Mn Oxide Particles Research Articles

Pseudocapacitive properties of carbon nanotube/manganese oxide electrode deposited by electrophoretic deposition

Nanocrystalline manganese oxide powder prepared by spray pyrolysis (SP) was mixed with multi-walled carbon nanotubes (MWCNTs) in a suspension and subsequently co-coated onto graphite substrates via an electrophoretic deposition technique (EPD). The deposited coatings with or without CNTs mix were examined by X-ray diffractometry (XRD); the coatings were examined by cycling voltammetry (CV) and charge/discharge tests. Structural investigation by XRD revealed that the as-deposited Mn-oxide powder exhibited Mn 3O 4 phase with nanocrystalline structure. The CNTs/Mn-oxide coatings exhibited a porous structure with some hollow or fractured Mn-oxide particles inserted and possessed a high surface area for the electrochemical redox reactions. CV examination showed that the porous CNTs/Mn-oxide coatings exhibited the high specific capacitance of 260 F/g which was higher than the value (234 F/g) of Mn-oxide coatings without CNTs mix at a scan rate of 25 mV/s. After 500 cycles of CV tests, the specific capacitance decreased to 228 F/g, showing a comparatively good efficiency of 88%. The high CV cycling stability of CNTs/Mn-oxide mixture is due to the fact that the CNTs network existent in between the Mn-oxide particles inhibits the structural breakdown of Mn-oxide particles during the repetitive insertion–expulsion of cations from aqueous electrolyte.

Synthesis and microstructure of porous Mn-oxides

Porous Mn-oxide particles were synthesized by urea processing in combination with the thermal treatment of the precursor precipitated. The samples were characterized by XRD, FT-IR, DTA, FE-SEM and EDS. Upon heating of the precursor at 600 °C, α-Mn 2O 3 particles containing nanopores (cheese-like) were obtained. Most nanopores varied from ∼20 to 60 nm, and some were close to ∼100 nm in size. The α-Mn 2O 3 particles showed a strong twinning effect. At 1100 °C, Mn 3O 4 particles, obtained as a single crystal phase, formed a microporous 3D structure.

Nanometer-scale complexity, growth, and diagenesis in desert varnish

Nanometer-scale element mapping and spectroscopy of desert varnish from the northern Sonoran Desert in southwestern Arizona reveal a dynamic disequilibrium system characterized by postdepositional mineralogical, chemical, and structural changes activated by liquid water. Lack of equilibrium is suggested by the large variety of coexisting Mn phases. Sparse secondary Ba and Sr sulfates also occur, as do carbonaceous particles. Individual Mn-oxide particles contain variable concentrations of Ba and Ce, reflecting their role as repositories of trace elements, presumably derived from atmospheric aerosols. Desert varnish is analogous to more familiar sediments in displaying authigenic and diagenetic structures, but with total sediment thicknesses <1 mm and structures at the nanometer scale. As such, it is neither a weathering rind nor patina, but a unique subaerial sediment that is in dynamic disequilibrium. Our results suggest continuing adjustment of varnish to changing environmental conditions.

Transmission electron microscopy (TEM) investigations of Mn-oxide rich cathodic material from spent disposable alkaline batteries

Transmission electron microscopy (TEM) techniques were used to investigate the spent cathodic material of a single common brand of disposable alkaline batteries. Mn-oxide particles are anhedral and irregular in shape and compose an estimated 99-95% of the < 10 microm size fraction of sample material. Diameters of particles vary widely and typically are between 50 nm and 3 microm; however, most particles are approximately 200-400 nm in diameter. Chemical composition varies for Mn-oxide particles with concentrations being SiO2 (0.00-1.52 wt%), TiO2 (0.49-4.58 wt%), MnO (65.85-92.06 wt%), ZnO (1.00-7.53 wt%), K2O (4.97-20.48 wt%) and SO3 (0.43-2.21 wt%). Discrete prismatic zinc crystals occur and vary from a maximum of approximately 0.8 microm long x 0.15 microm wide, to 100 nm long x 20 nm wide. Titanium metal was also observed in samples and composes approximately 0.25-1.0% of the < 10 microm size fraction of sample material. Results of this study suggest that battery components may be recycled in some special applications. Examples are low energy-low material requirement products such as paint pigments and Zn nanoparticles. This investigation provides detailed constraints on the nature of spent cathodic materials to improve existing recycling methods and develop new technologies.

