In this study, the graphene reinforced aluminium matrix nanocomposite is fabricated through the combination of high energy ball milling (HEBM) and molecular level mixing (MLM) processes followed by ...spark plasma sintering (SPS) method. FTIR, XRD and FESEM analyses revealed that Cu/RGO nanocomposite was well synthesized by the MLM method with a uniform distribution of Cu nanoparticles on RGO surface. XRD and Raman spectroscopy showed that no Al4C3 phase was formed during the manufacturing process, but Al2Cu fine particles precipitated during the SPS treatment which were smaller in size and more uniform in distribution when RGO was used as reinforcement according to TEM analysis. Grain refinement of the nanocomposites was also investigated in the presence of RGO by EBSD method. The results showed that with increasing RGO content from 0 to 1 wt %, the coarse grained microstructure changed to bimodal microstructure. In addition, the mean grain size decreased from 3.9 to 1.6 μm, and dislocation density increased significantly with the increased RGO content. The SPS process also resulted in a nearly fully dense nanocomposite with a relative density higher than 99%. The investigation of mechanical properties of the sintered nanocomposite indicated an improvement of 79, 49 and 44% of yield strength, ultimate strength, and Vickers hardness, respectively, for only 1 wt % graphene containing nanocomposite in comparison to the unreinforced Al–4Cu alloy.
The anodic oxidation process is a common method for the surface modification of aluminium and its alloys. The increasing application of high-strength aluminium alloys therefore represents a ...challenge, since alloying elements, amongst them copper, significantly disturb the coating formation during anodising. Hence, flaws arise in the oxide layers and lead to the deterioration of their performance. Recent investigations have indicated the possibility of extenuating the negative influence of the alloying elements on the coating formation by applying time-variable electrical regimes. In case of the current density as the control factor in the coating process, this approach is related to as dynamic current control. For the anodic oxidation of AlCu4Mg1 (EN AW-2024), the effect of dynamic current control on the oxide layer properties is investigated by using a design of experiments (DOE). The parameter variation includes starting ramps, a step-wise change of the current density in the process and pulse current at electrolyte temperatures of 5°C and 15°C. A solution of 20vol% sulphuric acid with an addition of oxalic acid or nitric acid is used as the electrolyte. The produced oxide coatings are examined with regard to their thickness, hardness, their performance in the scratch test and their current density-potential behaviour in diluted NaCl solution. Further, the electrical energy consumption during the anodisation is considered. The results are evaluated with the help of an analysis of variance (ANOVA).
•The effect of the electrolyte and dynamic current control on the anodisation was investigated with a DOE.•Statistical relevance of the varied parameters was assessed via an analysis of variance (ANOVA).•Nitric acid additive decreased the electrical energy consumption for the anodisation without deteriorating coating properties.•Pulse current increased the hardness of the coatings.•A step-wise increase of the current density during the process improved the corrosion behaviour.
A patterned silicon electrode as the anode of lithium ion batteries is fabricated by microfabrication technology. An ultrathin alumina layer is coated on the patterned electrode by atomic layer ...deposition (ALD). This results in obviously enhanced coulombic efficiency and cycling performance.
Life cycle assessment was performed using a bottom-up approach combined with national and regional statistical data to estimate the environmental footprint of aluminum production in China. In the ...footprint of aluminum production, the environmental effects of bauxite, aluminum oxide, and electrolytic aluminum accounted for approximately 1.4%, 8%, and 90.6% of the overall environmental burden, respectively. The amounts of CO2, particulates, NOX and SO2 generated in the aluminum industry accounted for approximately 3.53%, 1.99%, 3.47%, and 5.34% of the total national emission in China in 2012, respectively. More than 94% of the global warming and fossil depletion potential impacts can be saved through aluminum recycling. Electricity and natural gas consumption, transport, and solid waste disposal were the dominant contributors to primary and secondary aluminum production. The use of bitumen and inorganic chemicals also influenced primary and secondary aluminum production, respectively. Effective approaches to reduce the environmental burdens of aluminum production include replacing coal with clean energy sources for electricity production, improving the efficiency of energy and raw material consumption, and increasing the national recycling rate of aluminum.
