纳米碳包镍/环氧树脂复合材料的NTC效应及其调节

采用磁场辅助固化工艺,制备了纳米碳包镍/环氧树脂复合材料,用SEM观察了复合材料的微观组织,测量了复合材料的直流电学特性,考察了磁场强度、纳米粒子含量、温度对电性能的影响。在无磁场情况下固化时,纳米粒子在环氧树脂中均匀分布;而施加磁场后,纳米粒子在基体中以纤维状线性排列;施加的磁场越大,纤维组织发育得越粗壮,获得的复合材料的电阻率越小。复合材料的I-U曲线呈现非线性特征,表明电导机制依赖于导电粒子之间的隧道传递,电阻率随温度上升而下降,显示奇怪的负温度系数（NTC）效应,且可由填料含量、磁场强度调节。为解释NTC起源,提出一个修正的量子隧道模型。根据该模型,复合材料的NTC效应归因于占统治地位的电子热活化隧道传递;另一方面,环氧树脂的低膨胀率促成了这一效果。      

Aligned carbon nanotube-polystyrene composites prepared by in situ polymerisation of stacked layers

In situ polymerisation provides a route to polystyrene (PS) matrix composites reinforced with aligned multi-walled carbon nanotubes (MWNTs). As shown, fully densified composites can be prepared; by varying the number of layers of aligned MWNT arrays, desired thickness of the composite can be manufactured. These aligned composites have characteristic anisotropic electrical and thermal properties.     

定向钢纤维水泥基复合材料断裂理论分析及试验

基于非线性铰模型研究了定向钢纤维水泥基复合材料的裂缝断裂全过程理论分析方法,结合不同尺寸试件的三点弯曲梁断裂试验对本文方法进行了验证。进而利用该方法预测了大尺寸三点弯曲梁试件的裂缝断裂全过程,并研究了试件尺寸对名义强度的影响。通过理论分析与试验结果对比,表明本文方法可较好地预测定向钢纤维水泥基复合材料的裂缝断裂全过程;此外,定向钢纤维水泥基复合材料的名义强度存在一定的尺寸效应,但尺寸效应表现不明显。     

Processing,microstructure, and physical properties of interpenetrating Al2O3/Ni composites

Abstract

Alumina/nickel composites have been fabricated by hot pressing powder blends of various volume fractions of nickel and alumina. The electrical resistivities and Young's moduli of these composites have been measured and their dependence on the volume fraction of reinforcement has been investigated. Microstructural parameters such as contiguity were measured to quantify the distribution of the phases in these composites, and existing property models based on these data were used to predict the properties of the composites. The percolation threshold of nickel was found to occur at between 7.5 and 15 vol.-%Ni. The Young's modulus decreases as the volume fraction of nickel increases and is dependent on the contiguity of alumina. Composites containing 25, 35, 50, and 65 vol.-%Ni display microstructures with interpenetrating networks of alumina and nickel. The property models were found to fit both the resistivity and modulus data well, although the percolation threshold was predicted at a lower volume fraction than measured experimentally.     

超顺排碳纳米管/硅橡胶复合材料各向异性的电学性能和力学性能

采用直接浸润法制备了具有不同层数的超顺排碳纳米管(SACNT)薄膜与硅橡胶的复合材料,使碳纳米管薄膜能够在硅橡胶基体表面均匀分散。测量了SACNT薄膜/硅橡胶复合材料在各个方向的导电性能和力学性能,研究了影响复合材料导电性和力学性能的因素。实验结果表明:SACNT薄膜/硅橡胶复合材料的导电性和杨氏模量都随着碳纳米管薄膜厚度的增加而增加,且具有显著的各向异性。垂直于碳纳米管排列方向的电阻率平均比平行方向的大一个数量级。当碳纳米管层数为240层时,平行于碳纳米管排列方向的杨氏模量为116.9 MPa(比纯硅橡胶基体增加了142倍),而垂直方向的杨氏模量仅为1.23 MPa(比纯硅橡胶基体增加50%),两者之间相差近100倍。结果表明,可以通过选择不同的参数,获得具有特定导电性和杨氏模量的SACNT薄膜/硅橡胶复合材料,并在实际中加以应用。     