Mine drainage water from the Sar Cheshmeh porphyry copper mine, Kerman, IR Iran

This paper presents the results of a study on stream and mine waters in the area of one of the world largest porphyry copper deposit located in the southeastern Iran, the Sar Cheshmeh porphyry copper mine. Trace metals are present as adsorption on Fe and Mn oxide and hydroxide particles, as sulfate, simple metal ions, and scarcely as adsorption on clay particles and hydrous aluminium oxides. Mean pH decreases and the mean concentration of trace elements, EC and SO4(2-) increases from the maximum discharge period (MXDP) during snow melt run off (May), through the moderate discharge period (MDDP; March and July) to the minimum discharge period (MNDP; September). Water samples have sulfatic character essentially, however, from the MNDP through the MDDP towards the MXDP they show a bicarbonate tendency. This study indicates that the surface waters draining the Sar Cheshmeh open pit have a higher pH and lower concentration of trace metals compared with some other porphyry copper deposits.

Rare Earth Elements in the hydrothermal system at Okinawa Trough back-arc basin

We present novel data sets of rare earth element (REE) distributions in a hydrothermal vent field at Yonaguni Knoll IV in the Okinawa Trough. Vertical REE profiles in three water columns showed horizontal variation of REE concentrations within 1000‐1200 m. Hydrothermal plumes were discovered by anomalous values of methane, manganese and transmissometry at that site. Europium anomalies in the North Pacific deep water (NPDW) (Nozaki et al., 1999) normalized pattern decreased with distance from the hydrothermal vent site, indicating that the dilution of hydrothermal fluid in the plume can be traced using REE. The horizontal variation of negative Ce-anomalies represents the continuous scavenging of REE by suspended matter in the plume. In addition, we measured nine hydrothermal fluid samples. The REE geochemistry of hydrothermal vent systems had been investigated intensively at sediment-starved mid-oceanic ridges, but few studies had examined sediment-hosted hydrothermal systems like those of the Okinawa Trough. The chondrite-normalized REE patterns of the fluids collected at Yonaguni Knoll IV show typical lighter rare earth elements (LREE) and Eu enrichment similar to at the Mid-ocean Ridge sites. A remarkable characteristic of the Yonaguni Knoll IV fluid pattern is its higher concentrations of heavier rare earth elements (HREE) and La composition than the hydrothermal fluids of the sediment-starved East Pacific Rise and Trans-Atlantic Geotraverse. Such a feature is explainable by influences of covering sediments in the back-arc basin Okinawa Trough. At the hydrothermal vent, lighter REE (LREE) in the fluid was reduced systematically during fluid mixing with seawater within the chimney. Light REE elimination resembles fractionation caused by particle scavenging within the water column. However, the lack of Ce depletion, which is a typical REE feature in the water column, along with distinctive Eu reduction, were unique in the Yonaguni Knoll IV fluid, suggesting that fluid REE fractionation at the vent site was induced predominantly by coprecipitation with hydrothermally originated minerals (e.g. sulfate and carbonate), not by adhesive removal by Fe and/or Mn oxide particles. Previous studies had shown that REE removal and fractionation of the hydrothermal system were observed only in deposit samples. Results of this study elucidated REE fractionation in fluid samples using previous analytical data. We were also able to distinguish REE removal mechanisms occurring at the vent site and water column using REE pattern characteristics.