•Aluminum production in China was subjected to bottom-up-based LCA.•Regionalized LCIA assessment model and national statistical data were used.•Primary aluminum production generates the most environmental burden.•The dominant contributor to environmental impact is energy consumption.•Changing electricity structure and improving energy use efficiency are vital.
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•Aluminum hydroxide nanoparticles were synthesized by wet oxidation methods.•The oxidation conditions of AlN/Al affect the morphologies of the reaction products.•No changes in the ...synthesized materials morphology occurred up to 1000 °C.•The maxima specific surface areas for the nanostructures were achieved at 500 °C.
A simple and environmentally friendly method to prepare aluminum oxyhydroxide and trihydroxide nanostructures by wet oxidation of AlN/Al composite nanoparticles was developed. The AlN/Al nanoparticles used were produced by electrical explosion of an aluminum wire in nitrogen atmosphere. The obtained nanostructures were characterized employing X-ray diffraction (XRD), transmission and high-resolution scanning electron microscopy (TEM and HRSEM), thermogravimetric analysis (TGA) and N2 adsorption-desorption technique (BET). By changing the wet oxidation conditions, aluminum hydroxides with different phase composition, morphology and texture characteristics were synthesized. After calcination at different temperatures, a range of transition and stable alumina nanostructures were obtained that preserved the morphology of the aluminum hydroxide precursors - agglomerated nanosheets, nanoplates or hexagonal nanorods, up to 1000 °C. Optimal process parameters for maximum surface area development for all the precursor materials have been established.
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•Current iron recovery techniques using red mud are depicted.•Advantages and disadvantages exist in different recovering processes.•Economic and environmental friendly integrated ...usage of red mud is promising.
Bauxite residue (red mud) is a hazardous waste generated from alumina refining industries. Unless managed properly, red mud poses significant risks to the local environment due to its extreme alkalinity and its potential impacts on surface and ground water quality. The ever-increasing generation of red mud poses significant challenges to the aluminium industries from management perspectives given the low proportion that are currently being utilized beneficially. Red mud, in most cases, contains elevated concentrations of iron in addition to aluminium, titanium, sodium and valuable rare earth elements. Given the scarcity of iron supply globally, the iron content of red mud has attracted increasing research interest. This paper presents a critical overview of the current techniques employed for iron recovery from red mud. Information on the recovery of other valuable metals is also reviewed to provide an insight into the full potential usage of red mud as an economic resource rather than a waste. Traditional hydrometallurgy and pyrometallurgy are being investigated continuously. However, in this review several new techniques are introduced that consider the process of iron recovery from red mud. An integrated process which can achieve multiple additional values from red mud is much preferred over the single process methods. The information provided here should help to improve the future management and utilization of red mud.
X-ray Raman scattering (XRS) spectroscopy and small angle x-ray scattering (SAXS) are used to study water in aqueous solutions of NaCl, MgCl(2), and AlCl(3) with the particular aim to provide ...information about the structure of the hydration shells of the cations. The XRS spectra show that Na(+) weakens the hydrogen bonds of water molecules in its vicinity, similar to the effect of increased temperature and pressure. Mg(2+) and Al(3+), on the other hand, cause the formation of short and strong hydrogen bonds between the surrounding water molecules. The SAXS data show that Mg(2+) and Al(3+) form tightly bound hydration shells that give a large density contrast in the scattering data. From the form factors extracted from the SAXS data, we found that Mg(2+) and Al(3+) have, respectively, an equivalent of one and one and a half stable hydration shells that appear as a density contrast. In addition, we estimated that the density of water in the hydration shells of Mg(2+) and Al(3+) is, respectively, ∼61% and ∼71% higher than in bulk water.
