聚合物/石墨纳米复合材料及其电学特性研究进展

从热固性树脂/石墨、热塑性树脂/石墨、橡胶/石墨和导电聚合物/石墨等几个方面综述聚合物/石墨纳米复合材料的研究现状。详细介绍了聚合物/石墨纳米复合材料的逾渗特性、伏安特性和压阻特性。对聚合物/石墨纳米复合材料的发展进行了展望。     

片式电容器用石墨浆料的分散稳定性

以石墨为导电填料,羧甲基纤维素钠(CMC)为分散剂,制备了片式电容器用石墨浆料。用吸光光度法对其进行了稳定性测试,讨论了CMC、聚乙烯醇(PVA)和苯丙乳液用量对浆料稳定性的影响和球磨时间对粒径的影响。结果表明:当CMC干料与石墨的质量比为0.035时,体系稳定性最好。苯丙乳液对体系稳定性影响不大,可作为成膜粘合剂使用。球磨90min为适宜时间,粒径集中在较小的范围,平均粒径6.374μm。     

导电混凝土的微观形貌研究

本文主要研究掺入石墨和碳纤维对混凝土微观形貌和宏观性能的影响,测试了导电混凝土的28天抗压强度和电阻率,通过SEM观察导电混凝土的微观形貌.结果显示石墨可以有效地降低混凝土的电阻率,但对抗压强度有不利影响.只有当石墨掺量高于2%时,导电混凝土的抗压强度才会随着碳纤维掺量的增加而增加,且石墨的层片状结构形貌明显,石墨片之间的片状连接状况较好.当碳纤维掺量为0.8%时,碳纤维与石墨和水化产物之间形成了致密的连接.复掺石墨和碳纤维能够形成致密和较为完整的导电网络,并且有利于混凝土的抗压强度的提高.     

石墨表面化学镀Ni-P非晶的制备与电磁性能

为了提高石墨吸收剂的阻抗匹配能力,改善其吸波性能,采用化学镀法对石墨表面进行镀Ni-P改性。研究了镀层的相组成、形貌、成分和样品的电磁吸波性能。结果表明:石墨表面包覆了一层非晶态Ni-P镀层;与原始石墨相比,在2GHz时,镀Ni-P非晶石墨复合材料的ε′和ε″分别明显降低至6.6和0.4,μ′和μ″分别略微增加至1.08和0.26,其吸收频带得到展宽,在14GHz的最小反射率为–7.0dB,反射率小于–5dB的吸收频带宽达4GHz。     

膨胀石墨体积膨胀率对红外遮蔽性能的影响

膨胀石墨是一种具有潜在军事应用价值的新型光电无源干扰材料。依次以硝酸和磷酸、硝酸和乙酸的混酸为插层剂,高锰酸钾为氧化剂,采用分步插层法制备出了不同体积膨胀率的膨胀石墨;采用扫描电镜分析了膨胀石墨微观结构随膨胀体积的变化;采用静态测试方法测试了不同体积膨胀率膨胀石墨的红外遮蔽性能。结果表明:随膨胀体积的增大,膨胀石墨的孔隙率增大,石墨片层被充分打开;膨胀石墨对红外辐射的遮蔽性能随膨胀体积的增大而增大,当膨胀体积从233 mlg-1增大到450 mlg-1时,其红外遮蔽率从66.43%增大到90.77%。     

微米级可膨胀石墨的制备和表征

选择冰醋酸和浓硫酸为插层物质,从反应物配比、反应温度、反应时间、干燥温度等方面探讨了微米级可膨胀石墨的制备工艺,并对产品粒径、表面形貌和红外消光能力进行了表征.实验结果表明,选择合适的反应物,并控制好反应物比例、反应温度和时间以及干燥温度等工艺条件,即可制得符合要求的微米级可膨胀石墨,该石墨在中、远红外区比微粉石墨具有更好的红外消光能力.     

