Effect of silver doped MWCNTs on the electrical properties of conductive MWCNTs/PMMA thin films

The transmittance and electrical properties of conductive multi-walled carbon nanotubes (MWCNTs)/poly(methyl methacrylate) (PMMA) films were investigated as a function of MWCNT content. The effect of silver doped MWCNTs (Ag-MWCNTs) on the surface resistance of the films was also determined. The surface characteristics of acid-treated MWCNTs were confirmed using FT-Raman. The dispersion and formation of a conductive network of MWCNTs in PMMA were observed by SEM and AFM analyses. The transmittance of the films observed by UV–vis–NIR was decreased from 89% to 64%, and the surface resistance of the films was decreased from 392 MΩ/sq to 293 kΩ/sq while increasing the MWCNT content due to the increase of the electron conductive pathway. The Ag-MWCNTs/PMMA films showed a lower surface resistance about 2–4 times than that of MWCNTs/PMMA films. This was probably due to the synergic effect induced between MWCNTs and Ag.     

复合电沉积Ni-MWCNTs及镍电结晶的研究

研究了水平阴极方式复合电沉积Ni-MWCNTs(Ni-多壁碳纳米管).采用硫酸镍基础电解液,添加适当表面活性剂和光亮剂,MWCNTs为2～2.5 g/L,电流密度为2.5 A/dm2时,获得的Ni-MWCNTs沉积层结构致密,复合沉积层中MWCNTs含量达22.45%.复合电沉积层表面微观形貌照片显示,MWCNTs在复合电沉积层中占主要体积,镍的电结晶形态呈球形,结晶点位置位于MWCNTs管壁缺陷处及部分管端处,MWCNTs的管端和管壁缺陷处的Ni晶粒相互连接,形成牢固的复合沉积层.复合电沉积层中MWCNTs含量受电解液中MWCNTs浓度、电流密度以及光亮剂影响,在MWCNTs上的Ni沉积层连续性直接受MWCNTs管壁上缺陷的数量和连续性影响,形成晶核的缺陷尺度至少在1 nm以上.     

Study of Carbon Nanotubes in Cu-Cr Metal Matrix Composites

A novel metal matrix composite (MMC), Cu-Cr-MWCNT (copper-chromium-multiwalled carbon nanotube), was manufactured using a powder metallurgy technique. Cu-Cr alloy is widely adopted for contacts in vacuum circuit breakers. MWCNT was incorporated in an effort to enhance electrical conductivity and decrease the usage of Cr as strategic metal. Optimized milling conditions and sintering profiles were utilized to minimize any significant damage to the MWCNTs but yet provide homogeneous distribution of all constituents. Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to determine the crystal structure orientation, microstructure, and morphology, respectively, of the composite. Raman peak shift and intensity ratios assessed the stresses induced and the degree of disorder of MWCNTs in the composite. TEM indicated carbide and oxide formations in the composite. SEM images revealed the presence of MWCNTs within the metal matrix. The corrosion resistances of the composite with and without MWCNTs was determined by cyclic potentiodynamic polarization (ASTM F 2129-08) in phosphate buffer saline solution at 37 °C.     

Electrolytic Synthesis of Ni-W-MWCNT Composite Coating for Alkaline Hydrogen Evolution Reaction

Nickel–tungsten multi-walled carbon nanotube (Ni-W-MWCNT) composite films were fabricated by an electrodeposition technique, and their electrocatalytic activity toward hydrogen evolution reaction (HER) was studied. Ni-W-MWCNT composite films with a homogeneous dispersion of MWCNTs were deposited from an optimal Ni-W plating bath containing functionalized MWCNTs, under galvanostatic condition. The presence of functionalized MWCNT was found to enhance the induced codeposition of the reluctant metal W and resulted in a W-rich composite coating with improved properties. The electrocatalytic behaviors of Ni-W-MWCNT composite coating toward HER were studied by cyclic voltammetry (CV) and chronopotentiometry techniques in 1.0 M KOH medium. Further, Tafel polarization and electrochemical impedance spectroscopy (EIS) studies were carried out to establish the kinetics of HER on the alloy and composite electrodes. The experimental results revealed that the addition of MWCNTs (having a diameter of around 10-15 nm) into the alloy plating bath has a significant effect on the electrocatalytic behavior of Ni-W alloy deposit. The Ni-W-MWCNT composite coating was found to show better HER activity than the conventional Ni-W alloy coating. The enhanced electrocatalytic activity of Ni-W-MWCNT composite coating is attributed to the MWCNT intersticed in the deposit matrix, evidenced by surface morphology, composition and phase structure of the coating through SEM, EDS and XRD analyses, respectively.     