Effect of minor elements and a Ce surface treatment on the oxidation behavior of an Fe–22Cr–0.5Mn (Crofer 22 APU) ferritic stainless steel

This paper details the oxidation behavior of coupons from three different Crofer 22 APU sheets. Oxidation tests were conducted at 800 ∘ C in moist air for 2300 h. The major features of the scales were similar in all three coupons, with a continuous Cr–Mn spinel layer forming at the gas–oxide interface and a Cr 2O 3 layer forming at the oxide–metal interface. Also, at the Cr 2O 3–metal interface, large Cr–Mn oxide particles formed in the base metal. Metal extrusions in the oxide scale were observed in the vicinity of these Cr–Mn oxide particles. All three alloys had internal oxide particles forming in the base metal beneath the oxide scale, and the extent of this internal oxidation was related to the Al and Si-content in the coupons (as also reported by Piron-Abellan J, Huczkowski P, Ertl S, Shemet V, Singheiser L, Quadakkers W. In: Fuel cell seminar, 2004. San Antionio, TX, November 1–5, 2004). Of note, discontinuous Ti-oxide and Mn-oxide particles formed above the outer spinel layer on the coupons with relatively high Al and Si contents. The effectiveness of rare-earth surface modification on improving oxidation resistance of this alloy was demonstrated. Pack cementation-like processes were used to treat the surface of the coupons with Ce. A continuous Cr–Mn outer oxide layer and a continuous inner Cr 2O 3 layer formed on the surface of the treated coupons during oxidation. However, the thickness of the scales and amount of internal oxidation were significantly reduced with the treatment, leading to the decrease in oxidation rate. The amount of internal oxidation was also reduced with the treatment. The treatment appeared to suppress the formation of SiO 2 at the scale–metal interface in high Si containing alloys. ASR measurements indicate that the treatment decreases the electrical resistance, which is a benefit for SOFC interconnect application.

Effects of Manganese on the Passivity of Fe-18Cr-xMn (x = 0, 6, 12)

Effects of Mn on the passivity of Fe-18Cr-xMn(x=0, 6, 12) were examined by various electrochemical tests including potentiodynamic test, micro-droplet cell test and photoelectrochemical test. With an increase in Mn content of Fe-18Cr-xMn(x=0, 6, 12) alloys, passivity of the alloys was significantly degraded in an acidified chloride solution. It was demonstrated through the micro-droplet cell tests conducted in 0.1 M NaCl solution that Mn decreased considerably the resistance to pitting corrosion of Fe-18Cr alloys even if any nonmetallic inclusions (NMI) was not included in the observed region. Passive film formed on Fe-18Cr-6Mn alloy in pH 8. 5 buffer solution is found to be composed of Cr-substituted gamma-Fe2O3 containing nano-sized Mn-oxide particles. The significant degradation in the resistance to localized corrosion of Fe-18Cr alloy, even if any NMI is absent in the alloy, appears to be associated with the nano-sized Mn-oxide particles present in the passive film.

