Aluminothermic Research Articles

Evolution of Viscosity and Structure Property during Aluminothermic Reduction of Vanadium‐Enriched Slag

Aluminum dross is a promising reductant for extracting vanadium to enable the direct production of ferrovanadium alloy in pre‐reduced vanadium‐rich slag (PVS). The evolution of the viscosity of PVS is measured with various A/M ratios (w(Al2O3)/w(FeO + Cr2O3 + MnO + V2O3 + Al2O3)), representing different reduction stages. The compositions and structural properties of the melts are analyzed using X‐ray powder diffraction, scanning electron microscopy, and Raman spectroscopy. The results show that with an increase in the mass ratio of Al2O3 to (FeO+Cr2O3+MnO+V2O3+Al2O3) in the slag transformed from a solid–liquid mixture to a single liquid phase at 1873 K. When A/M increases from 0.29 to 0.53, Q0 and Q1 polymerize into Q2, resulting in a slow increase in viscosity from 0.091 to 0.158 Pa s. As A/M further increased to 1.00, Q0 disappeared, Q3 appeared, and the fraction of Al–O–Si increased to 37.7%, indicating that the simple aluminosilicate structural units are polymerized into complex structural units. Meanwhile, the viscosity increases to 0.338 Pa s. Al2O3 acts as a network former and strengthens the degree of polymerization of the melt. The variation ranges of the apparent activation energy, structural complexity, and the average number of non‐bridging oxygen are 139.23–215.12 kJ mol−1, 0.57–2.97, and 2.16–1.05, respectively.

Aluminothermic reduction synthesis of porous silicon nanosheets from vermiculite as high-performance anode materials for lithium-ion batteries

Designing silicon with two-dimensional (2D) micromorphology and porous nanostructure has proven to be an effective route to obtain high capacities during cycling when adopted as anode materials for lithium-ion batteries. Here, a mild and cost-efficient chemical route is developed to synthesize Si nanosheets from vermiculite via a preliminary chemical delamination assisted with low-temperature aluminothermic reduction in a eutectic molten salt system. Benefiting from the self-templating role of multilayered crystal structure of vermiculite and the high reduction efficiency of aluminothermic reaction, the as-prepared Si nanosheets possess ultrathin 2D morphology and hierarchical porous structure. As anode materials for lithium-ion batteries, Si nanosheets exhibit a high reversible capacity of 1696 mAh g−1 at a current density of 0.2 A g−1 after 100 cycles, 1269 mAh g−1 at 1.0 A g−1 after 300 cycles and excellent rate capability with desirable capacities of 1314 mAh g−1 at 4.0 A g−1. This work provides a promising technical route for the transformation of low-cost natural vermiculite to value-added high performance silicon anode materials, which can be extended to other layered silicate minerals.

Chemical and Structural Analysis of Newly Prepared Co-W-Al Alloy by Aluminothermic Reaction.

This article is devoted to the characterization of a new Co-W-Al alloy prepared by an aluminothermic reaction. This alloy is used for the subsequent preparation of a special composite nanopowder and for the surface coating of aluminum, magnesium, or iron alloys. Due to the very high temperature (2000 °C–3000 °C) required for the reaction, thermite was added to the mixture. Pulverized coal was also added in order to obtain the appropriate metal carbides (Co, W, Ti), which increase hardness, resistance to abrasion, and the corrosion of the coating and have good high temperature properties. The phase composition of the alloy prepared by the aluminothermic reaction showed mainly cobalt, tungsten, and aluminum, as well as small amounts of iron, titanium, and calcium. No carbon was identified using this method. The microstructure of this alloy is characterized by a cobalt matrix with smaller regular and irregular carbide particles doped by aluminum.

Synthesis of self-regenerating NiAl-Al2O3 composite coatings

The aluminothermic reactions involved either in the mixtures or the stack of NiO and Al powders were elucidated in a previous work (Troncy et al., 2020) [1]. The present work now investigates the formation of potential self-regenerating coatings using the aluminothermic reaction between nickel oxide and aluminum. The use of this exothermic reaction allows the simultaneous formation of both alumina and nickel aluminides. The coatings were obtained by first pre-oxidizing the nickel substrate, then spraying an aluminum slurry before applying an adequate heat treatment. The most promising self-regenerating coatings display a first composite layer, made of an intermetallic compound (Al3Ni or NiAl) and alumina, and a second layer with a higher concentration of oxide. The first layer is expected to play the role of an Al reservoir coating and the second one that of a diffusion barrier to slow down the Al flux to maintain the Al reservoir in the coating. The effects of preoxidation time and of temperature on the resulting coating microstructures are discussed as a function of time.

