The study involves synthetic approaches towards the preparation of novel NHC complexes of low valent rhenium and manganese transition metals. Diverse methods of synthesis were studied. The direct approach, in which the ylidene obtained from deprotonation of 1,3-bis(2,4,6- trimethylphenyl)imidazolium chloride was added to the metal substrate, proved to be unsuccessful as isolation of the free carbene should rather be performed in an argon filled glove box under extreme inert conditions. By way of further investigation the ylidene was prepared by in situ methods and then quenched with the metal substrate. Different bases for deprotonation purposes and reaction conditions were explored. All routes employed were investigated and compared using group VII transition metal substrates Re(CO)5Br, Mn(CO)5Br, Re2(CO)10 and Mn2(CO)10. Isolation and purification of these products proved to be very challenging due to the insolubility in some organic solvents with consequent problematic spectroscopic analyses of the complexes. The tendency of the products to undergo various side reactions is observed in all reactions. Specifically, hydrolysis of the imidazolium ligand, followed by vinyl formation, yielded the mesitylformamide compound (3). The results obtained for some of the monometal substrates indicated that the target complexes were formed but could not be isolated. However, the synthesis route employing deprotonation by nBuLi as base and [Mn2(CO)10] as dimetal substrate lead to the isolation of the target dinuclear complex [Mn2(CO)9IMes] (9). Other novel complexes obtained during the course of this study include the biscarbene tetrarhenium complex [Re2(CO)9.C(OEt)C4H2OC(OEt)Re2(CO)9] (12) and various side reaction products. In many cases, metal-metal bond cleavage and carbonyl insertion was observed, as is evident in the complex IMesH[ReO4] (6) and ketene product (13). Structural and theoretical studies were performed to investigate the bond character between the carbene ligand and the metal. / Dissertation (MSc)--University of Pretoria, 2010. / Chemistry / unrestricted

East Fork Poplar Creek (EFPC) in Oak Ridge, TN was highly contaminated with elemental mercury in the 1950 and 1960. The area is still experiencing the effects of mercury contamination, and researchers are searching for ways to remediate the EFPC. One possible mechanism for bioremediation is the use of biogenic Mn oxides to remove heavy metals from water systems. Native Pseudomonas bacteria species were isolated from EFPC in order to examine biogenic Mn oxides production and bioremediation of Oak Ridge slurries. Pseudomonas isolates did produce Mn oxides which bound to mercury, and mercury bound to organic matter significantly decreased. However, after a significant decrease of dissolved mercury, dissolved mercury was cycled back into the water system on day 10. Given a longer experimental timeline, biogenic Mn oxides have the potential to decrease mercury cycling.

No description available.

BACKGROUND: While manganese (Mn) is essential for growth and development, evidence for Mn as a developmental neurotoxicant is mounting. However, inconsistencies in exposure metrics, susceptibility factors and neurobehavioral outcomes muddle the understanding of Mn effects on the developing nervous system. OBJECTIVE: To estimate Mn-neurobehavioral associations in varied neurobehavioral tasks and evaluate susceptibility factors (sex differences, co-exposures, exposure timing). METHODS: Research aims were conducted using the Public Health Impact of Mixed element Exposure (PHIME) study, including 720 Italian adolescents living near ferro-manganese industry. Blood, hair, nails, urine and saliva were collected in adolescence and metals [Mn, lead (Pb), copper (Cu), chromium (Cr)] were measured using ICP-MS. Mn was measured in deciduous teeth in a subset of participants (n=195) using LA ICP-MS to represent prenatal, postnatal and childhood exposure periods. Trained neuropsychologists administered a neurobehavioral battery to adolescents. In the first aim, we estimated associations of early-life Mn levels measured in deciduous teeth with visuospatial learning and memory, assessed using the Virtual Radial Arm Maze (VRAM), a novel animal-human translational neurobehavioral task. The second aim estimated associations of prenatal, early postnatal (0-1 year) and childhood (1~6 years) Mn measured in deciduous teeth with IQ scores and subtests measured by the Wechsler Intelligence Scale for Children (WISC-III). The third aim evaluated the association of a mixture of metals (Mn, Pb, Cu, Cr) measured in multiple biomarkers (hair, blood, urine, nails, saliva) and IQ. Data analysis included generalized additive models, linear regression, zero-inflated Poisson regression (for VRAM count outcomes), and Bayesian kernel machine regression (BKMR). RESULTS: In the first aim we observed U-shaped associations between prenatal Mn and VRAM outcomes among girls only, suggesting that low and high prenatal Mn levels may be harmful to visuospatial learning and memory. In the second aim, several associations were found with specific subtests that assess visuospatial ability, working memory, problem solving and attention, wherein estimates from the prenatal period suggested beneficial Mn associations, unlike the early postnatal and childhood periods. For the third aim we found inverse associations of adolescent Mn, measured either in hair or saliva, with verbal IQ (VIQ) scores, and an inverted U-shaped association for hair Cu. Strongest associations for the overall metals mixture were estimated with VIQ, where the joint increase in metals concentrations was associated with lower VIQ scores. / 2022-09-25T00:00:00Z

