Reduction Of Alumina Research Articles

Innovative Transformation and Valorisation of Red Mill Scale Waste into Ferroalloys: Carbothermic Reduction in the Presence of Alumina

Primary and secondary mill scales (MSs) are waste products produced by the surface oxidation of steel during the hot (800 to 1200 °C) rolling process in downstream steelmaking. While the primary MS is comprised of FeO, Fe3O4, and Fe2O3 in a range of proportions, the secondary MS primarily contain red ferric oxide (Fe2O3) (red MS). We report a novel route for extracting iron from red MS and transforming it into ferro-aluminium alloys using carbothermic reduction in the presence of alumina. The red MS powder was blended with high-purity alumina (Al2O3) and synthetic graphite (C) in a range of proportions. The carbothermic reduction of red MS-Al2O3-C blends was carried out at 1450 °C and 1550 °C under an argon atmosphere for 30 min and then furnace-cooled. The red MS was completely reduced to iron at these temperatures with reduced iron distributed around the matrix as small droplets. However, the addition of alumina unexpectedly resulted in a significant increase in the number and sizes of iron droplets generated, much higher reactivity, and the formation of ferrous alloys. A small amount of alumina reduction into metallic aluminium was also observed at 1450 °C. There is an urgent need to identify the true potential of industrial waste and the materials within it. This study showed that red MS is a valuable material source that could be transformed into ferro-aluminium alloys. These alloys find application in a range of industrial sectors such as construction, automotive, infrastructure, etc.

Aluminum precipitation on oxygen-deficient alumina in laser alumina reduction

Alumina reduction by thermal decomposition using CW laser ablation is being studied to obtain aluminum and oxygen on the lunar surface without the use of reducing agents such as carbon or hydrogen. When an alumina rod is heated by a laser beyond the ablation temperature, oxygen-deficient alumina (Al2O2.4-2.8) and aluminum microparticles are generated on the laser-irradiated surface. For this study, rods made of oxygen-deficient alumina were ablated to obtain more aluminum than normal alumina ablation. Results show that approximately 1.7 times as much aluminum was precipitated as that obtained from normal alumina ablation. The average particle size of the precipitated aluminum particles was found using SEM image analyses to be about 1.6 times larger than that of normal alumina.

Interface catalytic reduction of alumina by nickle for the aluminum nanowire growth: Dynamics observed by in situ TEM

Metal nanowires show promise in a broad range of applications and can be fabricated via a number of methods, such as vapor–liquid–solid process and template-based electrodeposition. However, the synthesis of Al nanowires (NWs) is still challenging from the stable alumina substrate. In this work, the Ni-catalyzed fabrication of Al NWs has been realized using various Al2O3 substrates. The growth dynamics of Al NWs on Ni/Al2O3 was studied using in situ transmission electron microscopy (TEM). The effect of alumina structures, compositions, and growth temperature were investigated. The growth of Al NWs correlates with the Na addition to the alumina support. Since no eutectic mixture of nickel aluminide was formed, a mechanism of Ni-catalyzed reduction of Al2O3 for Al NWs growth has been proposed instead of the vapor–liquid–solid mechanism. The key insights reported here are not restricted to Ni-catalyzed Al NWs growth but can be extended to understanding the dynamic change and catalytic performance of Ni/Al2O3 under working conditions.

In Situ H2 Reduction of Al2O3-Supported Ni- and Mo-Based Catalysts

Nickel (Ni)-promoted Molybdenum (Mo)-based catalysts are used for hydrotreatment processes in the chemical industry where the catalysts are exposed to high-pressure H2 at elevated temperature. In this environment, the catalyst transforms into the active phase, which involves the reduction of the oxide. Here, we report on the first in situ study on the reduction of alumina supported Ni- and Mo-based catalysts in 1 mbar H2 using ambient-pressure X-ray photoelectron spectroscopy (APXPS). The study confirms that mixing Ni and Mo lowers the reduction temperature of both Ni- and Mo-oxide as compared to the monometallic catalysts and shows that the MoO3 reduction starts at a lower temperature than the reduction of NiO in NiMo/Al2O3 catalysts. Additionally, the reduction of Ni and Mo foil was directly compared to the reduction of the Al2O3-supported catalysts and it was observed that the reduction of the supported catalysts is more gradual than the reduction of the foils, indicating a strong interaction between the Ni/Mo and the alumina support.

