Investigation on carbon nanomaterials: Coaxial CNT-cylinders and CNT-polymer composite

The macroscopic coaxial carbon cylinders (dia. ∼0.5 cm with varying lengths, ∼ 7–10 cm) consisting of aligned carbon nanotube (CNT) stacks have been prepared by controlled spray pyrolysis method. The coaxial carbon cylinders of CNT stacks have been formed directly inside the quartz tube. Another study is done on multi-walled CNTs (MWNTs)-polymer (e.g. polyethylene oxide (PEO), polyacrylamide (PAM)) composite films. We have investigated the structural, electrical and mechanical properties of MWNTs-PEO composites. Composites with different wt% (between 0 and 50 wt% of MWNTs) have been prepared and characterized by the scanning electron microscopic technique. Enhanced electrical conductivity and mechanical strength were observed for the MWNTs-PEO composites. We have also studied the electrical property of MWNTs-PAM composite films.     

Influence of dry grinding in a ball mill on the length of multiwalled carbon nanotubes and their dispersion and percolation behaviour in melt mixed polycarbonate composites

Ball milling of carbon nanotubes (CNTs) in the dry state is a common way to produce tailored CNT materials for composite applications, especially to adjust nanotube lengths. For Nanocyl^TM NC7000 nanotube material before and after milling for 5 and 10 h the length distributions were quantified using TEM analysis, showing decreases of the mean length to 54% and 35%, respectively. With increasing ball milling time in addition a decrease of agglomerate size and an increase of packing density took place resulting in a worse dispersability in aqueous surfactant solutions. In melt mixed CNT/polycarbonate composites produced using masterbatch dilution step, the electrical properties, the nanotube length distribution after processing, and the nano- and macrodispersion of the nanotubes were studied. The slight increase in the electrical percolation threshold in the melt mixed composites with ball milling time of CNTs can be assigned to lower nanotube lengths as well as the worse dispersability of the ball milled nanotubes. After melt compounding, the mean CNT lengths were shortened to 31%, 50%, and 66% of the initial lengths of NC7000, NC7000-5 h, and NC7000-10 h, respectively.     

碳纳米管增强铝基复合材料分散方法研究进展

碳纳米管与铝基体的结合,可以获得导电和导热性良好及综合力学性能优异的复合材料,有望成为新一代轻质高强、结构功能一体化的复合材料.在制备碳纳米管增强铝基复合材料过程中,碳纳米管的团聚将降低界面结合,诱发缺陷产生,导致性能大幅下降,因此,调控优化碳纳米管的分散状态、含量成为获取良好界面结合,获得高性能碳纳米管增强铝基复合材...     

高能球磨法制备高性能均一分散CNTs/Al5083复合材料

采用卧式高能球磨法制备0%~2%CNTs/Al5083(质量分数)复合材料,研究球磨时间和CNTs含量对复合材料性能的影响。采用扫描电镜(SEM)和透射电镜(TEM)对复合材料的形貌进行表征,测试复合材料的抗拉强度及硬度。结果表明:当球磨时间为1.5h时,CNTs可均匀分散在Al5083基体中;CNTs质量分数为1.5%时,CNTs/Al5083界面结合力最好,复合材料的抗拉强度和硬度分别为188.8MPa和136HV,比未加CNTs的Al5083合金基体分别提高了32.2%和36%。     

碳纳米管类型对CNTs/Lyocell复合纤维结构与性能的影响

分别采用单壁碳纳米管（SWNTs）和多壁碳纳米管（MWNTs）这两种碳纳米管（CNTs）制备不同的CNTs/Lyocell复合纤维,探讨了碳纳米管类型对复合纤维的结构与性能的影响。结果表明,碳纳米管类型并未影响CNTs/Lyocell纤维的结晶结构,质量分数为1%的SWNTs或MWNTs在Lyocell基体中分布都比较...     

