The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows. ?? Rate and degree of reduction of MnO and ores increased with increasing temperature. ?? Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C. ?? Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C. ?? In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced. ?? Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore. ?? Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3. ?? Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control. ?? High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO. Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.

Primary cultured astrocytes were treated with Mn in the absence and presence of proinflammatory cytokines to determine their effect upon stimulation of nitric oxide (NO) production. Treatments of manganese and cytokines raised NO production to intermediate levels, whereas combined treatment raised NO creation to much greater levels. Furthermore, this combined treatment differed from control only in its ability to elevate cellular NO levels at 24 hours, but not at earlier time points. Combined exposure in astrocytes derived from mice lacking the nos2 gene prevented any increase in production of NO. Thus, manganese and cytokines enhance NO production through activation of the nos2 gene. Additionally, pharmacologic ligands of the peroxisome proliferator-activated receptor gamma (PPARγ) were used to test the role of this orphan nuclear receptor in modulating Mn-dependent production of NO. The agonist, 1,1-Bis(3’-indolyl)-1-(p-trifluormethylphenyl) methane (cDIM1) diminished NO in a dose-dependent manner, whereas addition of the PPARγ antagonist, GW 9662, amplified cellular NO production, also in a dose-dependent fashion. Moreover, it was observed that NO production was both attenuated and augmented at similar rates, suggesting the agonist and antagonist work through similar mechanisms. To clarify the means by which NO levels are manipulated by PPARγ, we measured activation levels of the transcription factor NF-κB, a primary factor resulting in expression of NOS2. We found that NF-κB was slightly activated in cells treated solely with manganese or cytokines, whereas cells treated with both manganese and cytokines showed the highest levels of activation. Also, we found that these ligands function through an NF-κB dependent mechanism. Treatment of cDIM1 to astrocytes already treated with manganese and cytokines caused decreased activation of NF-κB, while addition of GW9662 to similarly treated cells resulted in increased activation of NF-κB. While these compounds were effective at manipulating induction of the nos2 gene, they had no effect on induction of guanosine tri-phosphate cyclohydrolase (GTPCH) the rate limiting enzyme for the production of tetrahydrobiopterin (BH4), a cofactor essential to the conversion of arginine to NO, Thus, these novel PPARγ ligands can influence manganese- and cytokine-induced production of NO by an NF-κB dependent mechanism.

Thesis (Ph. D. in Physics)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 11, 2010). Includes bibliographical references (p. 42-45).

Thesis (M.S.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 62-64). Also available on the World Wide Web.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. On t.p. "x̲" is subscript. Document formatted into pages; contains viii, 34 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 30-31).

Despite the environmental significance of microbial manganese reduction, the molecular mechanism of microbial manganese respiration remains poorly understood. Soluble Mn(III) has been recently found to be a dominant soluble species in aquatic systems, yet little is known about the identity of microbial populations catalyzing Mn(III) reduction in the environment nor the molecular mechanism of Mn(III) respiration. In this research, a suite of Mn(III) reduction-deficient mutant strains were isolated, including Mn(III) reduction-deficient mutant strain Mn3-1 that also displayed the ability to reduce soluble organic-Fe(III), but not solid Fe(III) oxides, demonstrating for the first time that the reduction of soluble organic-Fe(III) and solid Fe(III) oxides proceed through electron transport pathways with at least one distinct component. This work also shows that the electron transport pathway for Mn(III) reduction in S. oneidensis shares many of the electron transport components of Fe(III) and Mn(IV) reduction pathways and that Mn(IV) reduction to Mn(II) proceeds step-wise through two one-electron transfer reactions with Mn(III) as a transient intermediate. Finally, sediment incubations were carried out to enrich for NH4+ oxidizing- Mn(III) reducing consortia. The Mn(III) reducing consortium was found to be dominated by an electrogenic Ochrobactrum sp. and a Shewanella sp. The isolated Shewanella strain is able to oxidize acetate with Mn(III) as electron acceptor, an activity never observed before in a metal-reducing member of the Shewanella genus.

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Lithium ion batteries have been successful in portable electronics market due to their high energy density, adopting the layered LiCoO₂ as the cathode material in commercial lithium ion cells. However, increasing interest in lithium ion batteries for electric vehicle and hybrid electric vehicle applications requires alternative cathode materials due to the high cost, toxicity, and limited power capability of the layered LiCoO₂ cathode. In this regard, spinel LiMn₂O₄ has become appealing as manganese is inexpensive and environmentally benign, but LiMn₂O₄ is plagued by severe capacity fade at elevated temperatures. This dissertation explores the factors that control and limit the electrochemical performance of spinel LiMn₂O₄ cathodes and focuses on improving the performance parameters such as the capacity, cyclability, and rate capability of various spinel cathodes derived from LiMn₂O₄. From a systematic investigation of a number of cationic and anionic (fluorine) substituted spinel oxide compositions, the improvements in electrochemical properties and performances are found to be due to the reduced manganese dissolution and suppressed lattice parameter difference between the two cubic phases formed during the charge-discharge process. Investigations focused on fluorine substitution reveal that spinel LiMn[subscript 2-yz]LiyZnzO[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by solid-state reactions at 800 °C employing ZnF₂ as a raw material and spinel LiMn[subscript 2-y-z]Li[subscript y]Ni[subscript z]O[subscript 4-eta]F[subscript eta] oxyfluoride cathodes synthesized by firing the cation-substituted LiMn[subscript 2-y-z]LiyNi[subscript z]O₄ oxides with NH₄HF₂ at a moderate temperature of 450 °C show superior cyclability, increased capacity, reduced Mn dissolution, and excellent storage performance compared to the corresponding oxide analogs and the conventional LiMn₂O₄. Spinel-layered composite cathodes are found to exhibit better electrochemical performance with graphite anode when charged to 4.7 V in the first cycle followed by cycling at 4.3-3.5 V compared to the normal cycling at 4.3 - 3.5 V. The improved performance is explained to be due to the trapping of trace amounts of protons that may be present in the electrolyte within the layered oxide lattice during the first charge to 4.7 V and the consequent reduction in Mn dissolution. Electrochemical performances of 3 V spinel Li₄Mn₅O₁₂ cathodes are also improved by fluorine substitution due to the suppression of the disproportionation of Li4Mn5O12 during synthesis and the formation of the Li₂MnO₃ phase.