Al Nanocomposites Research Articles

Improvement of cement-based mortars by application of photocatalytic active Ti–Zn–Al nanocomposites

Photocatalytic active TiO2 has been extensively applied in construction material science due to its ability to remove pollutants from material surfaces. New inorganic–inorganic nanocomposite photocatalyst based on layered double hydroxides (LDHs) associated to TiO2 were introduced in order to increase the compatibility of photocatalyst with cement-based mortars. Different materials were prepared and characterized: cement paste with Ti–Zn–Al powder, mortar with cement paste finishing layer containing Ti–Zn–Al LDH and mortar with Ti–Zn–Al coatings. Degradation of methylene blue under UV light was selected as photocatalytic test reaction. The correlation between surface properties and photocatalytic activity was analyzed. The synergetic effect between TiO2 and Zn–Al-LDH contributes to pronounced photocatalytic performances, improving at the same time mortar performances as an important indicator of the compatibility of photocatalyst with mortar. The photocatalyst introduction procedure influences the active sites surface concentration, giving preference to surface coating method. However, introduction of photocatalyst into the bulk, having lower photocatalytic activity, results in an overall more stable system for prolonged application.

Thermal and photocatalytic behavior of Ti/LDH nanocomposites

The development of nanocomposite photocatalyst based on layered double hydroxides (LDHs) associated with TiO2 was the subject of this research. The thermally activated Zn–Al LDHs were selected as catalyst support precursor because of their proven photocatalytic activity and therefore their possible contribution to overall activity of novel Ti–Zn–Al nanocomposite. The catalyst precursor (Zn–Al LDH) was synthesized by low supersaturation coprecipitation method, and its association with active TiO2 component targeting the formation of novel Ti–Zn–Al nanocomposite was achieved by wet impregnation. Simultaneous thermal analysis (TG–DTA) was used to investigate the thermal behavior of Zn–Al LDH and Ti–Zn–Al LDHs. Complementary, morphology, texture, and structure characterization was carried out. The photocatalytic test reaction was performed under UV light using the methylene blue degradation. The results confirmed a successful impregnation of TiO2 on catalyst support precursor Zn–Al–LDH followed by considerable change in morphology and structure of Zn–Al LDH precursor. It was concluded that the synergic effect between TiO2 and Zn–Al LDH precursor contributes to the overall photocatalytic activity.

Fabrication of Al2O3–20 vol.% Al nanocomposite powders using high energy milling and their sinterability

In this study, alumina-based matrix nanocomposite powders reinforced with Al particles were fabricated and investigated. The sinterability of the prepared nanocomposite powder at different firing temperature was also conducted. Their mechanical properties in terms of hardness and toughness were tested. Alumina and aluminum powder mixtures were milled in a planetary ball mill for various times up to 30h in order to produce Al2O3–20% Al nanocomposite. The phase composition, morphological and microstructural changes during mechanical milling of the nanocomposite particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) techniques, respectively. The crystallite size and internal strain were evaluated by XRD patterns using Scherrer methods.A uniform distribution of the Al reinforcement in the Al2O3 matrix was successfully obtained after milling the powders. The results revealed that there was no any sign of phase changes during the milling. The crystal size decreased with the prolongation of milling times, while the internal strain increased. A simple model is presented to illustrate the mechanical alloying of a ductile–brittle component system. A competition between the cold welding mechanism and the fracturing mechanism were found during powder milling and finally the above two mechanisms reached an equilibrium. The maximum relative density was obtained at 1500°C. The harness of the sintered composite was decreased while the fracture toughness was improved after addition Al into alumina.