Evaluation of ablation plume temperature for laser intensity and alumina powder particle density in alumina reduction

We considered the application of lunar regolith for the construction of a lunar base. To obtain aluminum as building materials, alumina powder reduction was performed using 1-kW-class continuous-wave diode laser ablation. The possibility of reduction, and the temperature dependences of the ablation plume on the laser intensity, ambient pressure, and particle density were investigated, and surface analysis was conducted using SEM and XPS. The laser intensity, ambient pressure, and particle density were set as 0.32–1.3 GW m−2, 10–100 kPa, and 16%–56%, respectively. Alumina reduction was verified by observing the 394- and 396 nm spectra of Al(I). The plume temperature increased with laser intensity in the range of 2700–4500 K. We achieved temperatures of 5200 K and 1000 K higher than with the CO2 laser by powder compression. Spheres that appeared to be aluminum were observed on the irradiated surfaces. However, this could not be proved because of the aluminum oxide layer.

Aluminum particle production on alumina rod surface by continuous-wave laser ablation

Continuous-wave laser ablation has been applied to alumina reduction with the eventual goal of lunar resource utilization. Aluminum particles were detected on the alumina rod surface after laser ablation. Impurity precipitation has been proposed as the aluminum particle production mechanism. For this study, distributions of aluminum particles and temperatures after laser ablation on an alumina rod surface were measured using SEM and two-color method. Laser power affected the aluminum particle distribution. The mean aluminum particle radius varied: 0.11–1.7 μm. The minimum value was consistent with the critical radius for aluminum nucleation in heterogeneous nucleation. The time history of surface temperatures was found to be independent of laser power. Therefore, aluminum particle production is expected to change with oxygen deficiency, and to increase with laser power. The obtained condition for aluminum particle production is applicable for an aluminum collection system in the alumina reduction method using laser ablation: the plate temperature of T = 933–2300 K and the cooling rate of 600–800 K/s.

An innovative route for valorising iron and aluminium oxide rich industrial wastes: Recovery of multiple metals

Several industrial wastes including biomass, fly ashes, red mud, mill scales, water treatment residues, have significant concentrations of metal oxides: Fe2O3, Al2O3, TiO2, SiO2 etc. Several efforts have been made towards recovering metals within these wastes. Rather than recovering one metal at a time, we report a novel approach for simultaneously extracting multiple metals from mixed oxides in a single process step. Using three distinct furnaces/heating regimes, the carbothermic reduction of Fe2O3/Al2O3/SiO2 system was investigated at 1450–1700 °C for up to 2 h over a wide composition range. Complete reduction was achieved for both Fe2O3 and SiO2 in all cases leading to the formation of Fe and Fe–Si alloys. The reduction of alumina at moderate temperatures was the key challenge. No alumina reduction was observed during reductions at 1450 °C. A partial reduction of alumina and the formation of Fe–Al alloys was detected in the Al2O3/Fe2O3/C system at 1550 °C. The formation of Fe–Si–Al alloys was also observed in the Fe2O3/SiO2/Al2O3/C system at 1550 °C. Complete reduction of alumina was observed at 1600–1700 °C, even for up to 50 wt% alumina in the system. Optimal operating conditions and reference standards were established for the simultaneous recovery of multiple metals from waste oxides. While conserving natural resources, this novel route will lower the burden on waste storage facilities with significant contributions to the economic and environmental sustainability of industrial waste management.