Micro/nano-structure leads to super strength and excellent plasticity in nanostructured 304 stainless steel

Micro/nano-structure is one of the important types of multilayer construction, which can make nanocrystalline metals and alloys with excellent comprehensive mechanical properties. By means of Aluminothermic Reaction (AR) and subsequent rolling with deformation of 50% at room temperature (RT) and followed by annealed at 973 K for 1 h, a heterogeneous composite structure of micro/nano-structured 304 stainless steel (SS) is obtained. Such a stainless steel specimen exhibits a tensile strength as high as 1023 MPa and an elongation-to-failure of about 27.3%. In the process, the much elevated strength originates from martensite strengthening, austenite grain refinement and dislocation density increasing, while ductility promotes from the recrystallization of deformed austenite and recovery of strain induced martensite. Superior strength–ductility combination achieves in micro/nano-structured 304 SS, which demonstrates a novel approach for optimizing the mechanical properties in engineering materials.

Synthesis of As-Cast WCu Composite Containing Micro- and Nano-Size Tungsten Particles Using Aluminothermic Reduction

Synthesis of As-Cast WCu Composite Containing Micro- and Nano-Size Tungsten Particles Using Aluminothermic Reduction

Manganese and Aluminium Recovery from Ferromanganese Slag and Al White Dross by a High Temperature Smelting-Reduction Process.

The recovery of Mn and Al from two industrial waste of ferromanganese and aluminum production processes was investigated via implementing a high temperature smelting—aluminothermic reduction process. The experiments were carried out with or without CaO flux addition, and two dross qualities. It was observed that the prepared mixtures of the materials yield homogeneous metal and slag products in terms of chemical composition and the distribution of phases. However, the separation of produced metal phase from the slag at elevated temperatures occurs when a higher amount of CaO is added. Viscosity calculations and equilibrium study indicated that the better metal and slag separation is obtained when the produced slag has lower viscosity and lower liquidus. It was found that the process yields Al-Mn-Si alloys, and it is accompanied with complete recovery of Mn, Si and Fe and the unreacted Al in the process. Moreover, the quality of metal product was less dependent on the slightly different dross quality, and the concentration of minor Ca in metal is slightly increased with significant increase of CaO in the slag phase.

Thermophysical conditions for formation of structures and properties of a permanent joint obtained by the method of automatic submerged arc welding using a flux-cored wire with aluminothermic filler

High performance properties are important for enterprises focused on the use of technologies with low resource intensity and automation in the fabrication of metal products, permanent joints, and this segment is especially important for shipbuilding enterprises. To solve this problem, a series of experimental studies has been carried out to determine an effective mode of combined thermal exposure towards formation of structure and physical and mechanical properties of metal in the heat-affected zone of the weld fabricated by the method of automatic submerged arc welding using flux-cored wire with aluminothermic filler. The peculiarity of utilization of this wire is that the electric arc and aluminothermic process can be combined. As a result of the experimental study permanent joints made of steel St3sp have been obtained; its values of impact strength, tensile strength and yield strength are also presented. The optimal values of the thermal exposure mode during alumothermic welding have been determined, which lead to obtain the most preferable strength properties of the permanent joint.

Optimizacija dizajna kalupa za ulivanje termitnog čelika kod aluminotermijskog zavarivanja železničkih šina softverskom simulacijom

The aluminothermic welding process of rail welding has been used to join railway rails for more than a century. The benefits of this procedure include its flexibility, compactness of the weld, and ease of execution. It is not necessary to bring in outside energy to complete the process. It is provided by the exothermic effect of the chemical reactions of the aluminothermic mixture's constituents. The design of the mold with the pouring system, which should ensure even pouring of thermal steel, without turbulence, then even heat dissipation or cooling in order to obtain appropriate micro and macro structure of steel, without internal and external defects, is an important element for making a welded joint of the required quality. As a result, the mold's design was constantly evolving, requiring the use of costly experimental methods in industrial settings. Today, software packages are used to simulate traditional casting processes that can be used in the casting of thermite steel during the manufacture of welded railway joints, thereby avoiding costly and time-consuming industrial tests. The simulation of casting thermite steel in the mold cavity, i.e. in the weld joint for the 49E1 rail, using the NovaFlow & Solid CV software package, is presented in this paper. The simulation results were validated by establishing test welded joints in industrial settings and testing their quality in accordance with the EU 13740-1: 2017 standard.

