Fe Mn Research Articles

Effect of alloying content on microstructure and mechanical properties of Fe–Mn–Al–C low-density steels

A series of low-density steels with alloying contents of C from 0.6 to 1.5%, Mn from 20 to 35%, and Al from 6.0 to 12.0% were fabricated in the laboratory. The microstructure, density and mechanical properties of the resulting steels were examined to explore the effects of varying alloy content. The results reveal a significant influence of alloy content on the microstructure of the low-density steels after solution processing in terms of ferrite phase fraction, grain size, and κ-carbide size. It was found that the dependence of alloy density on the C, Mn, and Al content can be formulated ρ = 8.1–0.102C-0.10Al-0.01Mn g/cm3 (with the alloy content given as mass%). Both the yield strength and the work hardening rate varied significantly with alloying content, where the yield strength decreased with increasing Mn content, and increased with increasing Al and C content. The impact toughness of the low-density steels was found also to be strongly affected by the alloying content, showing Charpy impact toughness lower than 10 J for C content above 1.2%, for Mn content below 25%, and for Al content above 10%. The effects of alloy content on the mechanical properties are attributed to differences in the precipitation and coarsening of κ-carbides during the solution treatment process.

Magmatic Native Gold: Composition, Texture, Genesis, and Evolution in the Earth’s Crust

Abstract —Here we report results of microforms’ studies of native gold and its alloys in igneous rocks, modified to varying degrees by secondary processes. We discuss the composition and occurrence of both the deep-seated magmatic gold-bearing alloys and the products of their transformation under conditions of the upper Earth’s crust. Gold-bearing Kamchatka adakites and ankaramites, Ildeus massif mafic-ultramafic intrusions and adakites from the Stanovoy fold system as well as dacites from the Bolivian Andes were formed during melting of either the suprasubduction mantle wedge or the subducted oceanic crust. In depleted peridotites from the Avachinsky Volcano in Kamchatka as well as suprasubduction ophiolites from Polar Urals, Eastern Sayan and the Western Mediterranean Betic–Rifean belt, the gold-bearing mantle was hybridized by subduction-related melts and high-temperature fluids. Volcanic rocks associated with the Lesser Khingan Fe–Mn deposits and Zolotaya Gora Au deposit in Southern Urals as well as Taragai ultramafic rocks in the South Khingan Range display subduction-related geochemical characteristics. Gold-bearing trachytes in the Virginian Appalachians (USA) represent felsic differentiates of mafic intraplate magmas. We propose that one of the principal forms of gold transport into the upper crustal environments is represented by Cu–Ag–Au alloys, which precipitated from mantle-derived silicate melt enriched in chalcophile and siderophile elements. Such Cu–Ag–Au alloy-rich magmatic rocks can either constitute primary sources of precious metals in the mantle-crust system or serve as geochemical precursors to the formation of native gold assemblages in epithermal and mesothermal ore deposits. Presence of magmatic gold particles in subduction-related igneous rocks and mantle restites hybridized by subduction-derived melts and high-temperature fluids suggest the existence of gold-rich horizons in the Earth’s mantle at depths comparable to typical depths of generation of primary convergent zone and some within-plate magmas.

Thermal treatment of the tourmaline Fe-rich princivalleite Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O

Natural Fe2+-rich princivalleite was thermally treated in the air at 700 °C to study crystal-chemical and color variations due to changes in oxidation states of Fe and Mn and atom ordering. Overall, the experimental data (electron microprobe, structural refinement, Mössbauer, infrared, and optical absorption spectroscopy) show that thermal treatment of princivalleite results in an almost total Fe2+ oxidation to Fe3+ and an oxidation of approximately one-third of Mn2+ to Mn3+ along with a minor degree of disorder of Al–Fe–Mn over the Y and Z sites. This process is accompanied by a significant deprotonation of the sample. The YFe and YMn oxidation from + 2 to + 3 yields in a decrease in a-parameter, whereas the increased content of ZFe3+ results in a minor increase in the c-parameter. Optical absorption spectroscopy shows that the faint blue (azure) color of untreated princivalleite is caused by the presence of Fe2+ and the absence of Ti4+. Thermal treatment in air (700 °C) changed the color to dark brown due to the progressive oxidation of Fe2+ to Fe3+ and Mn2+ to Mn3+, as demonstrated by the evolution of optical absorption bands caused by electron transitions in these 3d-cations. However, the most evident result of the thermal treatment of the Fe-rich princivalleite sample is the simultaneous presence of Fe2+, Fe3+, Mn2+, and Mn3+, with a Fe3+/ΣFe and Mn3+/ΣMn ratio of 0.92 and 0.25, respectively. This observation suggests that the oxidation process during the heating experiments was largely controlled by kinetic factors.