Combined heat and power production based on renewable aluminium-water reaction

Reduction and oxidation of aluminium offers an affordable solution for long term energy storage. Aluminium can be produced by reduction of alumina in smelter plants based on an electrowinning process that uses renewable electricity. It can be stored loss-free for as long as desired, and used as a “renewable energy carrier” from which heat and power can be produced by oxidation. A combined heat and power production unit based on aluminium as a “renewable fuel” is presented in this paper. It includes an aluminium-water reaction that produces hydrogen, aluminium hydroxide and heat, as well as a fuel cell that produces electricity from the hydrogen. It was designed for a throughput of 50 g Al per hour and a hydrogen production rate of 5.5 g/h, corresponding to an energy turnover of 400 W. Experiments were carried out over several hours and the production of heat and hydrogen was recorded and quantified. The results demonstrate the general feasibility as well as a high conversion efficiency of more than 90%. Analysis and further treatment of the resulting solid reaction products confirmed that the obtained aluminium-hydroxide may be converted into alumina and thus eventually re-introduced into a process for the production of aluminium again.

CFD analysis and experimental measurements of the liquid aluminum spray formation for an Al–H2O based hydrogen production system

The paper proposes a combined approach between numerical modeling and experimental measurements for the analysis of a cogeneration system based on the reaction of liquid aluminum and water steam. Scrap aluminum is used for hydrogen production and the primary one is employed as an energy carrier to transport the energy from the alumina reduction system to the site of the suggested plant. The analysis focuses on the liquid aluminum injection phase immediately downstream the nozzle.High frequency thermo-cameras are employed to qualitatively assess the thermal behaviour the liquid aluminum jet. Fast imaging techniques are used to capture the multiphase flow pattern of the liquid metal jet during the injection phase.The experimental results are used to validate a 2D multi-phase CFD approach. The computational fluid dynamics model of the injection phase is created and used to extend the measurements and deepen the understanding of the thermo-fluid dynamics behaviour of the system. In particular, the influence of different nozzles diameters and different injection pressures on the liquid aluminum jet is investigated.A modular approach is adopted for the domain subdivision in order to represent accurately all the geometrical features, while the volume of fluid approach is used to model the multi-phase flow distribution in the real geometry under actual operating conditions. Finally, a good agreement between the measurements and the calculations is found.

Laser power and wavelength dependence of alumina reduction using YAG laser ablation considering inverse bremsstrahlung

Among the lunar surface regolith, alumina is confirmed to be present in about 10% in the whole moon, especially in the highlands about 23%, which is one of the representative substances. Although alumina itself is not a very versatile material, reduced aluminum has a lot of applications for future lunar activities including a base construction. The laser ablation is one of the promising reduction methods because it does not require reducing agency. In this study, alumina was reduced through YAG laser ablation and generated aluminum was collected using a copper plate. The collected aluminum mass was estimated by the volume of hydrogen gas evaporated in hydrochloric acid titration. Then, the reduction efficiency was estimated as the ratio of collected aluminum to the total ablated mass. They were investigated in terms of the variation of the three laser wavelengths: 355, 532 and 1064 nm. Besides as the experimental condition, the peak power, number of laser shots, and ambient pressure were set as 5–15 MW, 3000–12000 shots, and 1.0–600 Pa, respectively. As a result, we verified alumina reduction by observation of Al I, Al II, Al III spectra. Al mass of 0.34 mg and energy conversion efficiency of 13% were achieved in 355 nm and 9000 shots and 1.0 Pa.

