Mn Maximum Research Articles

Mechanical Analysis and Constitutive Modeling of Nonlinear Behavior of Silver-based Conductive Ink

Stretchable electronic devices are progressively deployed in many applications of mechanical, electrical, and bio-medical engineering. These circuits are made of stretchable and flexible substrate, as well as conductive ink, and various electronic components. The choice of components and layouts for the substrate and conductive ink can regulate the stretchability of stretchable circuits. On top of that, the substance utilized to create the conductive ink must have high electrical conductivity and strong adherence to the substrate in order to produce a high-quality stretchable printed circuit. Thus, this study focused on the development of stretchable conductive ink using silver powder as a conductive filler and PDMS-OH as a binder. The mechanical properties of the synthesized ink were investigated via simple uniaxial tensile testing method and nanoindentation technique, respectively. Accordingly, the modulus of elasticity, tensile stress and yield stress of the ink were obtained as 5.72 MPa, 1.195 MPa, and 0.86 MPa, congruently at 137% strain before undergoing failure. The experimental stress-strain data was then employed on the elastic-plastic constitutive model to investigate the elastomeric properties of the ink as it is an alternative method of lengthy and expensive procedures of validating different polymers. Moreover, the hardness and reduced modulus of the ink were evaluated by nanoindentation method using 5 mN maximum load with 0.5 mN/s loading/unloading rate and 2 secs holding time. Consequently, the hardness and reduced modulus values were obtained as 1.45 MPa and 34.53 MPa, respectively. These values were further validated by Oliver-Pharr method, and were in a good agreement.

Biological Uptake, Water Mass Mixing and Scavenging Limit the Transport of Manganese‐Rich Waters From the East Antarctic Shelf

AbstractManganese (Mn) is an essential element involved in photosynthesis, yet its concentrations in Southern Ocean open waters are very low, arising from biological uptake and limited external inputs. At southern latitudes, waters overlying the Antarctic shelf are expected to have much higher Mn concentrations due to their proximity to external sources. In this study, we investigated the potential export of Mn‐rich Antarctic shelf waters toward depleted open Southern Ocean waters. Our results showed that while high Mn concentrations were observed over the shelf, biological uptake decreased dissolved Mn concentrations in surface waters north of the South Antarctic Circumpolar Current Front (<0.1 nmol kg−1), limiting its export. Conversely, mixing between Mn‐rich Antarctic Bottom Waters and Mn‐depleted Lower Circumpolar Deep Waters combined with oxidative and scavenging processes led to a decrease in dissolved Mn concentrations within bottom waters, with distance from the coast. Particulate Mn concentrations also showed a decreasing trend with distance from the coast. A comparison with other Antarctic coastal regions suggests this bottom water Mn removal may be widespread and that East Antarctica may be characterized by lower Mn concentrations compared to other regions. Still, subsurface dissolved Mn maxima (0.3–0.6 nmol kg−1) represented a potential reservoir for surface waters. We hypothesize that these high subsurface values result from external sources near the shelf. Overall, these results suggest that the moderate lateral export of trace metal‐enriched waters contributes to the extremely low and potentially limiting Mn concentrations previously reported further north in this Southern Ocean region.

Assessment of concentration of the potentially toxic elements and associated human health risk from particulate matter exposure along road intersections in Ibadan, southwestern Nigeria

The harmful health effect of suspended particulate matter (PM10) is mostly associated with its mass concentrations and chemical compositions. Therefore, this study focuses on the determination of the particulate matter (PM10) concentrations and their potentially toxic elements (PTEs) composition from different road networks in Ibadan southwestern, Nigeria. In addition, human health risk assessment was estimated from the PTE data. The PM10 samples were collected from different road networks such as national highway roads (NHR), inner-city major roads (ICR), and remote roads (RRD) in Ibadan, Nigeria. The sampling was carried out with a high-volume air sampler (model #15000 manufactured by Science Resource, Walboro, USA) with a PM10 cut-off on a Whatman cellulose filter during the harmattan period. The PM10 concentrations and PTEs compositions (Al, Ba, Cd, Cu, Fe, La, Mo, Mn, Ni, Pb, V, and Zn) were determined by gravimetry and inductively coupled plasma-optical emission spectrometry (ICP-OES) methods (VISTA-MPX manufactured by Varian Incorporation), respectively. The PM10 concentrations in all three road networks were more than 3 folds higher than World Health Organization (WHO), United State Environmental Protection Agency (USEPA), and United Kingdom Environmental Protection Agency (UKEPA) standards (50 µg/m3) for 24 h. The maximum average contents of Ba, Cd, Cu, La, Mn, Pb, and V, were observed at NHR, while that of Al, Fe, Mo, and Zn, were found at ICR. The principal component analysis (PCA) showed that PC1 (Ba, Cd, Cu, La, Mo, Pb, and V) and PC4 (Zn) were characterised by elemental markers of both exhaust emission and non-exhaust emissions, while PC2 (Mn) and PC3 (Al, Fe) were characterised by crustal elements. The Enrichment factor (EF) analysis classified all the PTEs as moderately to very highly enriched, especially in NHR and ICR, except Al, Fe, and to some extent Mn. Both the maximum and average hazard quotient (HQ) levels of Cd, Cu, Mn, Pb, and Zn were < 1, which was within the permissible level. Also, the carcinogenic risk (CR) was also within the permissible limit.

