胶材料中的可循环性,通过提取离子液体及再吸附稀土铽配合物与离子液体的溶液,实现铽配合物在离子凝胶材料中均匀稳定的掺杂。合成了两种铽β-二酮配合物复合离子凝胶材料并研究材料光致发光性能,发现复合材料中铽配合物保持了Tb(Ⅲ)的特征发射,其荧光寿命在复合材料中略变短,该复合材料方法简单,合成条件温和且环保,材料的合成为稀土配合物的应用提供了又一类新型复合材料。     

锌对CaTiO3∶Pr3+发光亮度和余辉时间的影响

研究了Zn的不同掺入量、不同合成温度对CaTiO3∶Pr3+红色光致发光材料结晶、初试亮度和余辉时间的影响.用X射线衍射确定了材料的物相构成, Zn的掺入没有导致Ca2Zn4Ti15O36相的出现.发射光谱的峰值位于613 nm,对应了Pr3+的1D2-3F4跃迁发射,且受Zn掺入量的影响.激发光谱呈宽带,随Zn掺入量的不同而变化明显.同时, Zn的掺入量的增加可以显著降低材料的合成温度.适量的Zn的掺入,在适当的合成温度条件下,获得了具有高的初始亮度、余辉时间达1 h左右的红色长余辉材料.     

铈掺杂Y3Al5O12热障涂层陶瓷材料的制备与性能研究EI北大核心CSCD

采用高温固相反应合成法制备不同组分的铈掺杂Y3Al5O12热障涂层陶瓷材料，利用X射线衍射仪、X射线光电子能谱、扫描电子显微镜、维氏硬度仪和激光导热仪研究Ce掺杂量对陶瓷材料物相组成、微观形貌、硬度和热导率的影响规律。结果表明：当Ce掺杂量x为0.01和0.02时，(Y1-xCex)3Al5O12呈单一YAG相，(Y0.99Ce0.01)3Al5O12的硬度最大，约为18.93 GPa;(Y0.98Ce0.02)3Al5O12的热导率最低，1000℃时约为1.95W·m-1·K-1。随着Ce掺杂量的增加，材料中出现Ce O2第二相且Ce4+的占比增多，粉体颗粒尺寸增大，陶瓷晶粒尺寸减小，导致(Y1-xCex)3Al5O12陶瓷材料的硬度和热导率均有所下降。     

芳醚树枝形聚合物体系的设计合成及电子转移和三重态能量传递研究

<正>树枝形聚合物是一类具有特殊结构的大分子,通过可控合成,具有光捕获功能的官能团可以精确地分布在树枝形聚合物的核心或外围,甚至可以在支化单元的任何位置,随着代数的增加,官能团数目从核心向外围呈指数增长,树枝形聚合物的这种特殊结构被用来模拟光合作用中的光捕获体系.电子转移和能量传递是光合作用的关键过程,也是光化学研究的重要内容,因此,研究树枝形聚合物体系内的电子转移和能量传递是人工模拟光合作用的一个突破口,是目前相关研究工作的热点之一.本文设计合成了一系列一代到四代的芳醚树枝形聚合物,共24个新化合物,通过稳态、瞬态以及光化学反应的方法研究了芳醚树枝形聚合物体系内电子转移和三重态能量传递过程,得到了一系列有意义的研究结果:     

基于羟基氧化铁/石墨烯复合材料构建生物传感器用于ATP的检测

采用FeOOH-rGO复合材料作为光敏材料,并将负载了大量葡萄糖分子的功能化介孔二氧化硅纳米颗粒(MSNs)作为识别探针和信号放大系统构建生物传感平台用于ATP的检测.在目标物存在的情况下,ATP与适配体进行特异性结合,使得MSNs的孔道被打开,葡萄糖分子被释放并作为电子供体参与光电转换过程,引起光电流的增加.随着ATP浓度的增大,释放的葡萄糖分子增加,光电流信号增强,通过监测光电流信号从而实现对目标物ATP浓度的检测.     

六方氮化硼/聚合物导热复合材料研究进展

随着电子技术快速的发展,聚合物材料自身较低的热导率已不能满足现代电子器件的散热需求,因此提高聚合物热导率,实现高效率的传热具有重要意义。六方氮化硼(h-BN)具有良好的高电击穿强度,导热性能、介电性能、低吸湿率、高温耐氧化等诸多特性,是制备低介电常数、低介电损耗和高导热聚合物的理想填料。本文分别从目前制备BNNSs的主要方法及提高BN复合材料热导率的不同思路两个方面,综述了以六方氮化硼(h-BN)为填料的导热聚合物复合材料的研究现状。     

Modelling of transport processes in a developing char

A mathematical model, simulation results and laboratory experiments are reported to describe the degradation of fire retardant polymeric materials.The model describes the heat and mass balances of a polymer layer with finite thickness. The degradation is initiated by a constant heat flux at the top of the layer. It is assumed that the polymer degrades to a fixed mass of char and volatile gas in an instantaneous step, at the moment when the temperature reaches a critical value. The most important heat transport mechanism is conduction, which dominates the temperature profile. The mass transport of gas is described by Darcy's law, with a simplifying condition that the overall solid volume is constant during degradation. The transport processes have been modelled in one spatial dimension.Calculations and experiments have been carried out to establish the effects of critical parameters such as layer thickness, heat flux and material properties.     