氧化石墨烯/再生水泥基复合材料的制备

基于建筑垃圾再生细骨料替代天然砂,进行氧化石墨烯(GO)改性再生水泥基复合材料的综合物理性能和水化机制研究。采用超声分散GO及振动搅拌制备再生水泥基复合材料,综合耐久性能测试结果表明:和不掺GO再生水泥基复合材料相比,添加0.03% GO改性7 d龄期强度的GO/再生水泥基复合材料抗折和抗压强度分别提高了16%和21%;添加0.02% GO改性的28 d龄期强度的GO/再生水泥基复合材料抗折和抗压分别提高了13.7%和13.6%。GO/再生水泥基复合材料龄期7 d耐候、50次冻融循环后力学性能均良好;氯离子含量皆小于0.06%。放射性检测结果表明:GO/再生水泥基复合材料内照射指数I_Ra和外照射指数I_r均属于A类建筑材料。通过XRD、TG-DTA、SEM等手段对GO/再生水泥基复合材料水化机制研究表明:GO促进了钙矾石(AFt)晶体的大量生成及胶凝孔中存在更多的自由水,且对后期氢氧化钙(CH)的产生有抑制作用,进而提高了GO/再生水泥基复合材料综合物理性能。      

碳纳米管改性水泥基复合材料的研究进展

碳纳米管（CNTs）是一种具有独特结构和优异性能的新型材料,将其掺入到水泥基材料中可明显增强材料的各种性能。本文简要介绍了CNTs的基本结构和分散方法,并对CNTs改性水泥基材料的性能进行了阐述,这些性能包括：力学性能、水化与微结构特征、变形性能、耐久性能、导电导热和吸波性能等。在目前研究中可能存在的问题的基础上,对今后需进一步研究的方向提出了建议。     

Influence of polarization on properties of 0–3 cement-based PZT composites

In this paper, studies on a new 0–3 type cement-based PZT (lead zirconate titanate) composite are presented. Using a normal mixing and compacting method, up to 50 vol.% PZT ceramic powder can be easily incorporated into the composites. The behaviors of the cement-based PZT composites under different polarizing conditions have been investigated on the piezoelectric properties both theoretically and experimentally. It shows that cement-based PZT composites have their own unique characteristics. There is a good potential for the application of 0–3 type cement based piezoelectric composites in civil engineering.     

Optimizations of wear resistance and toughness of hydroxyapatite nickel free stainless steel new bio-composites for using in total joint replacement

The aim of this work was to produce novel bio-composites made of hydroxyapatite and nickel free stainless steel (prepared by heat treating bone ash) and studying their mechanical properties including their tribology under various loads, toughness, and compressive and bending strengths. Different amounts of nickel free stainless steel powder (30, 40, 50 and 60 wt.%) was added to this hydroxyapatite powder to get bio-composites. Their hardness, wear resistance and friction coefficient, as a function of the metal (nickel free stainless steel) content were investigated. Hardness and wear resistance were decreased by increasing of the weight percentage of stainless steel, while friction coefficient was increased. Strength and toughness of composites increases considerably by increasing of NFSS content. The toughness enhancement is contributed mainly by crack bridging and plastic deformation of the nickel free stainless steel. The strengthening effect is contributed by both the matrix grain refinement and the toughness enhancement. According to results of all mechanical tests done on composites, composite with 50 wt.% nickel free stainless steel has the most appropriate mechanical properties among other composites for using in orthopaedic applications.     

纳米SiO2改性聚合物水泥基复合材料早期微观结构及性能

利用纳米SiO₂(nano SiO₂)早期可促进聚合物水泥基复合材料水化速率、提升其力学性能、改善其界面过渡区(ITZ)性能及优化其孔隙结构等特点,借助XRD、SEM、EDS、显微硬度(MH)及压汞(MIP)等试验,揭示了nano SiO₂对聚合物水泥基复合材料早期性能影响的微观机制。结果表明:当nano SiO₂掺量为2wt%时,聚合物水泥基复合材料的力学性能最优,3 d和7 d龄期抗压强度分别为57.5 MPa和67.3 MPa,较仅仅掺加聚合物的水泥基复合材料分别提高了12.7%和13.9%;nano SiO₂的掺入改变了聚合物水泥基复合材料水化产物数量及微观形貌。对于ITZ性能,nano SiO₂掺入后,聚合物水泥硬化浆体-骨料的ITZ厚度减小,形貌变得更加致密;ITZ的钙硅比因nano SiO₂的加入变小而其显微硬度变大;此外,nano SiO₂加入后可以进一步填充聚合物水泥基复合材料更加细小的孔隙,使其凝胶孔比例变高,最可几孔径变小,大大优化了聚合物水泥基复合材料的孔隙结构。      

