石墨烯片协同氧化铝导热硅脂的制备及其导热性能研究

以石墨烯片和氧化铝(Al_2O_3)粉为导热填料填充到甲基硅油中制备了三种导热硅脂,采用3-ω法测定了所有样品的热导率,结果表明Al_2O_3复合石墨烯片硅脂的热导率达到1.32 W·m~(-1)·K~(-1),明显高于单纯添加石墨烯片和Al_2O_3的导热硅脂的热导率。将这三种导热硅脂装配到电脑中央处理器(CPU)系统中,测试样品的散热性能,发现Al_2O_3复合石墨烯片的导热硅脂具有更好的散热性。实验中选用扫描电子显微镜(SEM)和透射电子显微镜(TEM)测试了材料的形貌。     

多壁碳纳米管长度对导热硅脂导热性能的影响

本文以多壁碳纳米管为添加材料用于改善导热硅脂的导热性能,分别研究了碳纳米管长度和碳管表面改性对硅脂热性能的影响。结果表明碳管长度对硅脂的热性能有明显影响,硅脂的导热性能会随着添加的MWCNT长度的增加而降低,只有当MWCNT的长度小于一定值后,才能有效提高硅脂的导热性能,否则可能会产生相反的效果。碳管表面的功能化处理能提高硅脂的导热性能。透射电子显微镜分析表明,经过表面改性的MWCNT表面发生明显变化,功能团的附着使得碳管之间的分散性增强,从而使添加了改性后的MWCNT/硅脂导热系数增大,热阻降低。     

硅胶除湿转轮性能优化实验研究

为了提高除湿转轮的除湿性能,降低吸附热对除湿性能的影响,将导热硅脂作为传热基质负载在不同扇形区域的硅胶转轮转芯基体表面,搭建硅胶除湿转轮性能优化实验台,研究了除湿转轮动态除湿性能.实验结果表明:硅胶除湿转轮的除湿性能随导热硅脂负载区域的增大先增大后减小,导热硅脂负载区域为2/8时,具有最佳的除湿性能,除湿量达到了0.3...     

液态金属填充型硅脂导热性能实验研究

目前,市售热界面材料一般由固体颗粒和硅油复合制备而成,其普遍存在导热性能差的问题。本文首次提出了一种以室温液态金属流体作为导热填充材料、硅油为基体的新型复合导热硅脂。在前期研究的基础之上,采用对照实验的方法研究了在四种不同的热流密度下,液态金属填充型导热硅脂的实际导热性能。实验结果表明,该新型导热硅脂可大幅降低热源与热沉之间的接触温差,有望实际应用于各类高功率密度电子设备之中。     

石墨烯与纳米颗粒协同提高复合体系热导率

本文详细阐述了石墨烯和球形纳米颗粒间提高复合物热导率的协同效应。石墨烯和纳米颗粒在复合物中可形成紧密堆积结构,该结构阻止了石墨烯的团聚。二维的石墨烯能够在纳米颗粒之间架桥,为复合体系提供了更加有效的声子传输通道,降低了界面热阻。当石墨烯添加量为质量分数1.0%时,导热硅脂的热导率达到了3.45 W/(m·K),EVA复合材料的热导率达到了2.41 W/(m·K);在PC/ABS基体中,石墨烯添加质量分数0.5%时,热导率达到3.11 W/(m·K);在环氧树脂基体中,当负载银的石墨烯填充量为质量分数5.0%时,热导率到达了0.95 W/(m·K)。     

碳纳米管的稳定性研究

石墨晶体结构遭到破坏时,总是碎化为微小尺寸的片状粉末.孤立的石墨烯片在其边缘存在大量的悬挂键,使得石墨烯片的能量较高,状态也不稳定.石墨烯片卷曲形成碳纳米管后,悬挂键减少,系统能量相应降低.另一方面,石墨烯片卷曲形成碳纳米管将产生相应的形变势能,形变势能的产生将抵消由于减少石墨烯片边缘上的悬挂键所带来的能量降低,使碳纳米管的能量可能高于石墨烯片的能量,导致碳纳米管结构的不稳定.在建立碳纳米管生成的力学模型并进行深入理论分析的基础上得出了碳纳米管可以稳定存在的最小直径约为0.32nm的结论. 关键词： 碳纳米管 稳定性 形变势能 键能     

碳纳米管的稳定性研究

石墨晶体结构遭到破坏时，总是碎化为微小尺寸的片状粉末.孤立的石墨烯片在其边缘存在大量的悬挂键，使得石墨烯片的能量较高，状态也不稳定.石墨烯片卷曲形成碳纳米管后，悬挂键减少，系统能量相应降低.另一方面，石墨烯片卷曲形成碳纳米管将产生相应的形变势能，形变势能的产生将抵消由于减少石墨烯片边缘上的悬挂键所带来的能量降低，使碳纳米管的能量可能高于石墨烯片的能量，导致碳纳米管结构的不稳定.在建立碳纳米管生成的力学模型并进行深入理论分析的基础上得出了碳纳米管可以稳定存在的最小直径约为0.32nm的结论.     

