导热改性碳纤维增强聚合物复合材料的力-热特性

借助钉扎的方法制备了一种掺杂铜柱的三相碳纤维增强聚合物复合材料,以提高其厚度方向的导热性能。在传统混合定律模型的基础上,考虑钉扎铜柱的特征长度与排布形式的影响,提出了一种改进的理论模型来预报该新型三相复合材料的导热性能,并探讨了导热改性对其力学性能的影响。结果表明,改进的理论预报模型对这种三相复合材料导热性能的预报更为准确,尤其是在钉扎铜柱体积分数较小时。在研究范围内,这种钉扎方法导热改性效果明显,力-热综合性能较好。复合材料导热性能随着钉扎铜柱体积分数的提高而增加,且增加速率不断提高,这主要源于铜柱间热影响区的产生;复合材料拉伸性能及层间剪切性能随着钉扎铜柱体积分数的增加而降低,且降低速率不断减小。当钉扎铜柱体积分数相同时,钉扎铜柱的特征长度与排布形式对复合材料导热性能与拉伸性能及层间剪切性能的影响不大。材料失效主要以钉扎孔位置挤压开裂破坏占主导,钉扎体与基体界面间的自然连接性能较弱,预计通过金属镀铜法加以改善,并可进一步提升复合材料力-热一体化特性。

ACR/CPVC/石墨粉体共混导热材料的研究

使用丙烯酸酯共聚物(ACR)作为氯化聚氯乙烯(CPVC)的改性剂,使用超微细石墨粉体做填料,制备了具有导热性能的共混材料。实验结果表明,该材料的导热系数可以提高近20倍,维卡耐热温度达到135℃。

Microstructure and properties of Cu matrix composites reinforced with surface-modified Kovar particles

The thermal conductivity of Cu/Kovar composites was improved by suppressing element diffusion at the interfaces through the formation of FeWO_(4)coating on the Kovar particles via vacuum deposition.Cu matrix composites reinforced with unmodified(Cu/Kovar)and modified Kovar(Cu/Kovar@)particles were prepared by hot pressing.The results demonstrate that the interfaces of Cu/FeWO_(4)and FeWO_(4)/Kovar in the Cu/Kovar@composites exhibit strong bonding,and no secondary phase is generated.The presence of FeWO_(4)impedes interfacial diffusion within the composite,resulting in an increase in grain size and a decrease in dislocation density.After surface modification of the Kovar particle,the thermal conductivity of Cu/Kovar@composite is increased by 110%from 40.6 to 85.6 W·m^(-1)·K^(-1).Moreover,the thermal expansion coefficient of the Cu/Kovar@composite is 9.8×10^(-6)K^(-1),meeting the electronic packaging requirements.

Design and preparation of Al-Fe-Ce ternary aluminum alloys with high thermal conductivity

Ce element was introduced to modify Al−2%Fe(mass fraction)binary alloy.The microstructures,crystallization behavior,electrical/thermal conductivities and mechanical properties of these alloys were systematically investigated.The results indicated that the appropriate Ce addition decreased the recalescence temperature and growth temperature of Al−Fe eutectic structure,improved the morphology and distribution of Fe-containing phase,and simultaneously increased the conductivity and mechanical properties.The annealed treatment improved the thermal conductivity of these alloys due to the decreasing concentration of point defects.Rolling process further broke up the coarser Fe-containing phases into finer particles and made the secondary phases uniformly distributed in theα(Al)matrix.After subsequent annealing treatment and rolling deformation,the thermal conductivity,ultimate tensile strength and hardness of the Al−2%Fe−0.3%Ce(mass fraction)alloy reached 226 W/(m·K),(182±1.4)MPa and HBW(49.5±1.7),respectively.

Performance enhancement of filled-type solar collector with U-tube

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube(HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little.Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

Modified graphite filled natural rubber composites with good thermal conductivity

The rubber composites with good thermal conductivity contribute to heat dissipation of tires. Graphite filled natural rubber composites were developed in this study to provide good thermal conductivity. Graphite was coated with polyacrylate polymerized by monomers including methyl methacrylate, n-butyl acrylate and acrylic acid. The ratios between a filler and acrylate polymerization emulsion and those between monomers were varied. Eight types of surface modification formulas were experimentally investigated. Modification formula can affect coating results and composite properties greatly. The best coating type was achieved by a ratio of1:1 between methyl methacrylate and n-butyl acrylate. The coating of graphite was thermally stable in a running tire. Filled with modified graphite, the tire thermal conductivity reached up to 0.517–0.569 W·m-1·K-1. In addition, the mechanical performance was improved with increased crosslink density, extended scorch time and short vulcanization time.

Modified series model for cross-plane thermal conductivity of short-period Si/Ge superlattices

Superlattices have great application potentials in thermo-electric materials and solid laser techniques.Their complicated heat transport mechanisms due to size effects,multi-interfaces and mini-band are very important issues for the prediction of thermal conductivity.In this paper,the short-period Si/Ge superlattices are investigated by a modified series model based on the Debye-Callaway description.The Lambert Law is used to describe the phonon emission within hemisphere space.In addition,the phonon interface transmission coefficients obtained from the phonon wave packet simulation are incorporated into boundary condition of the model,which removes the fitting parameters in the model.Better agreement with experiment is obtained.The effects of temperature,wavelength-dependent phonon transmission,superlattice periods,as well as the thickness of Ge layer are considered in this paper.