氧化石墨烯增强水泥基复合材料的力学性能及微观结构

本文采用改进的Hummers法制备了氧化石墨烯（Graphene oxide,GO）悬浮液,通过FTIR、XRD和AFM等测试技术对GO晶体结构和尺寸形态进行了表征,考察了GO掺量和水灰比的变化对GO增强水泥基复合材料力学性能和微观结构的影响。结果表明：GO增强水泥基复合材料抗折抗压强度随GO掺量增加而先提高后降低,且对于抗折强度增强效果远超过抗压强度,当GO掺量为0.03%时,抗折强度达到最大值13.72 MPa;高水灰比条件下掺入GO对水泥胶砂强度的提高更显著;通过SEM对GO增强水泥基复合材料微观结构进行表征,发现GO能够优化水泥水化产物的微观结构形态,细化晶体尺寸,形成更加致密均匀的网络结构,从而改善水泥基复合材料的宏观性能。     

Influence of carbon nanotubes and dispersions of SiC on the physical and mechanical properties of pure copper and copper‐nickel alloy

This paper investigates the physical and mechanical properties of copper‐nickel alloy (at 50 wt.%–50 wt.%) and pure copper, mixed with various types of reinforcement materials such as carbon nanotubes (0.5 wt.%–2 wt.%) as nanoparticles, silicon carbide (1 wt.%–4 wt.%) as microparticles. The acquired composite specimens characteristics were estimated such as microstructure, density, electrical and thermal conductivity, hardness, and compression stress properties to determine the suitable reinforcement percentage that has the best physical and mechanical properties with different main matrix material whether copper‐nickel mechanical alloying or pure copper powder. The micron‐sized silicon carbide and nanosized carbon nanotubes were added to improve the mechanical and physical properties of the composite. The electrical and thermal conductivity of pure copper alloy enhanced compared with the copper‐nickel alloy matrix material. The hardness and compression yield stress of both pure copper and copper‐nickel composites have enhancement values and for copper‐nickel base composites hardness and compression yield stress have enhanced with the most positive enhancement values to examined an optimum percentage of reinforcing material.     

The effects of CNT alignment on electrical conductivity and mechanical properties of SWNT/epoxy nanocomposites

The single-walled carbon nanotubes (SWNTs) filled nanocomposite SWNT/epoxy resin composite with good uniformity, dispersion and alignment of SWNTs and with different SWNTs concentrations was produced by solution casting technique. Subsequently, the semidried mixture was stretched repeatedly along one direction at a large draw-ratio of 50 for 100 times at ambient atmosphere manually to achieve a good alignment and to promote dispersion of SWNTs in the composite matrix. Composite showed higher electrical conductivities and mechanical properties such as the Young’s modulus and tensile strength along the stretched direction than perpendicular to it, and the electrical property of composite rise with the increase of SWNT concentration. The percolation threshold value of electrical conductivity along the stretching direction is lower than the value perpendicular to the SWNTs orientation. In addition, the anisotropic electric and mechanical properties results, SEM micrograph and the polarized Raman spectra of the SWNT/epoxy composite reveal that SWNTs were well dispersed and aligned in the composites by the repeated stretching process.     

石墨烯含量对铜基石墨烯复合材料力学和电学性能的影响

为改进铜基复合材料的力学和电学性能,向铜基体分别加入0.2%、0.3%、0.4%(质量分数)的石墨烯,充分混合后,采用放电等离子烧结技术(SPS)制备了石墨烯/铜(G/Cu)复合材料。通过扫描电镜(SEM)、拉曼(Raman)光谱和XRD等表征了复合材料微观结构,测试了其硬度、屈服强度、抗压强度和导电率等性能,以确定石墨烯在铜基体中的合适掺杂量。结果表明:随着石墨烯含量的降低,其力电性能显著提高。当石墨烯质量分数为0.2%时,G/Cu复合材料的综合性能(力学及电学性能)达到最好匹配,实现了铜基材料的高强度、高导电性:其抗压强度和屈服强度分别为557.23 MPa和256 MPa,相对于用SPS方法制备的纯铜分别提高了59.21%和70.7%;电导率为52.3 MS/m,其IACS高达91.8%。     

Plant-based natural fibre reinforced cement composites: A review

The quest for sustainability in construction material usage has made the use of more renewable resources in the construction industry a necessity. Plant-based natural fibres are low cost renewable materials which can be found in abundant supply in many countries. This paper presents a summary of research progress on plant-based natural fibre reinforced cement-based composites. Fibre types, fibre characteristics and their effects on the properties of cement-based materials are reviewed. Factors affecting the fresh and hardened properties of cement-based composites reinforced with plant-based natural fibre are discussed. Measures to enhance the durability properties of cement-based composites containing plant-based natural fibres are appraised. Significant part of the paper is then focused on future trends such as the use of plant-based natural fibres as internal curing agents and durability enhancement materials in cement-based composites. Finally, applications and recommendations for future work are presented.     

