Increasing Mn Content Research Articles

Supported Inverse MnOx/Pt Catalysts Facilitate Reverse Water Gas Shift Reaction

Catalytic conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction has been identified as a promising approach for CO2 utilization and mitigation of CO2 emissions. Bare Pt shows low activity for the RWGS reaction due to its low oxophilicity, with few research works having concentrated on the inverse metal oxide/Pt catalyst for the RWGS reaction. In this work, MnOx was deposited on the Pt surface over a SiO2 support to prepare the MnOx/Pt inverse catalyst via a co-impregnation method. Addition of 0.5 wt% Mn to 1 wt% Pt/SiO2 improved the intrinsic reaction rate and turnover frequency at 400 °C by two and twelve times, respectively. Characterizations indicate that MnOx partially encapsulates the surface of the Pt particles and the coverage increases with increasing Mn content, which resembles the concept of strong metal–support interaction (SMSI). Although the surface accessible Pt sites are reduced, new MnOx/Pt interfacial perimeter sites are created, which provide both hydrogenation and C-O activation functionalities synergistically due to the close proximity between Pt and MnOx at the interface, and therefore improve the activity. Moreover, the stability is also significantly improved due to the coverage of Pt by MnOx. This work demonstrates a simple method to tune the oxide/metal interfacial sites of inverse Pt-based catalyst for the RWGS reaction.

Distribution of trace elements in growth zones and sectors of spodumene crystals (Pashki deposit, Nuristan, Afghanistan)

Regular distribution of several trace elements in spodumene crystals of the Pashki pegmatite Li deposits in Afghanistan (Nuristan province) is analyzed using secondary ion mass spectrometry (SIMS). Twenty seven local analyses of 19 elements were carried out in spodumene samples of different generations taken from pegmatites during feld works of 2023. We studied an early generation spodumene crystal from blocky spodumene-quartz-albite pegmatite and two late generation spodumene crystals including an euhedral crystal from a quartz core of pegmatite and a crystal extracted from a mineralized cavity together with quartz crystal, albite, and muscovite. It is found that the Fe, B, and Be content is signifcantly higher in the growth pyramid of the pinacoid face (010) than in the growth pyramid of the prism face (021). From early to late growth zones, the Be, B, Fe, and Mn content increases and the K, Rb and Ti content decreases. The heterogeneity of trace element composition of spodumene crystals thus mostly depends on their sectoriality, which is caused by different crystal chemical conditions of the incorporation of isomorphic trace elements into the mineral structure on faces parallel and perpendicular to the direction of pyroxene chains of Si–O tetrahedra along axis [001] rather than by their zonation. From early to late generations of spodumene, the content of most analyzed trace elements signifcantly decreases corresponding to the ideas about the change in the crystallization fractionation of elements during the evolution of the pegmatite process transiting from the closed to open physicochemical system.

Optical Probe of Magnetic Ordering Structure and Spin‐Entangled Excitons in Mn‐Substituted NiPS3

AbstractIn van der Waals magnets, the interplay between magneto‐excitonic coupling and optical phenomena opens avenues for directly probing magnetic ordering structures, manipulating excitonic properties through magnetic fields, and exploring quantum entanglement between electronic and magnetic states. Notably, NiPS3 stands out for its capacity to host spin‐entangled excitons, where the excitonic states are intricately tied with the material's spin configuration. Herein, it is experimentally showcased that the spin‐entangled excitons can be utilized for detecting the magnetic easy axis in Ni1‐xMnxPS3 (x = 0–0.1). The end members of this series exhibit distinct magnetic ordering patterns and easy axes: zigzag ordering with magnetic moments aligned along the a‐axis for NiPS3 versus Néel ordering with the out‐of‐plane easy axis for MnPS3. By combining angle‐resolved exciton photoluminescence with magnetic susceptibility measurements, it is observed that the magnetic easy axis rotates away from the local spin chain direction with increasing Mn content. Moreover, through a comprehensive thermal and substitution study, it is demonstrated that the energy and lifetime of spin‐entangled excitons are governed by two spin‐flip processes and are drastically influenced by disparate electronic states. These findings not only provide optical means to map out magnetic ordering structures but also offer insights into decoherence processes in spin‐exciton entangled states.

