碳纳米管增强铝基复合泡沫的阻尼性能

通过填加造孔剂方法制备了碳纳米管（CNTs）增强铝基复合泡沫,采用热机械分析仪研究了测试温度、频率、外加振幅、泡沫的孔隙率和CNTs含量对其阻尼性能的影响,并分析了相关阻尼机制。结果表明:复合泡沫铝的阻尼性能随孔隙率和振幅的增大而提高,随着频率的增加而下降。在环境测试温度25~200℃范围内,复合泡沫的损耗因子变化较小;当温度高于200℃后,损耗因子随温度升高有明显的提高。CNTs的加入可以显著提高泡沫铝的阻尼性能,常温下3.0% CNTs增强的铝基复合泡沫的损耗因子达0.27,为泡沫铝的3.71倍。复合泡沫的阻尼机制主要为位错阻尼、晶界阻尼、孔隙阻尼、CNTs的本征阻尼和CNTs-Al间界面阻尼,其中本征和界面阻尼发挥了重要的增强作用。      

碳纳米管增强2024铝基复合材料的力学性能及断裂特性

为了研究碳纳米管对铝基复合材料性能的影响,采用冷等静压、热挤压方法制备了质量分数1.0%的多壁碳纳米管增强2024Al基复合材料.采用扫描电镜、透射电镜和拉伸试验对复合材料的显微组织进行了观察和分析,并对其力学性能进行了测试.结果表明,碳纳米管均匀地分布在复合材料中,碳纳米管和铝基体的界面结合良好,没有发现界面产物Al4C3的形成;复合材料的断口上存在大量的撕裂棱,韧窝,并涉及碳纳米管的拔出或拔断与桥接,与2024Al基体材料相比,复合材料的硬度、弹性模量和抗拉强度显著提高,同时复合材料的延伸率却并不下降.碳纳米管的加入可以显著提高铝基复合材料的力学性能.     

Optical measurement in carbon nanotubes formation by pulsed laser ablation

Carbon nanotubes (CNTs) were produced by laser ablation of a graphite composite target in argon and nitrogen ambient gas. To investigate the effect of nitrogen gas on CNTs formation, the plasma plume was examined using optical emission spectroscopy. The vibrational temperature of C₂ molecules was estimated by fitting of a Swan band spectrum. The temperature in N₂ ambient gas is lower than that in Ar ambient gas. In a nitrogen atmosphere, the spectrum intensity of C₂ Swan band was enhanced and CN violet system was also observed. Soot collected in the reaction tube was observed using FE-SEM and TEM. The soot deposited in the nitrogen gas contained more bundled CNTs than those in Ar ambience.     

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.     

Simple method for synthesis of carbon nanotubes over Ni-Mo/Al2O3 catalyst via pyrolysis of polyethylene waste using a two-stage process

Synthesis of valuable multi-walled carbon nanotubes (MWCNTs) by thermal pyrolysis of low-density polyethylene (LDPE) waste was investigated via a two-stage process. The first stage was the thermal pyrolysis of LDPE to gaseous hydrocarbons, and the second stage was the catalytic decomposition of the pyrolysis gases over Ni-Mo/Al₂O₃ catalysts. Two catalysts with the compositions of 5.2%Ni-10.96%Mo/Al₂O₃ and 10%Ni-9.5%Mo/Al₂O₃ were tested for carbon nanotubes (CNTs) formation. The catalyst containing 10%Ni showed better activity in terms of CNTs production. Accordingly, the impact of either pyrolysis or decomposition temperatures was investigated using the 10%Ni-9.5%Mo/Al₂O₃ catalyst. TEM, XRD, Raman spectroscopy, TGA, TPR, and BET analysis tools were used to characterize the fresh catalysts as well as the obtained carbon nanomaterials. TEM images proved that MWCNTs with various morphological structures were obtained at all pyrolysis and decomposition temperatures. Moreover, cup-stacked carbon nanotubes (CS-CNTs) were observed at the decomposition temperature of 600°C. MWCNTs with the best quality were produced at decomposition temperature of 750°C. The optimum pyrolysis and decomposition temperatures in terms of CNTs production were at 700 and 650°C, respectively.     

