Thermal Conductivity of Platelet-Filled Polymer Composites

Platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer–ceramic composite materials. The conductivities of composites filled with hard, stiff ceramic particles exceeded 3.5 W·(m·K)⁻¹, or >20 times the conductivity of the polymer matrix, and were shown to be almost independent of the intrinsic filler conductivity range of 33–300 W·(m·K)⁻¹. In contrast, the thermal conductivity of composites filled with soft, platelet-shaped BN fillers reached over 13 W·(m·K)⁻¹. A mechanism is proposed whereby deformation of the soft filler particles provides improved particle-to-particle connectivity and allows greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles of similar initial morphology. Experimental results are discussed in light of various thermal conductivity prediction models in the literature.     

Thermal Diffusivity/Conductivity of Alumina—Silicon Carbide Composites

Thermal diffusivity and conductivity values for several Al₂O₃-SiC whisker composites were determined. The thermal diffusivity values spanned the range from 373 to 1473 K, and thermal conductivity data wre obtained between 305 and 365 K. The thermal diffusivity decreased with increasing temperature and increased with SiC-whisker content. An estimate of the thermal conductivity of the whiskers was obtained from the direct thermal conductivity measurements, but attempts to derive whisker conductivity values from the thermal diffusivity data were not successful because the laser flash method lacks the required accuracy and precision. Specimens were subjected to two different thermal quench experiments to investigate the effect of thermal history on diffusivity. In the most severe case, multiple 1073- to 373-K quenches, radial cracks were observed in the test specimens; however, there was no change in diffusivity. The lack of sensitivity to thermal cycling appears to be related to the sample size.     

Effect of Interfacial Reaction on the Thermal Conductivity of Al–SiC Composites with SiC Dispersions

The effect of interfacial reactions between Al and SiC on the thermal conductivity of SiC-particle-dispersed Al-matrix composites was investigated by X-ray diffraction and transmission electron microscopy (TEM), and the thermal barrier conductance ( h _c) of the interface in the Al–SiC composites was quantified using a rule of mixture regarding thermal conductivity. Al–SiC composites with a composition of Al (pure Al or Al–11 vol% Si alloy)–66.3 vol% SiC and a variety of SiC particle sizes were used as specimens. The addition of Si to an Al matrix increased the thermal barrier conductance although it decreased overall thermal conductivity. X-ray diffraction showed the formation of Al₄C₃ and Si as byproducts in addition to Al and SiC in some specimens. TEM observation indicated that whiskerlike products, possibly Al₄C₃, were formed at the interface between the SiC particles and the Al matrix. The thermal barrier conductance and the thermal conductivity of the Al–SiC composites decreased with increasing Al₄C₃ content. The role of Si addition to an Al matrix was concluded to be restraining an excessive progress of the interfacial reaction between Al and SiC.     

纳米SiO2对先驱体浸渍裂解法制备SiCf/SiC复合材料力学性能的影响

以纳米SiO2为填料,采用先驱体浸渍裂解法制备2.5D-SiCf/SiC（D为维数,SiCf为SiC纤维）复合材料,研究了前驱液中纳米SiO2含量对复合材料力学性能的影响。结果表明,纳米SiO2的添加能有效抑制先驱体裂解过程中的体积收缩,提高致密度,但过量引入易导致浸渍液黏度过高,浸渍效率降低。纳米SiO2含量对材料力学性能有较大影响,添加纳米SiO2后材料的抗弯强度和断裂韧性均高于没有添加的样品,材料抗弯强度随纳米SiO2含量的增加先增大后降低。当浸渍液中纳米SiO2含量为6%时,复合材料具有优异的力学性能,抗弯强度达到211.1MPa。     

Effect of 1600°C Heat Treatment on C/SiC Composites Fabricated by Polymer Infiltration and Pyrolysis with Allylhydridopolycarbosilane

Fiber-coating debonding observed by transmission electron microscopy is suggested as the cause for an ∼60% reduction in strength after one cycle of 1600°C heat treatment in a carbon/silicon carbide (C/SiC) composite fabricated by polymer infiltration and pyrolysis with pure allylhydridopolycarbosilane polymer as the matrix precursor. Infiltration with a slurry of SiC powder and the polymer precursor was effective in preserving the coating integrity and composite strength. This study demonstrates that the addition of powder in polymer infiltration and pyrolysis process may impact composite mechanical properties significantly by altering the fiber-matrix interface characteristics.     