Synthesis of a mineralizing agent for Portland cement from aluminum production waste

Priority directions in innovative technologies of the construction materials industry are the expansion of the use of mineral and chemical additives in the production of cements, as well as alternative raw materials and fuels in production processes. During the production of aluminum at the enterprise JSC RUSAL Krasnoyarsk, the method of electrolytic reduction of aluminum oxide or alumina dissolved in a cryolite-based melt generates fluorocarbon-containing (FCC) waste, which currently accumulates more than 16,000 tons per year. Due to the increased year-round generation of waste with a high content of carbon, fluorine and aluminum, it is urgent to develop technologies that will effectively use them as a new mineralizer product for the production of Portland cement clinker - calcium fluoride. This paper describes the thermal method of waste processing FCC for receipt of the mineralizing agent (fluorite). The disadvantage of FCC as a raw material is an increased concentration of alkali metals, whose oxides negatively affect the process of hydration of clinker minerals, and lead to the formation of efflorescence on products. To reduce their content, the finished fluorite was washed with water. Calcium fluoride as a mineralizing agent in the production of Portland cement, reduces the clinkerization temperature, increases the content of alite, changes the stability, polymorphism and reactivity of phases. The resulting fluorite with a high mass concentration of 73.9% CaF2 makes it possible to reduce the clinker formation temperature, which increases the energy efficiency of obtaining Portland cement. The technological process for removing alkaline components from the product will reduce the likelihood of destructive processes in concrete caused by the aggressive action of reactive silica aggregates and freezing and thawing processes.

On the Modified Design of Anode Assembly in Hall-Héroult Cell Using Finite Element Method

The Hall-Heroult process is the most commonly used process for aluminum production by aluminum through an electrolytic reduction of alumina dissolved in an electrolytic bath at 960 C. The voltage drop for the anode group represents about 8% of the total cell voltage. The resistance between the connections that link the different parts of the anode assembly causes the increase the anode voltage during the electrolysis process. The factors affecting the anodic voltage drop, temperature and stresses distribution were investigated using the finite element method. These factors included the stub diameter, thimble flutes number and steel stub number. Thermal and electrical measurements were carried out on ten prebaked anodes cells to verify and validate the modelled result. In this paper, study the electro thermal model under the influence of mechanical loading of the anode assembly confirmed that the design of the steel stubs (in terms of diameter and number) are the main factors that greatly influence the reduction of the anodic voltage, while the thimble flutes number might have a little effect on the anodic voltage drop.

Laser Spot Size and Preheating Effects on Alumina Reduction Using Laser Ablation

Alumina reduction by laser ablation has been researched toward the lunar resource utilization without reducing agents: especially carbon. Alumina preheating and laser spot size optimization were conducted to increase both the ablation rate and the molar reduction percentage in alumina reduction using laser ablation. A sintered alumina rod was heated to . Then, laser ablation was done using a kilowatt-class continuous wave (CW) laser in ambient argon at 1.0 atm. The ejected ablation plume temperature increased to , which is expected to be the superheating limit temperature of alumina. The molar reduction percentage increased to , which was 2.6 times higher than the percentage obtained without alumina preheating. The ablation rate per unit area increased monotonically with laser intensity and occupancy (the area ratio of the laser spot to an alumina rod). The ablation rate was increased to by laser spot size optimization at a laser intensity of and an occupancy of . In this condition, 75% of the input energy was consumed for alumina reduction.

Modeling of Two-Phase Flow during the Electrolysis of Water in an Electrochemical Reactor in Serpentine Array

Currently the characterization of the reaction environment within any filter-press type reactor through computational modeling is very important in the design to obtain an effective flow dispersion and therefore a uniform current and potential distribution [1]. During two-phase electrolysis such as chlorine production, water electrolysis, alumina reduction, electrocoagulation, and many other electrochemical processes appears gas release on the electrodes, H2 or O2 (bubbles), which imply a quite important electrical properties and electrochemical processes disturbance [2]. The bubbles are motion sources for the flow cells, and then hydrodynamic properties are strongly coupled with species transport and electrical performances, hence, the bubbles presence modifies the electrolysis cell performance and principally the hydrodynamics and current density distribution [3]. Therefore, this works deals with the two-phase modeling (H2O-H2) flow inside of a pre-pilot-scale continuous reactor with a stack of six cells in a serpentine array by solving the Reynolds-averaged Navier-Stokes (RANS) equations with κ-ε turbulence model (Euler-Euler approach). The hydrogen evolution reaction comes from the electrolysis of water. The electrodes were plates of aluminum, typically used in electrocoagulation processes. In order to perform a more complete flow pattern characterization, residence time distribution (RTD) studies were carried out to validate the CFD simulations in biphasic flow. The RTD simulations were calculated solving the averaged diffusion-convection equation. Close agreement between experimental and theoretical RTD simulations were attained. Finally, simulations of distribution of current and potential density distributions inside the pre-pilot-scale continuous reactor were carried out using the Bruggeman relation, observing the effect of bubble production on the distribution of potential along the electrodes.