Formation mechanism of Ti3AlC2 in TiO2–Al–C/TiC systems at high temperatures

Ti 3 AlC 2 /Al 2 O 3 composites were synthesized by aluminothermic reduction of TiO 2 /Al/C and TiO 2 /Al/TiC. The effects of carbon sources (carbon black and TiC), steps heating-up profile, and Al-excess of raw materials composition on the Ti 3 AlC 2 content in final products were investigated. The results showed that in contrast with carbon black, TiC used as a carbon source is beneficial to the formation of Ti 3 AlC 2 at lower temperatures. However, Ti 3 AlC 2 content in the product with carbon black was improved by the steps heating-up profile and Al-excess, promoting intermediate phases TiAl 3 and TiC. Furthermore, the formation mechanisms of Ti 3 AlC 2 with different carbon sources in aluminothermic reaction systems were also elucidated. For the TiO 2 /Al/C system, Ti 3 AlC 2 is precipitated from the Ti–Al melt at high temperatures via the dissolution-precipitation mechanism, which has slower nucleation but faster growth. In contrast, in the TiO 2 /Al/TiC system, Ti 3 AlC 2 is mainly growing from the intact TiC grains through the epitaxial nucleation mechanism, which has faster nucleation but lower growth.

Application of silicon nanoparticles extracted from the Padma river sand of Bangladesh as dopant in metal oxide semiconducting thin films

Fabrication of silicon nanoparticles (Si-NPs) from the Padma river sand of Bangladesh by a low-temperature, low-cost, and zero-CO2 emitting process and its application as a dopant in CuO and ZnO have been presented in this article with a motivation to see the influence of locally fabricated Si-NPs on the optoelectronic properties of CuO and ZnO thin films. The sand (SiO2) was reduced using a modified aluminothermic reaction, and leaching with hydrochloric acid (HCL) was used to purify the reaction product to extract > 98% pure Si. After cleaning and drying, the obtained Si powder was ultrasonicated for crushing them into tiny particles of 60–180 nm. The ultrasonicated silicon was further treated with a solution of hydrofluoric acid (HF) and 2-propanol for the etching of the native oxide and passivating the dangling bond with hydrogen (H). Thereafter, highly promising photoactive materials CuO and ZnO were doped with the extracted Si-NPs. Finally, Si-NPs doped CuO and ZnO thin films were deposited on a cleaned glass substrate by spin-coating. X-Ray Diffraction (XRD) confirmed the amorphous nature of Si particles. Dynamic Light Scattering (DLS) demonstrates the size distribution of Si-NPs of ~120 nm for 180 minutes of sonication time. DLS results refer that the higher sonication time offers a lower particle size of Si with controlled rate. The addition of Si-NPs nanoparticles tailors the energy band alignment at the metal oxide/NP interface which provides efficient charge carrier transport and enhanced optical absorption (~20%) as revealed by UV-Vis Spectroscopy. Experimental results indicate that the extracted Si-NPs can be efficiently used in thin-film based optical and electronic devices.

Research on temperature propagation law based on thermite plugging and abandonment technology

The continuous exploration and development of oil wells increases the risk of leakage from abandoned wells and brings challenges to the traditional plugging and abandonment technology. In order to overcome the above problems, a thermite plugging and abandonment technology is proposed in this field. The technology uses the aluminothermic reaction to melt the original or set material for sealing. The natural convection under different confinement conditions directly affects the heat flux transfer in the heat transfer process. In order to study the melting effect of the thermite reaction on sandstone, based on the heat conduction theory, a heat conduction model based on the temperature release law of the thermite reaction was established. The numerical simulation results show that the surrounding heat transfer conditions are the key factors affecting the heat transfer effect in the axial and radial directions without considering the particle size and dosage of the thermite itself. This work is of great significance for studying the temperature law of thermite reaction release and the future research of thermite plugging and abandonment technology.

A Sustainable Process to Produce Manganese and Its Alloys through Hydrogen and Aluminothermic Reduction

Hydrogen and aluminum were used to produce manganese, aluminum–manganese (AlMn) and ferromanganese (FeMn) alloys through experimental work, and mass and energy balances. Oxide pellets were made from Mn oxide and CaO powder, followed by pre-reduction by hydrogen. The reduced MnO pellets were then smelted and reduced at elevated temperatures through CaO flux and Al reductant addition, yielding metallic Mn. Changing the amount of the added Al for the aluminothermic reduction, with or without iron addition led to the production of Mn metal, AlMn alloy and FeMn alloy. Mass and energy balances were carried out for three scenarios to produce these metal products with feasible material flows. An integrated process with three main steps is introduced; a pre-reduction unit to pre-reduce Mn ore, a smelting-aluminothermic reduction unit to produce metals from the pre-reduced ore, and a gas treatment unit to do heat recovery and hydrogen looping from the pre-reduction process gas. It is shown that the process is sustainable regarding the valorization of industrial waste and the energy consumptions for Mn and its alloys production via this process are lower than current commercial processes. Ferromanganese production by this process will prevent the emission of about 1.5 t CO2/t metal.

