纳米材料改性树脂基耐烧蚀材料研究新进展

综述了近年来纳米材料改性树脂基耐烧蚀材料的研究进展。介绍了碳纳米管、石墨烯、蒙脱土、纳米SiO2、纳米碳粉等纳米材料在改性烧蚀材料中的研究近况,详细探讨和比较了改性材料的热稳定性、成炭率、力学性能等,同时分析了纳米材料改性树脂材料中存在的问题,并预测了纳米材料改性耐烧蚀树脂的发展趋势。提出纳米材料,特别是新型的纳米碳材料改性树脂基耐烧蚀材料的研究将是很有发展前景的研究领域,并会进一步得到人们的重视。     

三种碳纳米材料改性PTFE复合材料摩擦磨损特性

对3种碳纳米材料(碳纳米管、纳米石墨及碳黑)/PTFE(聚四氟乙烯)复合材料进行了摩擦磨损性能研究,对磨损表面进行了分析。结果表明:3种碳纳米材料均可改善PTFE复合材料耐磨性,以纳米碳黑改善效果较好,其最佳添加含量为7%。纳米石墨可减小PTFE复合材料摩擦系数,碳纳米管和纳米碳黑会增大PTFE复合材料摩擦系数,且含量越高,复合材料摩擦系数增幅越大。无定形纳米碳黑对PTFE耐磨性的改善效果较好,其表面为轻微粘着磨损;结晶型纳米石墨和碳纳米管与PTFE相容性差,其表面为严重粘着磨损。     

改性碳纳米材料在低温燃料电池中的应用

碳纳米材料(如炭黑、介孔碳、碳纳米管、石墨烯、碳纳米纤维、碳纳米角等)因其优异的电学性能和结构特性(良好的导电性能和超大的比表面积),被研究者广泛用作低温燃料电池贵金属催化剂的载体.然而,作为催化剂载体的这类碳纳米材料通常都存在电化学腐蚀的问题,碳载体的腐蚀通常会导致贵金属纳米催化剂的聚集,这将使催化剂的性能降低.为了改善碳载体的抗腐蚀性能,提高金属纳米粒子的活性和稳定性,许多研究工作致力于制备特殊结构的碳纳米材料,或对碳纳米材料进行表面修饰、掺杂等.与此同时,为了取代价格昂贵的贵金属催化剂,非贵金属催化剂的研究也成为一大热点,掺杂碳纳米材料就是研究热点之一.对近几年来围绕碳纳米材料制备、改性,以及这些改性碳纳米材料作为金属纳米粒子载体等的研究工作做了较为详细的综述,同时介绍了掺杂碳纳米材料作为氧还原催化剂的研究进展.     

改性碳纳米材料在低温燃料电池中的应用

碳纳米材料(如炭黑、介孔碳、碳纳米管、石墨烯、碳纳米纤维、碳纳米角等)因其优异的电学性能和结构特性(良好的导电性能和超大的比表面积),被研究者广泛用作低温燃料电池贵金属催化剂的载体。然而,作为催化剂载体的这类碳纳米材料通常都存在电化学腐蚀的问题,碳载体的腐蚀通常会导致贵金属纳米催化剂的聚集,这将使催化剂的性能降低。为了改善碳载体的抗腐蚀性能,提高金属纳米粒子的活性和稳定性,许多研究工作致力于制备特殊结构的碳纳米材料,或对碳纳米材料进行表面修饰、掺杂等。与此同时,为了取代价格昂贵的贵金属催化剂,非贵金属催化剂的研究也成为一大热点,掺杂碳纳米材料就是研究热点之一。对近几年来围绕碳纳米材料制备、改性,以及这些改性碳纳米材料作为金属纳米粒子载体等的研究工作做了较为详细的综述,同时介绍了掺杂碳纳米材料作为氧还原催化剂的研究进展。     

化学处理法制备碳包铜导热纳米流体及其性能表征

氩电弧等离子体法制备碳包铜纳米粒子,采用双氧水化学处理和添加十二烷基苯磺酸钠两种方法制备碳包铜-水纳米流体,探讨了不同分散方法对碳包铜纳米流体导热性能的影响.结果表明,双氧水化学处理碳包铜纳米粒子制备水介质分散体系具有比添加分散剂制备分散体系更高的导热性能.采用化学处理法,添加质量分数为2.0%的碳包铜-水纳米流体导热...     