Carbonate rocks as natural buffers: Exploring their environmental impact on heavy metals in sulfide deposits

Carbonate rocks are closely related to the genesis and spatial distribution of polymetallic sulfide deposits. The natural buffering of carbonate rocks can reduce the ecological impact of heavy metals produced by mining and smelting. Ignoring the buffering effect of carbonate rocks on the heavy metals in the mine environment leads to inaccurate ecological risk assessment, wasting land resources and funds. This study investigates Cd, Zn, and Pb distribution and speciation in the water and soil-rice system in the polymetallic sulfide deposit at Daxin, Guangxi. The study aims to reveal the effects of the natural buffering of carbonate rocks on the migration and transformation of heavy metals. The results show that the water Zn and Cd concentrations decreased from 1857.0 to 0.9 mg L−1 to 0.16 and 0.001 mg L−1, respectively, from the mining area to 4 km downstream. The natural buffering of carbonate increases the water pH from 2.80 to 7.64, resulting in a tendency for Cd, Zn, and Pb to separate from the aqueous phase and enrich the sediments. Soil Cd content in the mining area reached 110.0 mg kg−1 (mean value 55.88 mg kg−1), and rice Cd seriously exceeded the maximum limit. However, the weathering of carbonate reduces the migration ability and bioavailability of Cd. Soil Cd is mainly in the Fe–Mn bound and carbonate-bound fractions, resulting in lower Cd content in downstream soils (mean value 2.73 mg kg−1). Soil CaO, tFe2O3, and Mn hindered the uptake of soil Cd by rice rendering a lower exceedance of Cd in downstream rice. Therefore, this study recommends a farmland management plan under the premise of rice Cd content and integrated soil Cd content, which ensures food safety and fully utilizes farmland resources. This result provides a scientific basis for ecological risk assessment, mine environmental protection, and management in the carbonatite sulfide mine environment.

A comparative study on passive films of Fe–11Cr stainless steel and Fe–20Mn–11.5Al–1.4C–5Cr lightweight steel

Fe–20Mn–11.5Al–1.4C–5Cr (wt%) lightweight stainless steel (LWSS) was found to have equivalent or better resistance to pitting corrosion than Fe–11Cr (wt%) stainless steel (SS). The desirable resistance to pitting corrosion of the LWSS alloy was attributed to the formation of protective passive film. On LWSS, an (Al,Fe,Cr)-oxide was formed, and on SS, a (Fe,Cr)-oxide was formed. The passive film of LWSS had a higher Cr + Al content than that of SS. In addition, compared to the passive film of SS, the passive film of LWSS was found to be thick and the concentration of point defects was also low.

Geochemical characteristics and migration patterns of rare earth elements in coal mining subsidence lakes under the influence of multiple factors

