Mn Particles Research Articles

Effect of Pulse Duration on Corrosion and Impression Creep Properties of AA5083‐H111 Al–Mg Alloy Weldments Processed by P‐GTAW

In this work, the corrosion and impression creep properties of weldments are determined using potentiodynamic polarization test and impression creep test. It is evident that the shorter pulse duration results in comparatively finer grains and reduces the loss of magnesium in fusion zone, which facilitates an increase in precipitation of anodic β‐phase (Al3Mg2) and Mg2Si particles in the grain boundaries. It leads to the formation of pits by dissolving Mg atoms and propagate along the interdendritic region and finally corrode the surface thoroughly. On contrary, the increase in pulse duration results in uniform distribution of iron‐rich Al6(Fe,Mn) intermetallics as well as Fe and Mn particles in the interdendritic region which induce localized cathodic reaction and these localized cathodes assisted in achieving noble corrosion resistance by increasing the width of passive region. Also, an increase in creep resistance is attained with an increase in activation energy at a temperature of 573 K owing to the uniform dispersion of iron‐rich Al6(Fe,Mn) intermetallics in the grain boundaries of weldments processed with longer pulse duration. Hence, it is inferred from this research that the rise in pulse duration improves the corrosion and creep resistance of weldments by altering the morphology and surface distribution of intermetallics.

AMnO3 (A\u2009=\u2009Sr, La, Ca, Y) Perovskite Oxides as Oxygen Reduction Electrocatalysts

A series of perovskite-type manganites AMnO3 (A = Sr, La, Ca and Y) particles were investigated as electrocatalysts for the oxygen reduction reaction. AMnO3 materials were synthesized by means of an ionic-liquid method, yielding phase pure particles at different temperatures. Depending on the calcination temperature, particles with mean diameter between 20 and 150 nm were obtained. Bulk versus surface composition and structure are probed by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure. Electrochemical studies were performed on composite carbon-oxide electrodes in alkaline environment. The electrocatalytic activity is discussed in terms of the effective Mn oxidation state, A:Mn particle surface ratio and the Mn–O distances.

Structural and Mössbauer studies of nanocrystalline Mn2+-doped Fe3O4 particles

Nanocrystalline Mn2+-doped magnetite (Fe 3O4) particles of the composition Mn x Fe 3−y O4 \(\left (x = 0.0, 0.1, 0.2, 0.3, 0.4 \text { and } 0.5; y = \frac {2x}{3}\right )\), prepared using chemical precipitation under reflux with the Mn2+ ions substituting for Fe3+ ions rather than Fe2+ ones, are characterized mainly with XRD and 57Fe Mossbauer spectroscopy. All samples were found to have spinel-related structures with average lattice parameters that increase linearly with the Mn2+ concentration, x. The particle size for the samples varied from ∼8 nm to 23 nm. The oxidation of Fe2+ to Fe3+ at surface layers of the Fe 3O4 nanoparticles leading to the formation of maghemite (γ-Fe 2O3) was found to considerably weaken with increasing Mn2+ concentration. The percentage of the nanoparticles that exhibit short range magnetic ordering due to cationic clustering and/or superparamagnetism increases from 17% to 32% with increasing x. The dependence of isomer shifts of the 57Fe nuclei at the tetrahedral and octahedral sites on dopant Mn2+ concentration is emphasized. The electric quadrupole shifts indicate that the Mn x Fe 3−y O4 particles undergo Verwey transition. The effective hyperfine magnetic fields at both crystallographic sites decrease with increasing Mn2+ concentration reflecting a size effect as well as a weakening in the magnetic super-exchange interaction. The Mossbauer data indicate that for x ≤ 0.2, the dopant Mn2+ ions substitute solely for octahedral Fe3+ ions whereas for x > 0.2 they substitute for Fe3+ at both tetrahedral and octahedral sites.

Effect of frost on phosphorescence for thermographic phosphor thermometry

In this study, we analyzed phosphorescence lifetime and its accuracy by growing frost for thermographic phosphor thermometry in a low-temperature environment. Mg4FGeO6:Mn particles were coated on an aluminum plate and excited with a UV-LED to obtain phosphorescence signals. The surface temperature was maintained at −20, −15, −10 °C, and the phosphorescence signal was acquired as the frost grew for 3700 s. The lifetime was calculated and compared with the calibration curve under no-frost conditions. The error of the measured lifetime was within 0.7% of that in the no-frost conditions. A 2D surface temperature profile of the target plate was successfully obtained with the frost formation.