液相脉冲激光轰击石墨制备碳纳米材料研究进展

碳纳米材料具有特殊的力学、电学及物化性能,在微电子、航空航天、军用材料等领域具有广阔的应用前景,利用脉冲激光高效、可控制备新型碳纳米材料已成为研究热点。简要介绍了激光与碳材料的相互作用及纳米粒子的成形机理,详细阐述了液相脉冲激光制备纳米金刚石、碳纳米管、石墨烯等碳纳米材料的过程及其影响因素,并展望了激光轰击石墨制备碳纳米材料的主要研究方向。     

纳米材料改性聚磷酸铵在聚合物阻燃中的应用研究进展

综述了纳米材料改性聚磷酸铵(APP)的方法及其在聚合物材料中的协同阻燃作用。重点讨论了纳米二氧化硅(SiO2)、纳米碳酸钙(CaCO3)、海泡石、碳纳米管、纳米纤维素、纳米蒙脱土和可膨胀石墨改性APP协同阻燃聚合物材料方面取得的研究成果。提出了纳米材料改性APP在阻燃应用中存在的一些问题。     

石墨的纳米结构组装

本文在分析石墨微观结构和性能基础上, 综合分析了石墨加工改性方法, 提出了石墨纳米结构组装的概念, 介绍了几种石墨纳米结构组装的方法。通过结构组装, 引入纳米功能粒子, 制造活性功能空间, 合成新型石墨功能材料; 通过制备石墨层间化合物、碳石墨合金等方法引入纳米功能粒子组装碳石墨材料; 通过打开石墨层片, 制备二维层状材料制备纳米石墨烯片, 可以采用氧化活化等制造孔隙结构增加活性空间; 通过调节石墨晶体排布方向减少石墨材料的性能异向性, 提高性能均匀性; 通过石墨结构纳米组装设计, 设计新型石墨功能材料。纳米尺度的石墨加工和改性有可能推动石墨矿物资源的有效利用, 开发新型石墨储能材料和石墨烯片材料。     

微纳米复合导热材料的制备及导热性能

采用超声处理方法将膨胀石墨剥离成微纳米石墨片,并以制备的微纳米石墨片为导热填料采用溶液共混法对聚偏氟乙烯(PVDF)进行改性,制备出微纳复合导热材料。通过扫描电子显微镜对其微观结构进行了表征,结果表明通过超声处理可以使膨胀石墨发生部分剥离得到微纳米石墨片。导热性能测试结果表明,复合材料的导热性能随着超声处理时间的增加而增加;当超声处理时间为150min时,复合导热材料的导热系数是膨胀石墨填充PVDF的1.8倍。     

纳米SiO_2和石墨改性相变储热微胶囊的研究

以固体石蜡为相变芯材,三聚氰胺-尿素-甲醛共缩聚树脂为囊壁,采用原位聚合法制备了微胶囊型相变储热材料;并针对该相变材料热导率低及亲水性差缺点,用石墨和纳米SiO2对芯材和微胶囊进行了导热性和表面性能的改性研究。采用光学显微镜(OM)、红外光谱仪(FTIR)、差示扫描量热仪(DSC)、热重分析仪(TGA)等对产品的表面形态、化学结构、热性能等进行了测试和表征。结果表明:石蜡微胶囊化后能保持原有的储热特性,相变焓为47.5J/g;球状微胶囊平均粒径为45μm,表面粗糙,石蜡包封率达80%;纳米SiO2改性后微胶囊亲水性、耐热性能、机械强度均增强;石墨改性后导热性提高。     

碳纤维/环氧树脂预浸料固化过程中的热导率测定

采用调制式差示扫描量热技术(MDSC)实现了碳纤维/环氧预浸料固化过程中的热导率(垂直纤维方向和平行纤维方向)测定。在实验基础上建立了预浸料固化过程中的热导率二元二次函数模型, 确定了热导率随温度及固化度变化的函数关系。结果表明: T800/环氧预浸料沿纤维方向的热导率为1.15~1.40 W/(m·K), 垂直纤维方向热导率为0.85~1.25 W/(m·K)。在相同温度下, 预浸料的热导率值随固化度的增大而减小; 在相同固化度条件下, 预浸料的热导率值随温度的升高而增大。验证结果表明, 拟合所得热导率二元二次函数关系用于预浸料固化过程的数值模拟时, 将提高参数的准确性。     

The mechanical properties and thermal conductivity of carbon/carbon composites with the fiber/matrix interface modified by silicon carbide nanofibers

For modification, silicon carbide nanofibers (SiCNFs) are uniformly dispersed on the fiber surface of the unidirectional carbon preform. The modified unidirectional carbon preform was then densified to obtain SiCNF–C/C composites by chemical vapor deposition (CVD). The microstructure of SiCNF–C/C composites was investigated. The mechanical properties and thermal conductivity of the modified composites were analyzed as well. Results show that PyC preferentially deposits on the surface of SiCNFs with high degree of order. The interface between carbon fibers and matrix has high texture, resulting in a good bonding between them. The mechanical properties of C/C composites are adjusted. After modification, the fracture mode is changed and the flexural strength is enhanced, especially in vertical direction. The thermal conductivity of modified composites is also enhanced in both vertical and parallel directions.     