Microstructure and mechanism of in-situ Al2O3(p)/Al nano-composites synthesized by sonochemistry melt reaction

The Al2O3(p)/Al nano-composites were fabricated from Al—K2ZrF6—Na2B4O7 system by sonochemistry in situ reaction. The fabrication mechanisms, including high intensity ultrasonic influence on microstructures and reinforcement particles-aluminum matrix interface, were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that the component of the as-prepared composites is Al2O3 reinforcement. The SEM analysis results indicate that Al2O3 particles are uniformly distributed in the aluminum matrix. The TEM results show that the morphologies of Al2O3 particles present in nearly sphere-shape, the sizes are in the range of 20—100 nm, and the interfaces are net and no interfacial outgrowth is observed. Analysis with secondary development Image-J software shows that Al2O3 recoveries are firstly improved and then decreased with increasing ultrasonic power. When the power is 0.4 kW, the distribution is the best, and a maximum number of particles are obtained. The reaction mechanisms were investigated.

Machining characteristics of nanocomposites

Nanocomposites were prepared with Al/Al-Si alloys (LM 6 and LM 25) as matrix and multi wall carbon nanotube (MWNT) of 0.25, 0.5, 0.75, 1.0 and 1.5 wt. % as reinforcement through powder metallurgy (PM) followed by sintering and hot extrusion techniques. Fabricated nanocomposites were machined on a Panther 1530/1650 lathe by using tungsten carbide tool. Recurrence quantification analysis (RQA) was used to study the machining characteristics by using cutting force signal stability. Highest value of determinism (DET-one of the RQA parameter) was observed for 0.5 wt.% MWNT reinforced Al and Al-Si nanocomposites. This attributes better machining characteristic due uniformity of the signals. Also it is observed better mechanical properties at 0.5 wt.% reinforced nanocomposite and further reinforcement deteriorate the machinability and mechanical properties. Copyright © 2011 VBRI press.

High Strength Aluminum Nanocomposites Reinforced with Multi-Walled Carbon Nanotubes

Multi-walled carbon nanotube (MWCNT) reinforced aluminum (Al) nanocomposites were synthesized using powder metallurgy technique followed by hot extrusion. 0-3wt.% MWCNTs were incorporated. Simultaneous improvements in density, harness and tensile strength were obtained with the incorporation of MWCNTs in the Al matrix. An enhancement in tensile strength as high as 120% was obtained in the Al-2.0MWCNT compared to monolithic Al. A comparison was made between the experimental tensile strengths of the nanocomposites and the predicted ones determined by Kelly-Tyson model. It is found that declined value of the experimental result at higher MWCNT content (above 2wt.%), attributed to the clustering of the MWCNTs at higher addition.

Improvement in load support capability of a-C(Al)-based nanocomposite coatings by multilayer architecture

Due to severe operating conditions and long lifetime requirements for mechanical components, the great challenge is to develop coatings with anti-wear and high load support capability. The designs for nanocomposite protective coatings are very promising and provide an attractive alternative to take into account the multilayer architecture. In this work, a-C(Al)-based nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were constructed by Cr/CrN/CrCN multilayer. The microstructure, mechanical properties, friction and wear behaviors for these multilayer coatings were systemically investigated. Results showed that the top-layered nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were dominated by typically nanocrystallite/amorphous microstructure, and these nanocomposites constructed by multilayer approach presented superior mechanical properties which possessed relatively high hardness, low internal stress as well as high adhesion strength. Particularly, the as-fabricated nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) multilayer coatings exhibited superior anti-wear capability under relatively high applied Hertzian contact pressure compared to corresponding monolayer coatings. The improvement in friction and wear performances of as-fabricated multilayer coatings was mainly attributed to superior mechanical properties and formation of graphitized tribofilm as well as high load support capability by multilayer architecture, indicating that these coatings might be good candidates as solid lubrication materials in engineering applications.