Fabrication of various electroless Ni-P alloy/multiwalled carbon nanotube composite films on an acrylonitrile butadiene styrene resin

Ni-P alloy/multiwalled carbon nanotube (MWCNT) composite films were fabricated on acrylonitrile butadiene styrene (ABS) resin by electroless plating and their microstructures, adhesion strengths, and friction properties were investigated. Various types of MWCNTs were used. In addition, various electroless plating baths were prepared to form Ni-P alloy matrices with various phosphorus contents. To enhance the adhesion strength, the ABS resin substrate was subjected to roughening treatment. The microstructures of the composite films were examined by scanning electron microscopy and X-ray diffraction. Their adhesion strengths were measured by tensile tests. The friction properties of the composite films were investigated using the ball-on-plate method. Ni-P alloy/MWCNT composite films containing various types of MWCNTs and with Ni-P alloy matrices having various phosphorus contents were fabricated on the ABS resin substrates by electroless deposition. The adhesion strength between the Ni-P alloy/MWCNT composite films and the ABS resin substrate was more than 1300 N cm^− 2. The Ni-P alloy/MWCNT composite films had considerably lower friction coefficients than the Ni-P alloy films. The friction coefficients of the composite films were significantly affected by the type of MWCNTs used.     

Processing and characterization of carbon nanotube mat/epoxy composites

A carbon nanotube mat (CNT mat) with long (∼1 mm) multi-walled carbon nanotubes (MWCNTs) was used to process MWCNT/epoxy composites at high concentrations (4.4 and 10.0 wt.%) of MWCNTs by a simple method without the use of a solvent. The CNT mat circumvents several cumbersome processing steps, including the dispersion of CNTs in a solvent. Two different resin-impregnation processing methods were explored. The processing steps were chosen to prepare composite samples based on the performance of the composites and the simplicity of the processing techniques. Scanning electron microscopy (SEM) was used to examine the microstructures of the CNT mat and its composites. The mechanical and electrical properties were tested. The tensile strengths of the composites with 10.0 wt.% MWCNTs were increased by 17% to 90% when compared to that of neat epoxy samples. The electrical conductivity of the composite is 36.1 S/cm. 4.4 wt.%-MWCNT composites show very large strain valuesupon fracturing (> 15 %), and their electrical conductivity is 14.9 S/cm. These results show that CNT mat/epoxy composites can be used as flexible electrodes and as a matrix system for advanced fiber composites.     

Porous carbon nanotube electrodes supported by natural polymeric membranes for PEMFC

A new type of porous multiwalled carbon nanotube (MWCNT) electrode with a macroporous networking inner-structure was prepared. First, the MWCNTs were homogeneously introduced inside and outside of a bacterial cellulose membrane with a 3D inter-connected network structure using ultrasound treatment and vacuum filtration in order to form the GDL. Second, the CL was formed on the surface of the GDL through vacuum filtration of the Pt incorporated MWCNTs (Pt/MWCNTs). Finally, the electrode was created through freeze-drying. The final electrode had a sheet resistance of 80 Ω/□ and an electro-chemical active surface area (ECSA) of 10.1 m²/g. Although the ECSA of the electrode did not have the efficiency (14.3 m²/g) of a typical electrode (carbon cloth/Pt/carbon black), these results suggested that the new type of electrode has potential as a proton exchange membrane fuel cell.     