基于稳态电热拉曼技术的碳纳米管纤维导热系数测量及传热研究

利用稳态电热拉曼技术测量了碳纳米管纤维对流换热环境下的导热系数. 该方法基于材料拉曼信号与温度之间的关系, 实时探测一维材料在不同电加热(内热源)下的中心点温度, 利用对流环境下的稳态导热模型推导出材料的导热系数, 实现了一维微纳材料热物性的无损化和非接触式测量. 实验发现: 碳纳米管纤维的导热系数远低于单根碳纳米管的导热系数, 但高于碳纳米管堆积床的导热系数. 这表明碳纳米管体材料的热物性主要取决于内部管束的列阵和管束间的接触热阻.     

石墨烯碳纳米管复合结构渗透特性的分子动力学研究

采用经典分子动力学方法研究了压力驱动作用下水在石墨烯碳纳米管复合结构中的渗透特性.研究结果表明,水分子渗透通过石墨烯碳纳米管复合结构的渗透率明显高于石墨烯碳纳米管组合结构.水在石墨烯碳纳米管复合结构中的渗透率随着压强的升高而增大,随着电场强度的增大而减小.考虑了温度和复合结构中双碳管轴心距对水渗透性的影响规律.系统温度越高,水的渗透率越高;随着双碳管轴心距的增加,水的渗透率逐渐降低.通过计算分析水流沿渗透方向的能障分布,解释了各参数变化对水在石墨烯碳管复合结构中渗透特性的影响机理.研究结果将为基于石墨烯碳管复合结构的新型纳米水泵设计提供一定的理论依据.     

石墨烯/硅肖特基太阳能电池的光电特性

以甲烷作为反应气体,利用化学气相沉积法在硅衬底表面上沉积石墨烯薄膜,制备了石墨烯/硅肖特基太阳能电池.利用原子力显微镜和拉曼光谱观察了石墨烯薄膜的表面形貌,并用紫外-可见光光谱仪和光-电流测试仪器研究了石墨烯样品和太阳电池的光电特性.实验结果表明:制备的石墨烯薄膜厚度为几个原子层,薄膜表面均匀,并具有良好的电学特性,石墨烯/硅太阳能电池的能量转换效率可达3.7%.     

Graphene based silicone thermal greases

Two kinds of silicone grease containing graphene nanoplatelets or reduced graphene oxide were prepared, and their thermophysical properties have been investigated. When the volume fraction was 1%, the reduced graphene oxide was the most effective additive to enhance the heat transfer properties of silicone, and graphene nanoplatelet was slightly inferior to the former. While when the concentration was enhanced, the viscosity of silicone grease containing reduced graphene oxide became very large due to its rich pore structure. Graphene nanoplatelet was efficient for the thermal conductivity enhancement of silicone grease, and it provided a thermal conductivity enhancement was up to 668%$668\text{\%}$ (loading of 4.25 vol.%$4.25\text{vol.}\text{\%}$). The experimental result is in excellent agreement with the recently developed theoretical model analyzing the thermal conductivity of isotropic composites containing randomly embedded GNPs, and it validates that graphene is an effective thermally conducting filler to let grease have high thermal conductivity with low filler content.     

Effect of grease type on abnormal vibration of ball bearing

The abnormal vibration of ball bearings lubricated with grease was studied. The test bearings were lubricated with three types of grease: Li soap/silicone oil grease, Na soap/mineral oil grease and Li soap/mineral oil grease. In the experiments, the axial-loaded ball bearings were operated at a constant rotational speed, and the vibration and the outer ring temperatures of the test bearings were measured. In addition, the shear stress and shear rate of the greases were measured by a rheometer. The experimental results showed that the abnormal vibration occurs on the test bearings lubricated with all three types of grease. Based on the experimental results, the generating mechanisms of the abnormal vibrations were discussed. From the discussions, it seems reasonable to conclude: (1) Li soap/silicone oil grease and Na soap/mineral oil grease both have a negative damping moment characteristic. The abnormal vibrations of the ball bearings lubricated with these greases are generated by the negative damping moment. (2) The abnormal vibration of the ball bearings lubricated with Li soap/mineral oil grease is generated by the decreasing positive damping moment of the grease due to the rising temperature.     