Investigation on structural, electrical and magnetic properties: Dy0.4Sm0.6FeO3 orthoferrite with Mn doping at Fe site

This paper delves the structural and magnetic properties of Mn-doped Dy0.4Sm0.6Fe1-xMnxO3 (x = 0, 0.1, 0.2 and 0.3) orthoferrite. With an increase in Mn concentration, the a and c lattice parameters show a decreasing trend, while the b parameter shows a linear increase and an variance is observed in Fe–O–Fe and Fe–O-Sm bond angles and bond lengths, indicating a distortion in the FeO6 octahedra. FESEM images show that as the Mn content increases, the grain size increases and porosity decreases. EDX analysis confirms that, the prepared samples are high in purity and the elemental composition. The Dy0.4Sm0.6FeO3 (i.e., x = 0.0) orthoferrite demonstrates a spin reorientation transition at 234K. With an increase in Mn doping at the Fe site induces a complex magnetic structure, Mn/Fe3+-O-Mn/Fe3+ interactions weaken the antiferromagnetic nature thereby decreasing spin reorientation transition (SRT) temperature. The moderate Mn doping at the Fe site leads to a canted-like antiferromagnetic structure, playing a crucial role in tuning the magneto-electric properties at room temperature.

Citric Acid Inhibits Cd Absorption and Transportation by Improving the Antagonism of Essential Elements in Rice Organs.

Excessive cadmium (Cd) in rice is a global environmental problem. Therefore, reducing Cd content in rice is of great significance for ensuring food security and human health. A field experiment was conducted to study the effects of foliar application of citric acid (CA) on Cd absorption and transportation in rice under high Cd-contaminated soils (2.04 mg·kg-1). This study revealed that there was a negative correlation between Cd content in vegetative organs and CA content, and that foliar spraying of CA (1 mM and 5 mM) significantly increased CA content and reduced Cd content in vegetative organs. The Cd reduction effect of 5 mM CA was better than that of 1 mM, and 5 mM CA reduced Cd content in grains and spikes by 52% and 37%, respectively. CA significantly increased Mn content in vegetative organs and increased Ca/Mn ratios in spikes, flag leaves, and roots. CA significantly reduced soluble Cd content in vegetative organs and promoted the transformation of Cd into insoluble Cd, thus inhibiting the transport of Cd from vegetative organs to grains. The foliar field application of 1 mM and 5 mM CA could inhibit Cd absorption and transportation by reducing Cd bioactivity and increasing the antagonistic of essential elements in rice vegetative organs. These results provide technical support and a theoretical basis for solving the problem of excessive Cd in rice.

Study on Mn Volatilization Behavior During Vacuum Melting of High-manganese Steel

As an alloying element in steel, manganese can considerably enhance the mechanical properties of structural steel. However, the Mn volatilisation loss in vacuum melting is severe because of the high saturated vapour pressure, resulting in an unstable Mn yield and Mn content fluctuation. Therefore, a systematic study of the volatilisation behaviour of Mn in vacuum melting is required to obtain a suitable Mn control process to achieve precise control of Mn composition, thereby providing a theoretical basis for industrial melting of high-Mn steel. In order to explore the Mn volatilization behavior, the volatilization thermodynamics and volatilisation rate of Mn, as well as the influence factors are discussed in this study. The results shows that Mn is extremely volatilised into the vapour phase under vacuum, the equilibrium partial pressure is closely related to Mn content and temperature. With an increase in the Mn content, a higher C content has a more obvious inhibitory effect on the equilibrium partial pressure of Mn. The maximum theoretical volatilisation rate of Mn shows a linear upward trend with an increase in Mn content. However, a higher C content has a more obvious effect on the reduction of the maximum theoretical volatilisation rate with the increase of Mn content. This study provides an improved understanding of Mn volatilisation behaviour as well as a theoretical foundation for consistent Mn yield control during the vacuum melting process of high-Mn steel.