Clean preparation of V2O3 by one-step molten salt electrochemical reduction of soluble NaVO3

Vanadium oxides, such as V2O5 and V2O3, are important metallurgy products and mainly used to prepare V-based alloys for steelmaking. At present, vanadium oxides are mainly produced by complex sodium salt roasting process. Serious environmental pollution, such as emission of ammonia nitrogen wastewater and NH3, are restrictive problems. Here, a clean and sustainable method for V2O3 preparation is proposed by one-step molten salt electrochemical reduction of soluble NaVO3, i.e. an indispensable intermediate in traditional V metallurgy. The pollution issues are well solved. The theoretical decomposition voltages of different vanadate to various low-valence vanadium oxides were calculated. NaVO3 with a solubility of 14.7 wt% is the most suitable vanadate for the direct preparation of V2O3 by molten salt electrolysis. The effects of cathode structure, NaVO3 content, electrolysis temperature and voltage on current efficiency and electricity consumption were systematically studied. High-purity V2O3 with uniform particle distribution is obtained and the lowest electricity consumption is only 2.86 kWhkg−1. V2O3 is mainly produced by one-step electrochemical reduction of soluble NaVO3 through two-electron transfer process. The economic evaluation for ferrovanadium production is preliminarily carried out. Compared with the traditional process, the cost for ferrovanadium production is lower by the aluminothermic reduction of V2O3 which is prepared by clean one-step electrolysis of soluble NaVO3.

Recovering Value from End-of-Life Batteries by Integrating Froth Flotation and Pyrometallurgical Copper-Slag Cleaning

In this study, industrial lithium-ion battery (LIB) waste was treated by a froth flotation process, which allowed selective separation of electrode particles from metallic-rich fractions containing Cu and Al. In the flotation experiments, recovery rates of ~80 and 98.8% for the cathode active elements (Co, Ni, Mn) and graphite were achieved, respectively. The recovered metals from the flotation fraction were subsequently used in high-temperature Cu-slag reduction. In this manner, the possibility of using metallothermic reduction for Cu-slag reduction using Al-wires from LIB waste as the main reductant was studied. The behavior of valuable (Cu, Ni, Co, Li) and hazardous metals (Zn, As, Sb, Pb), as a function of time as well as the influence of Cu-slag-to-spent battery (SB) ratio, were investigated. The results showcase a suitable process to recover copper from spent batteries and industrial Cu-slag. Cu-concentration decreased to approximately 0.3 wt.% after 60 min reduction time in all samples where Cu/Al-rich LIB waste fraction was added. It was also showed that aluminothermic reduction is effective for removing hazardous metals from the slag. The proposed process is also capable of recovering Cu, Co, and Ni from both Cu-slag and LIB waste, resulting in a secondary Cu slag that can be used in various applications.

Dual carbon and void space confined SiOx/C@void@Si/C yolk-shell nanospheres with high-rate performances and outstanding cyclability for lithium-ion batteries anodes

Silicon-based anode materials with high theoretical capacity have great challenges of enormous volume expansion and poor electronic conductivity. Herein, a novel dual carbon confined SiOx/C@void@Si/C yolk-shell monodisperse nanosphere with void space have been fabricated through hydrothermal reaction, carbonization, and in-situ low-temperature aluminothermic reduction. Furthermore, the O/Si ratio and void space between SiOx/C core and Si/C shell can be effectively tuned by the length of aluminothermic reduction time. The SiOx/C core plays a role of maintaining the spherical structure and the void space can accommodate the volume expansion of Si. Moreover, the inner and outer carbons not only alleviate volume variation of SiOx and Si but also enhance the electrical conductivity of composites. Benefiting from the synergy of the double carbon and void space, the optimized VSC-14 anode affords prominent cycle stability with reversible capacity of 1094 mAh g−1 after 550 cycles at 200 mA g−1. By pre-lithiation treatment, the VSC-14 achieves an initial Coulombic efficiency of 93.27% at 200 mA g−1 and a reversible capacity of 348 mAh g−1 at 5 A g−1 after 4000 cycles. Furthermore, the pouch cell using VSC-14 anode and LiFePO4 cathode delivers a reversible capacity of 138 mAh g−1 at 0.2C. We hope this strategy can provide a scientific method to synthesis yolk-shell Si-based materials.

