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.

Chelation of first-row transition metals has many useful properties in the biomedical and industrial fields due to the stabilizing and/or property-altering effects that certain chelates can induce in these metals. One such useful design principle for these chelates is the addition of bulky steric groups which can have an added effect on these properties. Chapter I will explore the origins of these effects and show examples of how these effects are leveraged to produce useful complexes in a variety of applications. In Chapter II, we will discuss our choice of ligand design and the development of related synthetic procedures for all organic portions of the complexes. In Chapter III, we then study the effects of the series of bulky ligands with Mn2+ and Zn2+ on the formation of thermodynamically and kinetically inert complexes and investigate the subsequent effects on redox properties. Chapter IV furthers this investigation with Fe2+ and Co2+ using the bulkiest and least bulky versions of our ligand, where these metal complexes are investigated for the effects on redox properties and spin states. Lastly, a brief appendix details work performed on pyridine-imidazole systems bound to Mn2+ for their potential use in water oxidation catalysis.

Binuclear mixed biscarbene complexes of bithiophene were synthesized via the classical Fischer method of synthesis. The metal carbonyls, Mo(CO)6, Cr(CO)6, W(CO)6 and Mn(MeCp)(CO)3 were reacted with dilithiated bithiophene to afford complexes of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(OEt})M'(CO)5] (in case of manganese, M(CO)5 is replaced with MMeCp(CO)2), where [M] and [M'] are the metal carbonyls in different combinations. Quenching was achieved with triethyl oxonium tetrafluoroborate. In all the reactions the products included monocarbene complexes, biscarbene complexes and the decomposition products. C-C coupling reactions produced unexpected biscarbene complexes of Cr, W, and Mo having extended bithiophene spacers. The complexes were of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(R)-C(R)C4H2S-C4H2SC(OEt})M'(CO)5] (R = O, OH or OEt). These complexes were characterized with NMR, infrared spectroscopy and some with mass spectrometry. Furthermore, three biscarbene complexes of the metal combinations Mo(CO)6 and Cr(CO)6, W(CO)6 and Cr(CO)6, and Mn(MeCp)(CO)3 and Cr(CO)6 were all reacted with 3-hexyne. The result was the benzannulation or the Dötz products. / Chemistry / M. Sc. (Chemistry)

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Environmental Health Faculty of Applied Sciences Cape Peninsula University of Technology / Soil contamination by metals is a serious environmental problem that has significant implications for human health. Roadside soils have been shown to have considerable contamination due to depositions of metals by vehicles. Metal pollution poses significant environmental concerns because most metals are not biodegradable and often have long half-lives, thus predicating far reaching effects on biological systems, including the soil. Unleaded petrol has been available in South Africa since 1996. The conversion from leaded to unleaded petrol has been a slow process. Leaded petrol has been totally phased out since January 2006. The manganese-containing fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT) that was introduced to automobile fuel formulae as an octane boosting and “anti-knock” agent, to replace or reduce the lead content in petrol, was officially approved in some developed countries. Despite the fact that metal contamination of soil has long been known, few studies have been carried out into its vertical distribution in the soil. The objectives of this investigation were: firstly, to assess the accumulation of lead and manganese in soil along the N1 highway; secondly, to determine the vertical distribution of lead and manganese in soil along the N1 highway; and thirdly, to compare the concentrations of lead and manganese in soil along the N1 highway, before and after the banning of leaded petrol in South Africa. Six soil samples were taken at each site approximately two meters from the road verges and at a depth of approximately 0-2cm of surface soil. The sampling period commenced on the 16th of February 2011 and ended on the 28th of December 2011. Once-off soil samples were also collected at sites 1, 5 and 6 at depths of 0-2cm, 30cm and 60cm, respectively. Samples were digested with 10 ml 55% nitric acid. Lead and manganese concentrations were determined by using Inductively Coupled Plasma Mass Spectrophotometer (ICP–MS). The mean concentrations of lead found in the roadside soils of the N1 highway ranged between 7.32mg/kg and 2068.31mg/kg and these were of high concentrations when compared to studies done in other countries. Results from the vertical distribution of lead investigation showed that lead concentrations ranged from 52.72mg/kg to 215.94mg/kg at surface level, from 15.80mg/kg to 164mg/kg at a depth of 30cm and from 14.06mg/kg to 216.07mg/kg at a depth of 60cm from the surface. It was also shown that there is a positive correlation between lead concentration and the amount of organic content (although not statistical), concluding that as the amount of organic content increases lead concentrations also increase. The mean manganese concentrations found in the roadside soils of the N1 ranged between 12.17mg/kg and 221.47mg/kg. The levels of manganese in the soil were found to be relatively low when compared to other studies an indication of mild to low metal contamination of the sampled soils. Results from the vertical distribution of manganese concentrations showed that concentrations in the soil ranged from 39.23 mg/kg to 63.32 mg/kg at surface level, from 14.4mg/kg to 310.86mg/kg for depths of up to 30cm, and from 4.42mg/kg to 343.96mg/kg for depths of up to 60cm. No relationships of manganese levels in the soil were found at any of the sites when sites were compared prior to the banning of lead and after the banning of lead despite the increased traffic volumes and, thus, increased MMT usage over the years, indicating that manganese contribution from MMT is very low and does not significantly increase soil contamination along the N1 highway. However, further investigations are needed into the future to monitor manganese contamination that may possibly occur.