Low temperature garnet phase formation in Mn-substituted Y3Fe5-xMnxO12 nanoparticles via citrate combustion synthesis

In this article, we report on the formation of a low-temperature garnet phase in Mn-substituted Y3Fe5-xMnxO12 (x = 0, 0.05, 0.15, and 0.25) nanopowders. We studied the structural, microstructural, static, and dynamic magnetic properties of Mn-substituted Y3Fe5-xMnxO12 (YIG) nanopowders calcined at two different temperatures. The Mn-substituted garnet powders were synthesized using the citrate combustion method followed by calcination at 800 and 1200 °C for 3 h. An increase in Mn substitution (x = 0.15, 0.25) favored the growth of a single garnet phase at low temperatures, even at 800 °C. The lattice constant of these samples ranged from 12.3815 to 12.3679 Å. Microstructural and morphological studies revealed the growth of homogeneous and dense particles, with an average particle size in the range of ∼35–58 nm, close to the single-domain particle size in YIG. Microwave resonance spectra and magnetic hysteresis curves revealed the formation of a ferromagnetic phase in undoped and Mn-doped garnet ferrites at room temperature. The maximum saturation magnetization (26 emu/g) was observed for the sample with Mn content x = 0.05 at 1200 °C, while the largest coercivity (33 Oe) was found for the sample with Mn content x = 0.15 at 1200 °C, among all the samples. The increase in Mn content led to a decrease in peak-to-peak linewidth of FMR spectra from 698.8 to 569.4 G at 800 °C and from 916 to 614.7 G at 1200 °C. This study suggests that Mn substitution in YIG garnet improves structural properties and enhances magnetic anisotropy.

Structural, Optical, and Morphological Study of Manganese Substituted Cobalt Ferrite and Its Effect on the Magnetic and Dielectric Properties of PVA Composites

Nanopowders of Mn-substituted CoFe2O4 were prepared in different proportions using the sol-gel auto-combustion method and were structurally and morphologically studied. In another step, composites based on polyvinyl alcohol (PVA) with Mn-substituted CoFe2O4 fillers were prepared, and the effect of the Mn-substituted CoFe2O4 on the optical, magnetic, and dielectric properties was studied. X-ray analysis revealed the formation of polycrystalline Mn-substituted CoFe2O4. The results showed a decrease in the lattice constant with Mn2+ substituted and incorporated into the crystal structure of CoFe2O4. The Fourier confirmed the spinel structure of the Mn-substituted CoFe2O4 transform infrared spectrum where absorption bands appeared at 569–561 and 446–407 cm-1, which are attributed to tetrahedral and octahedral groups. The magnetic properties were affected when Mn ions were substituted with CoFe2O4, as shown by the results of VSM. It was observed that the saturation magnetization, remnant magnetization, and coercivity decreased with increasing Mn content. The dielectric constant and loss tangent of PVA/MnxCo1−xFe2O4 were also studied. The difference in the diameters of the substituted and host ions causes the dielectric constant to increase following the substitution of Mn ions.

Influence of the Mn/Fe ratio on structural, optical, electrical and magnetic characteristics of MnFeMgNiO spinel ferrites