2024Al和SiCp／2024Al基复合材料阳极氧化膜的耐蚀性

用动电位阳极极化和电化学阻抗技术研究了SiCp／2024Al复合材料硫酸阳极氧化膜在3．5％NaCl水溶液中的耐蚀性；作为比较，对2024Al的阳极氧化膜耐蚀性也进行了研究。结果表明，经阳极氧化处理的SiCp／2024Al复合材料具有良好的耐NaCl溶液腐蚀的能力，其腐蚀速度较未处理的样品降低了2个数量级以上。但其耐蚀性不如2024Al合金的阳极氧化膜。这是由于氧化膜中SiC颗粒的存在破坏了氧化膜的完整性和均匀性所致。对SiCp／2024Al MMC，采用小电流密度来进行阳极氧化处理，可获得较好的防护效果。此外，阳极氧化膜层的抗蚀性随浸泡时问的增加有降低的趋势。     

The effect of YAG laser surface treatment on corrosion resistance of Al18B4O33w/2024Al composite

As a new material, aluminum borate whisker reinforced aluminum composite has been considered for a wide range applications. However, addition of reinforcements to aluminum will change the corrosion behavior significantly. A pulsed YAG laser installation was used to produce surface treatment on Al₁₈B₄O₃₃w/2024Al composite. Electrochemical method was used to study the corrosion resistance in 3.5% sodium chloride (NaCl) solution. The crystalline phases of the composites with and without laser surface treatment were analyzed using X-ray diffraction (XRD) measurement technique. The cross-section morphologies of the laser-treated composite were characterized by scanning electron microscope (SEM). Polarization experiments showed that the sensibility to pitting corrosion for the laser treated specimen was greatly lower than that of the untreated specimen. The reduction of reinforcement Al₁₈B₄O₃₃ whisker and intermetallics CuAl₂ on the surface of the laser-treated composite along with the formation of the homogeneous and defect free microstructure in the laser-modified layer led to improvement on the corrosion resistance of the laser-treated composite.     

Thermal expansion behaviors of aluminum composite reinforced with carbon nanotubes

The coefficient of thermal expansion (CTE) of aluminum matrix composite reinforced with 1.0wt.% multi-wall carbon nanotubes (MWNTs) fabricated by cold isostatic pressing and hot squeeze technique was measured between 25 and 400 °C with a high-precision thermomechanical analyzer, and compared with those of pure aluminum and 2024Al matrix fabricated under the same processing. The results show that the CTE of the composite obviously reduces in relation to those of pure aluminum and 2024Al matrix due to the introduction of MWNTs. The addition of 1.0wt.% MWNTs to 2024Al matrix decreases the CTE by as much as 12% and 11% compared with those of pure aluminum and 2024Al matrix at 50 °C, respectively, which indicates that carbon nanotube reinforced metal matrix composite may be a promising materials with low CTE.     

Investigation of chlorination process in aluminum production by carbothermic-chlorination reduction of Al2O3 under vacuum

The chlorination process in aluminum production by carbothermic-chlorination reduction of Al₂O₃ under vacuum has been investigated by XRD, SEM and thermodynamic analysis. The results of thermodynamic calculations indicated that the chlorination of Al₄C₃ or Al₄O₄C possibly proceeded at temperature 1300 °C under 5-50 Pa. The experiment results showed that aluminum could be produced by the chlorination of Al₄C₃ or Al₄O₄C and the decomposition of AlCl(g). According to the analysis of experiment results, Al₄C₃ and Al₄O₄C were the main reactants participated in chlorination process in aluminum production by carbothermic-chlorination reduction of Al₂O₃ under vacuum. AlCl(g) generated in chlorination of Al₄C₃ or Al₄O₄C would decompose into Al and AlCl₃(g), and then aluminum product would condense in condensation tower.     

碳纳米管对激光选区熔化成形Al基复合材料的影响

基于激光选区熔化（SLM）方式,通过改变扫描速度,制备不同碳纳米管（CNTs,质量分数分别为0、0.5wt%、1.0wt%、1.5wt%、2.0wt%）含量的CNTs/Al复合材料试件,探究不同CNTs含量与激光扫描速度对试件性能的影响。结果表明,CNTs含量小于1.0wt%时,分散效果较好,大部分CNTs以单根状态黏附于Al粉表面;含量大于1.0wt%时,CNTs团聚尺寸增大、数量增多。相同SLM成形工艺下,低CNTs含量的CNTs/Al复合材料试件内部孔隙较少,致密度较高;高CNTs含量的CNTs/Al复合材料试件内部孔隙逐渐增多,致密度降低。激光扫描速度为1 300 mm/s工艺下,随着CNTs质量分数的增加,CNTs/Al复合材料试件硬度呈先上升后下降趋势,在CNTs含量为1.0wt%显微硬度达到最高。CNTs/Al复合材料试件平均晶粒尺寸相对于铝合金试件更加细化,在CNTs含量大于1.0wt%时,尽管晶粒依然细化,但试件致密度降低造成显微硬度下降明显。     

