Decomposition Of Ferrite Research Articles

The enrichment and transformation mechanism of Pb and Cu in suspension magnetization roasting and magnetic separation from iron tailings

Magnetic iron concentrate (MIC) and nonmagnetic tailings (NT) are obtained from magnetization roasting of iron tailings (IT). MIC containing Pb adversely affects blast furnace ironmaking, while Cu in NT poses leaching risks. This study utilizes fast pyrolysis-suspension magnetization roasting to recover iron from IT. The enrichment of Pb, Cu, and the phase transformation mechanism of Cu in the process of suspension magnetization roasting and magnetic separation were clarified. Results show 96.13 % of Cu in IT is in limonite and 47.23 % of Pb is associated with iron. At 750 °C, with 10 % dosage of biomass pyrolysis and 10 min roasting, Pb, Cu and Fe contents in MIC are 0.96, 2.14 and 3.17 times that of NT. Increasing roasting temperature enhances Cu associated with iron enrichment into the MIC, while oxidation of free copper oxide associated with iron forms magnetic copper ferrite. Increased pyrolyzed biomass leads to over-reduction of magnetite associated with Cu to FeO associated with Cu, promoting magnetic copper ferrite decomposition into FeO and free copper oxide. This research holds significant importance in controlling the quality of MIC and the storage risk of IT, and provides theoretical guidance for the regulation and recovery of valuable metals in subsequent processes.

A novel leaching process of zinc ferrite and its application in the treatment of zinc leaching residue

Zinc ferrite is a refractory phase generated in the pyrometallurgical process of zinc and steel production. Much energy is invested in the decomposition of zinc ferrite to recycle zinc since zinc ferrite is difficult to leach. In this work, a novel leaching process targeted at decomposition of zinc ferrite was proposed to save energy and improve metal recovery efficiency. The key of this novel leaching process was the use of copper powder as the reductant. Leaching of zinc ferrite in the presence of copper powder was investigated. The extraction of zinc was 100% when molar ratio of copper to zinc ferrite was 1.5 while the extraction of zinc was only 19.3% without copper. Effects of leaching temperature, acid concentration, the ratio of liquid to solid and reaction time were studied. Under the conditions: 60 °C, ≥ 70 g·L1 H2SO4, the ratio of liquid to solid ≥ 25 mL/g and the molar ratio of copper to zinc ferrite ≥ 1.5 at the open system, the synthetic zinc ferrite was dissolved completely within 60 min. Besides, the zinc ferrite-bearing zinc leaching residue from a roast-leach-electrowin plant was analyzed and leached under the optimal conditions. It was found that most of zinc ferrite in the zinc leaching residue was removed, remaining unreacted lead sulphate in the leached residue. The leaching efficiency of zinc in zinc leaching residue reached 94.2%. The results suggest that copper powder enhanced facile and efficient zinc extraction from zinc ferrite without concentrated acid, high temperature, long reaction time and specific investment. The recyclability of copper and its intrinsic commodity value showed the potential application in industrial zinc and iron containing wastes.

Selective extraction of zinc from high iron-bearing zinc calcine by reduction and magnetization roasting

A novel process that combined reduction roasting with magnetization roasting was developed to intensify the decomposition of zinc ferrite for the selective extraction of zinc from high iron-bearing zinc calcine. The decomposition mechanism of zinc ferritewas investigated in detail by thermodynamics analysis and roasting experiments. The results indicated that 94.65% of the zinc ferrite was decomposed into zinc oxide and ferrous oxide under the optimal reduction roasting conditions of 8 vol.% CO, 750 °C, 50 vol.% CO/(CO+CO2), and 90 min. The generated ferrous oxide was further converted to ferriferrous oxide by magnetization roasting under an air atmosphere at 450 °C for 30 min. After that, 93.62% of zinc contained in the calcine could be selectively extracted by low acid leaching, whereas more than 90% of iron was concentrated in the leaching slag in the form of magnetite, which could be recovered by the subsequent magnetic separation.