MnxFe2-xMg0.5Ni0.5O4spinel ferrite nanoparticles (0.0 ≤ x ≤ 1) were prepared utilizing a flash auto-combustion technique. The as-prepared ferrite nanoparticles have been investigated and characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared analysis (FTIR). The dielectric, optical and magnetic characteristics of the synthesized spinel ferrite samples were investigated using broadband dielectric spectroscopy (BDS), diffuse reflectance spectroscopy (DRS) and vibration sample magnetometers (VSM). The cubic phase spinel ferrite with space group Fd-3m was identified through XRD. X-ray diffraction indicates that the lattice constant increases and the crystallite size declines with increasing Mn concentration. The positions of the cations and their vibrational modes in the crystal structure with oxygen ions are demonstrated through the FTIR spectra. The morphology was examined using HRTEM showed polycrystalline cubic spinel structure with faceted planes. The optical band gap Eg was determined using Kubelka–Munk model where, it decreased from 1.79 eV to1.24 eV as Mn content increases. The replacement of manganese significantly affects the dielectric characteristics of the synthesized spinel ferrites. The real (ε′), imaginary (ε″) parts of dielectric constant and ac conductivity exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases. The presence of a relaxation phenomenon in all prepared samples except the undoped sample (Ni0.5Mg0.5Fe2O4) is shown by the imaginary modulus’s (M′′) dependence on frequency. The magnetic properties exhibited soft ferrite nature with small hysteresis curve for all spinel ferrites samples. The magnetic properties of MnxFe2-xMg0.5Ni0.5O4 nanoparticles were measured and analysed, including saturation magnetization (Ms), remanence (Mr), coercivity (Hc), and squareness ratio. (Ms), and (Mr), exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases while squareness ratio decreased. The magnetic parameters greatly affected by Mn substitution ratio.

Controlling the physical properties of Ni1-xMnxFe2O4 multiferroic by the enhancement of ferroelectric phase through the increase of Mn content

The nanoparticles of the spinel ferrite system Ni1-xMnxFe2O4 with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared using the auto combustion flash method technique, by using the nitrates as cations source and urea as a fuel agent for combustion. The XRD pattern validates the formation of cubic spinel structure of Ni1-xMnxFe2O4 nanoparticles and traces of hematite phase. By increasing the annealing temperature, the lattice parameter and crystallite size were increased. At various frequencies, the dielectric properties and initial permeability were measured as a function of temperature. The DC resistivity was found to have a linear relationship with temperature, with two regions and one break point at Curie temperature (TC). SEM and TEM analyses are used to investigate the morphology of the samples, as well as the size and shape of the crystallites. The samples' morphology revealed the formation of a uniform and spherical structural distribution. The material transfer to multiferroic at high Mn content accordingly the ferroelectric and ferrimagnetic properties appear, which give the ability of the material to become magnetoelectric material.

Enhancing ferromagnetism in the Sm(Co, Mn)5 system: Impact on phase stability and magnetic properties

This work demonstrates that Mn can be a beneficial candidate for the performance modulation of permanent magnetic materials like SmCo5. Theoretical calculations reveal that Mn has a large positive contribution to the magnetization of SmCo5, owing to the strong ferromagnetic exchange interaction between Co and Mn atoms. It is also found that Mn could occupy both 2c and 3g crystal sites because of the minute energy difference between them can be easily overcome through thermal activation. Co atoms on the same site with Mn have increasing moments with the increase in Mn content, whereas those on the other sites show decreasing moments. The experimental substitution of Mn for Co leads to a contraction of the SmCo5 single-phase region, and thus pure Sm(Co, Mn)5 phase could only be obtained through subtle control of Sm content by annealing. Significantly, a 13 % increase in saturation magnetization of SmCo5 is achieved through Mn substitution. A slight rise in the Curie temperature is also obtained, suggesting that Mn substitution does not strongly disturb the exchange interactions of the Co sublattice. This study offers a new option for enhancing magnetic properties in Sm–Co systems and introduces novel physical phenomena resulting from Mn substitution, which is worthy of further investigation.

