The safety and longevity of key blast furnace (BF) equipment determine the stable and low-carbon production of iron. This paper presents an analysis of the heat transfer characteristics of these components and the uneven distribution of cooling water in parallel pipes based on hydrodynamic principles, discusses the feasible methods for the improvement of BF cooling intensity, and reviews the preparation process, performance, and damage characteristics of three key equipment pieces: coolers, tuyeres, and hearth refractories. Furthermoere, to attain better control of these critical components under high-temperature working conditions, we propose the application of optimized technologies, such as BF operation and maintenance technology, self-repair technology, and full-lifecycle management technology. Finally, we propose further researches on safety assessments and predictions for key BF equipment under new operating conditions.
The substantial arsenic (As) content present in arsenic-containing bio-leaching residue (ABR) presents noteworthy environmental challenges attributable to its inherent instability and susceptibility to leaching. Given its elevated calcium sulfate content, ABR exhibits considerable promise for industrial applications. This study delved into the feasibility of utilizing ABR as a source of sulfates for producing super sulfated cement (SSC), offering an innovative binder for cemented paste backfill (CPB). Thermal treatment at varying temperatures of 150, 350, 600, and 800°C was employed to modify ABR’s performance. The investigation encompassed the examination of phase transformations and alterations in the chemical composition of As within ABR. Subsequently, the hydration characteristics of SSC utilizing ABR, with or without thermal treatment, were studied, encompassing reaction kinetics, setting time, strength development, and microstructure. The findings revealed that thermal treatment changed the calcium sulfate structure in ABR, consequently impacting the resultant sample performance. Notably, calcination at 600°C demonstrated optimal modification effects on both early and long-term strength attributes. This enhanced performance can be attributed to the augmented formation of reaction products and a densified microstructure. Furthermore, the thermal treatment elicited modifications in the chemical As fractions within ABR, with limited impact on the As immobilization capacity of the prepared binders.
With the continuous development of mineral resources to high altitude areas, the study of sulfide ore flotation in unconventional systems has been emphasized. There is a consensus that moderate oxidation of sulfide ore is beneficial to flotation, but the specific suitable dissolved oxygen value is inconclusive, and there are few studies on sulfide ore flotation under low dissolved oxygen environment at high altitude. In this paper, we designed and assembled an atmosphere simulation flotation equipment to simulate the flotation of pyrite at high altitude by controlling the partial pressure of N2/O2 and dissolved oxygen under atmospheric conditions. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrophotometer, zeta potential, and contact angle measurements were used to reveal the effects of surface oxidation and agent adsorption on pyrite at high altitude (4600 m dissolved oxygen (DO) = 4.0 mg/L). The results of pure mineral flotation indicated that the high altitude and low dissolved oxygen environment is favorable for pyrite flotation. Contact angle measurements and XPS analysis showed that the high altitude atmosphere slows down the oxidation of pyrite surface, facilitates S n 2−/S0 production and enhances surface hydrophobicity. Electrochemical calculations and zeta potential analysis showed that the influence of atmosphere on the form of pyrite adsorption is small, and the different atmospheric conditions are consistent with dixanthogen electrochemical adsorption, with lower Zeta potential under high altitude atmosphere and significant potential shift after sodium isobutyl xanthate (SIBX) adsorption. The results of FT-IR, UV-vis, and AFM analysis showed that SIBX adsorbed more on the surface of pyrite under high altitude atmosphere and adsorbed on the surface in a mesh structure composed of column/block. The results of the experimental study revealed the reasons for the easy flotation of sulfide ores at high altitude with less collector dosage, and confirmed that the combined DO–pH regulation is beneficial to achieve more efficient flotation of pyrite.
Malachite is a common copper oxide mineral that is often enriched using the sulfidization–xanthate flotation method. Currently, the direct sulfidization method cannot yield copper concentrate products. Therefore, a new sulfidization flotation process was developed to promote the efficient recovery of malachite. In this study, Cu2+ was used as an activator to interact with the sample surface and increase its reaction sites, thereby strengthening the mineral sulfidization process and reactivity. Compared to single copper ion activation, the flotation effect of malachite significantly increased after stepwise Cu2+ activation. Zeta potential, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF–SIMS), scanning electron microscopy and energy dispersive spectrometry (SEM–EDS), and atomic force microscopy (AFM) analysis results indicated that the adsorption of S species was significantly enhanced on the mineral surface due to the increase in active Cu sites after Cu2+ stepwise activation. Meanwhile, the proportion of active Cu–S species also increased, further improving the reaction between the sample surface and subsequent collectors. Fourier-transform infrared spectroscopy (FT-IR) and contact angle tests implied that the xanthate species were easily and stably adsorbed onto the mineral surface after Cu2+ stepwise activation, thereby improving the hydrophobicity of the mineral surface. Therefore, the copper sites on the malachite surface after Cu2+ stepwise activation promote the reactivity of the mineral surface and enhance sulfidization flotation of malachite.