Green synthesis,crystal growth,and some physicochemical studies on an inter-molecular compound of anthranilic acid and <Emphasis Type="Italic">m</Emphasis>-nitro-benzoic acid system

Nanofluids are prepared by suspending the nanoparticles in the base fluid and can be substantially enhanced the heat transfer rate compared to the pure fluids. In this paper, experimental investigation of the effects of volume concentration and temperature on dynamic viscosity of the hybrid nanofluid of multi-walled carbon nanotubes and aluminum oxide in a mixture of water (80%) and ethylene-glycol (20%) has been presented. The nanofluid was prepared with solid volume fractions between 0.0625 and 1%, and experiments were performed in the temperature range of 25–50 °C. The measurement results at different shear rates showed that the base fluid and nanofluid samples with solid volume fractions of less than 0.5% had Newtonian behavior, while those with higher solid volume fractions (0.75 and 1%) exhibit a pseudoplastic rheological behavior with a power law index of less than unity. The results showed that viscosity has a direct relationship with solid volume fraction of the nanofluid. The value of maximum enhancement is which occurred in 25 °C. Moreover, the consistency index and power law index have been obtained by accurate curve fitting for samples with non-Newtonian behavior of nanofluids. The results also revealed that the apparent viscosity generally increases with an increase in the solid volume fraction.     

Thermophysical Properties of High-Temperature Reacting Mixtures of Carbon and Water in the Range 400–30,000 K and 0.1–10 atm. Part 1: Equilibrium Composition and Thermodynamic Properties

This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water mixtures together with the need of transport coefficients computation.     

On the Henry constant and isosteric heat at zero loading in gas phase adsorption

The Henry constant and the isosteric heat of adsorption at zero loading are commonly used as indicators of the strength of the affinity of an adsorbate for a solid adsorbent. It is assumed that (i) they are observable in practice, (ii) the Van Hoff's plot of the logarithm of the Henry constant versus the inverse of temperature is always linear and the slope is equal to the heat of adsorption, and (iii) the isosteric heat of adsorption at zero loading is either constant or weakly dependent on temperature. We show in this paper that none of these three points is necessarily correct, first because these variables might not be observable since they are outside the range of measurability; second that the linearity of the Van Hoff plot breaks down at very high temperature, and third that the isosteric heat versus loading is a strong function of temperature. We demonstrate these points using Monte Carlo integration and Monte Carlo simulation of adsorption of various gases on a graphite surface. Another issue concerning the Henry constant is related to the way the adsorption excess is defined. The most commonly used equation is the one that assumes that the void volume is the volume extended all the way to a boundary passing through the centres of the outermost solid atoms. With this definition the Henry constant can become negative at high temperatures. Although adsorption at these temperatures may not be practical because of the very low value of the Henry constant, it is more useful to define the Henry constant in such a way that it is always positive at all temperatures. Here we propose the use of the accessible volume; the volume probed by the adsorbate when it is in nonpositive regions of the potential, to calculate the Henry constant.     

Calculating the effect of vacancies on the thermodynamic functions and frequencies of normal vibrations of a Lennard-Jones monoatomic crystal

Four main functions of a Lennard-Jones defect argon crystal with an FCC lattice are considered in the context of the lattice gas model: Helmholtz free energy, entropy, internal energy, and heat capacity at a constant volume (allowing for normal vibrations of a solid). Properties of the defect crystal are calculated from the distribution function of the frequencies of an ideal crystal, and corrections to it that reflect local atomic vibrations around vacancies, in the context of the Lifshits linear approximation according to vacancy density. To find the free energy of a defect-free ideal crystal, frequencies of normal vibrations of the crystal are calculated with allowance for the interactions of the four nearest neighbors. The nonlocality of the chemical potentials of the atoms of a solid is discussed, and the influence of contributions from various segments of the vibrational spectrum to the values of thermodynamic functions is investigated. It is shown that ignoring the acoustic or antiphase segments of the spectrum when calculating the free energy leads to increasing of its deviation from the one calculated using the full vibrational spectrum with an increase in temperature. It is concluded that the nonequilibrium state of the defect crystal can lead to negative values of heat capacity at a constant volume.     