High strain rate induced localized amorphization in cubic BN/NiCrAl nanocomposite through high velocity impact

Localized amorphous layer induced by a high-velocity impact in a cubic BN particle-reinforced face-centered cubic Ni (Cr, Al) nanocomposite was observed by high-resolution transmission electron microscopy. The Ni-based amorphous layer, which had a thickness ranging from ∼3 to ∼8 nm, was located at the cBNp/NiCrAl interface and was surrounded by the crystalline Ni-based alloy. These Ni-based alloy crystals exhibited a preferred orientation with the {1 1 1} planes frequently parallel to the interfaces of cBN/NiCrAl.

Wear behaviour of Al–Al2O3 nanocomposites prepared by mechanical alloying and hot pressing

In the present study, the wear characteristics of Al nanocomposites containing various amounts of nanosized Al2O3 (4, 8, 12 and 16 wt-%) particulates in pin on disc dry sliding tests were investigated. The results showed that the hardness and wear resistance increased with increasing Al2O3 content of the nanocomposites. The specific wear rate, as well as the wear and friction coefficients, has been evaluated from wear data to understand the roles of subsurface plastic deformation and work hardening on wear behaviour. Examination of the wear surfaces suggested that wear involves the removal of softer Al as flakes and transfer of Fe from the steel pin to the surface of the composite disc. The dominating wear mechanisms appear to be adhesion and delamination in Al–Al2O3 with lower and higher percentage of Al2O3 respectively.

Sb-MOx-C (M = Al, Ti, or Mo) Nanocomposite Anodes for Lithium-Ion Batteries

Sb-MOx-C (M = Al, Ti, and Mo) nanocomposites have been synthesized by a mechanochemical reduction of Sb2O3 with, respectively, Al, Ti, and Mo, in the presence of carbon (acetylene black). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) data reveal that these nanocomposites are composed of uniformly dispersed nanostructured antimony in the amorphous Al2O3, TiO2, or MoO3 matrix, along with conductive carbon. These composite electrodes exhibit excellent electrochemical cycling performance and rate capability in lithium cells, compared to pure antimony. Among the three Sb-MOx-C systems studied, the M = Al system with Al2O3 as the amorphous phase exhibits the best electrochemical performance, offering a capacity of >430 mAh/g after 100 cycles. The improvement in the cycling performance, compared to that of pure antimony, is attributed to a homogeneous distribution of the electrochemically active Sb nan...

Mechanical properties and microstructures of carbon nanotube-reinforced Al matrix composite fabricated by in situ chemical vapor deposition

This work reports CNT-reinforced Al nanocomposites fabricated with in situ chemical vapor deposition process for achieving homogeneous dispersion of CNTs and good interfacial bonding between CNT and metallic matrices. The mechanical strength of CNT/Al nanocomposites is dependent on CNT addition, while the fracture strain degrades compared with that of pure metal. The good reinforcement of CNT/metal nanocomposites is attributed to the strong interfacial bonding as well as the homogeneous dispersion of CNTs in the matrix. Furthermore, the strong interfacial bonding is due to the existence of transition thin layer of Al 4C 3 between CNTs and Al matrix.

Polyethylene/aluminum nanocomposites: Improvement of dielectric strength by nanoparticle surface modification

AbstractThe effect of the surface modification with a silane coupling agent (octyl‐trimethoxysilane) of aluminum (Al) nanoparticles on the dielectric breakdown behaviors of polyethylene (PE)/Al nanocomposites was investigated in comparison of the influence of the improvement of the interfacial adhesion between Al nanoparticles and PE using a compatibilizer (maleic anhydride grafted polyethylene). It was found that when compared with the other modification approaches, the surface‐treated Al nanofiller with the silane coupling agent makes it possible for the PE/Al nanocomposites to still keep the relatively higher breakdown strength even in the higher Al loading level above 14 vol %, which can be understood in terms of the better interfacial adhesion between the surface‐treated particle dispersion and the matrix. The combined effects of the Al nanoparticles on the different factors which influence the dielectric breakdown processes in polymer matrix such as microstructure, conductivity, and crystallinity of the nanocomposites were discussed in detail. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Correlation between rheological, electrical, and microstructure characteristics in polyethylene/aluminum nanocomposites