The Piezoresistive Performance of CuMnNi Alloy Thin-Film Pressure Sensors Prepared by Magnetron Sputtering

Effects of varying Mn and Ni concentrations on the structure and piezoresistive properties of CuMnNi films deposited by magnetron sputtering with a segmented target were investigated. An increase in the Ni content refines the CuNi film grains, inducing an increase in defects such as internal micropores and a decrease in film density. At the same time, the positive piezoresistive coefficient of the film changes to negative. When 17.5 at.% Ni was added, the negative piezoresistive coefficient of the CuNi film was −2.0 × 10−4 GPa−1. The doping of Ni has a weakening effect on the positive piezoresistive effect of the film. Adding Mn into Cu refines the film grains while increasing the film density. The surface roughness of the film decreases with the increase in Mn content. When the Mn content was 16.7 at.%, the piezoresistive coefficient reached the largest recorded value of 23.81 × 10−4 GPa−1, and the film exhibited excellent repeatability in multiple piezoresistive tests. After the CuMn film with 16.7 at.% Mn was annealed at 400 °C for 2 h, the film grains grew slightly and the film residual stress decreased. The optimization of the film structure can reduce the scattering of electrons during transportation. The piezoresistive coefficient of the film was further improved to 35.78 × 10−4 GPa−1.

Manganese substitution effect on physical properties of sol-gel derived DyFeO3 orthoferrite

A simple composite DyFe(1-x)MnxO3 (x = 0, 0.1, 0.3, 0.5) powders were successfully prepared by the sol–gel method. The effect of Mn modification on the structure, thermal and phase transition behaviour of DyFeO3 orthoferrite was investigated. Mn modification didn't show any structural change and all the samples confirmed the pure orthorhombic phase with Pbnm space group. However, a contradicting trend in the variation of lattice parameters were observed due to the presence of mixed oxidation state of Dy, Fe and Mn in the sample leading to oxygen vacancies. The presence of mixed oxidation state was confirmed through X-ray photoemission spectra (XPS). Scanning electron microscopy (SEM) and Williamson Hall (WH) plot confirmed a decrease in particle sizes with increasing Mn concentration leading to an increase in the specific surface area which suggested an inhibition of grain growth with Mn modification. The defects-initiated change in physical behaviour in terms of structural, thermal, microstructural and dielectric are analyzed and discussed in detail.

Manganese reductive dissolution coupled to Sb mobilization in contaminated shooting range soil

A “redox-stat” RMnR bioreactor was employed to simulate moderately reducing conditions (+ 420 mV) in Sb-contaminated shooting range soils for approximately 3 months, thermodynamically favoring Mn(IV) reduction. The impact of moderately reducing conditions on elemental mobilization (Mn, Sb, Fe) and speciation [Sb(III) versus Sb(V); Fe2+/Fe3+] was compared to a control bioreactor RCTRL without a fixed redox potential. In both bioreactors, reducing conditions were accompanied by an increase in effluent Sb(V) and Mn(II) concentrations, suggesting that Sb(V) was released through microbial reduction of Mn oxyhydroxide minerals. This was underlined by multiple linear regression analysis showing a significant (p < 0.05) relationship between Mn and Sb effluent concentrations. Mn concentration was the sole variable exhibiting a statistically significant effect on Sb in RMnR, while under the more reducing conditions in RCTRL, pH and redox potential were also significant. Analysis of the bacterial community composition revealed an increase in the genera Azoarcus, Flavisolibacter, Luteimonas, and Mesorhizobium concerning the initial soil, some of which are possible key players in the process of Sb mobilization. The overall amount of Sb released in the RMnR (10.40%) was virtually the same as in the RCTRL (10.37%), which underlines a subordinate role of anoxic processes, such as Fe-reductive dissolution, in Sb mobilization. This research underscores the central role of relatively low concentrations of Mn oxyhydroxides in influencing the fate of trace elements. Our study also demonstrates that bioreactors operated as redox-stats represent versatile tools that allow quantifying the contribution of specific mechanisms determining the fate of trace elements in contaminated soils.Key points• “Redox-stat” reactors elucidate Sb mobilization mechanisms• Mn oxyhydroxides microbial reductive dissolution has a major role in Sb mobilization in soils under moderately reducing conditions• Despite aging the soil exhibited significant Sb mobilization potential, emphasizing persistent environmental effects

Structure relations with transport properties in p-type thermoelectric materials: Iron silicides

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe1-xMnxSi2 (0≤x≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe2Si5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi2) through heat treatment. The amount of β-FeSi2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (nH of holes) but decrease the mobility (μH). By substituting Mn to β-FeSi2, the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties.