Cycling of Biogenic Mn-Oxides in a Model Microbial Predator-Prey System

The phase distribution and bioavailability of both essential and toxic trace metals can be profoundly impacted by trophic transfer in microbial food webs. A model microbial predator-prey system was used to elucidate the possible transformations of biogenic manganese oxides as they were consumed by protozoan predators along with their bacterial prey. The ciliated protozoan Tetrahymena thermophila and the Mn-oxidizing bacterium Leptothrix discophora SS-1 were chosen as predator and prey species, respectively. The following processes were evaluated: adsorption and pinocytosis of Mn(II), regeneration and bioaccumulation of biogenic Mn-oxides, and excretion of Mn associated with waste matter. Changes in Mn oxidation state and phase distribution were assessed by observation of dissolved Mn(II) concentrations coupled with a comparison of Mn-oxide and total Mn concentration over time. Mn(II) adsorption to and pinocytosis by T. thermophila were not significant at Mn levels up to 100 μM. At the experimental pH of 7.0, the oxidation state and phase distribution of Mn at Mn levels up to 60 μM was not affected by T. thermophila's predation of L. discophora strain SS-1 and the accompanying consumption of Mn-oxide particles. Addition of an Mn+2 spike to one reactor revealed that ingested biogenic Mn(III/IV)-oxide solubilized as dissolved Mn(II) would have been quickly re-oxidized or adsorbed under the experimental conditions. Although biogenic Mn-oxide particles were observed by microscope to be consumed by T. thermophila during grazing, this consumption is likely to have represented only a small portion of the total Mn in the system. The overall results obtained suggest that the consumption of biogenic Mn-oxide particles associated with bacterial prey by microbial predators does not significantly change the solid/solution phase distribution of Mn and it does not have a major impact on the geochemical cycling of Mn. An adaptive advantage postulated as a rationale for bacterial catalysis of Mn(II) oxidation is that the resulting extracellular coating of biogenic Mn-oxide may protect cells from microbial predators. The observed reduction in L. discophora population size through predation by T. thermophila was comparable at all levels of biogenic Mn oxide tested and no beneficial effect could be observed.

Manganese(II) oxidation driven by lateral oxygen intrusions in the western Black Sea

Mn(II) oxidation in the suboxic zone of the water column was studied at four stations in the western Black Sea. We measured Mn(II) oxidation rates using 54Mn tracer and tested the hypothesis of alternative oxidants for Mn(II) other than dissolved oxygen. In anoxic incubation experiments with water from different depths of the chemocline, Mn(II) was not oxidized by nitrite, nitrate, or iodate. In the presence of light, Mn(II) also was not oxidized under anoxic conditions as well. Anaerobic Mn(II) oxidizing microorganisms could not be enriched. In oxic incubation experiments, the addition of alternative oxidants did not significantly increase the Mn(II) oxidation rate. The lack of an anaerobic Mn(II) oxidation in our experiments does not unambiguously prove the absence of anaerobic Mn(II) oxidation in the Black Sea but suggests that dissolved oxygen is the only oxidant for biologically catalyzed Mn(II) oxidation. Lateral intrusions of modified Bosphorus water were shown to be the main mechanism providing dissolved oxygen in the suboxic and the upper anoxic zones and explaining observed Mn(II) oxidation rates. Maximum in situ Mn(II) oxidation rates in the suboxic zone were 1.1 nM Mn(II) per h in the central Black Sea, 25 nM Mn(II) per h on the Romanian continental slope and 60 nM Mn(II) per h on the Anatolian continental slope. These rates correlate with the amount of particulate Mn and the number of Mn-oxide particles and are in agreement with rates measured 13 yr before. Our study highlights the importance of lateral intrusions of oxygen for the ventilation of the suboxic zone and the anoxic interior and for the regulation of different oxidation-reduction processes in the chemocline, including Mn(II) oxidation, which may be significant for other anoxic basins as well.

Mine-drainage water from coal mines of Kerman region, Iran

Two types of mine-drainage water were recognized in Kerman coalfield, namely neutral to alkaline and acid (AMD). Both types contain a high level of trace-metal concentrations with a higher level in AMD. Trace metals from the coal-mine waters of Kerman coalfield are mainly present as adsorption on Fe and Mn oxide and hydroxide particles, and to a lesser extent as sulfate, simple metal ions and as metal sorption on clay particles and hydrous aluminum oxides.

Nanocasting, templated syntheses and structural studies of manganese oxide nanoparticles nucleated in the pores of ordered mesoporous silicas (SBA-15)

We have used 2D hexagonal SBA-15 silicas as templates for the nanofabrication of Mn oxide particles. Despite challenging aspects (several oxidation states of manganese, several polymorphs for each oxidation state), manganese oxides were chosen because of the high economical and environmental significance associated with their ion-exchange, molecular adsorption, electrochemical, magnetic and catalytic properties. We show that single phase MnO x nanoparticles can be prepared within SBA-15 mesopores. The interest of diffraction and absorption measurements recorded in situ upon calcination to follow the crystallization of these particles at increasing length scales is illustrated. To cite this article: V. Escax et al., C. R. Chimie 8 (2005).