Reaction mechanism and kinetics of ferrotitanium preparation by aluminothermic reduction of CaTiO3

A ferrotitanium alloy production process by aluminothermic reduction and using perovskite as materials was studied in laboratory. The thermodynamics of the Al-CaO, Al-CaO-CaTiO3, Al-CaO-Fe-CaTiO3 system was calculated and the reduction process of CaTiO3 to prepare ferrotitanium was investigated. The Freeman-Carroll method was used to analyze the kinetics of aluminothermic reduction process. The results show that ferrotitanium alloys can be produced by aluminothermic reduction using perovskite as material. In the reduction process, the reduction reaction of TiO2 in CaTiO3 by aluminum proceeds at 1000–1100 ℃, and the formation temperature of ferrotitanium alloy is between 1400 ℃ and 1500 ℃. CaO not only acts as a slag-forming agent in the reaction process, but also participates in the reduction reaction process. The apparent activation energy and the reaction order at the reduction peak decrease with the increasing of heating rate which indicates that the reaction is easier with the increase of heating rate.

Study on the mechanism of Al-Si alloy preparation via aluminothermic reduction–molten salt electrolysis in KF–AlF3 molten salt

In this study, Al–Si alloy, a precursor of the solar-grade silicon, was prepared via the aluminothermic reduction–molten salt electrolysis of SiO2 in KF–AlF3 molten salt by employing liquid aluminum as the working cathode. The reaction mechanism of the aluminothermic reduction of SiO2 in KF–AlF3 molten salt at 750 °C was determined by thermogravimetry–differential scanning calorimetry. The reaction rate equation for the aluminothermic reduction of SiO2 in KF–AlF3 molten salt was:dαdt=7.156×1024e−4.688×105RT(1−α)1.734. In 49.4 wt% KF–47.6 wt% AlF3–3 wt% SiO2 molten salt at 750 °C, the Si content in the Al–Si alloy obtained by the aluminothermic reduction–molten salt electrolysis of SiO2 was 24.53 wt%. Compared with solely aluminothermic reduction of SiO2, the current efficiency in the process of the aluminothermic reduction–molten salt electrolysis of SiO2 was evaluated. The results reveal that the Al–Si alloy is predominantly prepared in the aluminothermic reduction step, while supplemented by electrolysis. The calculated Faradic current efficiency of the proposed aluminothermic reduction–molten salt electrolysis process was 28.4%.

Matryoshka-type carbon-stabilized hollow Si spheres as an advanced anode material for lithium-ion batteries

Silicon (Si) is regarded as the potential anode for lithium-ion batteries (LIBs), due to the remarkable theoretical specific capacity and low voltage plateau. However, the rapid capacity decay resulting from volume variation and slow electron/ion transportation of Si limit its practical application. Here, matryoshka-type carbon-stabilized hollow silicon spheres (Si/C/Si/C) are synthesized by an aluminothermic reduction and calcination process. The Si/C/Si/C anode materials prepared at 500 °C (Si/C/Si/C-500) exhibit unique structures, in which amorphous region and porous structure are preserved in the Si layers. The anode based on Si/C/Si/C-500 displays an initial specific capacity of 2792 mAh/g at a current density of 100 mA/g. At 1000 mA/g, this anode retains a reversible capacity of 1673 mAh/g, 86.9% of the initial capacity after 200 cycles. Such synthetic strategy can be employed to fabricate other high-capacity anode materials with large volume variation during charge/discharge process

Effect of in-situ Al2O3 on tensile strength and ductility of AlSi10Mg alloy fabricated by selective laser melting

The in-situ Al2O3 modified AlSi10Mg alloy was fabricated by selective laser melting using AlSi10Mg/ZnO mixed powders. The results show that the aluminothermic reaction between the Al and ZnO occurs when the laser fuses the AlSi10Mg/ZnO mixed powders. This leads to the in-situ formation of Zn and Al2O3 nanoparticles in the AlSi10Mg alloy. The Zn can exist in the Al matrix as solid solution atoms. The effect of Zn on the tensile strength and ductility of the AlSi10Mg alloy is rather limited. However, the in-situ Al2O3 impedes the motion of dislocations and thus improves the strength of the AlSi10Mg alloy. Moreover, the dislocations accumulated around the in-situ Al2O3 are gradually annihilated along the Al/Si boundaries. Thus the ductility of the AlSi10Mg alloy is scarcely affected by the in-situ Al2O3.