硅/碳复合材料的高温热解法制备及其电化学性能

采用高温热解方法成功地合成了高容量硅/碳复合负极材料.通过X射线衍射分析、热重分析、扫描电子显微镜观察、透射电子显微镜观察、恒电流充放电测试、循环伏安法等手段研究了复合材料的性能.结果表明：硅/碳复合材料由Si、C以及少量SiO2组成;硅/碳复合材料中碳的质量分数约在39%左右;经电化学性能测试,在电流0.2 mA下,该硅/碳复合材料首次充电容量768 mAh·g-1,首次库仑效率75.6%,70次循环后可逆比容量仍为529 mAh·g-1,平均容量衰减率为0.44%.这些性能改善归因于硅/碳复合材料中碳的引进,硅表面存在的碳涂层提供了一个快速锂运输通道,降低了电池的阻抗并且充放电过程中稳定了电极的组成.     

碳纳米管增强一维高导热C/C复合材料的微观结构与物理性能

以中间相沥青基炭纤维和中间相沥青为主要原料,并添加一定量多壁碳纳米管,通过热压成型和高温热处理工艺制备一维高导热C/C复合材料。采用偏光显微镜、扫描电镜、激光热导仪、电子万能试验机等对复合材料的微观结构、导热性能和力学性能进行表征。结果表明,碳纳米管的添加导致复合材料的孔隙率下降和体积密度升高,而且对复合材料的力学性能及不同方向的导热性能都有显著影响。随着碳纳米管添加量的增加,复合材料沿炭纤维轴向的室温热扩散系数逐渐降低,而垂直于纤维轴向的抗弯强度和室温热扩散系数均呈现先上升后下降的趋势。经过2900℃石墨化处理后,添加体积分数3%碳纳米管的复合材料垂直于纤维轴向的抗弯强度为113.4 MPa、热扩散系数为40.1mm~2/s,较未掺杂碳纳米管时分别提高了56%和79%。     

竹炭/硅橡胶高导电复合材料的制备及性能研究

以竹炭为导电填料,通过改变竹炭、气相法白炭黑、羟基硅油、过氧化二异丙苯(DCP)的添加量,以正交试验设计法对竹炭/硅橡胶复合材料的导电性能和力学性能进行了研 究。分析了竹炭的体积电阻率、粒径以及竹炭的添加量对竹炭/硅橡胶复合材料导电和力学性能的影响。结果表明：当甲基乙烯基硅橡胶(MVQ)、竹炭(粒径小于25 μm,体积电阻率 为0.11 Ω·cm)、气相法白炭黑、DCP、羟基硅油质量比为100∶130∶3∶3∶2时,制备的复合材料的电阻率为0.63 Ω·cm,拉伸强度为118 MPa,伸长率为132 %,达到了竹炭/ 硅橡胶高导电复合材料的体积电阻率要求。     

纳米碳/聚偏二氟乙烯高介电复合材料

以多壁碳纳米管及多层石墨烯作为添加剂与聚偏二氟乙烯基体复合,制备介电性能优异的纳米碳/聚合物复合材料。通过SEM,TEM,AFM,XPS,FT-IR等手段对添加剂的结构、成分及其在聚合物基体中的分散性进行了表征。对多壁碳纳米管进行羧基及酯基修饰后,提高其在聚合物基体中的分散性,复合材料的介电性能明显提高。对多层石墨烯进行强碱水热处理后,多层石墨烯表面羟基含量增加,多层石墨烯/聚偏二氟乙烯复合材料的导电阈值增加,复合材料的介电性能大大增强,表现出比碳纳米管掺杂的复合材料更加优异的介电性能。     

纳米碳/聚偏二氟乙烯高介电复合材料

以多壁碳纳米管及多层石墨烯作为添加剂与聚偏二氟乙烯基体复合,制备介电性能优异的纳米碳/聚合物复合材料。通过SEM,TEM,AFM,XPS,FT-IR等手段对添加剂的结构、成分及其在聚合物基体中的分散性进行了表征。对多壁碳纳米管进行羧基及酯基修饰后,提高其在聚合物基体中的分散性,复合材料的介电性能明显提高。对多层石墨烯进行强碱水热处理后,多层石墨烯表面羟基含量增加,多层石墨烯/聚偏二氟乙烯复合材料的导电阈值增加,复合材料的介电性能大大增强,表现出比碳纳米管掺杂的复合材料更加优异的介电性能。     