Distribution and stability of Mn complexes in the ocean: Influence of hydrothermal plumes and weather events

AbstractWe measured the speciation of dissolved Mn from the surface to just above the hydrothermal vents at 9°50′N East Pacific Rise in the open ocean of the Pacific over a 3‐week period. Total dissolved Mn concentrations ranged from 2.2 to 135 nmol L−1 with a significant contribution of dissolved Mn(III) bound to humic acid in one third of our samples representing up to 64% of the total dissolved Mn. These humic complexes were mostly detected in the hydrothermal vent plume and at the redox boundaries of the oxygen minimum zone in the water column. In the hydrothermal plume, the Mn(III)‐humic acid stabilized the manganese in solution up to a ~ 10,000‐fold dilution of the venting water. In the upper water column, Mn(III)‐humic acid was only detected after a squall and rain event, which indicates that it is a transient species, persistent over days to weeks. This temporal variability highlights the importance of non‐steady‐state processes in the open ocean, which may help to explain previous observations of a dissolved Mn maximum within oceanic oxygen minimum zones.

Biogeochemical cycling of Cd, Mn, and Ce in the Eastern Tropical North Pacific oxygen‐deficient zone

AbstractOxygen‐deficient zones (ODZs) play an important role in the distribution and cycling of trace metals in the ocean, as important sources of metals including Fe and Mn, and also as possible sinks of chalcophile elements such as Cd. The Eastern Tropical North Pacific (ETNP) ODZ is one of the three largest ODZs worldwide. Here, we present results from two sectional surveys through the ETNP ODZ conducted in 2018, providing high‐resolution concentrations of several metals, along with complimentary measurements of nutrients and iodine speciation. We show that samples obtained from the ship's regular rosette are clean for Cd, Mn, Ni, and light rare earth elements, while uncontaminated Fe, Zn, Cu, and Pb samples cannot be obtained without a special trace‐metal clean sampling system. Our results did not show evidence of Cd sulfide precipitation, even within the most oxygen‐depleted water mass. High Mn and Ce concentrations and high Ce anomalies were observed in low‐oxygen seawater. These maxima were most pronounced in the upper water column below the oxycline, coincident with the secondary nitrite maxima and the lowest oxygen concentrations, in what is generally considered the most microbially active part of the water column. High Mn and Ce features were also coincident with maxima in excess iodine, a tracer of shelf sediment sources. Mn and Ce maxima were most prominent within the 13°C water mass, spanning a density horizon that enhances isopycnal transport from the shelf sediments, resulting in transport of Mn and Ce at least 2500 km offshore.

Sediments in Sea Ice Drive the Canada Basin Surface Mn Maximum: Insights From an Arctic Mn Ocean Model