Mediating phase decomposition to avoid thermal aging embrittlement in a duplex stainless steel

Due to the presence of miscibility gap in the body-centered-cubic structure iron‑chromium alloy system, the ferrite will decompose into the Fe-rich α phase and Cr-rich α´ phase, resulting in the inherent “475 °C embrittlement”. In this study, a pulsed electric field is introduced to mediate the phase decomposition for avoiding aging embrittlement. Combining nanoindentation testing and atomic-scale characterization, the results show that almost no aging hardening and phase decomposition behaviors occur with the pulsed electric field intervening, and the thermodynamic analysis indicates that the pulsed electric field can shrink the spinodal domain. Further, the life evaluation shows that the equivalent aging time of the duplex stainless steel is 18.2 years without the application of the pulsed electric field, while the equivalent aging time of the duplex stainless steel is 1.2 years under the action of the pulsed electric field, which is equivalent to an extension of the service life by 17 years. This study offers an opportunity for resisting the aging embrittlement process to prolong the longevity of components. • The ferrite decomposition is suppressed by pulsed electric field during thermal aging. • Spinodal decomposition plays the major role in thermal aging embrittlement. • Pulsed electric field induces the spinodal domain to shrink for avoiding phase decomposition. • The equivalent service life of duplex stainless steel is extended by 17 years.

Effect of Isothermal Holding at 750 °C and 900 °C on Microstructure and Properties of Cast Duplex Stainless Steel Containing 24% Cr-5% Ni-2.5% Mo-2.5% Cu

Changes in the microstructure and selected mechanical properties of two-phase ferritic-austenitic cast steel containing 24% Cr-5% Ni-2.5% Mo-2.5% Cu after isothermal holding at 750 °C and 900 °C are presented. The choice of the two temperatures of isothermal holding was dictated by the precipitation of brittle phases within a range of 600 °C-950 °C, while the holding time depended on the casting cooling time in the mould. Changes in the microstructure were studied by the SEM-EDS and XRD techniques. As a result of the decomposition of the eutectoid ferrite, a σ phase that was rich in Cr, Mo, and Ni and a secondary γ2 austenite with Widmannstätten morphology were formed. Compared to the austenite, the chemical composition of the secondary γ2 austenite showed depletion of Cr and Mo. In the ferrite, the presence of Cr2N nitrides was also detected. After a holding time of 3 h at 900 °C, these phases increased the hardness of the tested cast steel to approximately 275 HV10. At the same time, the UTS value was recorded to decrease with the increasing temperature based on the tensile test results. At 750 °C, the value of UTS was 250 MPa for 1 h of holding and 345 MPa for 3 h of holding. These values decreased after increasing the temperature to 900 °C and amounted to 139 for 1 h holding and 127 MPa for 3 h holding. It was also found that the elongation values at 750 °C ranged from 7-10%, while they amounted to 35-37% at 900 °C. A fracture analysis of the tested cast steel showed that in the prevailing part, the fractures were made of ductile nature with an arrangement of dimples that is typical for this type of fracture. Non-metallic inclusions that are typical for cast steel (i.e., oxides and nitrides) were also found in the area of the fractures.

Reductive leaching of indium and zinc from zinc neutral leach residue with sulphuric acid and sulphur dioxide

ABSTRACT Indium and zinc extractions from zinc neutral leach residue were investigated with sulphuric acid and sulphur dioxide. Sulphur dioxide maintained a low concentration of Fe3+ in the solution and promoted the decomposition of zinc ferrite. More zinc, indium, and iron dissolve into the solution, while copper co-precipitates with arsenic and sulphur into the residue. The optimal reductive leaching conditions were determined as 120 g/L H2SO4, 200 kPa sulphur dioxide partial pressure, a liquid-to-solid ratio of 8 mL/g and a stirring speed of 500 r/min at 105°C for 4 h. Extractions of 95.24% of zinc, 98.66% of iron, 95.04% of indium and 0.036% of copper were achieved. Copper in final residue exist as sulphides and can be recovered by subsequent oxygen pressure leaching. Selective recovery of valuable metals from zinc neutral leach residue is realised.