Nickel particle based electrical resistance heating cementitious composites

In this study, electrical resistance heating cementitious composites are developed by employing nickel particles as conductive fillers and heating elements. The conductive properties of cementitious composites with different types and different content levels of nickel particles are investigated. The electrical resistance heating performance of the composites is studied. Deicing and snow-melting experiments are also performed in refrigerator and outdoor environment, respectively. Experimental results show that the cementitious composites with nickel particles can achieve a temperature increment of about 50 °C within 30 s when the input voltage is 20 V. At an input voltage of 15 V, the cementitious composites with nickel particles (12.0 vol.% and 2.6–3.3 μm diameter) can deice 3 mm of ice in 478 s under an ambient temperature of − 16.0 °C and melt 2 cm of snow in 368 s under an ambient temperature of − 5.3 °C, respectively. These findings indicate that the fabricated cementitious composites with nickel particles have a superior electrical resistance heating performance.     

0-3型压电陶瓷-硫铝酸盐水泥复合材料的压电性能

采用压制成型法,以快硬硫铝酸盐水泥为基体制备了水泥基压电复合材料。分析讨论了极化工艺条件和PZT含量对水泥基压电复合材料压电性的影响。结果表明,较高的极化电场强度和较长的极化时间均有利于压电性能的提高,但当极化电场强度和极化时间达到4.0 kV/mm和45 min后,压电应变常数d₃₃趋于稳定; 随着PZT含量的增加,硫铝酸盐水泥基压电复合材料的压电应变常数d₃₃、压电电压常数g₃₃和机电耦合系数K_P、K_t均显著增大。当PZT质量分数达到85%时,K_P和K_t可达28.54%和28.19%。      

New alignment procedure of magnetite–CNT hybrid nanofillers on epoxy bulk resin with permanent magnets

The main properties of epoxy composites reinforced with aligned carbon nanotubes (CNTs) have been studied. The alignment was carried out in a specific designed device applying a weak magnetic field (0.3 T) with permanent magnets. CNTs were modified with magnetite nanoparticles (Fe₃O₄) functionalized, in a one-stage-process which does not require use of strong acids or aggressive treatments which could affect the structural integrity of CNTs. The study by transmission electron microscopy confirmed that the Fe₃O₄ nanoparticles were closely bonded over CNT surfaces. The thermo-mechanical and tensile properties of composites measured were higher than neat epoxy resin and were similar for both composites: reinforced with neat CNTs and magnetite–CNT hybrid nanofillers. The electrical behaviour indicates a high anisotropy for aligned composites, showing an increase of one order of magnitude for the electrical conductivity in the direction of aligned nanotubes.     

Novel transcatheter aortic heart valves exhibiting excellent hemodynamic performance and low-fouling property

Transcatheter aortic heart valves (TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate (PEGDA) hydrogels and anisotropic high-shrinkage polyethylene terephthalate/polyamide6 (PET-PA6) fabric (PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses (DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties (i.e., storage moduli ～23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ～9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic (contact angle ～41.6° ± 3.8°) and had low-fouling properties without platelet adhesion, suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area (1.75 cm²) and low regurgitation (3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore, PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future.     

电场诱导多壁碳纳米管有序排列对多壁碳纳米管/环氧树脂复合材料性能的影响

采用交流（AC）电场诱导法制备了多壁碳纳米管（MWCNTs）均匀分散且定向有序排列的MWCNTs/环氧树脂复合材料。采用SEM、偏振拉曼光谱等研究了电场强度、MWCNTs含量、加电时间及温度（黏度）等因素对MWCNTs定向排列的影响,讨论了MWCNTs有序排列对MWCNTs/环氧树脂复合材料电学和力学性能的影响。结果表明：MWCNTs沿电场方向有序排列;MWCNTs/环氧树脂复合材料施加AC电场后的拉曼强度明显高于未施加电场的情况;当MWCNTs含量从0wt%增加到0.025wt%时,MWCNTs/环氧树脂复合材料导电率从2.3×10^-12 S/cm增加到1.3×10^-8 S/cm,增加了约4个数量级;MWCNTs含量为2.5wt%时,MWCNTs/环氧树脂复合材料拉伸强度提高了26.3%。