Polyurethane/PEG-modified MWCNT composite film for the chemical vapor sensor application

The changes of electrical resistance of the polymer composites on exposure to chemical vapors have been applied for the production of vapor sensors. In this study, to confirm the ability of elastomer as chemical vapors sensors, polyurethane/PEG-modified MWCNT composite film was prepared by in situ condensation polymerization and solution casting. The responses of this elastomer composite film for various organic vapors (polar and non-polar solvents) were calculated by monitoring the change in the resistance of the composite film when exposed to the organic vapors. The changes of electrical resistance of the composite films were explained on the basis of volume expansion as swelling and polar interaction of various vapors on the composite. Therefore, we were able to interpret the behavior of the polyurethane/PEG-modified MWCNT composite film as a chemical vapor sensor through diffusion, sorption, and permeation coefficients of the polymer film–analyte systems.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1-x)La0.8Sr0.2MnO3/xYSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1-x)La0.8Sr0.2MnO3/xYSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm2) was the highest and that of the monolayer cathode (0.13 A/cm2) was the lowest. The polarization resistance (Rp) of the triple-layer graded composite cathode was only 0.182Ω·cm2 and that of the monolayer composite cathode was 0.323Ω·cm2. The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

An electrochemical study of the synthesis and properties of multi-walled carbon nanotube/poly ortho aminophenol composites

Composites of multi-walled carbon nanotubes (MWCNTs) and poly ortho aminophenol (POAP) with good uniformity for use as electrodes in electrochemical capacitors were prepared by electropolymerization by using the ionic surfactant as electrolyte, for dispersing CNTs within conducting polymer/carbon nanotube composite films. The capacitance properties were investigated with cyclic voltammetry (CV), discharge tests and ac impedance spectroscopy. The composite electrode shows much higher specific capacitance, better power characteristics and is more promising for application in the capacitor than a pure POAP electrode. The effect and role of MWCNT in the composite electrode are discussed in detail. In comparison with a Ni–POAP/glassy carbon (GC), a Ni–MWCNT–POAP/GC electrode shows a better catalytic performance for the electrocatalytic oxidation of methanol.     

Parametric optimization of dry sliding wear loss of copper–MWCNT composites

The wear behavior of multi-walled carbon nano-tubes (MWCNTs) reinforced copper metal matrix composites (MMCs) processed through powder metallurgy (PM) route was focused on and further investigated for varying MWCNT quantity via experimental, statistical and artificial neural network (ANN) techniques. Microhardness increases with increment in MWCNT quantity. Wear loss against varying load and sliding distance was analyzed as per L16 orthogonal array using a pin-on-disc tribometer. Process parameter optimization by Taguchi's method revealed that wear loss was affected to a greater extent by the introduction of MWCNT; this wear resistant property of newer composite was further analyzed and confirmed through analysis of variance (ANOVA). MWCNT content (76.48%) is the most influencing factor on wear loss followed by applied load (12.18%) and sliding distance (9.91%). ANN model simulations for varying hidden nodes were tried out and the model yielding lower MAE value with 3-7-1 network topology is identified to be reliable. ANN model predictions with R value of 99.5% which highly correlated with the outcomes of ANOVA were successfully employed to investigate individual parameter's effect on wear loss of Cu–MWCNT MMCs.     

Electrochemical properties of carbon nanotube-dispersed PEO-LiX electrolytes

Multi-wall nanotubes (MWCNTs) were added to PEO-LiClO₄ solid electrolytes in order to assess their enhancement of ionic conductivity. PEO-LiClO₄-SiO₂ composite electrolytes were also manufactured for comparison. In spite of the electrical conductivity of MWCNTs, PEO-LiClO₄-MWCNT composites can be sucessfully used as solid electrolytes, provided that additive carbon nanotubes have discontinous forms and are homogeneously distributed within the PEO-LiClO₄ matrix. Shortening and uniform dispersion of MWCNT were identified as crucial factors for the performance of PEO-LiClO₄-MWCNT composite electrolytes. Compared with the PEO-LiClO₄-SiO₂ composite, the addition of MWCNT to PEO-LiClO₄ resulted in greater enhancement in ionic conductivity. This might be attributable to enhanced amorphization by local modification of PEO chains from crystalline to disordered arrangements.     