Synthesis of multi-walled carbon nanotubes via pyrolysis of plastic waste using a two-stage process

The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al₂O₃ catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/g_cat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock.     

Processing and interfacial bonding strength of 2014 Al matrix composites reinforced with oxidized SiC particles

The SiC powder with a SiO₂ protective layer is used as the reinforcements for 2014 Al/SiC_p composites to suppress the reaction between the Al matrix and the SiC particle. 2014 Al/SiC_p composites were fabricated by vacuum hot pressing (VHP) and subsequent extrusion using 2014 Al powders and the SiC particles covered with a SiO₂ layer. The interfacial product was found to be Mg spinel (MgAl₂O₄) formed mainly by the chemical reactions of the SiO₂ layer covered on SiC particles with the Mg, Al in the 2014 Al alloy matrix. Also the interfacial bonding strength of the composites was investigated using push-out tests of SiC rods with the SiO₂ oxidation layer, which were processed within 2014 Al alloy.     

Decoration of carbon nanotubes with nearly monodisperse MFe2O4 (MFe2O4, M = Fe, Co, Ni) nanoparticles

Magnetic monodisperse ferrite MFe₂O₄ (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe₂O₄ nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.     

Evaluation of thermal stability of ultrafine grained aluminium matrix composites reinforced with carbon nanotubes

The effect of carbon nanotubes on the thermal stability of ultrafine grained aluminium alloy processed by the consolidation of nano-powders obtained by mechanical alloying was evaluated via measurements of grain size and mechanical property changes upon annealing at various temperatures. It was found that the grain size of the samples containing carbon nanotubes is stable up to high temperatures and even after annealing at 450 °C (0.7T_m) no evident grain growth was observed. The limited grain boundary migration was attributed to the presence of entangled networks of carbon nanotubes located at grain boundaries and to the formation of nanoscale particles of aluminium carbide Al₄C₃. It was also revealed that carbon nanotubes decompose at a relatively low temperature of 450 °C and form fine Al₄C₃ precipitates. This transformation does not significantly affect the mechanical properties due to the nanoscale size of the carbides.     

The effect of H2-anneal on the adhesion of Al2O3 scales on a Fe3Al-based alloy

Abstract

The cyclic (1,100°C, air) and isothermal (1,000°C, O₂) oxidation behavior of a Fe-28Al-5Cr (at%) alloy, with and without a prior H₂-anneal heat treatment at 1,200°C for 100 h, was studied. Changes in interfacial chemistry were evaluated using Scanning Auger Microscopy after removal of the oxide film in ultra high vacuum. This was achieved by making a scratch on the specimen surface, which caused spallation of the film at various locations along the scratch. The scale thickness and the temperature drop at which spallation took place during cooling were utilized to semi-quantitatively compare the adherence of the scales. Porosity at the scale–alloy interface and the scale microstructure were determined from scanning electron microscope observations. It was found that H₂-anneal greatly improved scale adhesion and resulted in a pore-free and sulfur-free interface. The effects were similar to that of a 0.1 at% Zr-containing alloy, except that the improvement in scale adhesion was not as great as that from Zr doping. This implies that oxide/alloy interfaces are not intrinsically strong and the effect of reactive elements, such as Zr, is more than preventing impurity from segregating to the interface. Results are also compared with the effect of H₂-anneal on other model alloys, such as NiCrAl, FeCrAl and NiAl, and on single crystal superalloys.     