Structure and properties of cocoons and silk fibers produced by <Emphasis Type="Italic">Hyalophora cecropia</Emphasis>

This paper shows that silk fibers produced by cecropia (Hyalophora cecropia) have similar tensile properties but different amino acid composition than that of mulberry (Bombyx mori) silk. The cecropia fibers are also much finer and have better strength and modulus than tasar silk, the most common non-mulberry silk. Cecropia is one of the largest silk producing moths and has similar lifecycle to that of mulberry silk but is easier to grow and produces larger cocoons than mulberry silk. In this study, we have characterized the composition, morphology, physical and tensile properties, and thermal behavior of the cecropia silk. Cecropia cocoons have a three tier structure and are larger (750 mg) than the cocoons produced by B. mori (650 mg). Fibers in the three layers in cecropia cocoons have tensile properties similar to that of B. mori silk but are finer (1.7–2 denier) and have higher strength (3.8–4.3 g/denier) and modulus (68–92 g/denier) than tasar silk.     

表儿茶素修饰BN对BN@表儿茶素/环氧树脂复合材料性能的影响

用表儿茶素(EC)作为非共价改性剂,对BN进行表面处理,研究了不同质量分数EC修饰的BN对BN@EC/环氧树脂(EP)复合材料性能的影响。采用FTIR、 XRD、 SEM、 TG等对BN、 BN@EC和BN@EC/EP复合材料的结构和性能进行表征,研究证明EC对BN改性成功,且改性过程中没有对BN的晶型结构产生影响;经EC改性后的BN在树脂基体中的分散性得到改善;SEM测试结果表明,与未改性的BN粒子相比,经EC改性后的BN粒子的团聚程度降低, BN@EC在基体中的分散性更好;经改性的BN@EC在水中的稳定性得到提高;当EC质量分数为10wt%时, BN@EC/EP复合材料的导热性能最好,热导率达1.27 W·m^-1·K^-1,与BN/EP的热导率(0.62 W·m^-1·K^-1)相比提高了106%。最后,分析了EC的加入对复合材料热稳定性能和硬度的影响,结果表明, EC的加入会略微提高复合材料的热稳定性。     

Thermal Diffusivity of Compounds Loaded with Carbon Nanofibers

In this work, the thermal enhancement in silicone grease-based compounds as a function of carbon nanofiber (CNF) volume fraction was investigated. The thermal diffusivity of the samples was determined by a photopyroelectrical technique with a sample thickness scan. The results show that heat transport on these compounds strongly depends on the CNF volume fraction, due to the high thermal conductivity of CNF compared to the matrix; hence, a low loading percentage of the fibers produce a significant growth in the thermal diffusivity of the composite. The results show that the thermal diffusivity values of the CNF-silicone composite are comparable with commercial thermal compounds based on diamond and Ag microparticle fillers. The thermal conductivity of the samples was calculated, and its enhancement was analyzed using a modified Lewis–Nielsen model, taking into account the dependence of the maximum packing fraction and the form factor with the aspect ratio of the CNF. The influence of the Kapitza thermal resistance was discussed. These materials might find practical applications in systems in which the CNF improves the ebbing of heat away from semiconductor devices or in any other application in which heat dissipation is needed.     

石墨和炭纤维分别改性热塑性聚酰亚胺 复合材料的导热行为

采用石墨、 炭纤维填充改善热塑性聚酰亚胺(TPI)材料的导热性能, 研究了填料物性对材料力学性能和导热行为的影响。在此基础上, 用Nielsen理论模型和有限元方法模拟了复合材料的导热行为, 进一步探讨了填料形状对材料导热系数的影响。研究表明: 炭纤维、 石墨填充TPI均能提高复合材料的导热性能; 用Nielsen理论模型预测石墨、 炭纤维填充TPI材料导热系数与实验值存在一定偏差; 采用有限元法模拟二维复合材料稳态导热行为, 能有效地预测复合材料的导热系数。基于材料内部热流分布模拟分析发现, 填料自身导热性能对复合材料导热行为的影响不明显; 与圆形填料相比, 方形填料改善材料导热性能效果显著。      

Measurement of the thermal conductivity of individual carbon nanotubes by the four-point three-omega method