Globally regional life cycle analysis of automotive lithium-ion nickel manganese cobalt batteries

Electric vehicles based on lithium-ion batteries (LIB) have seen rapid growth over the past decade as they are viewed as a cleaner alternative to conventional fossil-fuel burning vehicles, especially for local pollutant (nitrogen oxides [NOx], sulfur oxides [SOx], and particulate matter with diameters less than 2.5 and 10 μm [PM2.5 and PM10]) and CO2 emissions. However, LIBs are known to have their own energy and environmental challenges. This study focuses on LIBs made of lithium nickel manganese cobalt oxide (NMC), since they currently dominate the United States (US) and global automotive markets and will continue to do so into the foreseeable future. The effects of globalized production of NMC, especially LiNi1/3Mn1/3Co1/3O2 (NMC111), are examined, considering the potential regional variability at several important stages of production. This study explores regional effects of alumina reduction and nickel refining, along with the production of NMC cathode, battery cells, and battery management systems. Of primary concern is how production of these battery materials and components in different parts of the world may impact the battery’s life cycle pollutant emissions and total energy and water consumption. Since energy sources for heat and electricity generation are subject to great regional variation, we anticipated significant variability in the energy and emissions associated with LIB production. We configured Argonne National Laboratory’s Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET®) model as the basis for this study with key input data from several world regions. In particular, the study examined LIB production in the US, China, Japan, South Korea, and Europe, with details of supply chains and the electrical grid in these regions. Results indicate that 27-kWh automotive NMC111 LIBs produced via a European-dominant supply chain generate 65 kg CO2e/kWh, while those produced via a Chinese-dominant supply chain generate 100 kg CO2e/kWh. Further, there are significant regional differences for local pollutants associated with LIB, especially SOx emissions related to nickel production. We find that no single regional supply chain outperforms all others in every evaluation metric, but the data indicate that supply chains powered by renewable electricity provide the greatest emission reduction potential.

Evaluation of very high cycle fatigue zones in 42CrMo4 steel with plate-like alumina inclusions

Quenched and nitrided 42CrMo4 specimens, treated by different reactive filters were tested in very high cycle fatigue regime using ultrasonic method. Despite total alumina reduction fatigue limit showed no improvement due to large alumina plates whose parameters were studied. Areal roughness of fatigue crack zones was measured by confocal laser scanning microscopy. Periodic arrest marks were studied and used for crack growth rate calculation. Smooth area was experimentally defined as a zone between fine granular area and fisheye by imaging, roughness minima, fixed ΔK = 6.4 and crack growth rate of ∼10−10 m/cycle. Classification of internal crack zones is proposed.

Oxidation Resistance of Modified Aluminide Coatings

The application of protective aluminide coatings is an effective way to increase the oxidation resistance of the treated parts and prolongs their lifetime. The addition of small amount of noble metals (platinum or palladium) or reactive elements such as: hafnium, zirconium, yttrium and cerium has a beneficial effect on oxidation behavior. This beneficial effect includes an improvement of adhesion of alumina scales and reduction of oxide scale growth rate. Platinum and hafnium or zirconium modified aluminide coating were deposited on pure nickel using the electroplating and CVD methods. The coatings consisted of two layers: an outer, β-NiAl phase and the interdiffusion γ’-Ni3Al phase. Palladium dissolved in the whole coating, whereas hafnium and zirconium formed inclusions on the border of the layers. Samples were subjected to cyclic oxidation test at 1100 °C for 200h. Oxidation resistance of the palladium, Hf+Pd and Zr+Pd modified coatings deposited on pure nickel does not differ significantly, but is better than the oxidation resistance of the non-modified one.