Mining activities cause surface subsidence and the formation of subsidence lakes, which dynamically change with the continuous coal mining activities. Under the combined influence of various human activities such as agriculture, aquaculture, and floating photovoltaic (FPV), the lake environment undergoes continuous changes, thereby altering the geochemical characteristics of rare earth elements (REEs) in the sediment. This study focused on the subsidence lakes in the Huainan coalfield in eastern China to examine the REEs content in the sediment, elucidated the temporal variations and geochemical characteristics of REEs distribution, explored the main controlling factors of REEs in the sediment, and revealed the migration and transformation behavior of REEs during dynamic subsidence processes. The study revealed that the migration pattern of REEs in the sediment was closely related to the duration of subsidence. The average content of REEs in lake sediments with subsidence duration <5 years increased from 219 μg·g−1 to 248 μg·g−1 compared to the soil, showing an enrichment model primarily driven by rainwater runoff, groundwater input retention, and mineral dissolution. With further subsidence, the processes of reduction dissolution of Fe–Mn oxides/hydroxides, organic colloid adsorption, and hydraulic disturbance gradually replaced the aforementioned enrichment behavior as the main migration pathways, resulting in a decrease in the average REEs content in the sediment to 179 μg·g−1 for subsidence durations exceeding 10 years. There was no strong correlation between REEs fractionation and subsidence duration. Artificial activities, such as FPV, are important factors causing Cerium and Erbium anomalies in some subsidence lake sediments. This study was not only of significant importance for understanding the migration, distribution, and environmental behavior of pollutants in aquatic environments under the interference of human activities but also provided a solid theoretical foundation for the future management of coal mining subsidence lakes.

Investigation of the applicability of Cu–Fe–Mn–Ni based high entropy and compositionally complex alloys as metal matrix composites for cobalt free hot-pressed diamond tools

Due to the rising demand and carcinogenic effect of cobalt, alternative metal matrixes need to be developed for hot-pressed diamond tools. Due to this reason High-Entropy alloys without cobalt were calculated via phase fraction diagrams. Three alloys of the Al–Cu–Fe–Mn–Ni system Al30Cu30Fe5Mn25Ni10, Al11.25Cu35Fe5Mn20Ni28.75 and Al5Cu20Fe25Mn25Ni25 were chosen due to their different crystal structures ranging from pure bcc, eutectic fcc-bcc to pure fcc crystal structure. Cr5Cu20Fe25Mn25Ni25 was chosen to verify the change of one element on the consolidation properties. The alloys were mechanically alloyed and hot-pressed at 800 °C for 3 min without and at 900 °C for 3 min with diamonds. Porosity increased with the fraction of bcc solid solution in the investigated alloys of the Al–Cu–Fe–Mn–Ni system. Samples consisting of Cr5Cu20Fe25Mn25Ni25 showed the lowest porosity, which was attributed to precipitation of a second copper-rich fcc solid solution around the remaining pores. At a process temperature of 800 °C and 3 min isothermal hold the samples featured a porosity of only 2.72%. Within the XRD patterns and SEM images of the hot-pressed samples with diamonds no graphitization or formation of carbides could be observed. Therefore, Cr5Cu20Fe25Mn25Ni25 was identified as a promising cobalt free metal-matrix candidate for diamond tools.

Simultaneous improvement of corrosion and wear resistance of Fe–Mn–Al–C lightweight steels: The role of Cr/Mo

Fe–Mn–Al–C lightweight steel has promising applications due to its low density and excellent mechanical properties. This study investigates the influence of Cr/Mo on the electrochemical corrosion and wear behavior of lightweight steel. The results showed that adding Cr/Mo significantly improved the corrosion resistance in NaCl/NaHSO3 solution. This improvement was attributed to the presence of protective Cr/Mo oxides and the reduction of harmful Mn oxides, which increased the compactness and charge transfer resistance of the oxide film. The primary wear types of lightweight steels include abrasive, adhesive, fatigue and oxidative wear. The wear test results showed that adding Cr/Mo improved the wear resistance of lightweight steel, which can be attributed to the increased toughness and hardness gradient.