Creep behaviour of carbon containing Fe3Al alloy

Abstract

Tensile creep of a Fe–16 wt-%Al–0·5 wt-%C alloy was investigated over a temperature range of 773 to 873 K and stress range of 80 to 200 MPa. Creep curves exhibited very limited primary and secondary creep regimes. An extended tertiary creep regime was observed for all the test conditions. Stress dependence of minimum creep rate can be represented by a power-law equation with stress exponents being in the range 4 to 5. The activation energy for creep was found to be ～340 kJ mol^?1. The observed stress exponent and activation energy for creep suggest that creep is controlled by dislocation climb. Creep fracture in Fe₃Al–C alloy is predominantly by transgranular ductile mode by nucleation, growth and coalescence of microvoids formed at FeAlC_0·5 particle/matrix interface by decohesion as well as fracture of elongated particles. Extended tertiary creep observed in the alloy was analysed in the light of the mechanisms proposed for nickel based superalloys.     

Toxicity mechanism of carbon nanotubes on Escherichia coli

The influences of carbon nanomaterials on bacteria were investigated using three types of dispersed and functionalized carbon nanomaterials (F-CNMs), viz. functionalized carbon nanopowder (F-CNP), functionalized single-walled carbon nanotubes (F-SWCNTs), and functionalized multi-walled carbon nanotubes (F-MWCNTs). F-CNMs with different aspect ratios were used to study the influence of material configuration on the viability of Escherichia coli (E. coli). Although these materials were functionalized to improve their dispersibility, the original morphologies and chemical properties of the materials were maintained. Traditional bacteria quantitative plating analysis was conducted, and the results of which revealed that the F-CNP and the F-SWCNTs showed a less significant effect on the viability of E. coli, while the F-MWCNTs obviously inhibited cell viability. A Fourier transform infrared spectroscopy and a scanning electron microscopy were used to verify the functionalization of the F-CNMs and to examine the interaction of F-CNMs with E. coli, respectively; in addition, we adopted chemiluminescence assays to measure the concentration of adenosine triphosphate (ATP) released from the damaged cells. The results showed that the ATP of the F-MWCNTs sample is two-fold higher than that of the control, indicating direct piercing of E. coli by F-MWCNTs leads to bacteria death. Furthermore, F-SWCNTs were concluded to have less influence on the viability of E. coli because ultra-long F-SWCNTs used in this study performed less rigidity to pierce the cells.     

Wear resistant coatings: Silica sol-gel reinforced with carbon nanotubes

Pin-on-disc wear experiments have been carried out on sol-gel silica coatings reinforced with 0.1 wt.% carbon nanotubes (CNTs) deposited on WE54 magnesium alloy substrates by the dip-coating technique. Sol-gel solutions were fabricated using two different procedures: mechanical mixing (MM) and ultrasonic probe mixing. Dry sliding wear tests have been carried out at load of 1 N, speed of 0.1 m/s and sliding distance of 60 m. Friction coefficients were obtained from the tests and the specific wear rates (k) were calculated. The fabrication procedure of the coating influences its morphology and wear resistance. Friction coefficient was found to vary slightly with the addition of the CNTs. The wear volume of the magnesium substrate coated decreased by 40% and 80%, in terms of k, by using unreinforced and CNT-reinforced MM coatings, respectively. In MM layers reinforced with CNT uniform dispersion of the nanotubes was reached and toughening of the ceramic coating by pull-out and crack bridging mechanisms was observed.     

A theoretical analysis of flexional bending of Al/Al2O3 S-FGM thick beams

In this paper, an elastic, rectangular, and simply supported, sigmoid functionally graded material (S-FGM) beam of thick thickness subjected to uniformly distributed transverse loading has been investigated. The S-FGM system consists of ceramic (Al₂O₃) and metal (Al) phases varying through the thickness of beam. Major classes of representative theories such as classical laminate beam theory (CLBT), first-order shear deformation theory (FSDT) and high-order theories (HOTs) have been considered and a unified kinematic formulation is then proposed. The Poisson’s ratio of the thick S-FGM beam is assumed to be constant, but their Young’s moduli vary continuously throughout the thickness direction according to the volume fraction of constituents defined by sigmoid function. The numerical illustrations concern bending response of S-FGM rectangular beams. Qualitative and quantitative assessments of displacement and stress fields have been presented and discussed.     

Corrosion Behavior and Protection Efficiency of 2024Al and SiCp／2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite(SiCp/2024Al MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy.The results showed that the SiCp/2024AlMMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCl.For 2024Al,the anodized coating provides excellent corrosion resistance to 3.5%NaCl.The anodized coating on the SiCp/2024Al provides satisfactory corrosion protection,but it is not as effective as that for 2024Al because the structure of the anodized layer is affected by the SiC particulates.