Thermal conductivity measurement of InGaAs/InGaAsP superlattice thin films

The thermal conductivities of InGaAs/ InGaAsP superlattices with different period lengths were measured from 100 to 320 K using 3ω method. In this temperature range, the thermal conductivities were found to decrease with an increase in temperature. For the period length-dependant thermal conductivity, the minimum value does exist at a certain period length, which demonstrates that at a short period length, superlattice thermal conductivity increases with a decrease in the period length. When the period is longer than a certain period length, the interface thermal resistance dominates in phonon transport. The experimental and theoretical results confirmed the previous predictions from the lattice dynamics analysis, i.e. with the increase in period length, the dominant mechanisms of phonon transport in superlattices will shift from wave mode to particle mode. This is crucial for the cutoff of the phonons and lays a sound foundation for the design of superlattice structures.     

聚丙烯腈改性碳纳米管复合材料的电性能

采用溶液聚合的方法制备聚丙烯腈,对聚丙烯腈进行热处理改性后,与碳纳米管共混制备复合材料.与未改性处理的复合材料相比,电导率提高了2个多数量级.用FTIR、Raman和XPS等方法进行研究,结果表明聚丙烯腈经热处理改性后,部分腈基(—C=N)转变为亚胺基(-C=N),其链状结构向环状结构转化,MWNTs上的π电子与改性后聚丙烯腈的π电子之间形成强的π-π共轭,增强了改性聚丙烯腈与碳纳米管之间的相互作用,提高了复合材料的导电性能.     

C/C-SiC复合材料的导热性能及其影响因素

以炭纤维针刺毡为预制体,采用化学气相渗透法和熔融渗硅法相结合制得C/C-SiC复合材料;研究C/C-SiC材料在室温至1300℃之间的导热性能以及预制体结构、基体炭结构和石墨化处理对其热扩散率的影响.研究结果表明:C/C-SiC材料的比热容随着温度的升高不断增大,在700℃时达到最大值2.18 J/(g·K),随后降至1300℃时的0.57 J/(g·K),其导热系数在1300℃时为3.95 W/(m·K);C/C-SiC材料的热扩散率在室温时为0.12 cm2/s,随着温度的升高不断降低并趋于常量,平行摩擦面方向的热扩散率明显比垂直于摩擦面方向的大;以全网胎为预制体的C/C-SiC材料其垂直和平行摩擦面的热扩散率相当,树脂炭质量分数增大及石墨化处理均可显著提高C/C-SiC材料的热扩散率.     

Thermal conductivity model of filled polymer composites

Theoretical and empirical models for predicting the thermal conductivity of polymer composites were summarized since the 1920s. The effects of particle shape, filler amount, dispersion state of fillers, and interfacial thermal barrier on the thermal conductivity of filled polymer composites were investigated, and the agreement of experimental data with theoretical models in literatures was discussed. Silica with high thermal conductivity was chosen to mix with polyvinyl-acetate (EVA) copolymer to prepare SiO₂/EVA co-films. Experimental data of the co-films’ thermal conductivity were compared with some classical theoretical and empirical models. The results show that Agari’s model, the mixed model, and the percolation model can predict well the thermal conductivity of SiO₂/EVA co-films.     

Thermal conductivity of nanoscale thin nickel films

The inhomogeneous non-equilibrium molecular dynamics (NEMD) scheme is applied to model phonon heat conduction in thin nickel films. The electronic contribution to the thermal conductivity of the film is deduced from the electrical conductivity through the use of the Wiedemann-Franz law. At the average temperature of T=300 K, which is lower than the Debye temperature ΘD=450 K, the results show that in a film thickness range of about 1?11 nm, the calculated cross-plane thermal conductivity decreases almost linearly with the decreasing film thickness, exhibiting a remarkable reduction compared with the bulk value. The electrical and thermal conductivities are anisotropic in thin nickel films for the thickness under about 10 nm. The phonon mean free path is estimated and the size effect on the thermal conductivity is attributed to the reduction of the phonon mean free path according to the kinetic theory.