Extraction and recovery of zinc and indium from residue rich in zinc ferrite

Indium is regarded as critical metal due to its scarce availability and increasing demand. The extraction of indium from primary sources is important as an effort to alleviate indium availability given its potential role in sustainable technological advancement. This study introduces a process based on zinc ferrite reduction for the extraction of indium in addition to zinc from zinc residues. Zinc ferrite in zinc residue was partially reduced at 600 °C with a reducing gas containing 10% H2 and the roasting product was subjected to leaching at various conditions to study extraction of target elements. Decomposition of zinc ferrite led to a significant increment on the leaching kinetics of zinc residue. Multiple-step leaching was also explored to enrich the indium concentration in aqueous liquor followed by precipitation of indium. A maximum of 0.121 g/L indium concentration was obtained in multiple step leaching. The effect of temperature, acid concentration, liquid–solid ratio (L/S) and oxalic acid addition on leaching has also been discussed. The proposed process yields an aggregate of about 89% and 88.3% Zn and In extraction respectively along with significant indium concentration in the aqueous leach solution. The precipitation of synthetic solution showed that indium can be precipitated to obtain a concentrate containing about 8% In.

Effect of Ni, Mo and Mn content on spinodal decomposition kinetics and G-phase precipitation of aged model cast austenitic stainless steels

• Effect of Ni, Mo and Mn content on ferrite decomposition. • Thermal ageing of cast austenitic stainless steels (CASS) and model alloy. • Spinodal decomposition kinetics and G-phase precipitation. During ageing, the ferritic phase of Cast Austenitic Stainless Steels (CASS) undergoes decomposition by spinodal decomposition and G-phase precipitation, which leads to increasing hardness and decreasing impact toughness. Mo-bearing steels are more prone to ageing than Mo-free steels. To study the effects of Ni, Mo, and Mn, duplex model alloys were thermally aged at 350 °C and 400 °C. The microstructure evolution during ageing was characterized by atom probe tomography. Only Ni additions seem to affect the spinodal decomposition kinetics. Ni accelerates the spinodal decomposition kinetics regardless of the presence of Mo or Mn. Additions of Mo and Mn promote the precipitation of G-phase.

Acceleration of 475 °C embrittlement in weld metal of 22 mass% Cr-duplex stainless steel

The present study has demonstrated the differences in the 475 °C embrittlement behavior of the base and weld metals of a 22 mass% Cr-duplex stainless steel. A grade 2205 solution-annealed plate was used as the base metal. The corresponding Ni-rich weld metal, which comprised multiple layers, was fabricated using a grade 2209 filler wire. The base and weld metals were subjected to isothermal aging for various durations (up to 1000 h) at 400 °C. Microstructural characterization, Charpy impact toughness testing, and Vickers microhardness measurements were conducted before and after aging. Furthermore, the microstructure of the ferrite phase, after aging, was evaluated using transmission electron microscopy (TEM). There was a substantial decrease in the impact toughness in both the base and weld metals with increasing aging time, although the decrease in the impact toughness was more pronounced for the weld metal. The hardening of ferrite was more prominent in each layer of the weld metal than in the base metal. The TEM observations indicated that the ferrite phase in both the base and weld metals underwent spinodal decomposition, which was accelerated in the weld metal. Regarding the major alloying elements (i.e., Cr, Mo and Ni) contained in the ferrite phase, the content of each, Cr and Mo, was lower in each layer of the weld metal than in the base meal, while the Ni content was, conversely, higher in each layer of the weld metal than in the base metal. The higher Ni content promoted the decomposition of ferrite in each layer of the weld metal during aging. This resulted in an acceleration of the 475 °C embrittlement in the multilayered weld metal of the 22 mass% Cr duplex stainless steel compared to the base metal.

The Microstructure and Mechanical and Corrosion Behaviors of Thermally Aged Z3CN20-09M Cast Stainless Steel for Primary Coolant Pipes of Nuclear Power Plants

The effects of thermal aging time at 400 °C on the microstructure and mechanical and corrosion behaviors of Z3CN20.09M cast stainless steel were investigated; and the corresponding thermal aging mechanism was studied. It was revealed that the changes in mechanical properties after thermal aging were mainly caused by the iron-rich phase (α) and the chromium-rich phase (α’) produced by the amplitude-modulation decomposition of ferrite. A similar trend of thermoelectric potential during thermal aging was determined in relation to the Charpy impact energy. However, the corrosion resistance of Z3CN20.09M cast stainless steel deteriorates as thermal aging time increases. When the thermal aging is longer than 3000 h, the precipitation of G phase has a great influence on the corrosion resistance. The interfacial matching relationship between G phase and the surrounding ferrite was established by selected area electron diffraction of HRTEM. The relationship is of cube-on-cube phase boundary type. The impact fracture mechanisms in relation to thermal aging time were also studied and compared.