PAPy/MWNTs复合材料的制备及其导电性能研究

通过原位化学氧化聚合法制备了聚3-乙酰基吡咯(PAPy)/多壁碳纳米管(MWNTs)复合材料。利用FT-IR、1 H-NMR、XRD、FE-SEM、FE-TEM、TGA等方法对单体和复合材料进行了结构和性能表征。红外光谱显示PAPy与MWNTs间并没有发生化学反应,MWNTs仅作为3-乙酰基吡咯(APy)单体聚合的模板。FE-SEM与FE-TEM分析表明,PAPy仅涂覆在MWNTs的外表面,涂覆厚度取决于APy与MWNTs间的质量比。热重分析表明,MWNTs可以提高PAPy/MWNTs复合材料的热稳定性。利用四探针法对样品进行了电导率测试,发现通过MWNTs与PAPy复合,可以显著地提高复合材料的导电性,并通过控制投料比,可以使复合材料的电导率接近MWNTs的电导率。     

Evaluating the orientation and dispersion of carbon nanotubes inside nanocomposites by a focused-ion-beam technique

Poly ether ether ketone (PEEK)/multi-walled carbon nanotubes (MWNTs) nanocomposites were fabricated to characterize and understand the orientation and dispersion of carbon nanotubes (CNTs) in a polymer matrix. A focused-ion-beam (FIB) technique was used for milling the nanocomposite by a focused gallium ion beam, and the MWNTs were carefully observed. The PEEK preferentially disappeared when the Ga⁺ ion beam milled the composite, and MWNTs were exposed on the surface of composites. Using this method, it is very easy to estimate and directly evaluate the orientation of the MWNTs in the polymer matrix even though they are embedded in the polymer matrix. Transmission electron microscopy (TEM) was employed to characterize the detailed position of the nanotubes in the PEEK matrix.     

Multi-walled carbon nanotube/silver nanoparticles used for thermal transportation

A green method was applied to prepare composites of multi-walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (Ag-NPs). MWNTs were functionalized using ball milling technology in the presence of ammonium bicarbonate, and the traditional method of silver mirror was used to decorate MWNTs to obtain Ag/MWNT composite. The obtained Ag/MWNT composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transmission infrared spectroscopy, and Brunauer–Emmet–Teller (BET) surface area analysis. SEM characterization showed that Ag-NPs distributed uniformly on the walls of MWNTs. The content and size of Ag-NPs could be controlled by adjusting the redox time. XRD patterns demonstrated that the Ag-NPs are composed of pure Ag and crystallized well. BET analysis indicated that the specific surface areas of Ag/MWNT decrease with increasing the content of Ag-NPs, and this result is similar to that of the literature. The measurement results of the thermal property showed that the thermal conductivity of the nanofluid containing Ag/MWNT composites was higher than that of nanofluid containing pristine or functionalized MWNTs.     

Structure,mechanical and thermal properties of BMI/E-44/CNTs ternary composites via amination method

Multi-walled carbon nanotubes(CNTs) were modified by an amination treatment with hexamethylenediamine(HMD), and then bismaleimide(BMI)/epoxy(E-44)/CNTs ternary composites were prepared using modified CNTs as the reinforcement via a simple mixing and curing molding method. The results show that the surfaces of CNTs are grafted polymer with the thickness of 3 nm and the dispersity of surface grafted carbon nanotubes(SG-CNTs) in the resin composites can be improved. The prepared composites contain C-C, C-N, C=O and-COOH groups and can keep a smooth surface. In addition, the composites have the flexural strength of 152 MPa, the tensile strength of 73 MPa and the impact strength of 87 k J m~(-2),respectively, when the weight ratio of BMI to E-44 is 1:8 and the content of SG-CNTs is 2 wt%. However,the thermal stability of the composites with SG-CNTs is a little lower than that of the composites without SG-CNTs.     