纳米Fe3O4/环氧树脂基复合材料制备及导热性研究

选用水热法制备Fe3O4纳米粒子为填料,通过直接混合分散法制备了纳米Fe3O4/环氧树脂基复合材料。测试分析了Fe3O4纳米粒子的形貌、结构和磁性能。并且复合材料的导热系数也被测定,结果表明,随着粒子填充体积增加,复合材料导热系数增大。当添加28.47%的纳米Fe3O4粒子时,复合材料导热系数达到0.409 W/（m.k）,是纯环氧树脂E-44的2.54倍。通过对Y.Agari导热模型分析计算,得到了能对该复合材料导热系数进行较好预测的方程。     

Large-Scale Fabrication of Flexible EVA/EG@PW Phase Change Composites with High Thermal Conductivity for Thermal Management

The working electronic devices and batteries generate a lot of heat, if this heats not release quickly, it will not only have a great impact on the performance of the devices, but also cause certain safety hazards. The passive thermal management based on organic phase change materials (PCMs) stands out due to its excellent temperature regulation capability as well as the buffer protection capability for device overload. In view of these, a series of flexible EVA/EG@PW (EE@P) phase change composites (PCCs) with high thermal conductivity are prepared by efficiently constructing porous skeletons and thermal conductive pathways through sacrificial template method, and introducing paraffin wax (PW) by simple vacuum impregnation technique. The PCC exhibits high thermal conductivity (2.6 W m⁻¹ K⁻¹), high enthalpy (153.5 J g⁻¹), and good flexibility. In addition, the PCC possesses excellent cycling stability and thermal stability. In practical application, the PCC shows good temperature control ability for LED and shows great potential application in the field of thermal management.     

EP/GNs/MWCNTs复合材料的导热性能

以多壁碳纳米管(MWCNTs)和石墨烯纳米微片(GNs)为导热填料,环氧树脂(EP)为基体采用溶剂和超声分散法,制备了EP/GNs/MWCNTs导热复合材料,并与EP/MWCNTs及EP/GNs复合材料的导热性能进行了对比。采用透射电子显微镜观察其微观结构,采用Hot Disk热导率测试仪测试其导热性能,采用差示扫描量热法和热重分析仪测试其耐热性及热稳定性。结果表明,MWCNTs和GNs共同作为EP导热填料时,相比于单组分填料(MWCNTs或GNs)更易形成导热网络;EP的热导率、玻璃化转变温度(Tg)和热分解温度均随着MWCNTs或GNs含量的增加而提高,其中,GNs更有利于提高EP的热导率和热分解温度,MWCNTs更有利于提高EP的Tg。在相同的导热填料含量下,相对于其中的任一单一填料,MWCNTs/GNs共同作用时,对热导率的提高有更显著的效果,且随着其中GNs比例的增加,热导率逐渐增大。当GNs和MWCNTs的体积分数分别为0.6%和0.4%时,EP/GNs/MWCNTs复合材料的热导率、Tg和起始分解温度分别为0.565 W/(m·K),152℃和316℃,分别比纯EP提高了132.5%,34.5%和8.2%。     

Inverse Problem for Composites with Imperfect Interface: Determination of Interfacial Thermal Resistance, Thermal Conductivity of Constituents, and Microstructural Parameters

An explicit method is introduced to solve inverse problems for composites with imperfect interfaces. We apply the method to determine the thermal conductivity of constituents and the interfacial thermal resistance in SiC-particulate-reinforced aluminum-matrix composites and to estimate the whisker thermal conductivity, the interfacial thermal resistance, and the whisker alignment distribution in two types of SiC-whisker-reinforced lithium aluminosilicate glass-ceramic composites from their measured effective thermal conductivity reported in the literature. Certain bounds for these three properties of both SiC-whisker-reinforced glass-ceramic composites are obtained, and reasonable estimates for their exact values from room temperature to 500°C are made. The inverse problem is quite sensitive to noise in the measurements. We also comment on existing estimates.     