Investigation of the processes of dust processing gas cleaning of steelmaking industries

The article deals with the issues of processing of dust from electric steelmaking production by the method of thermodynamic extraction of iron, zinc and lead in order to reduce the environmental impact and increase the resource base of the industry. The paper presents various methods of zinc extraction from dust and gas purification, thermodynamic calculation of the decomposition and reclaiming of zinc ferrite.

Effect of Thermal Treatment at Inert Atmosphere on Structural and Magnetic Properties of Non-stoichiometric Zinc Ferrite Nanoparticles

Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES, Mössbauer Spectroscopy, XPS, XAFS). Magnetic studies proved the paramagnetic response of stoichiometric ZnFe2O4 (ZF) nanoparticles, while superparamagnetic behavior was observed in as-synthesized, non-stoichiometric ZnxFe3−xO (NZF) nanoparticles. Upon annealing up to 1400 °C in an inert atmosphere, a significant change in the saturation magnetization of NZF nanoparticles was observed, which rose from approximately 50 up to 140 emu/g. We attribute this effect to the redistribution of cations in the spinel lattice and reduction of Fe3+ to Fe2+ during high-temperature treatment. Iron reduction is observed in both ZF and NZF nanoparticles, and it is related to the decomposition of zinc ferrite and associated sublimation of zinc oxide.

Evolution of δ ferrite in a CF3 cast stainless steel upon neutron irradiation to 3, 5, 10, 20, and 40 dpa

The microstructural evolution of delta ferrite in a CF3 cast stainless steel irradiated to 3, 5, 10, 20, and 40 dpa with two dose rates was studied with atom probe tomography (APT) and transmission electron microscopy. Spinodal decomposition and G-phase precipitates induced by neutron irradiation and thermal aging were quantified systematically. The neutron irradiation significantly enhances the spinodal decomposition in delta ferrite as both the spinodal wavelength (i.e. a characteristic repeat distance) and amplitude (i.e. magnitude of elemental concentration fluctuation) increase after irradiation. The wavelength only varies slightly when the dose increases from 5 to 40 dpa, while the amplitude increases dramatically from 10 to 20 dpa and starts to saturate before 20 dpa. The dose rate and irradiation temperature also have a notable effect on the spinodal wavelength and amplitude. The study shows that higher dose rate promotes a larger wavelength at given irradiation doses. Regarding the G-phase precipitates, a slightly lower irradiation temperature would result in a smaller mean size of G-phase precipitates, while a lower irradiation dose rate would lead to a larger G-phase precipitates at a given temperature and dose. Overall, the spinodal decomposition and G-phase precipitates in the delta ferrite continue to evolve with the increasing dose beyond 10 dpa. This study confirms that the formation of G-phase precipitates at the interdomain region between alpha and alpha-prime is facilitated by the Si and Mo atoms rejected from Fe rich alpha phase and the Ni and Mn atoms rejected from Cr rich alpha-prime phase. Neutron irradiation plays a dominant role in the ferrite instability, and the effect of prior thermal aging at 400°C for 10,000 hours is negligible as the dose is 3 dpa and above.

Microstructural Evolution and Mechanical Behavior of Thermally Aged Cast Duplex Stainless Steel.