AbstractPolyethylene (PE)/aluminum (Al) nanocomposites with various filler contents were prepared by a solution compounding method. We investigated the influence of the surface modification of Al nanoparticles on the microstructure and physical properties of the nanocomposites. The silane coupling agent octyl‐trimethoxysilane was shown to significantly increase interfacial compatibility between the polymer phase and Al nanoparticles. Rheological percolation threshold values were determined by analyzing the improvement in storage modulus at low frequencies depending on the Al loadings. Lower percolation threshold values were obtained for the composites prepared with the original nanoparticles than those prepared with the silane‐modified Al nanoparticles. A strong correlation between the time and concentration dependences of dc conductivity and rheological properties was observed in the different nanocomposite systems. The rheological threshold of the composites is smaller than the percolation threshold of electrical conductivity for both of the nanocomposite systems. The difference in percolation threshold is understood in terms of the smaller particle–particle distance required for electrical conduction when compared with that required to impede polymer mobility. It was directly shown by SEM characterization that the nanoparticle surface modification yielded better filler dispersion, as is consistent with our rheological and electrical analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2143–2154, 2008

Effect of annealing treatment on the oxidation of an electrodeposited alumina-forming Ni–Al nanocomposite

An electrodeposited alumina-forming Ni–Al nanocomposite having a nanocrystalline Ni matrix dispersing Al nanoparticles was annealed in vacuum at 600 °C, leading to coarsened Ni grains that were doped with a certain amount of Al atoms diffused from the nanoparticles. Oxidation in air at 1000 °C indicated that the annealing decreased the oxidation of the nanocomposite, due to a promotion in the formation of a protective alumina layer. A progressive-oxidation mode demonstrating the competing growth of alumina on the as-deposited and annealed nanocomposites was proposed, as an explanation of the accelerated development of the alumina layer on the annealed nanocomposite.

Preparation, microstructure and properties of polyethylene aluminum nanocomposite dielectrics

Linear low density polyethylene (PE) aluminum (Al) nanocomposites were prepared and their morphology and properties were investigated. The particular attention was given to the structure/property relationship of the nanocomposites and an equivalent electric circuit model was proposed to interpret the dependences of the dielectric behaviors of the PE/Al nanocomposites on the nanoparticle concentration and the measuring frequency. The increase of the dielectric constant shows the effectiveness of Al nanoparticles in altering the intrinsic dielectric properties of PE. The microstructure transition revealed by morphological investigations has been also verified at the same composition as that from the rheological data. And also, it has been found that the nanocomposites at high filler concentrations still keep good mechanical properties and breakdown strength, which is very important for practical applications.

Morphology and Magnetic Properties of Fe and Al Nanocomposites Prepared with Single and Double-Glow-Discharge Sources

Fe and Al nanocomposites have been prepared using the plasma-gas-condensation cluster deposition system and investigated by transmission electron microscope and magnetization measurements. In Fe-Al alloy clusters assemblies prepared with the single glow discharge source there are bcc Fe-Al and B2-type ordered FeAl phases. In Fe/Al cluster composites prepared with double glow discharge sources, coreshell clusters are obtained: Fe cores are covered by Al and/or Al-oxide crystallites. In magnetization curves of the Fe-Al alloy cluster assembly and Fe/Al cluster composite, magnetic coercivity values are much smaller than that of an Fe cluster assembly. These results indicate that Fe-rich ferromagnetic Fe-Al phases exist in the Fe-Al alloy cluster assembly and Fe cores are covered and their magnetic coupling are weakened by Al and/or Al-oxide layers in the Fe/Al cluster composite. [doi:10.2320/matertrans.MRA2007280]