AbstractBiogeochemical cycles in the Arctic Ocean are sensitive to the transport of materials from continental shelves into central basins by sea ice. However, it is difficult to assess the net effect of this supply mechanism due to the spatial heterogeneity of sea ice content. Manganese (Mn) is a micronutrient and tracer which integrates source fluctuations in space and time while retaining seasonal variability. The Arctic Ocean surface Mn maximum is attributed to freshwater, but studies struggle to distinguish sea ice and river contributions. Informed by observations from 2009 IPY and 2015 Canadian GEOTRACES cruises, we developed a three‐dimensional dissolved Mn model within a 1/12° coupled ocean‐ice model centered on the Canada Basin and the Canadian Arctic Archipelago (CAA). Simulations from 2002 to 2019 indicate that annually, 87%–93% of Mn contributed to the Canada Basin upper ocean is released by sea ice, while rivers, although locally significant, contribute only 2.2%–8.5%. Downstream, sea ice provides 34% of Mn transported from Parry Channel into Baffin Bay. While rivers are often considered the main source of Mn, our findings suggest that in the Canada Basin they are less important than sea ice. However, within the shelf‐dominated CAA, both rivers and sediment resuspension are important. Climate‐induced disruption of the transpolar drift may reduce the Canada Basin Mn maximum and supply downstream. Other micronutrients found in sediments, such as Fe, may be similarly affected. These results highlight the vulnerability of the biogeochemical supply mechanisms in the Arctic Ocean and the subpolar seas to climatic changes.

Baseline on rare earth elements in the marine sediments of a Mediterranean commercial port as environmental tracers and their relationships with inorganic contaminants

The Port of Genoa (north-western Mediterranean Sea) receives sediments from two different catchment areas (Bisagno and Polcevera torrents). The aim of the work is to evaluate if Rare Earth Elements (REEs) could be used to identify the two sedimentary inputs and to unravel the origin of inorganic contaminants in an anthropised basin. REE results constitute a baseline for this port. The main REE-bearing minerals are phosphates and zircon. As, Cd, Hg, Pb, and Sn concentrate in the sediments closer to the Bisagno Torrent mouth, and the correlation with Ca and Light-REEs suggests their plausible geological origin. Co, Mn, and Ni maxima lie in the sediments closer to the Polcevera Torrent. Their correlation with Middle-REEs and Mg suggest that ophiolitic rocks could explain their presence. Cr, Cu, V, and Zn do not show a clear correlation with REEs, and their origin probably is a combination of natural and anthropogenic sources.

Strengthening of aluminum 7000 alloy by addition of manganese particles

Micron sized Manganese particles of different percentage (0.2, 0.4, 0.6 and 0.8 wt%) have been added during the melting phase of the Al-2wt%Zn-2wt%Mg alloy. Mechanical testing and microstructural characterization have been performed to investigate the change incorporated by the addition of Mn particles. It was found that with the addition of Mn particles the ultimate tensile strength (UTS) of the alloy gradually improved up to an optimum percentage followed by rather reduction for the higher percentages. For optimum percentage of Mn (0.6% Mn) maximum 14% improvement in the UTS was achieved. The percentage of strain before fracture followed opposite trend to the UTS. Optical microscopy and scanning electron microscopy (SEM) of the alloys indicated that optimum percentage of Mn particles provided the microstructure with uniform dispersed second phase in the alloy matrix. These dispersed second phase effectively acted as a barrier to the dislocation motion, and consequently, improved the strength of the alloy as well as reduced the total elongation before fracture. Rockwell hardness test result showed that addition of Mn particles significantly improved the hardness of the alloy with successive addition. The hardness of the base alloy found to be improved by maximum up to 47.3% for 0.8% of Mn particles.

Improvement in photovoltaic response of bismuth ferrite by tuning its ferroelectric and bandgap properties

Pristine and Mn-doped bismuth ferrite samples were prepared by sol–gel method. XRD patterns showed rhombohedral to orthorhombic phase transition with Mn doping in BiFeO3 sample. The surface morphology of the samples was carried out by scanning electron microscope which exhibited a decrease in grain size with Mn doping. Magnetic hysteresis curves exhibit that manganese doping induces modification in magnetic properties of bismuth ferrites. Significant modification was observed in dielectric with Mn doping and maximum value was recorded for BiFe0.8Mn0.20O3 sample. P–E hysteresis curves were recorded to evaluate the ferroelectric properties of all samples at room temperature. A significant improvement was observed in ferroelectric properties in doped samples. Bandgap values of BiFe1−xMnxO3 in UV–Vis region decreases with Mn doping and minimum for BiFe0.80Mn0.20O3 sample as evaluated from Tauc’s plots. I–V studies of pristine and Mn-doped samples were carried out with light and without light. Enhanced photocurrent density was observed in Mn-doped BFO samples. Hence, these modifications in ferroelectric and photovoltaic properties of BiFe1−xMnxO3 samples make bismuth ferrites a good candidate for photovoltaic applications.