石墨上多晶硅薄膜的制备及择优取向的调控

利用磁控溅射在石墨衬底上制备了非晶硅薄膜,并使用快速热退火对薄膜进行了晶化处理。XRD分析表明,直接溅射沉积在石墨衬底上的硅薄膜经过快速热退火后具有高度的(220)择优取向。通过在硅薄膜和石墨衬底界面处引入一定厚度的ZnO中间层,晶化后的多晶硅薄膜择优取向实现了从(220)向(400)的转变,从而非常有利于将成熟的制绒工艺应用于该材料体系的电池制备过程中。对于择优取向的转变提出了解释,认为Si(100)面和ZnO(001)面晶格匹配是主要原因。喇曼分析表明ZnO中间层的引入提高了多晶硅薄膜的晶体质量。     

硝酸铁浓度对石墨片上生长的碳纳米管场发射性能的影响

石墨衬底先分别浸泡于0.1~1mol/L不同浓度的硝酸铁溶液后,采用低压化学气相沉积法于700℃在石墨衬底上生长碳纳米管薄膜。根据扫描电子显微镜照片及拉曼光谱分析碳纳米管的形貌和构成。碳纳米管的场发射性能的研究采用标准电流-电压测试。浸泡于0.6mol/L硝酸铁溶液的石墨片上所生长的碳纳米管的场发射性能最佳。     

Efficiency of the intercalation of aluminum atoms under a monolayer and submonolayer two-dimensional graphite film on a metal

Intercalation of aluminum atoms under a two-dimensional graphite film on a metal was studied by high-resolution Auger spectroscopy. The spectra were recorded directly from the highly heated (up to 2100 K) sample. It is shown that the efficiency of this process increases significantly if the film is of the island type, rather than continuous, and if part of the metal surface is not covered with graphite. It is concluded that the graphite-island boundaries are the defects via which the intercalating atoms penetrate under the graphite film.     

水性石墨导电涂料性能研究

研制了以石墨为导电填料,苯丙乳液为基料的水性涂料。分析了石墨、水的用量、固化温度与体积电阻率的关系以及涂层电阻与温度的关系。结果表明:w(石墨)在14%~20%,w(水)在55%~65%,固化温度为70℃时,涂料的导电性能最好,ρv约为0.25Ω·cm。涂料的阻温特性表现为在升温过程中先出现PTC效应,然后出现NTC效应。     

珠光体灰口铸铁激光硬化层中石墨相行为研究

利用光学显微镜、电子探针等微观分析手段对灰口铸铁激光硬化层中石墨相行为进行了较为深入的分析。结果表明,石墨在熔化层中完全溶解,且扩散较均匀;相变硬化层中石墨部分溶解,而扩散不均匀;在过渡层中石墨则基本不溶解。由分析可知,石墨的这些行为与硬化层的组织及硬化效果有极其密切的关系。     

Pill-box capless thermal-heat-pulse annealing of ion-implanted GaAs

A capless annealing method for GaAs, employing short (1-10-s) thermal heat pulses from a graphite strip heater, is described. Results with²⁹Si+ implanted into semi-insulating chromium-doped HB and chromium-doped LEC GaAs are presented. The samples were annealed at temperatures as high as 1000°C in a stationary N2atmosphere with the implanted surface in close contact with a flat graphite strip heater surface. The wafers were covered with a graphite lid, effectively confining the volatile arsenic to a very small volume around the sample and providing a uniform temperature environment. Implantation efficiencies were high, and the quality of the implanted surface remained excellent after annealing.     

Carbothermal reduction growth of ZnO nanostructures on sapphire—comparisons between graphite and activated charcoal powders

Zinc oxide (ZnO) nanostructures were grown by the vapour phase transport (VPT) method on a-plane sapphire substrates via carbothermal reduction of ZnO powders with various carbon powders. Specifically, graphite powder and activated charcoal powder (of larger total surface area but similar mesh size) were used. ZnO nanostructures can be grown at lower temperatures (∼800 °C) using activated charcoal than those required using graphite powder. Furthermore, the morphologies of ZnO nanostructures obtained using activated charcoal were different to those obtained using graphite. At higher temperatures (∼950 °C), where well-aligned nanorods were obtained using graphite powder, no nanostructures were found using activated charcoal. In contrast to previous results on Si substrates we find that the effects on ZnO nanostructure growth on a-sapphire cannot be explained solely in terms of increased Zn vapour pressure due to the enhancement of the carbothermal reduction reaction rate by the high surface area activated charcoal.     

Structural and Chemical Comparison of Graphite and BN/AlN Caps Used for Annealing Ion Implanted SiC

The effectiveness of AlN/BN and graphite annealing caps for ion implanted SiC was examined morphologically, structurally, chemically, and electrically. The AlN/BN cap more effectively blocks the out-diffusion of silicon because it is essentially inert. Relatively small amounts of silicon from the SiC diffuse out into the graphite cap and react with it. This has the effect of lowering the Si vapor pressure so that it does not create blow holes in this relatively weak structure. The graphite cap can be removed easily with an oxygen plasma, while warm KOH has to be used to remove the nitride cap, and not all of it can be removed after an 1800°C anneal. The out-diffusion of silicon through the graphite cap is most severe at 1800°C, where it roughens the SiC surface and forms reaction products when the Si reacts with the graphite at a significant rate. At lower temperatures these reaction products form small particulates on the surface that are visible only at higher magnifications. In those regions where the graphite cap crystallized, isolated morphological damage on the SiC surface was also detected, appearing to be in the vicinity of the grain boundaries. Scratches on the substrate surface were not affected even at temperatures as high as 1800°C.     