Development of Cu-matrix, Al/Mn-reinforced, multilayered composites by accumulative roll bonding (ARB)

In this work, nanostructured Cu/Al/Mn multilayered composites were successfully fabricated by the accumulative roll bonding (ARB) method. The microstructure of the produced composites was studied by X-ray diffraction and scanning electron microscopy. Also, the hardness, tensile and corrosion behaviors of the composites were studied as a function of ARB cycles. It was observed that by increasing the number of ARB cycles, the thickness of the Al layers is decreased from 0.3 mm to 0.25 μm, where a Cu-matrix, Al/Mn-reinforced, multilayered composite with homogeneously distributed Al layers and Mn particles was achieved after nine ARB cycles. Also, the results revealed the development of nanostructures with the mean crystallite size of about 50 nm in the produced composites. According to the tensile experiments, by increasing ARB cycles, the strength of the composites was increased and reached 420.8 MPa. The electrochemical corrosion behavior of the produced composites was also investigated in a 3.5 wt % NaCl solution by a potentiostat-galvanostat device. It was found that the corrosion rate of the composite is increased by increasing ARB cycles from 5 μA/cm2 to 12.2 μA/cm2 and then decreased to 9.5 μA/cm2.

The acceleration of dissolved cobalt's ecological stoichiometry due to biological uptake, remineralization, and scavenging in the Atlantic Ocean

Abstract. The stoichiometry of biological components and their influence on dissolved distributions have long been of interest in the study of the oceans. Cobalt has the smallest oceanic inventory of inorganic micronutrients and hence is particularly vulnerable to influence by internal oceanic processes including euphotic zone uptake, remineralization, and scavenging. Here we observe not only large variations in dCo : P stoichiometry but also the acceleration of those dCo : P ratios in the upper water column in response to several environmental processes. The ecological stoichiometry of total dissolved cobalt (dCo) was examined using data from a US North Atlantic GEOTRACES transect and from a zonal South Atlantic GEOTRACES-compliant transect (GA03/3_e and GAc01) by Redfieldian analysis of its statistical relationships with the macronutrient phosphate. Trends in the dissolved cobalt to phosphate (dCo : P) stoichiometric relationships were evident in the basin-scale vertical structure of cobalt, with positive dCo : P slopes in the euphotic zone and negative slopes found in the ocean interior and in coastal environments. The euphotic positive slopes were often found to accelerate towards the surface and this was interpreted as being due to the combined influence of depleted phosphate, phosphorus-sparing (conserving) mechanisms, increased alkaline phosphatase metalloenzyme production (a zinc or perhaps cobalt enzyme), and biochemical substitution of Co for depleted Zn. Consistent with this, dissolved Zn (dZn) was found to be drawn down to only 2-fold more than dCo, despite being more than 18-fold more abundant in the ocean interior. Particulate cobalt concentrations increased in abundance from the base of the euphotic zone to become ∼ 10 % of the overall cobalt inventory in the upper euphotic zone with high stoichiometric values of ∼ 400 µmol Co mol−1 P. Metaproteomic results from the Bermuda Atlantic Time-series Study (BATS) station found cyanobacterial isoforms of the alkaline phosphatase enzyme to be prevalent in the upper water column, as well as a sulfolipid biosynthesis protein indicative of P sparing. The negative dCo : P relationships in the ocean interior became increasingly vertical with depth, and were consistent with the sum of scavenging and remineralization processes (as shown by their dCo : P vector sums). Attenuation of the remineralization with depth resulted in the increasingly vertical dCo : P relationships. Analysis of particulate Co with particulate Mn and particulate phosphate also showed positive linear relationships below the euphotic zone, consistent with the presence and increased relative influence of Mn oxide particles involved in scavenging. Visualization of dCo : P slopes across an ocean section revealed hotspots of scavenging and remineralization, such as at the hydrothermal vents and below the oxygen minimum zone (OMZ) region, respectively, while that of an estimate of Co* illustrated stoichiometrically depleted values in the mesopelagic and deep ocean due to scavenging. This study provides insights into the coupling between the dissolved and particulate phase that ultimately creates Redfield stoichiometric ratios, demonstrating that the coupling is not an instantaneous process and is influenced by the element inventory and rate of exchange between phases. Cobalt's small water column inventory and the influence of external factors on its biotic stoichiometry can erode its limited inertia and result in an acceleration of the dissolved stoichiometry towards that of the particulate phase in the upper euphotic zone. As human use of cobalt grows exponentially with widespread adoption of lithium ion batteries, there is a potential to affect the limited biogeochemical inertia of cobalt and its resultant ecology in the oceanic euphotic zone.