The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels (AHSSs). In this study, the direct strip casting (DSC) technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si–Mn steel with the help of quenching & partitioning (Q&P) concept to address these issues. Compared this method with the conventional compact strip production (CSP) process, the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were investigated. The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite, while the initial structure of the CSP sample consists of pearlite and ferrite. The volume fraction and carbon content of retained austenite (RA) in DSC samples are usually higher than those in CSP samples after the same Q&P treatment. DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample. The DSC sample partitioned at 300°C for 300 s (DSC-Pt300) achieves the best comprehensive mechanical properties, with yield strength (YS) of 1282 MPa, ultimate tensile strength (UTS) of 1501 MPa, total elongation (TE) of 21.5%, and product of strength and elongation (PSE) as high as 32.3 GPa·%. These results indicate that the excellent mechanical properties in low-alloy Si–Mn steel can be obtained through a simple process (DSC–Q&P), which also demonstrates the superiority of DSC technology in manufacturing AHSSs.
The effects of deformation temperature on the transformation-induced plasticity (TRIP)-aided 304L, twinning-induced plasticity (TWIP)-assisted 316L, and highly alloyed stable 904L austenitic stainless steels were compared for the first time to tune the mechanical properties, strengthening mechanisms, and strength–ductility synergy. For this purpose, the scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), tensile testing, work-hardening analysis, and thermodynamics calculations were used. The induced plasticity effects led to a high temperature-dependency of work-hardening behavior in the 304L and 316L stainless steels. As the deformation temperature increased, the metastable 304L stainless steel showed the sequence of TRIP, TWIP, and weakening of the induced plasticity mechanism; while the disappearance of the TWIP effect in the 316L stainless steel was also observed. However, the solid-solution strengthening in the 904L superaustenitic stainless steel maintained the tensile properties over a wide temperature range, surpassing the performance of 304L and 316L stainless steels. In this regard, the dependency of the total elongation on the deformation temperature was less pronounced for the 904L alloy due to the absence of additional plasticity mechanisms. These results revealed the importance of solid–solution strengthening and the associated high friction stress for superior mechanical behavior over a wide temperature range.
In low-density steel, κ-carbides primarily precipitate in the form of nanoscale particles within austenite grains. However, their precipitation within ferrite matrix grains has not been comprehensively explored, and the second-phase evolution mechanism during aging remains unclear. In this study, the crystallographic characteristics and morphological evolution of κ-carbides in Fe–28Mn–10Al–0.8C (wt%) low-density steel at different aging temperatures and times and the impacts of these changes on the steels’ microhardness and properties were comprehensively analyzed. Under different heat treatment conditions, intragranular κ-carbides exhibited various morphological and crystallographic characteristics, such as acicular, spherical, and short rod-like shapes. At the initial stage of aging, acicular κ-carbides primarily precipitated, accompanied by a few spherical carbides. κ-Carbides grew and coarsened with aging time, the spherical carbides were considerably reduced, and rod-like carbides coarsened. Vickers hardness testing demonstrated that the material’s hardness was affected by the volume fraction, morphology, and size of κ-carbides. Extended aging at higher temperatures led to an increase in carbide size and volume fraction, resulting in a gradual rise in hardness. During deformation, the primary mechanisms for strengthening were dislocation strengthening and second-phase strengthening. Based on these findings, potential strategies for improving material strength are proposed.
Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace, automotive, and energy industries owing to its extraordinary thermomechanical properties. The effects of different two-step solid solution treatments on microstructure and δ phase precipitation of Inconel 718 alloy were studied, and the transformation mechanism from γ″ metastable phase to δ phase was clarified. The precipitates were statistically analyzed by X-ray diffractometry. The results show that the δ phase content firstly increased, and then decreased with the temperature of the second-step solid solution. The changes in microstructure and δ phase were studied by scanning electron microscopy and transmission electron microscopy. An intragranular δ phase formed in Inconel 718 alloy at the second-step solid solution temperature of 925°C, and its orientation relationship with γ matrix was determined as and (010)δ//(111)γ. Furthermore, the Vickers hardness of different heat treatment samples was measured, and the sample treated by second-step solid solution at 1010°C reached the maximum hardness of HV 446.84.