Development and Characterization of Freestanding Poly (Methyl Methacrylate)/Monolayer Graphene Membrane

Graphene-polymer based materials are gaining more popularity among researchers due to its mechanical properties that are found to be suitable to be used in various micro/nanoscale application requiring highly sensitive sensors. This research ventured into the fabrication and characterization process of a freestanding poly (methyl methacrylate) (PMMA) on monolayer graphene (Gr) yielding a (PMMA/Gr) membrane. In the process of transferring the chemical vapor deposition (CVD) graphene film over a cavity that was developed on a silicon substrate, the wet transfer method was used. Five repetitions of the nanoindentation testing had been carried out on the flexible membrane which resulted in a reproducible deflection, when exerted with a maximum loading of 10 mN. The indented (PMMA/Gr) membrane showed an identical elastic behavior with Young's modulus of 0.18 GPa. The highest deflection of approximately 22 μm at 1.6 mN maximum loads and the tensile stress of 0.58 MPa was obtained from the indentation testing analysis. The combination of PMMA-Graphene materials as a membrane has shown impressive changes to its mechanical properties. Besides maintaining its viscoelastic-plastic behavior which contributed to its flexibility, the presence of a graphene layer provided strong support to prevent damages to the membrane. Meanwhile, PMMA properties with low elastic modulus have contributed to the increased of the mechanical sensitivity of the membrane. Based on this research, the mechanical sensitivity of (PMMA/Gr) is reported to be 0.15 nm/Pa, which is much higher compared to a typical conventional membrane. It was proven that the hybrid (PMMA/Gr) membrane was extremely sensitive to the subjected pressures, thus, shown its potential to be applied as a micro-electro-mechanical systems (MEMS) capacitive pressure sensor.

Post-depositional manganese mobilization during the last glacial period in sediments of the eastern Clarion-Clipperton Zone, Pacific Ocean

Numerous studies have provided compelling evidence that the Pacific Ocean has experienced substantial glacial/interglacial changes in bottom-water oxygenation associated with enhanced carbon dioxide storage in the glacial deep ocean. Under postulated low glacial bottom-water oxygen concentrations (O2bw), redox zonation, biogeochemical processes and element fluxes in the sediments must have been distinctively different during the last glacial period (LGP) compared to current well-oxygenated conditions.In this study, we have investigated six sites situated in various European contract areas for the exploration of polymetallic nodules within the Clarion-Clipperton Zone (CCZ) in the NE Pacific and one site located in a protected Area of Particular Environmental Interest (APEI3) north of the CCZ. We found bulk sediment Mn maxima of up to 1 wt% in the upper oxic 10 cm of the sediments at all sites except for the APEI3 site. The application of a combined leaching protocol for the extraction of sedimentary Mn and Fe minerals revealed that mobilizable Mn(IV) represents the dominant Mn(oxyhydr)oxide phase with more than 70% of bulk solid-phase Mn. Steady state transport-reaction modeling showed that at postulated glacial O2bw of 35 μM, the oxic zone in the sediments was much more compressed than today where upward diffusing pore-water Mn2+ was oxidized and precipitated as authigenic Mn(IV) at the oxic-suboxic redox boundary in the upper 5 cm of the sediments. Transient transport-reaction modeling demonstrated that with increasing O2bw during the last glacial termination to current levels of ∼ 150 μM, (1) the oxic-suboxic redox boundary migrated deeper into the sediments and (2) the authigenic Mn(IV) peak was continuously mixed into subsequently deposited sediments by bioturbation causing the observed mobilizable Mn(IV) enrichment in the surface sediments. Such a distinct mobilizable Mn(IV) maximum was not found in the surface sediments of the APEI3 site, which indicates that the oxic zone was not as condensed during the LGP at this site due to two- to threefold lower organic carbon burial rates. Leaching data for sedimentary Fe minerals suggest that Fe(III) has not been diagenetically redistributed during the LGP at any of the investigated sites. Our results demonstrate that the basin-wide deoxygenation in the NE Pacific during the LGP was associated with (1) a much more compressed oxic zone at sites with carbon burial fluxes higher than 1.5 mg Corg m−2d−1, (2) the authigenic formation of a sub-surface mobilizable Mn(IV) maximum in the upper 5 cm of the sediments and (3) a possibly intensified suboxic-diagenetic growth of polymetallic nodules. As our study provides evidence that authigenic Mn(IV) precipitated in the surface sediments under postulated low glacial O2bw, it contributes to resolving a long-standing controversy concerning the origin of widely observed Mn-rich layers in glacial/deglacial deep-sea sediments.