Chemostratigraphy of the Paleocene/Eocene (P/E) boundary sediments at Gabal el-Qreiya, Nile Valley, Egypt

In a detailed investigation of the sedimentology, mineralogy and trace element geochemistry of the stratigraphic interval spanning the Paleocene/Eocene (P/E) boundary in the Gabal el-Qreiya section, the author attempts to reconstruct environmental changes across the boundary especially for the interval representing the Paleocene-Eocene Thermal Maximum (PETM). The PETM interval consists of three distinct thin units of phosphatic shales followed by a calcareous phase. The basal unit is a laminated clay layer, whose base represents the base of the Eocene. It is enriched in silica and aluminium and is slightly phosphatic (bone-bearing). The middle unit is CaCO 3 -rich and bone-bearing, with a higher proportion of phosphatic components than the basal clay layer. The upper unit is coprolite-rich. These sediments contain different abundances of barite, Mn-oxide particles and grains of detrital origin. The PETM interval at Gabal el-Qreiya is characterized by high anomalies in most chalcophiles and REEs especially in the basal clay layer and the bone-bearing bed. It is concluded that these trace elements are incorporated into the phosphatic components (fish debris and coprolites) and organic matter. The three phosphatic shale units reflect euxinic marine environments and deposition in anoxic H 2 S-containing bottom waters rich in organic matter. The sedimentological, mineralogical and geochemical data show that the PETM interval represents deposition in a relatively deep water environment. However, it reflects slight fluctuations of sea level, a humid climate, high rain fall and oxidation conditions during weathering.

Magnetic properties of nanostructured Mn oxide particles

Nanostructured Mn oxide particles with an average size of about 7 nm have been prepared by a microemulsion method. X-ray diffraction analysis indicates that the particles possess orthorhombic structure of MnO(OH). The particles are ferromagnetic at low temperature. The Curie temperature is about 35 K and each MnO(OH) molecule generates a magnetic moment of about 0.7 μB. The appearance of the ferromagnetism at low temperature may result from size effect.

The Influence of Redox Reactions on the Uptake of Dissolved Ce by Suspended Fe and Mn Oxide Particles

Laboratory experiments were conducted to evaluate the partitioning ofrare earth elements (REE) between solution and suspended particles. Becauseof their strong tendency to complex, the REE can be used to study a varietyof marine processes and in particular particle scavenging. In this study, anemphasis was placed on examining abiotic redox processes that influence theuptake of dissolved Ce by particles. Batch sorption experiments wereconducted with REE and synthetic mineral phases over the range of pH4–9. The solutions varied in ionic strength between 0 and 0.7 M andconsisted of individual solutes (NaNO3, NaCl, andNa2SO4), ionic mixtures that duplicate theseawater composition, and natural seawater. The uptake of REE from solutionwas also studied at a Pt electrode coated with \(\delta {\text{ - MnO}}_{\text{2}} \)using cyclic voltametry.

Magnetic thermal stability of Mn and Co volume-doped acicular iron oxide particles

The magnetic thermal stability of Mn and Co volume-doped acicular /spl gamma/-Fe/sub 2/O/sub 3/ particles was studied. These MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles with a coercivity about 950 Oe and Co content about 3.5 wt.% have been prepared by high temperature ion diffusing and step annealing. The MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles exhibit a much higher transverse field stability than that of Co-/spl gamma/-Fe/sub 2/O/sub 3/ particles. The induced effective uniaxial anisotropy constant, K/sub u/ and the magnetocrystalline anisotropy constant, K/sub 1/ of the particles were determined by the analysis of torque curves. The high magnetic thermal stability of these particles is mainly due to the higher and more stable induced uniaxial anisotropy, which is the result of the anisotropic arrangements of cobalt ions promoted by the presence of manganese ions during the step annealing. The MnCo-/spl gamma/-Fe/sub 2/O/sub 3/ particles show a smaller irreversible decrease of uniaxial anisotropy with temperature and time in a magnetic field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Surface studies of powder metallurgical stainless steel