Influence of Thermo-Mechanical Process and Nb-V Microalloying on Microstructure and Mechanical Properties of Fe–Mn–Al–C Austenitic Steel

In present study, a novel Nb-V microalloyed Fe–Mn–Al–C steel and a non-microalloyed Fe–Mn–Al–C austenitic steel were treated with different thermo-mechanical processes. The microstructure of the test steels was observed by scanning electron microscope, transmission electron microscope, electron probe micro-analyzer, and X-ray diffractometer. A tensile test was conducted to estimate the mechanical properties of the test steels. Results show that the equiaxed austenitic grains are obtained in both test steels, while hot rolling reduces the grain size significantly. The grain size of the Fe–Mn–Al–C steel decreases by 40%–55% after the addition of Nb-V due to the precipitation of nanoscale (Nb,V)C particles within the austenite matrix. Compared with the solid solution treated specimens, the strength of the hot-rolled or aged specimens is improved. Meanwhile, the strength of the Fe–Mn–Al–C steel with Nb-V microalloying is also increased by 55 MPa due to the precipitation strengthening and fine grain strengthening, while the elongation is decreased. The Nb-V microalloyed Fe–Mn–Al–C steel, after hot rolling + aging treatment, obtains the maximum strength, with the yield and tensile strength of 669 MPa and 1001 MPa, respectively. The strengthening mechanisms that contribute significantly to the yield strength are solid solution strengthening and dislocation strengthening. They are 185 MPa and 211 MPa, respectively, for the Nb-V microalloyed Fe–Mn–Al–C steel at hot rolling + aging conditions. Meanwhile, the segregation of carbon atoms after aging treatment also improves the yield strength significantly.

Room temperature deformation mechanisms of a Fe–Mn–Al–C steel

This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C steel at room-temperature through uniaxial tensile tests, strain rate sensitivity and stress relaxation analysis. Through numerical analysis and microstructural studies, this investigation reveals that increasing strain leads to the formation of low-angle boundaries (LABs) at the vicinity of grain boundaries. Consequently, these LABs play a facilitating role in the stress-assisted diffusion of carbon atoms, thereby triggering the dynamic strain aging (DSA) phenomenon. The evidence for this is substantiated by the strain rate sensitivity coefficient and stress relaxation results obtained from numerical analysis during uniaxial tensile tests. As deformation progresses, the misorientation of LABs increases, influencing the strain hardening behavior. The intensified DSA contributes to enhanced work hardening, while substructure development results in softening, creating a trade-off between these contrasting effects.

Predicting the stacking fault energy in FCC high-entropy alloys based on data-driven machine learning

The properties of high-entropy alloys (HEAs) depend primarily on the composition and content of elements. However, getting the optimal composition of alloying elements through the traditional "trial and error" method is challenging, especially for non-equiatomic HEAs with a wide range of composition space. In this study, based on the knowledge that stacking fault energy (SFE) is the most crucial intrinsic property to determine the deformation mechanism and to optimize the mechanical properties of FCC HEAs, classical machine learning classification models including support vector classification (SVC) and random forest (RF), and deep learning regression model (Back Propagation Neural Network) were established to predict the stacking fault energy of Co–Cr–Fe–Mn–Ni–V–Al high-entropy alloys. These models can obtain the SFE data of any atomic ratio composition of the FCC structured Co–Cr–Fe–Mn–Ni–V–Al high-entropy alloy quickly and accurately. The high accuracy of these models indicates that using the compositions as features to predict stacking fault energy is feasible. Meanwhile, the monotonic relationship between alloying elements and SFE makes it possible to change the SFE of high-entropy alloy by fine-tuning the composition to realize the control of material deformation mechanism and mechanical properties. Component-based machine learning models provide a new method for rapidly discovering high-entropy alloys with exceptional strength and flexibility.

Temporal–Spatial Distributions and Influencing Factors of Heavy Metals As, Cd, Pb, and Zn in Alluvial Soils on a Regional Scale in Guangxi, China