Mechanical property enhancement of kinetic sprayed Al coatings reinforced by multi-walled carbon nanotubes

Significant mechanical property enhancement was observed when kinetic sprayed (KS) Al coatings were reinforced by the addition of multi-walled carbon nanotubes (MWCNTs). Embedding the MWCNTs in a ductile Al matrix through mechanical milling to fractions of 0.5 and 1.0 wt.% led to significant improvements in elastic modulus, micro-hardness, and wear resistance. Reinforcement of the Al matrix with MWCNTs is based on the mechanical interaction of MWCNTs with the Al, i.e. elastic wave reflection and dispersion hardening and toughening. These effects were able to overcome the innate ductility of the Al, thereby widening the potential applications of Al coatings. This study provides insight into the strengthening mechanisms of KS MWCNT reinforced Al composite coatings with respect to the spray process, microstructure and mechanical properties.     

Preparation and characterization of conductor–insulator–semiconductor sandwich-structured MWCNT/double-layer polymer hybrid nanocomposites

The conductor–insulator–semiconductor sandwich-structured MWCNT/double-layer polymer hybrid nanocomposites (MWCNT-PS-PAA/PAn), multiwalled carbon nanotubes (MWCNTs) encapsulated with polystyrene (PS) inner layer and polyacrylic acid (PAA) doped polyaniline (PAn) outer layer via covalently linking, were fabricated through combining the successive surface-initiated atom transfer radical polymerization (SI-ATRP) and in situ chemical oxidative polymerization techniques. The sandwiched structure was confirmed by the XPS and TEM analysis. Due to their conductor–insulator–semiconductor sandwich structure, the electrical conductivity of the nanocomposites obtained was far less than the similar small acids doped PAn/carbon nanotubes composites. Furthermore, the dispersibility of the sandwiched hybrid nanocomposites in organic solvent obviously improved compared with the pristine carbon nanotubes.     

Bent-shape effects of multi-walled carbon nanotube on the electrical conductivity and rheological properties of polycarbonate/multi-walled carbon nanotube nanocomposites

In this study, polycarbonate (PC)/multi-walled carbon nanotube (MWCNT) nancomposites have been prepared by pretreating MWCNT solutions with ultrasonication. We demonstrate that the electrical conductivity and rheological properties of PC/MWCNT nanocomposites strongly depend on the mesoscopic shape factor (l_sp/d), which is represented by the ratio between the static bending persistence length (l_sp) and outer diameter (d) of the MWCNT. The electrical conductivity of PC/MWCNT nanocomposites increases linearly with increasing (l_sp/d)² and the percolation threshold of PC/MWCNT nanocomposites decreases linearly with increasing (l_sp/d)² of MWCNTs. The storage modulus of PC/MWCNT nanocomposites increases linearly with increasing (l_sp/d)² of MWCNTs at all frequency ranges.     

碳纳米管复合水性丙烯酸涂层的腐蚀性能研究

目的制备碳纳米管复合水性丙烯酸涂层,探索分析碳纳米管含量对涂层力学和防腐性能的影响规律。方法采用高速球磨方式制备3%,1%,0.5%三种含量(以质量分数计)的碳纳米管复合涂层,对涂层附着力、耐冲击性、耐弯曲性等力学性能进行测试,以电化学阻抗技术来评价碳纳米管复合涂层的防腐性能。结果添加碳纳米管显著提高了涂层的附着力,并且随着碳纳米管含量的增加,附着力上升;其他力学性能,如耐冲击性、耐弯曲性,在不同含量下均保持良好。对改性和未改性的涂层进行了电化学阻抗测试,其中1%的碳纳米管涂层电化学性能最优,在浸泡36 h后,未改性涂层低频区阻抗模值|Z|0.01为2.5×103Ω·cm2,0.5%的碳纳米管涂层为1.1×106Ω·cm2,1%的为1.4×108Ω·cm2,3%的为7×102Ω·cm2。结论由于碳纳米管本身的纳米效应,在较低含量时即可提高涂层的性能,并存在最优含量,超过此含量后性能有所下降。     

Preparation,fabrication and response behavior of a HTBN/TDI/MWCNT composite sensing film by in situ dispersed polymerization