In situ polymerized nanocomposites: Polystyrene/CNT and Poly(methyl methacrylate)/CNT composites

Carbon nanotubes (CNTs) were incorporated into polystyrene (PS) and poly(methyl methacrylate) (PMMA) matrices via in situ emulsion and emulsion/suspension polymerization methods. The polymerizations were carried out using various initiators, surfactants, and carbon nanotubes to determine their influence on polymerization and on the properties of the composites. The loading of CNTs in the composites varied from 0 to 15 wt.%, depending on the CNTs used. Morphology and dispersion of the CNTs were analyzed by transmission and scanning electron microscopy techniques. The dispersion of multi-walled carbon nanotubes (MWCNT) in the composites was excellent, even at high CNT loading. The mechanical properties, and electrical and thermal conductivities, of the composites were also analyzed. Both electrical and thermal conductivities were improved.     

Alumina powder assisted carbon nanotubes reinforced Mg matrix composites

Mg matrix composites reinforced by carbon nanotubes (CNTs)-Al₂O₃ mixture, which was synthesized by in situ growing CNTs over Al₂O₃ particles through chemical vapor deposition (CVD) using Ni catalyst, were fabricated by means of powder metallurgy process, followed by hot-extrusion. By controlling synthesis conditions, the as-grown CNTs over Al₂O₃ particles possessed high degree of graphitization, ideal morphology, higher purity and homogeneous dispersion. Due to the ‘vehicle’ carrying effect of micrometer-level A₂O₃, CNTs were easy to be homogeneously dispersed in Mg matrix under moderate ball milling. Meanwhile, Al₂O₃ particles as catalyst carriers, together with CNTs, play the roles of synergistic reinforcements in Mg matrix. Consequently, the Mg matrix composites reinforced by CNTs-Al₂O₃ mixture exhibited remarkable mechanical properties.     

碳纳米管表面处理及其在铜基复合材料中的应用

碳纳米管因特殊结构带来的优异性能而被海内外学者广泛关注,以碳纳米管为增强相制备铜基复合材料是使铜基导体同时具有高强度和高导电性能的有效途径。然而,由于碳纳米管表面能高、表面反应活性低,碳纳米管/铜复合材料制备的过程中存在增强体分散性差和界面结合强度弱两大问题,从而阻碍了复合材料高性能的实现。在碳纳米管/铜复合材料的制备过程中,采用适当的方法对碳纳米管进行表面处理能改变碳纳米管的表面结构和反应活性,在改善碳纳米管的分散性的同时增强碳纳米管与铜基体的界面结合,从而提高碳纳米管的增强效率,保证复合材料良好的综合性能。然而,表面处理过程可能会破坏碳纳米管的结构完整性,影响碳纳米管的本征性能,进而影响其增强效果,或可能在基体中引入其他杂质,影响复合材料的导电和导热性能。因此,在进行表面处理时应综合考虑其对碳纳米管结构性能及复合材料增强作用的影响。近年来,研究者们通过优化碳纳米管表面处理工艺突破了碳纳米管/铜复合材料在制备过程的难点,在保证铜基体优异的导电、导热性能的同时,大幅提高了碳纳米管/铜复合材料的力学性能。碳纳米管表面处理工艺类型大致可分为机械球磨、化学表面改性、表面镀层和联合表面处理四类。传统的机械球磨表面处理对碳纳米管的结构破坏较大;化学表面改性又分为共价表面改性和非共价表面改性,非共价表面改性在保持碳纳米管完整的管状结构和优异性能的同时,提高了碳纳米管在溶液中的分散性,但用于复合材料制备时会给基体引入有机杂质,影响复合材料性能;共价表面改性和表面镀层是铜基复合材料制备过程中最为常用和有效的表面处理方法,其能够在提高碳纳米管在基体中的分散性能的同时改善碳纳米管表面的反应活性,从而形成碳纳米管和铜基体之间强度较高的反应结合界面,实现碳纳米管/铜复合材料高强高导的综合性能。此外,可通过综合利用各种表面处理方法,结合各表面处理工艺的优势,获得更为优异的改性效果。本文从碳纳米管表面处理工艺的基本类型以及碳纳米管表面处理对铜基复合材料结构和性能的影响两方面阐述了碳纳米管表面处理在铜基复合材料中的应用和研究进展,并对其未来的研究方向进行了展望。     