Production of Green energy via Water Splitting mechanism by Mn- doped Cobalt Ferrites [Co1-xMnxFe2O4] based Hydroelectric Cells

In our current study, we have investigated the impact of manganese (Mn) doping on the structural, magnetic properties, and hydroelectric cell properties of cobalt ferrite with chemical formula [Co1-xMnxFe2O4, x=0.00, 0.125]. The solid-state approach has been utilized to synthesize the material. XRDmeasurements revealed the formation of an inverse spinel cubic structure with the space group Fd-3m. FTIR spectra hold a shift in the octahedral and tetrahedral bands with the increase in Mn content in cobalt ferrites. The subsequent rise in ferroelectric behavior has been observed with the net maximum saturation polarization of 1.08μC/cm2. The variation in the permittivity values has been also studied with the increase in Mn content for dry as well as wet hydroelectric cells. The impedance measurements helped us understand the contribution of grains/grain boundaries in the prepared ferrites. The enhanced value of magnetization has been noticed from 48.258 emu/g to 73.089 emu/g upon doping of Mn ions in cobalt ferrite spinel structure lattice.The Mndoped CFO exhibited enhanced performance in hydroelectric cells which demonstrates the great ionic diffusion mechanism with the incorporation of Mn ions. The obtained output makes Mn doped CFO a suitable material for studying microelectronic and hydroelectric cell applications. The purpose of this study is to enhance both ferroelectric as well as ferromagnetic behavior along with the improved value of current in hydroelectric cells.

Toughness behavior and deformation mechanisms in FCC-based Fe45Co30Cr10V10Ni5-xMnx high-entropy alloys: Insights from instrumented Charpy impact tests

This study investigated toughness properties of FCC-based Fe45Co30Cr10V10Ni5-xMnx high entropy alloys (HEAs). Ductile-dimpled rupture mode in all alloys and test temperatures complicated precise explanations on Charpy impact energy, but the instrumented Charpy test provided a breakdown of total energy (ET) into initiation energy (EI) and propagation energy (EP), offering critical insights into Mn-content- and temperature-related energy variations. Pmax and TP, reflecting maximum flow stress and time, respectively, until initiation of crack propagation from the notch tip, involved a transition of deformation mechanisms from slip to TWIP, then to BCC-TRIP, thereby inducing increased strain hardening and delaying plastic instability at the notch tip. At 25 °C, an increase in Mn content prompted a transition in deformation behavior from slip to TWIP and subsequently to BCC-TRIP, correlating well with increased Pmax and TP and consequently ET due to enhanced strain hardenability. At −196 °C, predominant BCC-TRIP activity in all alloys led to increased formation of BCC martensite, intensifying strain hardening and requiring higher Pmax for crack initiation than at 25 °C. Due to minimal slip line field formation associated with reduced plastic deformation, however, cracks initiated directly from the notch-tip center, representing fast initiation of crack propagation and consequently reduction in EI and ET. Thus, utilizing parameters from instrumented Charpy tests, including Pmax, TP, EI, EP, and ET, provided insights into fracture phenomena and their interrelations in the present HEAs.

Experimental and theoretical insights into vanadium-based alloys for room temperature hydrogen storage on the example of Ti16Cr22Zr5V55-xFe2Mnx (x=0–3) alloys

In this work, the microstructures and hydrogen storage properties of the Ti16Zr5Cr22V55-xFe2Mnx (x =0, 1, 2, 3) hydrogen storage alloys were comprehensively investigated toward application under ambient conditions. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images of the alloys indicated that all of the alloys consist of a BCC main phase and a small amount of C14 Laves secondary phase. All of the studied alloys have a good activation performance and fast absorption/desorption kinetics at 298 K. The flatness of desorption plateau of alloy is improved by the tiny Mn introduction. With the increase of Mn content, the lattice parameter of BCC main phase, electron density and hydrogen absorption/desorption capacity decrease, and the desorption plateau pressure at 298 K increases in the range of 0.1–1 MPa. In addition, the essence of the dependence of high hydrogen capacity on electron density was revealed based on Fermi level. The Tilt, hysteresis, and width of plateau of PCT curve of vanadium-based alloys were clarified on the basis of Sievert's law. And a good quadratic fitting between desorption plateau pressure and Mn content was manifested.