Bibliography: leaves 131-153. This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.

The biogenic reduction of Mn(IV) oxides is one of the most favorable anaerobic electron transfer processes in aquatic systems and likely plays an important role in the redox cycle of both carbon and nitrogen in anaerobic environments; yet, the different pathways involved in the microbial transformation of Mn(IV) oxides remain unclear. The coupling between the reduction of Mn(IV) to Mn(II) and the oxidation of organic carbon to CO₂ is largely catalyzed by microorganisms in various environments such as redox stratified water columns and sediments. The recent discovery that soluble Mn(III) exists in natural systems and is formed during biological oxidation of Mn(II) implies the possibility that Mn(III) is formed as an intermediate during the microbial reduction of Mn(IV). In this dissertation, mutagenesis studies and kinetic analysis were combined to study the mechanism of microbial reduction of Mn(IV) by Shewanella oneidensis MR-1, one of the most studied metal-respiring prokaryotes. We show for the first time that the microbial reduction of Mn(IV) proceeds step-wise via two successive one-electron transfer reactions with soluble Mn(III) as intermediate produced in solution. The point mutant strain Mn3, generated via random chemical mutagenesis, presents a unique phenotype that reduces solid Mn(IV) to Mn(III) but not to Mn(II), suggesting that these two reduction steps proceed via different electron transport pathways. Mutagenesis studies on various in-frame deletion mutant strains demonstrate that the reduction of both solid Mn(IV) and soluble Mn(III) occurs at the outer membrane of the cell and Mn(IV) respiration involves only one of the two potential terminal reductases (c-type cytochrome MtrC and OmcA) involved in Fe(III) respiration. Interestingly, only the second electron transfer step is coupled to the respiration of organic carbon, which opposes the long-standing paradigm that microbial reduction of Mn(IV) proceeds via the single transfer of two electrons coupled to the mineralization of carbon substrates. The coupling between anaerobic nitrification and Mn reduction has been demonstrated to be thermodynamically favorable. However, the existence of this process in natural system is still in debate. In this dissertation, characterization of coastal marine sediments was combined with laboratory incubations of the same sediments to investigate the effect of Mn oxides on the redox cycle of nitrogen. Our slurry incubations demonstrate that anaerobic nitrification is catalyzed by Mn oxides. In addition, mass balance calculations on NH₄⁺ link the consumption of NH₄⁺ to anaerobic ammonium oxidation in the presence of Mn oxides and confirm the occurrence of Mn(IV)-catalyzed anaerobic nitrification. The activity of anaerobic nitrification is greatly affected by the initial ratio of Mn(IV) to NH₄⁺, the reactivity of Mn oxides, and the reducing potential of the system. Overall, Mn(IV)-catalyzed anaerobic nitrification may be an important source of nitrite/nitrate in anaerobic marine sediments and provide an alternative pathway for subsequent nitrogen losses in the marine nitrogen cycle.

Not available / text

Bibliography: leaves 131-153. / xiii, 153 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996

Binuclear mixed biscarbene complexes of bithiophene were synthesized via the classical Fischer method of synthesis. The metal carbonyls, Mo(CO)6, Cr(CO)6, W(CO)6 and Mn(MeCp)(CO)3 were reacted with dilithiated bithiophene to afford complexes of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(OEt})M'(CO)5] (in case of manganese, M(CO)5 is replaced with MMeCp(CO)2), where [M] and [M'] are the metal carbonyls in different combinations. Quenching was achieved with triethyl oxonium tetrafluoroborate. In all the reactions the products included monocarbene complexes, biscarbene complexes and the decomposition products. C-C coupling reactions produced unexpected biscarbene complexes of Cr, W, and Mo having extended bithiophene spacers. The complexes were of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(R)-C(R)C4H2S-C4H2SC(OEt})M'(CO)5] (R = O, OH or OEt). These complexes were characterized with NMR, infrared spectroscopy and some with mass spectrometry. Furthermore, three biscarbene complexes of the metal combinations Mo(CO)6 and Cr(CO)6, W(CO)6 and Cr(CO)6, and Mn(MeCp)(CO)3 and Cr(CO)6 were all reacted with 3-hexyne. The result was the benzannulation or the Dötz products. / Chemistry / M. Sc. (Chemistry)

M.Sc. (Geology) / Refer to full text to view abstract