The microstructural evolution and mechanical behavior of cast duplex stainless steels (CDSSs) at 400 °C for different thermal aging times were investigated by transmission electron microscope (TEM) and small punch test (SPT). The results showed that the spinodal decomposition in ferrite was the main reason for the decrease in toughness, and G-phase did not play an important role in the embrittlement process. The change of membrane stretching zone (Wm) played an important role in the SPT load-displacement curve before and after thermal aging. During the deformation process of Wm in the SPT, for thermal aging for 10,000 h, some completely curved slip bands were generated inside the ferrite phase, which had no contact with the δ/γ phase interface and belonged to the slip bands produced by the independent deformation of ferrite. The combined effect of the curved slip bands and stress concentration led to the initiation of obvious micro-cracks at the δ/γ phase interface. The micro-cracks propagated along the ferrite phase curved slip bands, and eventually penetrated the entire hardened ferrite phase.

Effect of cold rolling on phase separation in 2202 lean duplex stainless steel

The effect of plastic deformation (cold rolling) on the thermal aging of a lean 2202 duplex stainless steel at intermediate temperatures (280 °C–450 °C) was studied using a combination of atom probe tomography and thermoelectric power measurements. In the undeformed condition, spinodal decomposition of ferrite was shown to be the prime aging process with an activation energy of 206 kJ/mol. Plastic deformation enhanced the aging and the austenite partly transformed into martensite. When no precipitation or phase transformation was observed in austenite, both ferrite and martensite decomposed. The spinodal decomposition kinetics of ferrite increased with increasing deformation rate. The FeCr-rich martensite also decomposed at 450 °C, via a nucleation and growth process, owing to a decrease of the Cr content in the matrix. Chromium nitrides, G-Phase, and Cu-rich precipitates were observed in the decomposed martensite.

Microstructure investigation of duplex stainless steel welds using arc heat treatment technique

A heat treatment technique was applied on standard duplex stainless steel welds in order to investigate the influence of thermal treatments, e.g., multi-pass welding, on the microstructure. By using a stationary arc, a spatial steady-state temperature field ranging from liquidus to room temperature evolves within a single sample and results in a graded microstructure. The arc heat treatment was applied for 10 and 60 min respectively, and the experimental results were compared against thermodynamic calculations. Metallographic investigations revealed the formation of secondary phases within distinct zones. For the 10 min arc heat treated sample, the formation of sigma phase was observed in a temperature range of 730–1000 °C and chi phase was found above 700 °C. For the 60 min sample, sigma phase formed between 675 and 1025 °C, while chi phase formed above 600 °C. In both samples, transformation of chi phase to sigma phase as well as the formation of secondary austenite at 575–1100 °C was observed. Hardness measurements identified brittle regions, which correlated with the regions enriched in sigma phase and decomposition of ferrite. Compared to the initial microstructure, regions with secondary phases showed increased sensitization to local corrosion, when tested according to ASTM A262-Practice A.

Investigation of the effect of low temperature aging on the mechanical properties and susceptibility to sulfide stress corrosion cracking of 22%Cr duplex stainless steel

Duplex stainless steels (DSS) are corrosion resistant alloys largely used in the oil and gas production industry. Optimum properties are usually obtained with equal fractions of ferrite (δ) and austenite (γ) in the microstructure, which can be obtained by a proper solution heat treatment. However, work hardening can be used for applications where mechanical resistance must be increased, such as in casing and tubulars for oil and gas production. These pipes operate under high pressure in a harsh environment, composed by oil and high chloride water, low pH and high H2S and CO2 partial pressures. Additional strengthening can also be provided by low temperature aging which promotes the fine precipitation of a Cr-rich α’ phase by spinodal decomposition of ferrite. In this work, a DSS with 22%Cr (UNS S31803) received with an un-balanced microstructure (64% of ferrite), was aged at 475 °C for 8 h. For comparison, the material was correctly solution treated to obtain a balanced microstructure, and aged in the same way of the as received one. The effects on tensile mechanical properties, hardness and impact toughness were determined. The sulfide stress corrosion (SSC) susceptibility was evaluated by slow strain rate tensile (SSRT) tests in low pH and high pH2S chloride solution.