Analysis of the atomic structure of colloidal quantum dots of the CdSe family: X-ray spectral diagnostics and computer modelling

Colloidal quantum dots of the CdSe family have been studied by X-ray absorption near edge structure (XANES) spectroscopy and computer modelling. CdK edge XANES spectra in colloidal quantum dots based on varisized CdSe nanoparticles have been recorded. Atomic structure of CdSe particles and also CdSe particles doped by transition metal atoms Mn and Co has been modelled based on the density functional theory. The embedding of the doping atoms is shown to result in considerable changes in the local atomic structure of CdSe particles. XANES spectra have been calculated above the CdK edge in CdSe particles, above the MnK edge in CdSe:Mn particles, above the CoK edge in CdSe:Co particles. The sensitivity of XANES spectroscopy to small changes in structural parameters of the nanoparticles of CdSe family has been demonstrated that furnishes an opportunity to apply it for the verification of atomic structure parameters around positions of cadmium and doping atoms of transition metals in quantum dots based on CdSe.

The influence of minor Mn additions on creep resistance of die-cast Mg–Al–RE alloys

Magnesium alloys normally contain minor amounts (~0.3%) of Mn to achieve improved corrosion resistance by controlling the level of Fe during melting. It has been reported recently that minor Mn additions can significantly enhance the age hardenability of die-cast Mg–Al–RE alloys. This paper reports that minor Mn additions also have a remarkable influence in improving the creep resistance of die-cast Mg–Al–RE alloys. The secondary creep rate of Mg–4Al–3La alloy at 175°C/75MPa is reduced by more than three orders of magnitude (from 5.9×10-7s-1 to 3.0×10-10s-1) by the addition of 0.32% Mn. The improvement in creep resistance is associated with the dynamic precipitation of nanoscale Al–Mn particles during creep. The findings in this work shed new light on creep resistance of Mg–Al based alloys.

Synthesis of Birnessite in the Presence of Phosphate, Silicate, or Sulfate.

Layered manganese (Mn) oxides, such as birnessite, are versatile materials in industrial applications and common minerals mediating elemental cycling in natural environment. Many of birnessite properties are controlled by Mn(III) concentration and particle sizes. Thus, it is important to synthesize birnessite nanoparticles with controlled Mn(III) concentrations and sizes so that one can tune its properties for many applications. Birnessite was synthesized in the presence of oxyanions (phosphate, silicate, or sulfate) during reductive precipitation of KMnO4 by HCl and characterized using multiple synchrotron X-ray techniques, electron microscopy, and diffuse reflectance UV-vis spectroscopy. Results indicate that all three anions decrease MnO6 sheet sizes, attributed to oxyanion adsorption on edges of the sheets, inhibiting their lateral growth. As a result of decreased sizes, sheets undergo significant structural contraction. Meanwhile, Mn(III) concentration significantly increases with increasing oxyanion/Mn ratio. The increased Mn(III) concentration, along with the decreased size, enlarges both direct and indirect band gaps of birnessite. Phosphate imposes the strongest influence, followed by silicate and then by sulfate, consistent with their decreasing adsorption affinity. Reacting with 1 M KOH solution effectively removed the adsorbed oxyanions while leading to increased sheet sizes, probably due to oriented attachment-driven particle growth mechanisms. The results have important implications for developing highly performed birnessite materials, for example, small size Mn(III)-rich birnessite for photochemical and catalytic applications, as well as for understanding chemical compositional variations of naturally occurring birnessite.