The influence of creep on cake solid volume fraction during filtration of core–shell particles

The solid volume fraction vs. pressure relationship used in conventional filtration models is determined by measuring the cake solid volume fraction after consolidation. However, some cakes creep during consolidation, so the solid volume fraction increases at constant pressure. Thus, the conventional method for determining the solid volume fraction vs. pressure relationship cannot be used for materials with significant creep. Cake creep has been observed when core–shell particles with hard poly(styrene) cores and water-swollen poly(acrylic acid) shells are filtered. The Terzaghi–Voigt combined model has been fitted to data obtained during consolidation to determine the transition point where creep begins to be dominating for cake compression. The solid volume fraction increases by 17–35% after the transition point, particularly in the case of particles with thick poly(acrylic acid) shells and thus a high initial water content. Hence, the solid volume fraction can increase significantly during cake creep and if the solid volume fraction vs. pressure relationship that controls the initial stages of filtration is to be determined then the filtration experiments must be stopped before creep dominates. This can be done by measuring the liquid pressure at the interface between piston and sample, and stop the experiment when the liquid pressure is lower than 5% of the applied pressure.     

Effect of Reynolds number on heat transfer and flow for multi-oxide nanofluids using numerical simulation

A numerical simulation model for laminar flow of nanofluids in a pipe with constant heat flux at the wall has been built to study the effect of Reynolds number on heat transfer and pressure loss. The investigation was performed for metallic oxide and multi-oxide nanoparticles suspended in water. The thermal conductivity and dynamic viscosity were measured for a range of temperature (10–60 °C) and volume fraction of multi-oxide nanofluid. Comparison of the thermal conductivity for monocular oxide and multi-oxide nanofluids reveals a new way to control the enhancement in nanofluid conductivity. The numerical results obtained were compared with existing well-established correlations. The predictions of the Nusselt number for nanofluids are in agreement with the Shah correlation, and the deviation in the results is less than 1 %. It is found that the pressure loss increases with the Reynolds number, nanoparticle density, and volume fraction for multi-oxide nanoparticles. However, the flow demonstrates enhancement in heat transfer which improves with increasing Reynolds number of the flow.     

Calorimetry and other methods in the studies of expansive cement hydrating mixtures

In this study, the calorimeter was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The shrinkage-less and expansive binders were produced by mixing of Portland cement with an expansive additive produced by sintering and composed of calcium sulfoaluminate (yeelimite), calcium sulfate (anhydrite) and lime. The studies were focused on the synthesis of this aluminate??sulfate??lime additive (temperature of burning process as a parameter controlling the relative activity of components) from the materials being the by products and subsequently on the mixture proportions to ensure the hydration process resulting in non-shrinkage or expansion effect. In the experiments the proportions of expansive mixture and cementitious materials were variable. The investigations with aim to find the relationship between the volume changes and composition of initial mixtures in cement pastes and mortars (with sand) were also carried out. The phase composition and microstructure of products were characterized. The expansive additive in the environment of hydrating cement transforms into ettringite and gives an increase of volume when the plastic material transforms to the more rigid matter but before the ultimate hardening takes place. Proper, moderate setting and hardening in strongly modified mixtures is achieved when the calorimetric curve corresponding to the heat evolution on hydration is analogous to that for the basic Portland cement. The rate of heat evolution data are well compatible with the other results related to the other methods of hydration kinetics assessment (e.g. chemical shrinkage) and discussed in terms of the phase composition of hydration products.     

乙醇和甲苯组成的最低共沸混合物热力学性质的研究

The molar heat capacity of the azeotropic mixture composed of ethanol and toluene was measured by a high precision adiabatic calorimeter from 80 to 320 K. The glass transition and phase transitions of the azeotropic mixture were determined based on the heat capacity measurements. A glass transition at 103.350 K was found. A solid-solid phase transition at 127.282 K, two solid-liquid phase transitions at 153.612 and 160.584 K were observed, which correspond to the transition of metastable crystal to stable crystal of ethanol and the melting of ethanol and toluene, respectively. The thermodynamic functions and the excess ones of the mixture relative to the standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

Cw-laser thermal lens spectrometry in binary mixtures of water and organic solvents: composition dependence of the steady-state and time-resolved signals

The thermal lens effect obtained in binary liquid systems composed of water and ethanol, propanol and acetonitrile has been investigated. The dependence of dn/dT upon the solvent volume fraction follows polynomials up to sixth order and cannot be precisely predicted using the additive rule. The sensitivity of the thermal lens method upon the addition of organic solvent in water varies as the temperature-dependent refractive index gradient to thermal conductivity ratio of the mixture provided that the signal is sampled correctly. Otherwise, especially when steady-state experiments are carried out, the thermally induced concentration gradient, known as the Soret effect, can change the thermo-optical properties of the solution locally in the irradiated area and produce an additional signal. This effect depends on the solvent and is maximum at low solvent composition. At the critical solvent volume fraction of 0.1-0.15, the Soret component may represent up to 25% of the pure thermal lens signal and has a time constant which is 200-400 times greater than the characteristic time constant of the thermal lens.