The thermal conductivity of individual multiwalled carbon nanotubes was measured by utilizing the four-point-probe third-harmonic method, based on the fact that the third harmonic amplitude and phase as a response to applied alternate current at fundamental frequency, omega, can be expressed in terms of thermal conductivity and diffusivity. To this end, a microfabricated device composed of four metal electrodes was modified to manufacture nanometer-sized wires by using a focused ion beam source. A carbon nanotube could then be suspended over a deep trench milled by the focused ion beam, preventing heat loss to the substrate. Compared with the two-point-probe technique, a significant improvement in accuracy is assured by using four probes, because the contact contribution to the determination of the thermal conductivity is eliminated, making it possible to measure the correct signals of first and third harmonics. The multiwalled carbon nanotube was modeled as a one-dimensional diffusive energy transporter and its thermal conductivity was measured at room temperature under vacuum to be 300 +/- 20 W/mK.     

Computational analysis of the lattice contribution to thermal conductivity of single-walled carbon nanotubes

Molecular dynamics based heat-flux auto-correlation functions are combined with a Green-Kubo relation from the linear response theory to quantify the lattice contribution to thermal conductivity of single-walled carbon nanotubes with three different chiralities (screw symmetries). The interactions between carbon atoms within a nanotube are analyzed using the Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential. The results obtained show that, due to a long-term exponential-decay character of the heat-flux auto-correlation functions, converging values of the lattice thermal conductivities can be obtained using computational cells considerably smaller than the phonon mean free path. However, to obtain accurate values of the thermal conductivity, a spectral Green-Kubo relation and a phonon-based extrapolation function are found to be instrumental for quantifying the thermal conductivity contribution of the long-wavelength phonons not allowed in the computational cells of a finite size. The results further show that chirality of the carbon nanotubes can affect the lattice contribution to the thermal conductivity by as much as 20%. Also, the simulation results of the effect of temperature on the thermal conductivity clearly show a competition between an increase in the number of phonons and an increased probability for phonon scattering at higher temperatures.     

双组元掺杂钛硅再结晶石墨传导性能的研究

用煅烧石油焦作填料,煤沥青作粘结剂,钛粉和硅粉作添加剂,采用热压工艺制备了一系列双组元掺杂再结晶石墨.考察了不同质量配比的添加剂对再结晶石墨的热导率、电阻率和抗弯强度的影响以及微观结构的变化.实验结果表明,与相同工艺条件下制备的纯石墨材料相比较,掺杂15wt％钛粉再结晶石墨的传导以及力学性能有较大幅度的提高.在掺杂钛粉15wt％、硅粉<2wt％时,双组元再结晶石墨的常温热导率随着硅粉的掺杂量的增加有所提高.当掺杂钛粉及硅粉分别为15wt％和2wt％时,再结晶石墨RG-TiSi-152的常温热导率可达494W/m·K.但是当掺杂钛粉15wt％、硅粉>2wt％时,随着硅粉的继续增加,再结晶石墨的常温热导率反而降低.而双组元掺杂钛硅再结晶石墨的导电以及力学性能却随着硅粉的掺杂量的增加而降低.XRD分析表明,对于双组元掺杂钛硅再结晶石墨而言,钛元素最终在材料中以碳化钛形式存在,而硅元素则大都以气态形式被逸出,XRD物相图谱中未发现硅及其碳化物的存在.材料RG-TiSi-152的微晶尺寸La以及晶面层间距d₀₀₂分别为864和0.3355nm.     

石墨烯硅橡胶复合材料的性能研究

本文采用复配的石墨烯、碳纳米管和氧化铝为导热填料制备了具有导热功能的有机硅复合材料。研究了石墨烯、碳纳米管和氧化铝的复配比例对复合材料体积电阻率、导热系数、拉伸强度等性能的影响;同时,以Gr-C-4#样品为基础配方,采用硅烷偶联剂Si-G-1分别对石墨烯、碳纳米管及氧化铝进行改性,并用改性后的填料配制石墨烯硅橡胶复合材料Gr-C-Si-1#,对比样品Gr-C-4^#与Gr-C-Si-1^#的性能差异,分析了改性复配填料对复合材料性能的影响。采用石墨烯硅橡胶复合材料对电缆终端进行了封装,对封装好的电缆终端开展了100、150、200A电流下的温升实验,未出现局部过热,并测定水浸泡前后的电缆终端电阻,封装后的电缆终端电阻未出现明显上升,实验结果表明本材料可以在电缆终端或中间连接处进行灌封,可对封铅连接处的良好的保护作用,工程应用意义重大。