Understanding the temporal–spatial distribution and influencing factors of heavy metals on a regional scale is crucial for assessing the anthropogenic impacts and natural variations in elemental geochemical behavior. This study evaluated the spatial distributions of the heavy metals As, Cd, Pb, and Zn as well as the driving mechanisms over the past 31 years in Guangxi, China, using three geochemical baseline projects (the Environmental Geochemical Monitoring Network Project (EGMON) project 1992–1996; the Geochemical Baseline (CGB) 1 project 2008–2012; and the CGB2 project 2015–2019). By calculating the variable importance using the random forest algorithm, it was found that natural factors are the primary drivers of the spatial distribution of heavy metals in the EGMON project, especially precipitation for As, the digital elevation model (DEM) for Cd and Pb, and temperature for Zn. Surface alluvial soils showed obvious heavy metal enrichment in the CGB1 project, with the gross domestic product (GDP) driving the spatial distribution of all heavy metals. In addition, the anomalous intensity and range of heavy metals in the CGB2 project decreased significantly compared with the CGB1 project, especially owing to the normalized difference vegetation index (NDVI) as a positive anthropogenic factor that improves the degree of rocky desertification, thus reducing the heavy metal contents of As and Pb, and the precipitation promoting the decomposition of Fe–Mn concretions and thus the migration of Cd and Zn. This research promotes an understanding of anthropogenic and natural influences on the spatiotemporal distribution of heavy metals and is of great significance for environmental monitoring and governance.

Engineering Seed-like Fe–Mn Nanomedicine with Ultrasmall Structure and ATP-Responsive Function for Tumor Metabolic and Redox Subversion

Engineering Seed-like Fe–Mn Nanomedicine with Ultrasmall Structure and ATP-Responsive Function for Tumor Metabolic and Redox Subversion

Distribution, source and contamination of rare earth elements in sediments from lower reaches of the Xiangjiang River, China

Rare earth elements (REEs) are emerging micropollutants in aquatic environments. In this study, concentrations of REEs and major elements, and mineralogical compositions of sediments from lower reaches of the Xiangjiang River (China) were analyzed using ICP-MS technique. The results suggested that sediments were characterized by terrigenous compositions TiO2, SiO2, Al2O3, K2O, Na2O and P2O, and contained high concentrations of REEs with mean total REE concentrations (∑REE) of 318.7 mg/kg. REEs were moderately enriched in upper river sediments, and slightly or less enriched in downriver sediments. The normalized REE distribution pattern for sediments was characterized by flat shalelike and Eu depleted V-shape REE patterns, which indicated REEs in sediments were lithologically contributed from sedimentary rocks and granites distributed in the watershed respectively. REEs in sediments were hosted mainly in Fe–Mn oxides, and sulfide and organic matters that were characterized by middle REEs (MREE) enrichments relative to light REEs (LREE) and heavy REEs (HREE), and the distribution and differentiation of REEs in sediments were controlled by clays, Fe–Mn oxides, organic matters and finer grains; and also by accessory minerals (e.g., zircon) from granite. The distribution features of REEs in sediments and BCR extraction results suggested that the sediment REE enrichment resulted from additional REE input from anthropogenic sources, including those in discharges from sulfide-ore smelting industries at Zhuzhou city and from phosphate fertilizer plants at Xiangtan city along the river. Thus, sediments were contaminated with REEs in moderate degree in upper river area, and REE contamination was then formed by superimposing anthropogenic REEs on lithological residues. Finally, concentrations of Ce > 100 mg/kg, Gd > 8.12 mg/kg, ∑REE >274.9 mg/kg, ∑LREE >252.3 mg/kg and ∑HREE >28.8 mg/kg here were recommended as the REE contamination levels that represented as REE indices for identifying and rating REE contamination in this mining impacted river.

The Effect of Nb/Mo on the Microstructures and Mechanical Properties of Fe–Mn–Al–Ni–C Austenitic Steels

The microstructures and mechanical properties of Fe–24Mn–10Al–6Ni–1C steels microalloyed by Nb, Mo, and Nb–Mo coaddition in both solid solution and aging states are evaluated. The results show that the addition of Nb, Mo, or Nb–Mo leads to a decrease in austenitic grain size and a suppression in κ‐carbides precipitation during aging. Besides, Mo slightly promotes precipitation of both B2 bands and particles as a ferrite stabilizer. However, Nb and Nb–Mo increase the volume fraction of B2 particles together with decreasing B2 bands due to the formation of NbC and (Nb, Mo)C. The strengths and ductility are improved simultaneously after adding microalloying elements. The coaddition of Nb–Mo achieves a best combination of strength and ductility. After aging, the precipitation of κ‐carbides and B2 leads to a further enhancement in yield strength but a reduction in plasticity for all the experimental steels. Additionally, the effect of Nb/Mo on the strain hardening behavior is also analyzed.