Accelerator Mass Spectrometry (AMS) has been a frequently used technique for analysis of low-level concentrations of 26Al in environmental, biological and space samples with detection limits down to ...0.01 fg. Al2O3 targets have been mostly used in ion sources for the production of aluminium negative ions because of high-temperature stability, non-toxicity, in-air stability, and relatively easy production procedures. It is well known, however, that aluminium does not yield as intense negative ion beams as other elements used in tandem AMS accelerators. An alternative solution could be to use as the target material AlN, which can yield higher Al− currents. On the other hand, the AlN targets are more difficult to synthesize, and they decompose with water in the air to form Al(OH)3 and ammonia. Commercially available compounds of Al2O3 and AlN were mixed with copper, silver and iron high-purity powders and sputtered in a MC-SNICS ion source for studying ionization yields. Since the production of magnesium and nitrogen negative ions is negligible, a production of MgN− molecules has been questionable. Obtained results indicate that the aluminium nitride matrix could be a suitable material for AMS measurements as the production of 27Al− is higher by a factor of 1.8 from the aluminium oxide matrix, while aluminium sulphate and aluminium fluoride showed a very low sputtering efficiency. The formation probability of the MgN− was tested using AlN and Mg3N2 matrices. The AMS measurements of 26Al using AlN− as injected ions from the AlN matrix, similar to AlO− ions from Al2O3 matrix, have shown that further isobar suppression due to a high 26Mg3+ production rate will be needed.
Soluble inorganic aluminium compounds like aluminium sulfate or aluminium chloride have been challenged by the European Chemical Agency to induce germ cell mutagenicity. Before conducting ...mutagenicity tests, the hydrolysis products in water and in physiological solutions should be determined as a function of the concentration and pH. We used different 27Al NMR spectroscopic techniques (heteronuclear Overhauser effect spectroscopy (HOESY), exchange spectroscopy (EXSY), diffusion ordered (DOSY)) in this work to gain the information to study the aluminium species in solutions with Al2(SO4)3 concentrations of 50.0, 5.0, and 0.5 g/L and their pH and time dependent transformation. At low pH, three different species were present in all physiological solutions and water: Al(OH)n(H2O)6 − n(3 − n)+ (n = 0–2), Al(H2O)5SO4+, and Al2(OH)2(H2O)84+. Increasing pH reduced the amounts of the two monomer species, with a complete loss at pH 5 for solutions with a concentration of 50.0 g/L and at pH 4 for solutions with a concentration of 5.0 g/L. The dimer species Al2(OH)2(H2O)84+ is present in a pH range between 3 and 6. Less symmetric oligomeric and probably asymmetric aluminium species are formed at pH of 5 and 6. The pH value is the driving force for the formation of aluminium species in all media, whereas the specific medium had only minor effect. No conclusive information could be obtained at pH 7 due to signal loss related to fast quadrupole relaxation of asymmetric aluminium species. A slight reduction of the content of the symmetric aluminium species due to the formation of oligomeric species was observed over a period of 6 weeks. Reference 27Al NMR experiments conducted on saturated water solutions of AlCl3 and those with a concentration of 50 g/L show that the type of salt/counter ion at the same concentration and pH influences the hydrolysis products formed.
Aluminum is an ideal material for metallic fuel cells. In this research, different grain sizes of aluminum anodes are prepared by equal channel angular pressing (ECAP) at room temperature. ...Microstructure of the anodes is examined by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Hydrogen corrosion rates of the Al anodes in 4 mol L−1 NaOH are determined by hydrogen collection method. The electrochemical properties of the aluminum anodes are investigated in the same electrolyte using electrochemical impedance spectroscopy (EIS) and polarization curves. Battery performance is also tested by constant current discharge at different current densities. Results confirm that the electrochemical properties of the aluminum anodes are related to grain size. Finer grain size anode restrains hydrogen evolution, improves electrochemical activity and increases anodic utilization rate. The proposed method is shown to effectively improve the performance of Al–air batteries.
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•Higher electrochemical performance of Al anode with finer grain size.•The capacity and energy density of 2308 mAh g−1 and 3525 mWh g−1 with finer grain size Al anode.•Improvement by 41.5% of capacity density and 55.5% of energy density as compared with the cast anode.
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