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Thesis (Ph.D.(Physics)) -- University of Limpopo, 2020 / We employ molecular dynamics simulations, using DL_POLY code, to study the structural behaviour of β-MnO2 cathode material during discharging through lithium-ion intercalation into the bulk, nanoparticle, nanorod, nanosheet, and nanoporous β-MnO2. It is shown that lithium-ions have an average coordination number of about 5.70 and prefer surface sites with high oxygen coordination. The average lattice parameter values at intercalation of 0.85 Li/Mn are found to be under 4% relative to the experimental values obtained at 0.92 Li/Mn. Moreover, all the lithiated β-MnO2 structures did not collapse at 0.85 Li/Mn as observed in the β-MnO2 mesoporous in experimental work. As lithium is limited, sodium is a good alternative charge carrier in lithium-ion batteries. As a result, we have also performed studies on sodium intercalation into bulk, nanoparticle, nanorod, nanosheet and nanoporous β-MnO2. The microstructures and radial distribution functions show that the β-MnO2 structures could be intercalated up to 0.24 Na/Mn without any obvious structural degradation. Beyond this sodium concentration, the microstructure collapses and become amorphous thus predicting a potentially lower capacity for Na-MnO2-β batteries. Also, as the voltage is an important factor in the energy density of lithium-ion batteries, we have studied the trends in the average intercalation potentials in relation to the various nano architectures. The trend, in increasing value of average intercalation potentials, were found to be bulk structure, nanorod, nanosheet, nanoporous and nanoparticle. This suggests that nanostructuring can enhance cell voltage. Mechanical properties studies on the pure and lithiated bulk and nanorod β-MnO2 were also performed through uniaxial compressive and tensile strain application. The results show that under compressive strain the bulk structure and nanorod mitigate stress through the contraction and collapse of the inherent tunnel structures, known to cause electrochemical inactivity, and also through the shifting of the MnO6 octahedral planes. The collapsing of tunnels was found to occur more on the bulk structure and less on the nanorod, while the MnO6 octahedral plane shifts were found to occur more on the nanorod and less on the bulk structure. Unoccupied 1x2 or conjoined 1x2 were found to result in structural collapse irrespective of the host nanoarchitecture. The X-ray diffraction pattern (v) plots suggest that lithium intercalation and compressive stress application have a similar impact on the underlying structure of the various nanostructures. The microstructure analysis for bulk β-MnO2 under tensile strain reveals that fracture occurred in the brookite region and along the dislocation/stacking fault. The nanorod β-MnO2 mitigated stress through a rutile-to-brookite phase transition which occurred in the unstrained Li0.73MnO2-β and under tensile strain in LixMnO2-β for x = 0.00, 0.03, 0.12, and 0.24. In both the bulk and nanorod β-MnO2 the brookite phase was succeeded by structural breakdown leading to fracture and served as an indicator for imminent structural failure upon more tensile strain application. / National Research Foundation (NRF)

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2020. / This dissertation presents the results of the ab-initio based computational studies of spinel lithium manganese oxide (LiMn2O4) bulk, surfaces, and the adsorption of an organic electrolyte, ethylene carbonate. The spinel LiMn2O4 is one of the most promising cathode materials for Lithium-ion batteries because of its affordability, nontoxicity, and improved safety compared to commercially used LiCoO2. However, it also suffers from the irreversible capacity due to the electrolyte-cathode interactions which lead to manganese (Mn) dissolution. Using the spin-polarized density functional theory calculations with on site Coulomb interactions and long-range dispersion corrections [DFT+U−D3−(BJ)], we investigated the bulk properties, surface stability and surface reactivity towards the ethylene carbonate (EC) during charge/discharge processes. Firstly, we explored the structural, electronic, and vibrational bulk properties of the spinel LiMn2O4. It was found that the bulk structure is a stable face-centred cubic structure with a bandgap of 0.041 eV and pseudo-gap at the Fermi level indicating electronic stability. Calculated elastic constants show that the structure is mechanically stable since they obey the mechanical stability criteria. The plotted phonon curves show no imaginary vibrations, indicating vibrational stability. To study the charge/discharge surfaces, we modelled the fully lithiated and the partially delithiated slabs and studied their stability. For the fully lithiated slabs, Li-terminated (001) surface was found to be the most stable facet, which agrees with the reported experimental and theoretical data. However, upon surface delithiation, the surface energies increase, and eventually (111) surface becomes the most stable slab as shown by the reduction of the plane in the particle morphologies. Finally, we explored the surface reactivity towards the ethylene carbonate during charge/discharge processes. The ethylene carbonate adsorption on the fully lithiated and partly delithiated facets turn to enhance the stability of (111) surface. Besides the strong interaction with the (111) surfaces, a negligible charge transfer was calculated, and it was attributed by a large charge rearrangement that takes place within the surfactant upon adsorption. The wavenumbers of the C=O stretching showed a red shifting concerning the isolated EC molecule