Yes / The effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe–3·5Mn–0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H2 /25N2 or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (20 K min-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (<-60°C), and a getter powder can all contribute to the reduction or prevention of oxidation of the manganese, in particular formation of oxide networks in the sintered steels. For 600 MPa compaction pressure densities up to 7·1 g cm-3 were obtained; these were not significantly affected by sintering at temperatures up to 1180°C. The sintered microstructures were sensitively dependent on the cooling rate. Irrespective of the presence of Mo, slow furnace cooling at 4 K min-1 resulted in mainly pearlitic structures with some ferrite and coarse bainite, whereas fast cooling at 40 K min-1 produced martensite and some retained austenite, very fine pearlite, bainite, and some ferrite. Young's modulus, determined by tensile and ultrasonic tests, was in the range 110–155 GPa. Sintering with -60°C dewpoint resulted in tensile and transverse rupture strengths of 420 and 860 MPa for the Mn steel, rising to 530 and1130 MPa as a result of the Mo addition. This contrasts with strength decreases observed when processing included use of high oxygen containing ferromanganese and sintering with -35°C dewpoint.

<p> The optical absorption in manganese fluoride has been studied in the range of 30 to 300 cm^-1 with emphasis placed on the possible multiple magnon absorptions (other than two-magnon) and an induced single magnon absorption. It is shown that theoretically one can expect four-magnon processes by expanding the Heisenberg spin hamiltonian to higher orders in the creation and annihilation operators introduced by the Holstein-Primakoff transformation. However, neither an induced one magnon nor four magnon process was observed. The absorptions which were seen in the spectra were attributed to phonon processes.</p> / Thesis / Master of Science (MSc)

This dissertation demonstrates that substantial ductility improvement is possible for low-manganese transformation induced plasticity steel compositions through the quenching and partitioning heat treatment approach using a Gleeble thermo-mechanical simulator. Two investigated compositions had unique microstructures and mechanical behavior from an identical applied quenching and partitioning process. Electron backscattered diffraction analyses indicate that Comp-2 and Comp-5 both contained retained austenite which resulted in enhanced ductility. The face-centered cubic phase (austenite) more efficiently mitigates strain incompatibilities when located at martensitic grain boundaries known for hot spots and damage initiation. This location effect leads to enhanced ductility and improved toughness in a lean, transformation induced plasticity steel. However, the increase in ductility in Comp-2 and Comp-5 is limited; the partitioning of carbon cannot stabilize austenite to reach strength/ductility targets set by the Department of Energy. Comp-2 and Comp-5 lack sufficient manganese to stabilize austenite to a higher degree. Chem-2A will be explored to determine if the partitioning stage can stabilize austenite closer to the martensite finish temperature. Periodic intercritical annealing will be applied to Chem-1A to see if mechanical properties can be increased further than current research values. Ultimately, through literature, Manganese is proven to be a more effective austenite stabilizer than carbon, and with tailored heat-treatment, the DOE targets can be reached.

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No description available.

<p> Cathodic electrodeposition method has been developed for the fabrication of manganese oxide films for application in electrochemical supercapacitors (ES). The manganese oxide films prepared from KMn04 and NaMn04 aqueous solution showed an increasing deposition yield with the deposition time. The deposition rate decreases with increasing the concentration of deposition precursor. The obtained films were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), thermogravimetric and differential thermal analysis (TGA/DTA). The SEM observations revealed uniform films of highly porous nanostructure on different substrates. The capacitive behavior of the deposits was investigated by cyclic voltammetry and chronopotentiometry method in 0.1M NaS04 aqueous solutions. As prepared deposits exhibited pseudocapacitive behavior in the potential window of 0-1.0 V versus SCE with excellent cyclability. A maximum specific capacitance (SC) of 353 Fig was obtained for the 45 μg/cm2 film deposited from KMn04 solution on stainless steel foil, at a scan rate of 2 m V /s in the 0.1 M Na2S04 solution. It was found that the SC decreased with increasing deposit thickness and scan rate. No significant effect was obtained on the films prepared from 20 mM KMn04 on stainless steel after heat treatment at various temperatures. The capacitance of as-prepared electrode did not change by changing the electrolyte from Na2S04 to K2S04 solutions. However, higher capacitance values were observed by using electrolyte with higher concentration. Different structures of manganese oxides were obtained when different deposition precursors were used. No significant difference in capacitive behavior was found between the films prepared from different deposition precursor. However it was concluded that conductivity of the film is key in determining the performance of the electrodes. The effect of substrates on the electrochemical behavior has also been investigated by using stainless steel and nickel foils. </p> / Thesis / Master of Applied Science (MASc)