Deformation induced dynamic recrystallization and precipitation strengthening in an Mg[sbnd]Zn[sbnd]Mn alloy processed by high strain rate rolling

The microstructure of a high strain-rate rolled MgZnMn alloy was investigated by transmission electron microscopy to understand the relationship between the microstructure and mechanical properties. The results indicate that: (1) a bimodal microstructure consisting of the fine dynamic recrystallized grains and the largely deformed grains was formed; (2) a large number of dynamic precipitates including plate-like MgZn2 phase, spherical MgZn2 phase and spherical Mn particles distribute uniformly in the grains; (3) the major facets of many plate-like MgZn2 precipitates deviated several to tens of degrees (3°–30°) from the matrix basal plane. It has been shown that the high strength of the alloy is attributed to the formation of the bimodal microstructure, dynamic precipitation, and the interaction between the dislocations and the dynamic precipitates.

Effect of metal particles on the rate of Si etching with N-fluoropyridinium salts

The effect of Cr, Mn, Fe, Ni, Cu, Zn, Pd, Ag, Pt, or Au metal particles on the rate of Si etching using N-fluoropyridinium salts was examined. The average etching depth increased when N-fluoropyridinium salts were mixed with Cu particles. The activation energy determined from the temperature dependence of the average etching rate for the Cu particles is lower than that without a metal. The Cu particles greatly improve the etching of Si with the salts compared with the other metals. The magnitude of the effect of the Cu particles on the rate of Si etching with the salts is larger than that of the Mn, Fe, Ni, or Zn particles. This can be explained by the order of the relative stabilities of the complexes formed by bivalent ions of transition metals. The etching method involves the application of easy-to-handle salts containing Cu particles as etchants on the Si surface and has the potential to be a simple and less expensive form of Si etching.

Use of sacrificial anode technology to mitigate non-enzymic Maillard browning

Experiments were performed to examine the effects of Maillard browning induced in the presence of metallic elements. The rate of brown pigment formation was shown to be reduced in model Maillard reactions performed in the presence of electropositive metals. Experiments involved reactions of d-xylose, d-arabinose and d-ribose with glycine, α-l- or β-alanine and l-valine in pH 7.0 phosphate buffer at ca. 100°C. “Browning” measured spectrophotometrically at 420nm was significantly lower (compared with controls) in selected reactions containing elemental Mg, Al, Mn and Sn particles. It was hypothesized that the metals acted in sacrificial anode redox fashion to reduce or eliminate dehydroreductones believed to be key Maillard intermediates ultimately leading to less browning.

Manganese oxide shuttling in pre-GOE oceans – evidence from molybdenum and iron isotopes

The local occurrence of oxygen-rich shallow marine water environments has been suggested to significantly predate atmospheric oxygenation, which occurred during the Great Oxidation Event (GOE) ca. 2.4 billion years ago. However, the potential influence of such ‘oxygen oases’ on the mobility, distribution and isotopic composition of redox sensitive elements remains poorly understood. Here, we provide new molybdenum and iron isotopic data from shallow marine carbonate and silicate iron formations of the Koegas Subgroup, South Africa, that confirm local ocean redox stratification prior to the GOE.Mn concentrations correlate negatively with both δ98Mo and δ56Fe values, which highlights the substantial role of particulate manganese for the cycling of Mo and Fe in the Paleoproterozoic oceans. Based on these trends we propose that pore water molybdate was recharged (1) by the diffusional transport of seawater molybdate with high δ98Mo and (2) by the re-liberation of adsorbed molybdate with low δ98Mo during Mn oxide dissolution within the sediment. The relative contribution of isotopically light Mo is highest close to a Mn chemocline, where the flux of Mn oxides is largest, causing the negative correlation of Mn concentrations and δ98Mo values in the Koegas sediments. The negative correlation between δ56Fe values and Mn concentrations is likely related to Fe isotope fractionation during Fe(II) oxidation by Mn oxides, resulting in lower δ56Fe values in the uppermost water column close to a Mn chemocline. We argue that the preservation of these signals within Paleoproterozoic sediments implies the existence of vertically extended chemoclines with a smoother gradient, probably as a result of low atmospheric oxygen concentrations. Furthermore, we suggest that abiotic oxidation of Fe(II) by a Mn oxide particle shuttle might have promoted the deposition of the Koegas iron formations.