The basal texture of traditional magnesium alloy AZ31 is easy to form and exhibits poor plasticity at room temperature. To address these problems, a multi-micro-alloyed high-plasticity Mg–1.8Zn–0.8Gd–0.1Ca–0.2Mn (wt%) alloy was developed using the unique role of rare earth and Ca solute atoms. In addition, the influence of the annealing process on the grain size, second phase, texture, and mechanical properties of the warm-rolled sheet at room temperature was analyzed with the goal of developing high-plasticity magnesium alloy sheets and obtaining optimal thermal-mechanical treatment parameters. The results show that the annealing temperature has a significant effect on the microstructure and properties due to the low alloying content: there are small amounts of larger-sized block and long string phases along the rolling direction (RD), as well as several spherical and rodlike particle phases inside the grains. With increasing annealing temperature, the grain size decreases and then increases, and the morphology, number, and size of the second phase also change correspondingly. The particle phase within the grains vanishes at 450°C, and the grain size increases sharply. In the full recrystallization stage at 300–350°C, the optimum strength-plasticity comprehensive mechanical properties are presented, with yield strengths of 182.1 and 176.9 MPa, tensile strengths of 271.1 and 275.8 MPa in the RD and transverse direction (TD), and elongation values of 27.4% and 32.3%, respectively. Moreover, there are still some larger-sized phases in the alloy that influence its mechanical properties, which offers room for improvement.
To increase the processability and plasticity of the selective laser melting (SLM) fabricated Al–Mn–Mg–Er–Zr alloys, a novel TiB2-modified Al–Mn–Mg–Er–Zr alloy with a mixture of Al–Mn–Mg–Er–Zr and nano-TiB2 powders was fabricated by SLM. The processability, microstructure, and mechanical properties of the alloy were systematically investigated by density measurement, microstructure characterization, and mechanical properties testing. The alloys fabricated at 250 W displayed higher relative densities due to a uniformly smooth top surface and appropriate laser energy input. The maximum relative density value of the alloy reached (99.7 ± 0.1)%, demonstrating good processability. The alloy exhibited a duplex grain microstructure consisting of columnar regions primarily and equiaxed regions with TiB2, Al6Mn, and Al3Er phases distributed along the grain boundaries. After directly aging treatment at a high temperature of 400°C, the strength of the SLM-fabricated TiB2/Al–Mn–Mg–Er–Zr alloy increased due to the precipitation of the secondary Al6Mn phases. The maximum yield strength and ultimate tensile strength of the aging alloy were measured to be (374 ± 1) and (512 ± 13) MPa, respectively. The SLM-fabricated TiB2/Al–Mn–Mg–Er–Zr alloy demonstrates exceptional strength and thermal stability due to the synergistic effects of the inhibition of grain growth, the incorporation of TiB2 nanoparticles, and the precipitation of secondary Al6Mn nanoparticles.
A high-zinc composite, 12vol% SiC/Al–13.3 Zn–3.27 Mg–1.07Cu (wt%), with an ultra-high-strength of 781 MPa was successfully fabricated through a powder metallurgy method, followed by an extrusion process. The effects of solid-solution and aging heat treatments on the microstructure and mechanical properties of the composite were extensively investigated. Compared with a single-stage solid-solution treatment, a two-stage solid-solution treatment (470°C/1 h + 480°C/1 h) exhibited a more effective solid-solution strengthening owing to the higher degree of solid-solution and a more uniform microstructure. According to the aging hardness curves of the composite, the optimized aging parameter (100°C/22 h) was determined. Reducing the aging temperature and time resulted in finer and more uniform nanoscale precipitates but only yielded a marginal increase in tensile strength. The fractography analysis revealed that intergranular cracking and interface debonding were the main fracture mechanisms in the ultra-high-strength SiC/Al–Zn–Mg–Cu composites. Weak regions, such as the SiC/Al interface containing numerous compounds and the precipitate-free zones at the high-angle grain boundaries, were identified as significant factors limiting the strength enhancement of the composite. Interfacial compounds, including MgO, MgZn2, and Cu5Zn8, reduced the interfacial bonding strength, leading to interfacial debonding.