Comparative analysis of tissue compartmentalized heavy metal uptake by common forage crop: A field experiment

Heavy metal contamination of agricultural soils is a severe cause of concern globally. The heavy metals can enter crops through roots and can result in biomagnification in the different plant tissues such as roots, stems and leaves. From plants these metals are transferred into animal and human systems resulting in serious health problems. Various physical and chemical methods are available for heavy metal removal from soil but phytoremediation is considered as one of the most sustainable and cost-friendly method. Although many studies have been carried throughout the world to assess phytoremediation potential of plants in controlled conditions, few studies are available on the metal uptake capabilities of plants growing in natural conditions. Therefore, the present study was conducted to assess the phytoremediation potential of Trifolium alexandrinum (Berseem), an important forage crop growing in intensively cultivated agricultural soils of Punjab, India with main focus on the accumulation and mobility of metals (Cr, Cd, Cu, Co, Fe, Mn, Pb and Zn) in various plant tissues like roots, stems and leaves. The maximum contents of Cd, Co, Fe and Pb were observed in roots whereas for Cr, Cu, Mn and Zn maximum content was observed in leaves of Berseem. Overall among the metals studied Fe content was highest in all tissues of Berseem, which could be due to the higher content of Fe in soil. Metal Bioaccumulation Factor (BAF) and Translocation Factor (TF) calculated for assessing metal uptake and transport by plant tissues were found to be above 1 for the studied metals (except Co and Fe), which indicated Berseem to be a suitable accumulator of these metals in natural conditions.

Extraction and environmental risk assessment of heavy metal in the municipal dewatered sludge using rhamnolipid treatment

ABSTRACTHeavy metal could lead to serious environmental risk to the ecosystem, destroy human health via the food chain. The heavy metal removal from sludge is an emergent issue. In this work, rhamnolipid, an environment-friendly material, was used to enhance heavy metal extraction from the sludge. The results showed that Cu, Zn, Cr, Pb, Ni, and Mn maximum extraction efficiencies were 35.10 ± 2.31%, 45.33 ± 3.24%, 27.58 ± 3.35%, 24.12 ± 3.51%, 43.31 ± 2.53% and 22.10 ± 2.11%, respectively; most of exchangeable and reducible fractions, and partly oxidizable and residual fractions have been extracted by the rhamnolipid solution. After treatment, IR values of heavy metals increased in the treated sludge, the IR values for Cu, Zn, Cr, Pb, Ni, and Mn were 0.24 ± 0.01, 0.25 ± 0.03, 0.21 ± 0.02, 0.32 ± 0.03, 0.22 ± 0.021 and 0.41 ± 0.03, respectively. MF values indicated that heavy metal mobility order was Zn>Ni>Cu>Mn>Cr>Pb in the treated sludge. According to the two risk assessment methods (risk assessment code, RAC and potential ecological risk index, PERI), the risk assessment of heavy metal was investigated in the after treatment sludge, which indicated that rhamnolipid could extract the mobility of heavy metal and lead to no or low risk to the ecosystem. Therefore, rhamnolipid was utilized to enhance heavy metal extraction from dewatered sludge in this study, which is a promising technique for heavy metal extraction from the dewatered sludge.

TiTaCN-Co Cermets Prepared by Mechanochemical Technique: Microstructure and Mechanical Properties

Microstructure and mechanical characterization of (Ti,Ta)(C,N)-Co based solid solution cermets prepared by two mechanochemical synthesis processes (one- and two-step milling) and a pressureless sintering in protective helium atmosphere. Materials with composition of TixTa1-xC0.5N0.5-20%Co with two different Ti/Ta ratios (x = 0.9 and x = 0.95) were developed to prepare four groups of experimental materials. Microstructures were observed using confocal microscopy and grain size was evaluated using image analysis. Mechanical testing was carried out using nanoindentation equipment and nanohardness and indentation Young's modulus were obtained. Mechanical properties of individual phases were measured using single load/unload method with 20 mN maximum load (40 mN/min loading rate and maximum 10 s holding time for each indent). Mechanical properties of each material as a bulk were obtained also by single load/unload method with 300 mN maximum load (600 mN/min loading rate and maximum 10 s holding time). The resulting mechanical properties were comparable to that of typical industrial hardmetal cermets. Two-step milling resulted in finer microstructure but a wider range of grain size distribution. No significant dependence between mechanical properties and number of milling steps was found. However, the materials with higher amount of Ta showed slightly higher indentation elasticity modulus.