Diffusion timescale conundrum in contact metamorphism: Oxygen isotope and trace element profiles in dolomite

Successful application of diffusion chronometry is based on detailed knowledge of diffusion parameters obtained from laboratory experiments, which also need to be upscaled to be applied to natural samples. While generally applicable, several examples of disagreement with other dating techniques and discrepancies with geological observations highlight the importance of validating diffusion parameters and their use to geochronologic application by testing them on samples from well-characterized geologic environments.The incomplete dissolution and reprecipitation reaction of dolomite associated with infiltration along grain boundaries of a fluid of magmatic origin in a contact metamorphic environment is the starting point of this study. The reaction produces dolomite rims, which are characterized by lower δ18O values (about 16‰) and slightly higher Fe (∼1000 ppm) and Mn (∼200 ppm) concentrations. The cores, in comparison, have no Fe and Mn and a δ18O value of about 30‰. This compositional and isotopic gradient led to chemical re-equilibration through diffusion at the reaction interface. We acquired oxygen isotope profiles using a secondary ion mass spectrometer (SIMS), with spot sizes as small as 3 µm, and iron and manganese profiles with a NanoSIMS and a beam diameter of about 240 nm. These profiles were then compared against cumulative theoretical diffusion distances calculated for a modeled time – temperature path of the contact aureole using the experimentally determined diffusion parameters for O, Fe and Mn in dolomite.The oxygen isotope profiles yielded diffusion distances of ca. 10 µm, corresponding to a formation temperature of about 550 °C, which is concordant with phase petrology and a timing for fluid infiltration at the onset of cooling of the contact aureole (i.e., non-isothermal evolution of the dolomite marbles). The Fe and Mn profiles were very sharp, with a diffusion length of about 150 nm. Such short diffusion length would be achieved at near-surface temperature and corresponding cooling timescale are several orders of magnitude smaller than those derived from the oxygen diffusion profiles. From the mineralogy and textures, a decoupling of the oxygen isotopes and Fe–Mn reaction interface can be ruled out, suggesting that the published diffusion parameters are not fully representative, either due to the experimental conditions or by the assumed diffusion mechanism of natural processes. This case study is not the first example in the literature where the diffusion rate of Fe and Mn in natural dolomite seems to be substantially slower than predicted by experiments. Thus, there is a need to re-assess the experimental diffusivities before Fe and Mn diffusion in dolomite can be reliably used to determine duration, cooling or heating paths of metamorphic processes.

Formation of hydrothermal ferromanganese oxides from the Daigo-Kume Knoll in the middle Okinawa Trough, Japan

Many active hydrothermal sites resulting from active volcanism have been recognized in the Okinawa Trough, a nascent back-arc basin. Despite its importance for understanding whole hydrothermal circulation, low-temperature (LT) hydrothermal activity, which precipitates ferromanganese (Fe–Mn) oxides, has not been actively studied compared to high-temperature (HT) hydrothermal activity, which forms sulfide deposits. Therefore, in this study, we investigated the origin and formation of Fe–Mn oxides obtained from the outer rim of the Daigo-Kume Knoll caldera in the middle Okinawa Trough based on their chemical and mineral compositions. Composed of birnessite and todorokite, the Fe–Mn oxide samples contain low levels of trace elements, indicating their precipitation from LT hydrothermal fluids. This is the first report of hydrothermal activity at the Daigo-Kume Knoll. Based on an independent component analysis of elemental mapping data, it was determined that the hydrothermal activity consisted of two stages: a primary hotter LT hydrothermal fluid (roughly 30 °C–150 °C) that altered silicate debris and precipitated mainly Fe oxides, and a secondary colder LT hydrothermal fluid (roughly 30 °C) that precipitated mainly Mn oxides without alteration. The growth rate, estimated from the chemical composition, and the thickness of the Fe–Mn oxide samples indicated that the duration of the hydrothermal activity was about 17.7–29.5 kyr. In contrast to their LT hydrothermal origin, the high Mo/Mn ratio of the Fe–Mn oxide samples suggested that the LT hydrothermal fluids that precipitated the Fe–Mn oxide samples might be originally produced by HT water–rock interactions.