导热PE-HD／SiC复合材料的制备及性能研究

将碳化硅（SiC）粒子和高密度聚乙烯（PE—HD）经粉末混合后制得导热复合材料。研究了SiC粒子分散状态及含量对复合材料热导率、热阻、力学性能及电绝缘性能的影响，探讨了SiC粒径对热导率的影响。结果表明：复合材料中SiC粒子围绕在PE—HD粒子周围，形成了特殊的网状导热通路；随SiC粒径增加，热导率降低；在填料体积分数为30％时，复合材料热导率、热阻、拉伸强度及冲击强度、体积电阻率和介电常数分别为1．05W／（m·K）、0．75K／W、15MPa、13．2kJ／m^2、4．6×10^15 ·Ω·cm和3．03。此外，使用少量的氧化铝（Al2O3）纤维替代SiC组成混杂填料增强的材料各项性能均得到改善，并且与纯PE-FID相比具有优良的热传导能力。     

Role of Interfacial Carbon layer in the Thermal Diffusivity/Conductivity of Silicon Carbide Fiber-Reinforced Reaction-Bonded Silicon Nitride Matrix Composites

The role of an interfacial carbon coating in the heat conduction behavior of a uniaxial silicon carbide nitride was investigated. For such a composite without an interfacial carbon coating the values for the thermal conductivity transverse to the fiber direction agreed very well with the values calculated from composite theory using experimental data parallel to the fiber direction, regardless of the ambient atmosphere. However, for a composite made with carbon-coated fibers the experimental values for the thermal conductivity transverse to the fiber direction under vacuum at room temperature were about a factor of 2 lower than those calculated from composite theory assuming perfect interfacial thermal contact. This discrepancy was attributed to the formation of an interfacial gap, resulting from the thermal expansion mismatch between the fibers and the matrix in combination with the low adhesive strength of the carbon coating. In nitrogen or helium the thermal conductivity was found to be higher because of the contribution of gaseous conduction across the interfacial gap. On switching from vacuum to nitrogen a transient effect in the thermal diffusivity was observed, attributed to the diffusion-limited entry of the gas phase into the interfacial gap. These effects decreased with increasing temperature, due to gap closure, to be virtually absent at 1000°C.     

聚丙烯/石墨烯微片/碳化硅复合材料微观形态与导电导热性能研究

采用熔融共混法制备聚丙烯/石墨烯微片/碳化硅(PP/GNP/SiC)复合材料,研究了SiC用量对PP/GNP/SiC复合材料的微观形态、结晶度和导电导热性能的影响。SEM与XRD测试结果表明,SiC粒子有助于提高拉伸力场对GNP的剥离效果以及GNP在PP基体中的分散程度,随着SiC粒子用量的增加,GNP的片径尺寸和片层厚度均减小,并与SiC粒子相互搭接。导电导热分析结果表明,随着SiC粒子用量的增加,PP/GNP/SiC复合材料的电导率先升高后降低,热导率逐渐提高。SiC用量为5%时,复合材料的电导率最高;SiC用量为20%时,复合材料的热导率最高。     

Simultaneously Improved Thermal Conductivity and Dielectric Properties of NBR Composites by Constructing 3D Hybrid Filler Networks

This work aims to address the heat accumulation issue in electronic components during high-frequency operation through the preparation of novel thermally conductive composites. First, polydopamine (PDA) and in-situ growth of silver (Ag) nanoparticles are applied for the surface modification of graphene oxide (GO) and carbon nanotube (CNT) to prepare pGO@Ag and pCNT@Ag hybrid filler, respectively. Then, nitrile butadiene rubber (NBR) is chosen as the polymeric matrix and simultaneously incorporated with both pGO@Ag and pCNT@Ag to prepare polymeric composites with excellent thermal conductivity (TC) and dielectric constant (ɛ_r). Due to the construction of 3D heat conduction networks by utilizing 2D pGO@Ag and 1D pCNT@Ag, the fabricated NBR composites achieved the maximum TC of 1.0112 W/(mK), which is 636% higher than that of neat NBR (0.1373 W (mK)⁻¹). At the filler loading of 9 vol%, the TC of pGO@Ag/pCNT@Ag/NBR composite is 152% that of GO/CNT/NBR composite (0.6660 W (mK)⁻¹). Moreover, due to electron polarization effect of GO and CNT and micro-capacitor effect of Ag nanoparticles, a large ɛ_r of 147.12 is attained at 10 Hz for NBR composites. Overall, the development of dielectric polymer materials with high TC is beneficial for enhancing the service life and safety stability of the electronic components.     