Distribution of dissolved manganese in the Peruvian Upwelling and Oxygen Minimum Zone

The geochemistry of manganese (Mn) in seawater is dominated by its redox chemistry, as Mn(II) is soluble and Mn(IV) forms insoluble oxides, and redox transformations are mediated by a variety of processes in the oceans. Dissolved Mn (DMn) accumulates under reducing conditions and is depleted under oxidizing conditions. Thus the Peruvian upwelling region, characterized by highly reducing conditions over a broad continental shelf and a major oxygen minimum zone extending far offshore, is potentially a large source of Mn to the eastern Tropical South Pacific. In this study, DMn was determined on cruises in October 2005 and February 2010 in the Peruvian Upwelling and Oxygen Minimum Zone, to evaluate the relationship between Mn, oxygen and nitrogen cycle processes. DMn concentrations were determined using simple dilution and matrix-matched external standardization inductively coupled mass spectrometry. Surprisingly, DMn was depleted under the most reducing conditions along the Peruvian shelf. Concentrations of dissolved Mn in surface waters increased offshore, indicating that advection of Mn offshore from the Peruvian shelf is a minor source. Subsurface Mn maxima were observed within the oxycline rather than within the oxygen minimum zone (OMZ), indicating they arise from remineralization of organic matter rather than reduction of Mn oxides. The distribution of DMn appears to be dominated by non-redox processes and inputs from the atmosphere and from other regions associated with specific water masses. Lower than expected DMn concentrations on the shelf probably reflect limited fluvial inputs from the continent and efficient offshore transport. This behavior is in stark contrast to Fe, reported in a companion study which is very high on the shelf and undergoes dynamic redox cycling.

Hydrogeochemistry and arsenic contamination of groundwater in the Jianghan Plain, central China

Although high arsenic groundwater has been reported in the northwest of China, no data describing groundwater arsenic in the river plains of central China have been published to date. In this study, 186 groundwater samples were collected from the Jianghan Plain between the Yangtze and Han rivers. Major constituents, trace elements, dissolved organic carbon (DOC), and stable hydrogen and oxygen isotopic compositions were analyzed to characterize groundwater chemistry and evaluate the factors controlling arsenic concentration and distribution in the plain. The results show that the groundwater is mainly HCO3–CaMg type with circum-neutral pH and moderate to high electrical conductivity. Negative Eh and high concentrations of DOC clearly indicate strongly reducing conditions with abundant organic matter in the groundwater aquifers. The characteristics of H/O stable isotopes demonstrate that the groundwater in the study area is recharged by local precipitation and there is a slow evaporation effect. Groundwater with high arsenic was found in wells at depths of 10 to 45m along rivers. About 87% of the groundwater samples had As concentrations exceeding the WHO recommended value of 10μg/L, up to 2330μg/L. High concentrations of dissolved Fe (maximum value, 23mg/L), Mn (maximum value, 5mg/L) and P (maximum value, 4mg/L) were also observed in groundwater. Among the wells, 89% and 98% exceeded the WHO guideline for Fe and Mn, respectively. The concentrations of total As measured in sediments from the Jianghan Plain were much higher than the global average, ranging from 11 to 108mg/kg. All of the sediments had high Fe (Fe2O3 4–9%) and Mn (504–1064mg/kg) levels, which is consistent with Fe and Mn oxides/hydroxides considered to be the dominant minerals containing As in sediments and the main sources for As in groundwater of the Jianghan Plain. The main potential mechanism for the release of As is the reductive dissolution of Fe and Mn oxides/hydroxides under reducing conditions, while microbial degradation of organic matter may also facilitate the release of arsenic into groundwater. The competitive effects of other anions may also be important factors since the concentrations of DOC, HCO3− and dissolved P were high in many of the groundwater samples.