Modulated synthesis of MnO2-decorated Fe–Mn composite oxides：synergistic effects on boosting the performance of toluene oxidation

MnO2-decorated iron-manganese composite oxides were prepared via a novel method combining hydrolysis driving redox reaction and hydrothermal approach. The differences in physicochemical properties and microstructures were controlled by modulating the ratio of MnO2 to 5Mn1Fe (The molar ratio of Mn to Fe was 5:1). Characterization results displayed that the excellent efficiency of toluene removal over 3MnO2/5Mn1Fe catalyst was attributable to the special structure, strong low-temperature reducibility, high surface Mn3+/Mn4+ and Oads/Olatt molar ratios. The interaction between MnO2 and 5Mn1Fe played a predominant role in outstanding catalytic efficiency of the hetero-nanostructures. Among all as-prepared catalysts, the highest activity was achieved over the bayberry-like 3MnO2/5Mn1Fe catalyst with corresponding T90 of 233 °C, much lower than MnO2 for 313 °C and 5Mn1Fe for 280 °C. This successful strategy could not only be applied to VOCs catalytic oxidation but also provide a novel synthetic path for other catalysis systems.

An indices-based water quality model to evaluate surface water quality: A case study in Vaalwaterspruit, Mpumalanga, South Africa

Temporal variation assessments of surface water quality of the Vaalwaterspruit, a stream in Mpumalanga, South Africa, applied sixteen physicochemical parameters, anions, and trace metals, including pH, EC, TDS, Cl−, F−, alkalinity, hardness, Ca, Na, Mg, NO3−, SO42−, K, Al, Fe, and Mn, were measured monthly for a period of four years (January 2018–December 2021). Findings demonstrated water was scrambled under stress due to high amounts of Fe and Mn detected upstream. According to water quality indices, the stream category is poor and very poor (203–307.71) for the US-WQI, good and fair (76.34–82.35), for the CCME-WQI and fair state (0.61–0.87) for the CPI. CPI was best to categorize the water quality, which deteriorated more in the downstream area due to nutrients (Fluoride), trace metals (Al, Fe, and Mn), and particulate matter during the four-year study period. To evaluate the data and determine potential sources, the interrelation between the water quality data was applied using multivariate approaches. The findings showed that five eigenvalues were more significant than one, accounting for 74% of the overall variance. The five cluster results were TH-Ca-Mg, K–Fe–Mn, Cl–Na, F–SO4–Al, and TDS-Alkalinity. They were consistent with the PCA results, implying a common source and identifying summaries that sewage discharges and industrial effluents negatively affect surface water quality in addition to mining activities. Poor-quality water from anthropogenic sources should be carefully treated before releasing into surface water resources.

Investigation on strength and plasticity enhancement mechanism of 1180 MPa-grade quenching and partitioning steel

A comparative study on microstructures and mechanical properties of a low carbon Fe–Mn–Si steel with and without quenching pretreatment is performed to investigate the strength and plasticity enhancement mechanism. Microstructural analysis and 3D APT observation show that the lamellar microstructure obtained by introducing pre-quenching at 990 °C for 20 min prior to quenching and partitioning (Q&P) process mainly consists of ferritic laths, Mn-enriched tempered martensite and retained austenite with high mechanical stability. Mn enrichment in tempered martensite helps maintain a relatively high tensile strength. The refined alternative laths consisting of ferrite and tempered martensite share the same crystallographic orientation, which should be easier to hinder the crack propagation and delay the fracture. Compared to the polygonal-structured sample treated without quenching pretreatment, both higher frequencies of Σ3 CSL boundaries and higher volume fraction of stable retained austenite allow the pre-quenched sample exhibit an excellent strength-plasticity balance. The plasticity of the pre-quenched sample increases by nearly 90% and the product of strength and elongation (PSE) reaches higher than 24 GPa·%.