Carbon nanotube grease with enhanced thermal and electrical conductivities

A stable and homogeneous grease based on carbon nanotubes (CNTs, single-wall and multi-wall) in polyalphaolefin oil has been produced without using a chemical surfactant. For example, for a 11 wt% (7 vol%) single-wall CNT (diameter 1–2 nm, length 0.5–40 μm) loading, the thermal conductivity (TC) of the grease shows a 60–70% increase compared to that for no nanotube loading. In addition, the grease is electrically conductive, has a high dropping point, good temperature resistance, and does not react with copper at temperatures up to 177 °C. The performance of carbon nanotube grease could be much better with the improvement of nanotube quality and purity. A possible explanation for these results is that of a high loading of CNTs (>10 wt%), they become associated with each other by van der Waals forces in the grease to form three-dimensional percolation networks. Time-dependent magnetic results demonstrate that, even under the influence of a strong outside magnetic field, the TC value remains constant. This phenomenon can be attributed to the existence of networks that makes magnetic alignment of nanotubes impossible.     

微纳米电子器件散热过程中的物理问题

微纳米电子器件的散热问题是目前制约半导体工业发展的重要瓶颈。将电子器件工作时产生的热量传输到封装外壳后再耗散到环境中去需要好几个步骤,每个步骤需要不同的方法,其中有些步骤涉及到了固体中的界面热传导问题和高性能导热材料。文章先介绍了近期关于微纳米尺度器件散热问题中碰到的热传导问题在理论和实验两方面的研究进展。在热传导理论和计算方法方面,作者讨论了傅里叶定律在微纳米尺度的适用性,介绍了玻尔兹曼方程、分子动力学模拟和格林函数方法。在热传导实验方面,介绍了用扫描热显微镜测量样品表面温度和用超快激光反射法测量薄膜材料的热导率及其界面热阻。然后介绍了界面热传导问题,包括界面热阻的计算以及电子—声子相互作用对界面热阻的影响。最后作者介绍了关于高性能导热材料方面的最新进展,包括碳基导热材料、晶格结构类似于石墨烯的氮化硼材料、高分子有机材料以及界面热阻材料。     

Dependence of the solar cell performance on nanocarbon/Si heterojunctions

Solar cells that combine single-crystalline silicon(Si) with graphene(G) have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency(PCE) of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube(CNT) networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals(G/Si and CNT/Si). This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells.     

碳纳米管-石墨烯纳米带过渡连接处的力学稳定性与热传导性质研究

任何的非平面连接,材料连接处的材料失配都能导致材料局部或整体性质的改变.本文以纵向拉开的碳纳米管(CNT)为研究对象,采用非平衡态分子动力学(NEMD)的模拟方法,通过改变CNT纵向拉开的剧烈程度,即CNT向石墨烯纳米带(GNR)过渡转变的开角大小,研究其力学稳定性和热传导性质的变化.结果表明,CNT到GNR的过渡越剧烈,连接处的开角越大,其局部热导率越高,单位长度的热阻越小;对于不同管径的CNT来说,连接处的最大开角恒定不变,为16.3°.     

Controlling Thermal Conductivity of Few-Layer Graphene Nanoribbons by Using the Transversal Pressure

We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations.It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons.This improvement can reach 37.5%in the low temperature region.The pressure dependence of thermal conductivity is also investigated for diferent length,width and thickness of few-layer graphene.Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons.Furthermore,it maybe indicate a so-called pressure-thermal efect in nanomaterials.     

Controlling Thermal Conductivity of Few-Layer Graphene Nanoribbons by Using the Transversal Pressure

We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons. This improvement can reach 37.5% in the low temperature region. The pressure dependence of thermal conductivity is also investigated for different length, width and thickness of few-layer graphene. Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons. Furthermore, it maybe indicate a so-called pressure-thermal effect in nanomaterials.     

新型生物医药实验用低温冷冻干燥机的研制

本课题设计的低温冷冻干燥机以液氮为低温冷源,通过电加热器加热液氮使之汽化,通过控制气体的压力,压出液氮。液氮被压出后流入硅油池的换热器同硅油进行充分换热。在硅油池底部布置一个电加热盘,通过调节加热量,精确控制硅油温度。特制的不锈钢搁板浸入硅油池中进行硅油浴,能够实现良好的传热。测控制系统由上位PC机与下位可编程控制器和数据采集模块共同组成,在PC机上可设置控制参数并进行监控,温度曲线可程序控制,数据采集模块能够自动采集、存储、上传各项数据,数据可以在PC机上处理。