Application of zirconium carbide: assessment, determination of dominant trends and prospects

The analysis and systematization of information on the application of zirconium carbide in modern technology: in the production of hard alloys and products from them, in technologies of anti-emission coatings, surface modification of powder materials. Prospective directions are indicated: a component in composite materials technologies, a modifying phase of galvanic metal matrix composite coatings, a functional component of wettable coatings for cathodes of alumina reduction cells.

Alumina reduction by laser ablation using a continuous-wave CO2 laser toward lunar resource utilization

Aiming at development of a new method of alumina reduction that is useful for ore mined from the moon, experiments of alumina reduction using CW laser ablation were conducted with a kW-class CW CO2 laser with 400–2000 W power. After a laser beam was focused on a sintered alumina rod, the surface was heated to a temperature necessary for ablation of alumina. Ambient pressure in the test chamber was controlled by supplying Ar gas at 0–0.30 atm, 0.50 atm and 1.0 atm initially, with gas evacuated using a rotary vacuum pump. Under those conditions, an ablation plume was ejected continuously from the sintered alumina rod surface, which was not observed in vacuum. Ambient pressure was increased to 0.40 atm, 0.65 atm, and 1.2 atm. Moreover, emission spectra from the ablation plume were measured; Al I line spectra were detected. Results show that alumina reduction occurred without reducing stores. The equilibrium temperature varied with ambient pressure and laser intensity: 3100–3700 K. Molar reduction of 9.7% and energy conversion efficiency of 0.64% were achieved. Further improvement of the molar reduction percentage can be achieved using increased laser intensity and ambient pressure.

Simulations of H2-H2o Flow during the Electrolysis of Water in a Continuous Reactor Equipped with a Six-Cell Stack

Nowadays the electrochemical reactors in specific the filter-press type in parallel plates configuration are commonly used in industrial and laboratory applications and as multipurpose flow cells utilized in a widely range of electrochemical processes [1]. The characterization of the reaction environment inside of any filter-press reactor must be considered in the design to obtain effective flow dispersion, plus a uniform current and potential distribution. The hydrodynamics is so important inside the reaction environment, because the uniformity and magnitude of mass transport and therefore the current distribution depend on the flow pattern inside the cell, specifically near the electrodes. In many electrochemical processes such as chlorine production, water electrolysis, alumina reduction, electrocoagulation, and many other electrochemical processes appears gas release on the electrodes, H2 or O2 [2]. The hydrodynamic properties and the gas-flow motion in electrochemical cells is of great interest in practice, because the dispersed phase (gas) modifies the electrical properties of the electrolyte (as well as mass and heat transfers), and therefore the macroscopic cell performance. Therefore, this works deals with the H2O-H2 flow simulations inside of a pre-pilot-scale continuous reactor with a stack of six cells in a serpentine array by solving the Reynolds-averaged Navier-Stokes (RANS) equations with κ-ε turbulence model (Euler-Euler approach). The hydrogen evolution reaction comes from the electrolysis of water. The electrodes were plates of aluminum, typically used in electrocoagulation processes. In order to perform a more complete flow pattern characterization, residence time distribution (RTD) studies were carried out to validate the CFD simulations. The RTD simulations were calculated solving the averaged diffusion-convection equation. Close agreement between experimental and theoretical RTD simulations were attained. Finally, comparisons between H2O-H2 and single-phase flow (H2O) simulations were also performed, highlighting that the dispersed phase improves the dispersion of the continuous phase.