Rock varnish on architectural stone: microscopy and analysis of nanoscale manganese oxide deposits on the Smithsonian Castle, Washington, DC

The Smithsonian Institution Building, commonly referred to as the Castle, is located on the National Mall in Washington, DC, and was constructed in the mid-nineteenth century for the purpose of housing all museum and scientific functions for the newly formed institution. Matching gateposts designed by the Castle’s architect were erected more than a century later in the Enid A. Haupt Garden opposite the Castle. Black patches were recently noted on both structures, which are clad with locally quarried Seneca red sandstone. Portable x-ray fluorescence (XRF) spectrometry links the discoloration with elevated Mn concentrations. The discolored patches resemble rock varnish, a Mn-rich coating observed on rock surfaces formed in a variety of environments. Bulk rock and varnish chemistry, in addition to microscopy and microanalysis of the varnish, are presented here. On a bulk chemical basis, the Seneca sandstone is relatively poor in Mn, containing ~500 ppmw. In contrast, the rock varnish is greatly enriched in Mn relative to the stone and to a lesser degree in Pb, Ca, Zn, Cu and Ni. Cross sections of the black encrusted regions show that the stone’s red coloration has been modified by black pigmentation from the surface down to ~250 μm. X-ray diffraction of blackened particles produced no discernable pattern, indicating concentrations below the detection limit, poor crystallinity, or both. Scanning electron microscopy and EDS-based x-ray microanalysis of the uppermost portion of the cross section reveal nanometer scale (<20–200 nm) Mn-rich and clay particles concentrated in a thin film (≪1 μm) at the surface. Additionally, Mn oxide particles decorate the surfaces of fine-grained minerals in sandstone pores within the discolored zone. Imaging and microanalysis of the rock surface reveal that the Mn-rich varnish is a discontinuous film ≪1 μm in thickness with an estimated composition of Na0.2Ca0.1Mg0.1Al0.1Si0.5Mn1.9Fe0.5O6.7. This composition most likely represents a nanoscale mixture of a Mn oxide (e.g., birnessite or todorokite) and an Al-rich silicate mineral. Seneca sandstone on the Smithsonian Castle and gateposts is discolored in patches owing to the Mn-rich phase being deposited into two zones: (1) a vanishingly thin patina, and (2) nanoparticles coating grain boundaries and pores in the uppermost ~200–250 μm of the stone. While the mineralogy is similar to well-studied varnish formed in arid settings, rock varnish on the Smithsonian structures is significantly thinner. Because this architectural rock varnish is young, it may represent the earliest stages of formation of the more commonly described varnishes reported in the literature.

Phase control and formation mechanism of Al–Mn(–Fe) intermetallic particles in Mg–Al-based alloys with FeCl3 addition or melt superheating

In this study, we identify the crystal structures and elucidate the formation mechanism of Al–Mn(–Fe) intermetallic particles formed in Mg–Al-based alloys with varied Al contents, FeCl3 addition or melt superheating. The formed Al–Mn(–Fe) particles were collected through a newly developed particle extraction method for structural, chemical and morphological characterizations. It is found that increasing the Al content from 3 wt% to 9 wt% changes the major Al–Mn phase from τ-Al0.89Mn1.11 in AZ31 to γ2-Al8Mn5 in AZ91, and both FeCl3 addition and melt superheating promote the formation of γ2-Al8(Mn,Fe)5 in AZ31 and AZ63. In addition, through tuning FeCl3 addition level or melt superheating temperature, different morphologies of the γ2-Al8(Mn,Fe)5 particles are formed in AZ31 and AZ63, including quasi-cubes, octa-pod microstructures and polyhedral particles. This study provides several important approaches to control the crystal structure and morphology of Al–Mn(–Fe) intermetallic particles formed in Mg–Al-based alloys.