Влияние старения на микроструктуру, фазовый состав и микротвердость высокоазотистой аустенитной стали

The authors studied the effect of duration of age hardening at the temperature of 700 °C on the microstructure, phase composition and microhardness of high-nitrogen Fe-23Cr-17Mn-0.1C-0.6N (wt. %) steel. The study showed that age hardening at the temperature of 700 °C for half an hour causes the complex of phase transformations: the decomposition of δ-ferrite (with the formation of σ-phase and austenite) and the formation of cells of discontinuous decomposition on the austenitic grains boundaries (the formation of particles based on the chromium nitride Cr 2 N and the depletion of austenite by interstitials). After age hardening for more than 10 hours, besides the discontinuous decomposition of austenitic grains, a homogeneous (continuous) precipitation of chromium nitride occurs in those austenitic grains, which have not undergone discontinuous decomposition in the initial stages of aging. With an increase in the aging duration up to 50 hours, the authors observed the growth of decomposition cells in austenitic grains and the formation of mixed structure. Such structure consisted of austenite grains, which underwent discontinuous decomposition with the formation of lamellar precipitations of chromium nitride in austenite; austenitic grains with the dispersed particles formed by the mechanism of continuous decomposition; and the grains with σ-phase, chromium nitrides, and austenite formed as a result of the high-temperature ferrite decomposition during aging. The aging caused the increase in the microhardness, which value depends on the mechanism of precipitation hardening - continuous or discontinuous decomposition in austenite or the precipitation of intermetallic σ-phase and chromium nitrides plates in the grains of high-temperature ferrite.

Effects of thermal aging and low-fluence neutron irradiation on the mechanical property and microstructure of ferrite in cast austenitic stainless steels

The effects of low-fluence neutron irradiation on hardening and microstructure evolution in ferrite of solution annealed or thermally aged CF3, CF3M, CF8 and CF8M cast austenitic stainless steels (CASSs) have been investigated by means of nanoindentation tests and atom probe tomography (APT). Thermal aging was performed at 400 °C for 500 h. Neutron irradiation was carried out to a fluence of 4.84 × 1018 n/cm2 (E > 1 MeV) at the temperature ranging from 289 to 292 °C in the LVR-15 research reactor. Irradiation hardening in thermally-aged specimens was found to be similar with or smaller than that in the corresponding solution annealed specimens. Phase decomposition and formation of solute clusters acted two major factors for the hardening in ferrite with thermal aging and/or neutron irradiation. The phase decomposition of ferrite increased with either the thermal aging or the neutron irradiation for the solution annealed materials; however, the change in the phase decomposition of ferrite was neither significant nor apparent with the low-fluence neutron irradiation for the thermally-aged materials. Ni–Si–Mn enriched solute clusters were observed in the matrix of ferrite in the aged specimens, and the irradiated specimens with/without thermal aging. Mo in the CASSs appeared to inhibit the formation of solute clusters under the neutron irradiations. In the thermally-aged specimen with low-C and without Mo, neutron irradiation enhanced the formation of solute clusters significantly. For the first time we discussed the relationship between hardening and microstructure evolution in ferrite of CASSs with consideration of both thermal aging and neutron irradiation.

Characteristic of zinc ferrite decomposition by calcium and magnesium oxides

Electric arc furnace (EAF) dust generated in steelmaking is a valuable waste material with high content of zinc, lead and iron. Recovery of zinc by current industrial hydrometallurgical methods at zinc plants is difficult due to the presence of zinc in the hardly soluble ferrite form and high contents of chlorine and fluorine that are harmful impurities for further electrolysis. To decompose zinc ferrite and remove halogens from EAF dust there is a promising approach that promote zinc ferrite decomposition to highly soluble zinc oxide and volatilization of halogens in one pyrometallurgical stage, where EAF dust are calcined with lime at 900-1100°C. This paper aims to investigatekinetics of the reaction between pure ZnFe2O4 and CaO to determine its controlling step and evaluate its characteristics. The reaction between pure ZnFe2O4 and MgO is also considered. The investigation of the EAF dust sample has confirmed that majority of zinc is in the form of hardly soluble ferrite. The results of experiments have shown that the reaction of zinc ferrite with calcium oxide at 900-1000°C is kinetic controlled, so temperature has a significant effect of on the reaction rate. The degree of conversion of the reaction between zinc ferrite and magnesium oxide is negligible, so the application of MgO during the EAF dust processing is inexpedientat the studied temperatures.