A polyurethane inserted multi-wall carbon nanotube (MWCNT) composite conductive film was prepared by in situ dispersed polymerization reaction using hydroxyl-terminated poly(butadiene-acrylonitrile) liquid rubber as a linear diol, toluene diisocynate as a curative, ethylene glycol or glycerine or triethanolamine as a chain-extending agent and MWCNT as a conducive filler. The effect of various curing temperatures and chain-extending agents on vapor-induced electrical responsiveness of the conductive films was investigated. The structural characterization of the cured film was conducted by Fourier transformation infrared spectrophotometer (FTIR), differential scanning calorimeter (DSC), polarization microscope (POM) and wide angle X-ray diffraction (WAXD). The experimental results showed that the conductive composite film obtained in the present work exhibited a microphase separation resulting from the soft-hard segment domains, and possessed some crystalline behavior from the hard segment. The response intensity was enhanced with the curing temperature increased, while the reversibility could be improved at a relatively low curing temperature. The responsivity of the film produced by a linear difunctional group chain-extending agent was lower than that prepared by trifunctional group curatives, and the reversibility was vice versa. The experimental phenomena were explained from the viewpoint of the microphase separation, crystalline behavior, the structural characteristics of the soft-hard segment, and the electronic properties of multi-wall carbon nanotubes as well as a weak electrostatic or noncovalent interaction between polymer or analyte molecules and MWCNTs.     

Synthesis of Porous LiFePO4/C Composite Materials by CCVD Method

以C2H2为碳源,Fe为催化剂,纳米FePO4为原料,采用催化化学气相沉积法(CCVD)合成多孔LiFePO4/C正极材料。经BET、SEM、CHON有机元素分析仪、XRD等手段对复合材料进行结构分析表征。结果表明,该复合材料具有连续贯通的三维导电网络结构,大的比表面积以及多重孔隙的类球形结构,含碳量为4.42%(质量分数),低于传统碳热还原法所制备的材料。电化学测试表明,该材料在0.1、1、5、10 C倍率下,放电比容量分别为147,141,126,110 m Ah·g-1,高倍率充放电性能大大提高,另外,该材料1 C循环80次后,放电比容量基本没有降低,显示了良好的循环稳定性能。     

Atmosphere Plasma-Sprayed Carbon Nanotubes/Cordierite Nanocomposite Coatings for Microwave Absorption Applications

Multi-walled carbon nanotubes (MWCNTs)/cordierite (MAS) nanocomposite coatings with different MWCNT contents were prepared via atmosphere plasma spraying method. The characteristics of the MWCNTs/MAS powders and as-sprayed coatings, such as microstructure and phase constitution, were observed and measured. The dielectric properties and microwave absorption properties of MWCNTs/MAS powders and nanocomposite coatings have been investigated at the frequency of 8.2-12.4 GHz with different MWCNT contents and sample thicknesses. When the MWCNT content increased to 7%, the nanocomposite coating revealed the highest dielectric constant and optimal microwave absorption property. Further increase in MWCNT content led to severe oxidation of MWCNTs during the plasma spray process, which resulted in lower dielectric constants and poor microwave absorption property. Moreover, the sample thickness has a noticeable influence on the reflection loss (RL) of the MWCNTs/MAS coatings, and the coating of 2.4-mm thickness shows optical microwave absorption with a minimum RL of ?15.61 dB and bandwidth of 2.35 GHz.     

Multi-walled carbon nanotube-reinforced copper nanocomposite coating fabricated by low-pressure cold spray process

Multi-walled carbon nanotube (MWCNT)-reinforced copper (Cu) nanocomposite coatings were successfully deposited on aluminum (Al) substrate by a cold spraying process at a low pressure. The microstructure and the Raman spectrum of the low-pressure-cold-sprayed MWCNT–Cu nanocomposite coating showed that the MWCNTs maintained their tube structure in the Cu matrix, even though structural damage to the MWCNTs increased slightly. MWCNT–Cu nanocomposite-coated Al exhibits higher thermal diffusivity than pure-Cu-coated Al with a comparable hardness. The higher thermal diffusivity of the MWCNT–Cu coating could be explained by the dispersion of MWCNTs within the clean and closed CNT/Cu interfaces, which were achieved with the aid of compressive stress during the cold spraying.