钽电容器用石墨导电胶的研究

以石墨粉和热固性树脂混合配成导电胶,分析了石墨粉、稀释剂的用量,固化温度,固化时间等与电阻的关系。结果表明:当石墨含量在25%～35%,稀释剂含量在20%～25%(均为质量分数)时,在150℃下固化2～3 h得到的导电胶导电性最好,能够满足作为钽电容器阴极引出材料的需要。并用“逾渗理论”解释了导电胶的导电机理,与实验所得结论相符。     

Mechanism of graphite baffle gettering in organometallic vapor phase epitaxy; Adsorption of trimethylaluminum on graphite

The adsorption of trimethyaluminum (TMA) on graphite surfaces was investigated using a controlled gas flow system and a molecular beam mass spectrometer. Values for the amount of TMA adsorbed on graphite surfaces under a variety of conditions were determined by analyzing the transient response attending abrupt changes in input gas composition. Significant adsorption of TMA was observed, with a heat of adsorption of 15.7 kcal/mole. When graphite baffles are used in organometallic vapor phase epitaxy, there are several important practical consequences of the adsorption: the gettering of impurities; the doping efficiency; and difficulties in establishing sharp junctions.     

低功率密度激光合成金刚石的相变机制

为了延长激光法合成纳米金刚石的有效作用时间从而提高合成效率,提出采用功率密度低、脉宽长的毫秒脉冲激光照射循环水介质中石墨颗粒合成纳米金刚石的新工艺。高分辨透射电镜(HRTEM)及X射线衍射(XRD)分析结果表明,产物中含大量具有球形单晶体结构或五重孪晶结构的金刚石颗粒(平均颗粒尺寸约为5 nm)。通过对纳米金刚石微观组织结构的分析以及理论计算测算出低功率密度(106W.cm-2)毫秒脉冲激光照射时石墨颗粒表面可达到最高温度5300 K,认为该功率密度毫秒脉冲激光照射石墨颗粒时,不能产生碳等离子体,只能使石墨颗粒熔融,得到液态碳。因此生成纳米金刚石的相变机制为:激光脉冲开始时,石墨颗粒吸收激光能量快速升温并达到熔融状态,激光脉冲过后,碳液滴迅速冷却,金刚石形核并长大得到纳米晶。     

石墨掺杂对B/KNO_3点火药的激光点火特性的影响

用光声检测的实验方法研究石墨掺杂对B／KNO3点火药的激光点火性能的影响。根据对光声谱的分析，指出了石墨掺入B／KNO3会略降低B／KNO3的激光吸收能力并且掺入量增加时，药剂的光吸收能力会有所改善。石墨掺杂会增长B／KNO3的激光点火延迟期，这一规律与石墨掺杂对B／KNO3的吸光性能的影响规律一致。     

质子交换膜燃料电池的垫片机械性能研究

为了将石墨复合材料用于燃料电池的双极板材料中,研究了湿度环境对双极板力学性能的影响。制造了两种类型的样品,对两种样品进行了一系列的实验：吸水率、弯曲和拉伸试验的强度和模量。结果表明,添加石墨复合材料的试样吸水率低于没有石墨/环氧复合材料碳纤维织物的试样,所以有碳纤维织物试样的总吸水率较低。两种试样的弯曲强度和模量均会下降。另外在石墨-颗粒/环氧复合材料中加入碳纤维织物能够显著提高了拉伸强度。     

Effect of different types of carbon on microstructure and arcing behavior of Ag/C contact materials

Silver-carbon (Ag/C) contact materials with different types of carbon, including diamond, graphite, carbon black, and carbon nanotubes were fabricated by high-energy ball milling and hot-pressing. Their microstructures, arcing properties, and stability of the carbon structures were investigated. The results show that Ag/C nanotubes material displays a scallop-like morphology, which is significantly different from the microstructure of other Ag/C materials with dispersed particles. During the process of discharge, the diamond and carbon black in Ag/C materials are partially graphitized, while the morphology and crystal structure of graphite component have little change, indicating the graphite structure of Ag/C materials is the most stable of all.