预测聚合物基复合材料导热系数方法综述

由聚合物与高导热填料共混制得的导热聚合物基复合材料,被应用于防腐和节能要求较高的换热场合,符合换热设备新材料的要求;而聚合物基复合材料的等效导热系数预测比较复杂。总结了预测聚合物基复合材料等效导热系数的多种方法,包括最小热阻力法、热阻网络法、傅里叶定律法、均匀化方法和逾渗理论方法,归纳了这些模型和方法的特点,对应用这些模型和方法提出了建议。     

Studies on Preparation and Property Researches of EP/SiC Thermal Conductivity Composites

The epoxy resin/silicon carbide thermal conductivity composites were prepared via casting method. The content of SiC and coupling reagents effecting on the thermal conductivity, mechanical and thermal properties of composites were investigated. Results revealed that the thermal conductivity properties of the composites were improved with the increasing mass fraction of SiC, and the thermal conductivity coefficient λ was 0.7152 W/mk with 50% mass fraction of SiC, being over 3 times of that of native epoxy resin. The flexural strength and impact strength of the EP/SiC composites increased firstly, but decreased with excessive addition of SiC, and the properties of EP/SiC composites were maximum with 10 wt% SiC. DSC and TGA analysis showed that the glass transition temperature (Tg) of composites decreased, but the heat resistance increased with the addition of SiC. SEM observation of impact fracture revealed that the impact strength had the relationships of large or small fracturing ability and the fracturing extended ability and the resin elasticity deformation.     

高分子复合材料导热性能研究

以Al2O3、MgO和BN三种无机填料作为尼龙6(PA6)的导热填料,研究填料的种类、填充量、粒径大小和粒径配比等对复合材料热导率的影响。结果表明:PA6基复合材料的热导率随导热填料填充量的增加而增大,随导热系数大的填料填充量的增加增大较快;导热系数大的填料的粒径对复合材料的导热系数的影响比较明显;导热系数大的填料,不同粒径的复配可以显著提高复合材料的导热系。     

ZnO/EP复合材料的制备及其导热性能

采用溶胶-凝胶法制备纤锌矿型氧化锌(zinc oxide,ZnO)粉体,考察了煅烧温度对ZnO粉体质量的影响;将不同煅烧温度获得的ZnO填充于环氧树脂(epoxy resin,EP)得到系列ZnO/EP复合材料,采用红外光谱仪(Fourier transform infrared spectroscopy,FTIR)和...     

SiC纳米粉体悬浮液导热系数研究

本文作采用非稳态热丝法,测量了水中加平均粒为25nm的碳化硅粉（简称n-SiC),乙二醇中加n-SiC,水中加平均粒径为0.6μm的碳化硅粉（简称μ-SiC）和乙醇中加μ-SiC等4个系列不同固体积含量悬浮液的有效热系数,实验结果表明：对于所研究的悬浮液,其有效导热系数相对增加量随固相加入量的增加而线性增加;固相颗粒形貌对有效导热系数相对增加量有显著影响;基体液体虽对有效导热系数相对增加量无明显影响,但有效导热系数的绝对量由基体液体的导热系数决定。     

热塑性聚酰亚胺复合材料导热性能研究

采用稳态热板法测定铜粉（Cu）填充热塑性聚酰亚胺（TPI）复合材料的热导率，研究了Cu填充量对复合材料的力学性能和导热性能的影响，初步探讨了温度与复合材料热导率的关系。通过扫描电子显微镜观察了复合材料的微观形态。在此基础上，理论计算复合材料热导率。研究表明，Cu填充TPI可有效提高复合材料力学性能和导热性能。当Cu体积分数提高到26％时，填料聚集形成导热链，Cu／TPI复合材料的热导率是纯TPI树脂的3．5倍；当填料含量低于10％时，Maxwell—Eucken模型适合预测复合材料热导率；基于导热链考虑的Y．Agan模型可较好地反映复合材料热导率随填料含量的变化情况；随着温度的升高，Cu／TPI复合材料热导率先增大后趋于平缓。     

High Thermal Conductivity Polymer Composites Fabrication through Conventional and 3D Printing Processes: State-of-the-Art and Future Trends

The lifespan and the performance of flexible electronic devices and components are affected by the large accumulation of heat, and this problem must be addressed by thermally conductive polymer composite films. Therefore, the need for the development of high thermal conductivity nanocomposites has a strong role in various applications. In this article, the effect of different particle reinforcements such as single and hybrid form, coated and uncoated particles, and chemically treated particles on the thermal conductivity of various polymers are reviewed and the mechanism behind the improvement of the required properties are discussed. Furthermore, the role of manufacturing processes such as injection molding, compression molding, and 3D printing techniques in the production of high thermal conductivity polymer composites is detailed. Finally, the potential for future research is discussed, which can help researchers to work on the thermal properties enhancement for polymeric materials.