Effect of Mn addition on microstructure and corrosion behavior of AlCoCrFeNi high-entropy alloy

In this study, the effects of Mn content on the microstructure and corrosion resistance of AlCoCrFeNiMnx (x = 0, 0.25, 0.5, 0.75, and 1) high-entropy alloys were investigated. The results indicate that with increasing Mn content, the HEAs consistently comprise nanophase BCC geometry with different shapes embedded in the ordered B2-phase matrix, and the morphology of the microstructure changes from a coarse dendritic structure to a fine dendritic structure, then to a completely columnar dendrite structure. The microhardness of the HEAs increases gradually to 620 HV0.2 when x = 1, owing to the solid-solution and fine-grain strengthening. The corrosion resistance of the HEAs in 3.5 wt% NaCl solution first increases and then decreases, reaching a maximum with the lowest self-corrosion current density of 2.869 × 10−8 A∙cm−2 when x = 0.5. Improvement in corrosion resistance is related to a reduction in degree of composition segregation in the microstructure of HEAs, which leads to the formation of a dense and complete passivation film on the surface of the alloys. However, when the Mn content is in the range of 0–0.5, the pitting potential of the HEAs gradually decreases, although the passivation current density also gradually decreases. Higher Mn content (x > 0.5) leads to a transition of the HEAs from passivation to active dissolution. This indicates that the stability of the passivation film on the HEAs decreases with higher Mn content. XPS analysis revealed a gradual decline in the relative content of Cr2O3 and a gradual increase in the presence of unstable oxides such as MnO and Mn2O3 in the passivation film, leading to this phenomenon. The present work reveals that the addition of Mn in the AlCoCrFeNi HEA affects not only the microstructure and composition segregation but also the composition and stability of the passivation film, leading to a non-monotonic variation in the corrosion performance of the present HEAs with respect to the Mn content.

Effect of Manganese on the Strength-Toughness Relationship of Low-Carbon Copper and Nickel-Containing Hull Steel.

The influence of varying the manganese (Mn) contents of high-strength copper-containing hull steel on its microstructural evolution and mechanical properties was investigated. With increasing Mn content from 2 to 5%, the tensile strength of the steel increased by ~100 MPa, while the elongation of steel remained at ~23.5%, indicating good plasticity. However, the 2Mn sample had 128 J higher low-temperature (-84 °C) impact work than the 5Mn sample. The microstructures of different Mn steels were composed of fresh martensite (FM), ferrite/tempered martensite (F/TM), and reversed austenite (RA). The increase in Mn content markedly increased the presence of RA and intensified the work hardening caused by the transformation-induced plasticity (TRIP) effect during the tensile process. However, as the phase transformation in different Mn steels occurred in the early stage of strain and did not extend throughout the entire plastic deformation process, increasing plasticity via phase transformation was difficult. In addition, although the volume fraction of RA increased significantly in 4Mn and 5Mn steels, the stability of RA significantly decreased. The presence of numerous metastable blocks and coarse lath-like RA contributed little to low-temperature impact work and was even detrimental to toughness. The substantial fresh martensite resulting from phase transformation facilitated microcrack generation, owing to rapid volume expansion and mutual impacts, thus reducing the work required for crack formation. Additionally, the abundance of deformation twins significantly reduced the work needed for crack propagation. These combined actions significantly reduced the low-temperature toughness of 4Mn and 5Mn steels.