Die Forging of High-Strength Magnesium Alloys – the Structure and Mechanical Properties in Different Heat Treatment Conditions / Kucie Matrycowe Wysokowytrzymałych Stopów Mg – Struktura I Własciwosci Mechaniczne W Róznych Stanach Obróbki Cieplnej

The object of this study was to develop parameter of the die forging process, such as feedstock temperature and to investigate her impact on the structure and mechanical properties of magnesium alloys in different heat treatment conditions. Tests were carried out on a 2,5MN maximum capacity vertical hydraulic press using forgings of sample (model) shapes. Then, based on the results obtained in previous work, research was carried out to develop for items forged from magnesium alloys the parameters of heat treatment to the T5 and T6 condition in the context of achieving possibly homogeneous and fine-grained structure and, consequently, high mechanical properties.

Fluvial and hydrothermal input of manganese into the Arctic Ocean

A total of 773 samples were analysed for dissolved manganese (Mn) in the Arctic Ocean aboard R.V. Polarstern during expedition ARK XXII/2 from 28 July until 07 October 2007 from Tromsø (Norway) to Bremerhaven. Concentrations of Mn were elevated in the surface layer with concentrations of up to 6 nM over the deep Basins and over 20 nM in the Laptev Sea. The general distribution of Mn through the water column is consistent with previous studies, but there are differences in the absolute concentrations that are most likely related to differences in sample area, sampling and filtration. The elevated concentrations of Mn in the surface layer are related to fresh water input. This was visible in the strong negative correlations observed between dissolved Mn and salinity. The correlation between Mn and salinity and the correlation between Mn and the quasi conservative trace water mass tracer PO 4 ∗, showed fluvial and melt water input and the Pacific and Atlantic origin of the surface waters. A large portion of the Mn delivered by the Arctic rivers is removed in the shelf seas and does not pass into the central basins. Most likely a benthic flux is at the origin of the elevated concentrations of Mn near the sediments in the Barents and Kara Seas. These elevated concentrations of Mn apparently affected the deep basins as well, as maxima in the concentrations of Mn were observed that corresponded with lowered transmission over the continental slope. A maximum in the concentration of Mn in the deep basin corresponded with anomalies in light transmission, potential temperature and dissolved iron, confirming the hydrothermal origin. The hydrothermal plume was observed throughout the Nansen Basin and over the deep Gakkel Ridge around 2500 m depth and a smaller plume was observed around 3200 m. The concentration of Mn at the Mn maximum around 2500 m depth decreased exponentially, consistent with a first order scavenging model. The concentrations of Mn were extremely low in the deep Makarov Basin (∼0.05 nM) and slightly higher in the Eurasian Basin (∼0.1 nM) outside the influence of the hydrothermal activity.

Trace Metal Bioaccumulation by Soft-bottom Polychaetes (Annelida) of Sundarban Mangrove Wetland, India and Their Potential Use as Contamination Indicator

Bioaccumulation of trace metals in four soft-bottom polychaetes along with the host sediments was recorded from the intertidal regions of Indian Sundarban mangrove wetland. The enrichment of Mn (maximum 730 mg kg⁻¹) and Zn (maximum 320 mg kg⁻¹) was recorded for all the polychaetes followed by Cr, Cu, As, Co, Ni and Pb, showing sharp variations between the species. However, concentrations of Sn and Hg were very low with small variations between the species. An overall high bioconcentration factor (BCF) was recorded in the capitellid worm Mastobranchus indicus. The results of the investigation indicate the possibility of developing a standard test protocol for bioaccumulation by polychaetous annelids.

The Association of Cobalt with Iron and Manganese (Oxyhydr)oxides in Marine Sediment

Formation and dissolution of authigenic Fe and Mn (oxyhydr)oxides influence cycling of trace metals in oxic/suboxic surface sediments. We used the diffusive gradients in thin films technique (DGT) to estimate the association of cobalt with iron and manganese oxides. We compared Co, Fe and Mn maxima measured by DGT in the pore waters of fresh and aged marine sediment cores and estimated the Co/Fe and Co/Mn ratios in the metal oxides. A Mn maximum was not visible in DGT concentration profiles of freshly collected sediment cores, but after ageing the sediment, we observed a distinct Mn peak, presumably due to broadening of the depth range over which the various electron acceptors occur. Estimated Co/Mn ratios from both experiments are within the range of literature values for marine sediments, but the value from the aged experiment is at the lower end of the range. This is attributed to stimulation of sulphate reduction and precipitation of cobalt sulphides. The good correlation between Co and Fe maxima in the fresh sediments is attributed to the similarity of their reactions with sulphide rather than Co being released during authigenic Fe oxide reduction.