耐高温聚酰亚胺导电复合材料的性能

采用涂膜法制备了以碳纳米管(CNTs)、乙炔黑和石墨粉为导电填料的聚酰亚胺(PI)导电复合材料,研究了其电学性能、力学性能和粘接性能。结果显示,PI/CNTs导电复合材料有较好的综合性能。     

球磨对碳纳米管增强泡沫铝基复合材料压缩与吸能性能的影响

因碳纳米管（CNTs）具有优异的性能,被认为是金属基复合材料理想的增强体,因此如何制备得到CNTs增强体均匀分散的金属基复合材料一直是本领域的研究热点。本文通过原位化学气相沉积（CVD）、短时球磨和填加造孔剂的工艺成功制备了CNTs增强的泡沫铝基复合材料,着重研究了球磨过程对复合泡沫铝的微观形貌、压缩性能和吸能性能的影响规律。结果表明,随着球磨时间的延长,CNTs的分散性提高并逐步嵌入铝基体中,使复合泡沫铝的组织均匀性得到改善。相对于未球磨的含CNTs 3.0wt%的复合泡沫材料,当球磨时间增加至90 min时,复合泡沫铝的孔壁硬度、屈服强度和吸能能力分别提高了67%、126%和343%。     

聚氨酯/二氧化硅包覆多壁碳纳米管复合材料的导热与电绝缘性能

通过溶胶-凝胶法制备了厚度为30nm-50nm的二氧化硅(SiO2)包覆多壁碳纳米管(SiO2-MWNTs),并与聚氨酯(PU)复合制备了PU/SiO2-MWNT复合材料。研究了SiO2-MWNTs对PU导热电绝缘性能的影响。结果表明,SiO2包覆层增强了MWNTs与PU之间的界面相互作用,促进了MWNTs在PU中的分散。由于SiO2包覆层的电绝缘作用,PU/SiO2-MWNT复合材料保持了PU的电绝缘性能。同时SiO2包覆层作为过渡层,降低了PU与MWNTs间的模量失配,减少了声子的界面散射,提高了PU/SiO2-MWNT复合材料的导热性能。当SiO2-MWNTs的质量分数为0.5%和1.0%时,PU/SiO2-MWNT复合材料的热导率分别提高了53.7%和63.8%。     

Synthesis of sea urchin-like carbon nanotubes on nano-diamond powder

Carbon nanotubes (CNTs) have unique atomic structure and properties, such as a high aspect ratio and high mechanical, electrical and thermal properties. On the other hand, the agglomeration and entanglement of CNTs restrict their applications. Sea urchin-like multiwalled carbon nanotubes, which have a small aspect ratio, can minimize the problem of dispersion. The high hardness, thermal conductivity and chemical inertness of the nano-diamond powder make it suitable for a wide range of applications in the mechanical and electronic fields. CNTs were synthesized on nano-diamond powder by thermal CVD to fabricate a filler with suitable mechanical properties and chemical stability. This paper reports the growth of CNTs with a sea urchin-like structure on the surface of the nano-diamond powder. Nano-diamond powders were dispersed in an attritional milling system using zirconia beads in ethanol. After the milling process, 3-aminopropyltrimethoxysilane (APS) was added as a linker. Silanization was performed between the nano-diamond particles and the metal catalyst. Iron chloride was used as a catalyst for the fabrication of the CNTs. After drying, catalyst-attached nano-diamond powders could be achieved. The growth of the carbon nanotubes was carried out by CVD. The CNT morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean diameter and length of the CNTs were 201 nm and 3.25 microm, respectively.     