Electrical properties of polyethylene/aluminum nanocomposites

Understanding electrical properties of polymer nanocomposites is of great significance in order to diagnose and analyze physical and chemical behaviors of the composites as well as their own dielectric properties and can provide valuable data for improving the characteristics of the nanocomposites. In this work, the solution compounding method was used to prepare the polyethylene (PE)/aluminum (Al) nanocomposites. The dielectric permittivity and loss tangent of the PE/Al nanocomposites with different nanofiller loadings were investigated in the broad frequency range from 0.1 Hz to 10 MHz and the direct current (dc) conductivity and the dielectric breakdown strength of the PE/Al nanocomposites were also studied. The research results have shown that the dielectric permittivity shows different behaviors in the low and high frequency range. The permittivity values of the nanocomposites with the nanofiller loading levels of 0−48 wt % are found to show no percolative characteristics in the low frequency range below a few kilohertz whereas they tend to increase with the nanofiller loading increasing up to 24 wt % and show the percolative threshold. dc conductivity and dielectric breakdown strength of the nanocomposite are also observed to have percolation threshold characteristics, but the percolation phenomenon is observed to be rather early in the dielectric breakdown strength measurement than that found in the dielectric permittivity and dc conductivity tests because of the difference of the applied voltage level.

Cryomilling for the fabrication of a particulate B4C reinforced Al nanocomposite: Part I. Effects of process conditions on structure

Metal matrix composites (MMCs) are a relatively new category of engineering materials, which provide tailorable properties to meet specific needs. Cryomilling, mechanical milling at cryogenic temperatures, was employed in this study to fabricate nanostructured metal matrix composite powder with nanocrystalline aluminum alloys as the matrix and particulate B4C as the reinforcement. Cryomilling provided an extremely low temperature for the processing of this composite, which prevented the formation of secondary phases that are detrimental to mechanical properties. A uniform distribution of B4C in the Al and a clean strong interface between them were achieved. The contamination that results from cryomilling was analyzed. The effects of the B4C addition and the process control agent (PCA) on the microstructure of the composite powder were investigated. Results indicate that these additives had significant, yet opposing, effects on powder yield; a slight effect on contamination, particle size, and particle morphology; and no detectable effect on grain size refinement in the matrix.

Cyclic oxidation of alumina-forming Ni–Al nanocomposites with and without CeO 2 addition

CeO 2 nanoparticles were co-electrodeposited into an alumina-forming Ni–Al nanocomposite that was composed of nanocrystalline Ni matrix and dispersed Al nanoparticles. Cyclic oxidation in air at 1000 °C for 126 h showed that the alumina-forming nanocomposite scaled faster than its counterpart which contained a CeO 2 addition, due to the formation of numerous surface NiO nodules and internal oxidation of aluminum as a result of the composite intergranular cracking during the cycling. The intergranular cracking was profoundly prevented when the CeO 2 was present.

Thermal stability and oxidation properties of magnetron sputtered diamond-like carbon and its nanocomposite coatings

Diamond-like carbon or amorphous carbon (a-C) and its nanocomposite nc-TiC/a-C(Al) coatings have been exposed to temperatures up to 600 °C for one hour. Hardness and oxidation resistance have been studied using nanoindentation, Raman Spectroscopy, X-ray Diffraction and X-ray Photoelectron Spectroscopy. Pure a-C becomes thermally unstable at temperatures higher than 300 °C when coating hardness drastically drops with temperature because of graphitization that causes increase of sp 2 and decrease of sp 3 bonding structure. nc-TiC/a-C(Al) is stable up to 600 °C. Its hardness is not sensitive to temperature because the hardness mainly comes from the TiC nanocrystallites rather than sp 3 bonding. As such, the coating hardness experiences only a slight drop after annealing at 600 °C. The oxidation resistance of nc-TiC/a-C(Al) nanocomposite is much better than that of the pure a-C. Even after annealing in air at 600 °C for 1 h, nc-TiC/a-C(Al) coating still maintains its original thickness (while the pure a-C loses 60% of it).