Manganese and lead in dust fall accumulation in elementary schools near a ferromanganese alloy plant

Previous studies have shown elevated airborne manganese (Mn) in villages adjacent to a Mn alloy production plant in Brazil and negative associations between biomarkers of Mn and children's cognition and behavior. Since small Mn particles may be carried for long distances, we measured manganese (Mn) and lead (Pb) dust fall accumulation in 15 elementary schools, located between 1.25 and 6.48km from the plant in the municipality of Simões Filho, Bahia, Brazil. Passive samplers (polyethylene Petri dishes) were set in interior and exterior environments. After 30 days, the samplers’ content was solubilized with diluted nitric acid and Mn and Pb levels were analyzed by electrothermal absorption spectrometry. The overall geometric mean and range of Mn and Pb accumulation in dust fall (loading rates) were 1582μg Mn/m2/30 days (37–37,967) and 43.2μg Pb/m2/30 days (2.9–210.4). A logarithmic decrease in interior and exterior Mn loading rates was observed with distance from the ferro-manganese alloy plant. Multiple regression analyses of log-transformed Mn loading rate within the schools showed a positive association with Mn levels in outdoor dust, a negative association with distance from the plant; as well, wind direction (downwind>upwind) and school location (urban>rural) entered significantly into the model. For the interior school environments, located within a 2-km radius from the plant, loading rate was, on average, 190 times higher than the Mn levels reported by Gulson et al., (2014) in daycare centers in Sydney, Australia, using a similar method. Pb loading rates were not associated with distance from the plant and were lower than the rates observed in the same daycare centers in Sydney. Our findings suggest that a significant portion of the children in this town in Brazil may be exposed to airborne Mn at concentrations that may affect their neurodevelopment.

The influence of Mn on the microstructure and mechanical properties of the Al–5Mg–Mn alloy solidified under near-rapid cooling

Abstract

Age hardening in die-cast Mg–Al–RE alloys due to minor Mn additions

Die-cast Mg–Al–rare earth (RE) alloys are normally used in the as-cast condition without the application of heat treatment because it is a common perception that heat treatment will not provide benefit to these alloys. This paper reports, for the first time, that enhanced age hardenability can be achieved in die-cast Mg–Al–RE alloys with minor Mn additions. For example, the yield strength of Mg–4wt%Al–3wt%La alloy with 0.32wt% Mn is increased by ∼34MPa (∼26%) after ageing at 200°C for 32h (T5). The enhanced age hardenability is associated with the precipitation of nanoscale Al–Mn particles during ageing.

Mg–6%Al–1%Zn–2%Ca合金のMIG溶接

Effect of metal inert gas (MIG) welding parameters on tensile strength of weld joints in a Mg–6%Al–1%Zn–2%Ca (AZX612) flame retardant magnesium alloy was examined. Proper welding conditions were found by examining welding current from 70 to 140 A and welding speed from 45 to 70 cm/min. The ultimate tensile strength of weld beads was more than 70% of the strength of the base metal in all the conditions examined. The fracture origin was not Al2Ca second phase or Al–Mn particles, which was the fracture origin of the base metal, but blowhole or oxide inclusion. High weld strength was obtained in low heat input conditions, in which blowhole formation was suppressed. In case that an oxidized MIG welding wire was used for welding, the weld strength decreased and the large oxide fracture origin with the size of 2 mm was found. To obtain high weld strength, it is important to choose proper welding conditions in which blowhole formation was suppressed and to suppress the oxidation of MIG welding wire.

Application of a Rotor–Stator High-Shear System for Cr/Mn-Mediated Reactions in Eribulin Mesylate Synthesis

Potential issues associated with the scale up of a catalytic Nozaki–Hiyama–Kishi reaction and a Cr/Mn-mediated desulfonylation used in eribulin mesylate synthesis were evaluated, and countermeasures were investigated. When stir bar agitation, which is typically used for laboratory-scale reactions, was changed to impeller-type agitation upon scale up of these reactions, the conversion rate and yield decreased considerably. Traditional methods for overcoming such decreases, such as preactivation of the Mn or the use of fine particles of Mn, did not improve the conversion rate sufficiently, whereas a physical shearing approach was effective. Specifically, we found that the use of a rotor–stator high-shear system as a stirring device afforded the same conversion rate as that observed with a stir bar.