Fabrication and mechanical/conductive properties of multi-walled carbon nanotube (MWNT) reinforced carbon matrix composites

Multi-walled carbon nanotube (MWNT) reinforced carbon matrix (MWNT/C) composites have been explored using mesophase pitch as carbon matrix precursor in the present work. Results show that carbon nanotubes (CNTs)can enhance the mechanical properties of carbon matrix significantly. The maximal increment of the bending strength and stiffness of the composites, compared with the carbon matrix, are 147% and 400%, respectively. Whereas the highest in-plane thermal conductivity of the composites is 86 W m^− 1 K^− 1 which much lower than that of carbon matrix (253 W m^− 1 K^− 1).At the same time the electrical resistivity of the composites is much higher than that of matrix. It is implicated that CNTs seem to play the role of thermal/electrical barrier in the composites. FSEM micrograph of the fracture surface for the composites shows that the presence of CNTs restrains the crystallite growth of carbon matrix, which is one of factors that improve mechanical properties and decrease the conductive properties of the composites. The defects and curved shape of CNTs are also the affecting factors on the conductive properties of the composites.     

Improved processing of carbon nanotube/magnesium alloy composites

Carbon nanotubes (CNTs) are promising reinforcements for light weight and high strength composites due to their exceptional properties. However, until now, the main obstacle is to obtain a homogenous dispersion of the CNTs in the desired material matrix. Quite a few methods have been studied to help improving the dispersion of CNTs in a polymer matrix. But not much research has been conducted on how to disperse CNTs in metal matrices. In this study, a two-step process was applied. In the first stage, a block copolymer was used as a dispersion agent to pre-disperse multiwall carbon nanotubes (MWNTs) on Mg alloy chips. Then the chips with the well dispersed MWNTs on their surface were melted and at the same time vigorously stirred. The molten MWNT Mg alloy composites were poured into a cylindrical mould to solidify quickly. For the pre-dispersion step, the microstructures of the Mg alloy chips were studied under SEM. MWNTs were quite successfully dispersed on the surfaces of the Mg alloy chips. The mechanical properties of the MWNT/Mg composites were measured by compression testing. The compression at failure, the compressive yield strength and ultimate compressive strength have all been improved significantly up to 36% by only adding 0.1 wt% MWNTs to the Mg alloy. In order to predict the potential yield strengths of the MWNT reinforced Mg alloy composites, the contributions by load transfer, Orowan strengthening and thermal mismatch were added up.     

Sol–gel route to carbon nanotube borosilicate glass composites

Dense borosilicate glass matrix composites containing up to 3 wt% of multiwalled carbon nanotubes were produced by a sol–gel process. The three different silicate precursors employed (tetramethylsilane (TMOS), methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS)) yielded transparent xerogels which were subsequently crushed and densified by hot pressing at 800 °C. The dispersion of the carbon nanotubes was aided by using an organic–inorganic binder (3-aminopropyl triethoxysilane) which limited flocculation of the CNTs in the silica sol. After densification, the borosilicate glass composites containing up to 2 wt% CNTs showed significant improvements in hardness and compression strength, as well as thermal conductivity, whilst percolation effects lead to a dramatic increase in electrical conductivity above 1 wt%. This simple approach to disperse CNTs into a technical silicate glass matrix via the sol–gel process focusses specifically on the borosilicate system, but the procedure can be applied to produce other inorganic matrix composites containing CNTs.     

Preparation of high-yield multi-walled carbon nanotubes by catalytic decomposition of mixture of natural gas and propylene and their electrothermal properties

Abstract

Multi-walled carbon nanotubes (MWNTs) with high-yield were prepared by pyrolysis of mixture of natural gas (NG) and propylene (C₃H₆) over Fe-Ni/Al₂O₃-MgO catalyst. For C₃H₆/NG flow rate ratio ranging from 0 to 0.33, the carbon yield was increased from 903% to 4400%. The synthesized MWNTs after purification were dispersed by ball milling method and mixed with waterborne polyurethane to fabricate the electrothermal film. The mass fraction of CNT filler in the cured electrothermal film was controlled at 50%. The coating after drying was ca. 6?μm and the coating’s volume resistivity was 0.053 Ω·cm. The time-dependent temperature curves indicated that the heating rate of the electrothermal film was very fast under different low voltage and the steady-state temperatures were achieved within 100?s. The steady-state temperature reached 47.9?°C, 76.8?°C, and 102.8?°C, respectively at 10?V, 15?V, and 18?V.