Cobalt (Co) serves as a stabilizer in the lattice structure of high-capacity nickel (Ni)-rich cathode materials. However, its high cost and toxicity still limit its development. In general, it is possible to perform transition metal substitution to reduce the Co content. However, the traditional coprecipitation method cannot satisfy the requirements of multielement coprecipitation and uniform distribution of elements due to the differences between element concentration and deposition rate. In this work, spray pyrolysis was used to prepare LiNi0.9Co0.1−xW xO2 (LNCW). In this regard, the pyrolysis behavior of ammonium metatungstate was analyzed, together with the substitution of W for Co. With the possibility of spray pyrolysis, the Ni–Co–W-containing oxide precursor presents a homogeneous distribution of metal elements, which is beneficial for the uniform substitution of W in the final materials. It was observed that with W substitution, the size of primary particles decreased from 338.06 to 71.76 nm, and cation disordering was as low as 3.34%. As a consequence, the prepared LNCW exhibited significantly improved electrochemical performance. Under optimal conditions, the lithium-ion battery assembled with LiNi0.9Co0.0925W0.0075O2 (LNCW-0.75mol%) had an improved capacity retention of 82.7% after 200 cycles, which provides insight into the development of Ni-rich low-Co materials. This work presents that W can compensate for the loss caused by Co deficiency to a certain extent.
Developing high ionic conducting electrolytes is crucial for applying proton-conducting fuel cell (PCFCs) practically. The current study investigates the effect of alumina on the structural, morphological, electrical, and electrochemical properties of CeO2. Lattice oxygen vacancies are induced in CeO2 by a general doping concept that enables fast ionic conduction at low-temperature ranges (300–500°C) for PCFCs. Rietveld refinement of the X-ray diffraction (XRD) patterns established the pure cubic fluorite structure of Al-doped CeO2 (ADC) samples and confirmed Al ions’ fruitful integration in the CeO2 lattice. The electronic structure of the alumina-doped ceria of the materials (10ADC, 20ADC, and 30ADC) has been investigated. As a result, it was found that the best composition of 30ADC-based electrolytes induced maximum lattice oxygen vacancies. The corresponding PCFC exhibited a maximum power output of 923 mW/cm2 at 500°C. Moreover, the investigation proves the proton-conducting ability of alumina-doped ceria-based fuel cells by using an oxide ion-blocking layer.
BiFeO3 (BFO) has received considerable attention as a lead-free ferroelectric film due to its large theoretical remnant polarization. However, BFO suffers from a large leakage current, resulting in poor ferroelectric properties. Herein, the sol–gel method was used to deposit a series of BFO-based thin films on fluorine-doped tin oxide substrates, and the effects of the substitution of the elements Co, Cu, Mn (B-site) and Sm, Eu, La (A-site) on the crystal structure, ferroelectricity, and leakage current of the BFO-based thin films were investigated. Results confirmed that lattice distortion by X-ray diffraction can be attributed to the substitution of individual elements in the BFO-based films. Sm and Eu substitutions contribute to the lattice distortion in a pseudo-cubic structure, while La is biased toward pseudo-tetragonal. Piezoelectric force microscopy confirmed that reversible switching of ferroelectric domains by nearly 180° can be realized through the prepared films. The ferroelectric hysteresis loops showed that the order for the polarization contribution is as follows: Cu > Co > Mn (B-site), Sm > La > Eu (A-site). The current density voltage curves indicated that the order for leakage contribution is as follows: Mn < Cu < Co (B-site), La < Eu < Sm (A-site). Scanning electron microscopy showed that the introduction of Cu elements facilitates the formation of dense grains, and the grain size distribution statistics proved that La element promotes the reduction of grain size, leading to the increase of grain boundaries and the reduction of leakage. Finally, a Bi0.985Sm0.045La0.03Fe0.96Co0.02Cu0.02O3 (SmLa-CoCu) thin film with a qualitative leap in the remnant polarization from 25.5 (Bi0.985Sm0.075FeO3) to 98.8 µC/cm2 (SmLa-CoCu) was prepared through the synergistic action of Sm, La, Co, and Cu elements. The leakage current is also drastically reduced from 160 to 8.4 mA/cm2 at a field strength of 150 kV/cm. Thus, based on the increasing entropy strategy of chemical engineering, this study focuses on enhancing ferroelectricity and decreasing leakage current, providing a promising path for the advancement of ferroelectric devices.