AbstractThe reaction products formed on the surfaces of gas‐atomized 12Cr steel powder are determined using ESCA and AES. It is shown that Cr and Mn oxide particles larger than about 10 nm are formed at high temperatures during atomization. At lower temperatures and during subsequent handling, the remainder of the powder surface is covered by a thin (&lt;5 nm) layer of mainly Fe oxide. For particles larger than about 40 μm the average oxide thickness is about 5.5 nm, while smaller particles are less oxidized and also frequently covered by a thin (1 nm) S‐rich layer. On lowering the O2 availability, much less Mn, Cr and Fe oxides are formed and Si is oxidized instead. During hot isostatic pressing (HIPing), first Fe oxide and then Cr and Mn oxides are reduced as the temperature increases, while Si oxide particles are formed on the powder surfaces. Consequently, heating the powder in a temperature gradient causes reduction and oxidation at higher and lower temperatures respectively. The surface oxides on the particle boundaries provide sites for carbonitride precipitation. Local growth of manganese sulphide at 1200°C is noticed. The HIPing temperature should therefore be limited but high enough for reducing surface oxides and the pore system should be closed early during consolidation.

The genesis of carbon-supported FeMn and KFeMn catalysts from stoichiometric mixed-metal carbonyl clusters: II. Characterization by Mössbauer spectroscopy and [formula omitted

Mössbauer effect spectroscopy (MES) and transmission electron microscopy/energy-dispersive X-ray spectroscopy ( TEM EDS ) were used to study the chemistry of the iron particles produced by the thermal decomposition of Stoichiometric KFe, FeMn, and KFeMn mixed-metal carbonyl clusters on a high surface area carbon. Intermediate chemical states during the cluster decomposition process below 473 K were identified using MES, and they indicated that decarbonylation occurred via the formation of Fe(CO) 5 and [Fe 4(CO) 13] − during heating in H 2. Following decomposition at 473 K, the principal final phase was the D-structure, which has been associated with superparamagnetic Fe combined with an Fe 2+ state. Additionally, a doublet characteristic of Fe 3+ oxide and/or superparamagnetic carbide appeared in the spectrum. No evidence for a mixed spinel such as Fe 2MnO 4 was obtained, but the Fe and Mn appeared to remain in contact, presumably as MnO x on top of small Fe crystallites. A subsequent treatment in H 2 at 673 K caused the K-promoted catalysts to sinter and form separate phases of Mn oxide and large particles of α-Fe, as detected by MES and TEM EDS . For the unpromoted FeMn sample, little sintering occurred under H 2 at 673 K, and the particles existed in a phase which has been previously found in Fe-only Carbon-supported catalysts.

The effect of sediment-water exchange on manganese deposition and nodule growth in Jervis Inlet, British Columbia

The processes controlling Mn deposition in the vicinity of a nodule site in Jervis Inlet, a fjord in the British Columbia mainland coast, were studied. The results indicate that Mn, due to reductive remobilization in the subsurface sediments, undergoes intensive exchange across the sediment-water interface and, because of this exchange and the effects of water circulation processes within the inlet, tends to be stripped from shallow water sediments and to be redeposited as an oxide precipitate in the surface sediment of the deepest areas. There it undergoes diagenetic reactions in the subsurface sediments that, as demonstrated by saturation of the pore waters, finally result in its burial as a carbonate phase. The distribution of properties in the vicinity of the Mn nodule site indicates that concretion growth occurs in an area of strong currents and low sedimentation rate where rocks resting on the bottom act as centers to which Mn-oxide particles suspended in the bottom water are apparently being cemented.