NiMZn/C@melamine sponge-derived carbon (MSDC) composites (M = Co, Fe, and Mn) were prepared by a vacuum pumping solution method followed by carbonization. A large number of carbon nanotubes (CNTs) homogeneously attached to the surfaces of the three-dimensional cross-linked of the sponge-derived carbon in the NiCoZn/C@MSDC composite, and CNTs were detected in the NiFeZn/C@MSDC and NiMnZn/C@MSDC composites. Ni3ZnC0.7, Ni3Fe, and MnO in-situ formed in the NiFeZn/C@MSDC and NiMnZn/C@MSDC composites. The CNTs in the NiCoZn/C@MSDC composite efficiently modulated its complex permittivity. Thus, the composite exhibited the best performance among the composites, with the minimum reflection loss (RLmin) of −33.1 dB at 18 GHz and thickness of 1.4 mm. The bandwidth for RL of ≤−10 dB was up to 5.04 GHz at the thickness of 1.7 mm and loading of 25wt%. The optimized impedance matching, enhanced interfacial and dipole polarization, remarkable conduction loss, and multiple reflections and scattering of the incident microwaves improved the microwave absorption performance. The effects of Co, Ni, and Fe on the phase and morphology provided an alternative way for developing highly efficient and broadband microwave absorbers.
This study focused on the investigation of the edge effect of diamond films deposited by microwave plasma chemical vapor deposition. Substrate bulge height is a factor that affects the edge effect, and it was used to simulate plasma and guide the diamond-film deposition experiments. Finite-element software COMSOL Multiphysics was used to construct a multiphysics (electromagnetic, plasma, and fluid heat transfer fields) coupling model based on electron collision reaction. Raman spectroscopy and scanning electron microscopy were performed to characterize the experimental growth and validate the model. The simulation results reflected the experimental trends observed. Plasma discharge at the edge of the substrate accelerated due to the increase in Δh (Δh = 0–3 mm), and the values of electron density (n e), molar concentration of H (C H), and molar concentration of doubled at the edge (for the special concave sample with Δh = −1 mm, the active chemical groups exhibited a decreased molar concentration at the edge of the substrate). At Δh = 0–3 mm, a high diamond growth rate and a large diamond grain size were observed at the edge of the substrate, and their values increased with Δh. The uniformity of film thickness decreased with Δh. The Raman spectra of all samples revealed the first-order characteristic peak of diamond near 1332 cm−1. When Δh = −1 mm, tensile stress occurred in all regions of the film. When Δh = 1–3 mm, all areas in the film exhibited compressive stress.
Electric arc furnace (EAF) dust is an important secondary resource containing metals, such as zinc (Zn) and iron (Fe). Recovering Zn from EAF dust can contribute to resource recycling and reduce environmental impacts. However, the high chemical stability of ZnFe2O4 in EAF dust poses challenges to Zn recovery. To address this issue, a facile approach that involves oxygen-assisted chlorination using molten MgCl2 is proposed. This work focused on elucidating the role of O2 in the reaction between ZnFe2O4 and molten MgCl2. The results demonstrate that MgCl2 effectively broke down the ZnFe2O4 structure, and the high O2 atmosphere considerably promoted the separation of Zn from other components in the form of ZnCl2. The presence of O2 facilitated the formation of MgFe2O4, which stabilized Fe and prevented its chlorination. Furthermore, the excessive use of MgCl2 resulted in increased evaporation loss, and high temperatures promoted the rapid separation of Zn. Building on these findings, we successfully extracted ZnCl2-enriched volatiles from practical EAF dust through oxygen-assisted chlorination. Under optimized conditions, this method achieved exceptional Zn chlorination percentage of over 97% within a short period, while Fe chlorination remained below 1%. The resulting volatiles contained 85wt% of ZnCl2, which can be further processed to produce metallic Zn. The findings offer guidance for the selective recovery of valuable metals, particularly from solid wastes such as EAF dust.
The precipitation of Fe3O4 particles and the accompanied formation of Fe3O4-wrapped copper structure are the main obstacles to copper recovery from the molten slag during the pyrometallurgical smelting of copper concentrates. Herein, the commercial powdery pyrite or anthracite is replaced with pyrite–anthracite pellets as the reductants to remove a large amount of Fe3O4 particles in the molten slag, resulting in a deep fracture in the Fe3O4-wrapped copper microstructure and the full exposure of the copper matte cores. When 1wt% composite pellet is used as the reductant, the copper matte droplets are enlarged greatly from 25 µm to a size observable by the naked eye, with the copper content being enriched remarkably from 1.2wt% to 4.5wt%. Density functional theory calculation results imply that the formation of the Fe3O4-wrapped copper structure is due to the preferential adhesion of Cu2S on the Fe3O4 particles. X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer (FTIR), and Raman spectroscopy results all reveal that the high-efficiency conversion of Fe3O4 to FeO can decrease the volume fraction of the solid phase and promote the depolymerization of silicate network structure. As a consequence, the settling of copper matte droplets is enhanced due to the lowered slag viscosity, contributing to the high efficiency of copper–slag separation for copper recovery. The results provide new insights into the enhanced in-situ enrichment of copper from molten slag.