A research project assessing the effectiveness of potassium permanganate (KMnO4) for the treatment of iron (Fe) and manganese (Mn) has been conducted by the University of Central Florida (UCF) on behalf of the United States Navy with regards to the water supply on the island of Guam, located in the Marianas Islands. The study consisted of three basic investigative components: one that examined the use of potassium permanganate for iron and manganese control for Fena Lake, a second that examined the existing unit operations that comprised the Navy's water treatment plant (NWTP), and a third that examined iron and manganese field sampling analytical procedures. In the first and primary component of the research, surface water from Fena Lake located within the Naval Magazine in proximity of Santa Rita, Guam was collected at several different lake depths and initially analyzed for iron and manganese using inductively coupled plasma. Subsequent aliquots of Fena Lake collected at the various water depths were transferred to jars then dosed with varying amounts of potassium permanganate after which iron and manganese content was determined. The jars were covered to simulate actual lake to plant transfer conditions experienced at the Navy's on-island facilities. A portion of the jars was dosed with potassium permanganate prior to metals analysis in order to allow for comparisons of baseline conditions. To represent conventional treatment processes, the water samples were then coagulated with aluminum sulfate prior to filtration to remove the oxidized manganese and iron formed from the addition of the potassium permanganate. Coagulated aliquots were filtered and collected to evaluate residual dissolved iron and manganese content. Based on the results of the jar tests it was determined that manganese was reduced by 95% or greater and that iron was completely removed to below the analytical detection limit (0.001 mg/L). It was determined that the potassium permanganate dose required for oxidation of iron was 0.94 mg/mg iron and for manganese was 1.92 mg/mg manganese. It was also observed that when the jars containing aliquots that turned brown in color after potassium permanganate dosing meant that iron and manganese were present and were being oxidized; however, water samples that turned pink were found to be over-dosed with potassium permanganate. The pink water is an undesired characteristic and could result in customer complaints when distributed to the system. The second component of research focused on NWTP existing conditions. Water samples were collected after each key unit operation within the NWTP and analyzed for iron and manganese. This was to determine if pre-chlorination at Fena Lake was effective at removing iron and manganese that could be present in the source water. Analysis was conducted where pre-chlorination at Fena Lake was practiced as well as when no pretreatment was practiced prior to the NWTP. It was determined that the iron and manganese were not detected downstream of the coagulation unit operation within the NWTP even when pre-chlorination was not practiced. Consequently pre-chlorination of Fena Lake source water was not required for controlling iron and manganese under the conditions experienced in this study. A third study was also implemented to confirm that 0.1-micron filters are appropriate for use in preparing samples for analytical determination of iron and manganese analysis at various points within the NWTP. The filtration step is important to delineate between dissolved and suspended iron and manganese forms. Standard Methods 3120B recommends the use of 0.45-micron filters, although based on literature it has been shown that oxidized manganese particles may be smaller than a 0.45-micron pore size. Unless a coagulant was used, the oxidized manganese may not be fully removed via the 0.45-micron filter. To verify the effectiveness of using a 0.1-micron filter, a jar test was conducted to compare the use of a 0.1-micron filter, a 0.45-micron filter, and a 0.45-micron filter after the sample has been coagulated. It was found that the use of a 0.1-micron filter was superior to the use of 0.45-micron filters even with coagulant addition when directly comparing between dissolved and suspended iron and manganese forms. It is recommended that 0.1-microns be utilized in lieu of historically recommended 0.45-micron filters for sample preparation procedures.

Take-all is the most devastating root disease of wheat worldwide. The causal agent is <I>Gaeumannomyces</I> <I>graminis</I> (Sacc.) Arx & Olivier. Based on morphological characteristics and host ranges, three varieties of <I>G</I>. <I>graminis</I> have been recognized. <I>G</I>. <I>graminis</I> var. <I>tritici</I> Walker (Ggt) is the major causal agent of take-all of wheat and barley and the most economically important take-all pathogen. <I>G</I>. <I>graminis</I> var. <I>avenae</I> (Turner) Dennis (Gga) attack oats and causes take-all patch of turf grasses while <I>G</I>. <I>graminis</I> var. <I>graminis</I> (Ggg) is pathogenic on turf grasses but is non-pathogenic on wheat. Conventional diagnosis of take-all pathogens is based on field symptoms such as blackened roots, stunted growth, and white-heads and morphological characteristics such as hyphopodia type, size of perithecia, asci, and ascospores. These procedures are time-consuming, laborious, and often inconclusive. The objective of this study was to develop a rapid, simple, and specific method for differentiation of <I>G</I>. <I>graminis</I> varieties using PCR and molecular-based technology. Exploitation of genes associated with pathogenicity of <I>G</I>. <I>graminis</I> as markers for the test was proposed. Metabolic activities of <I>G</I>. <I>graminis</I> associated with pathogenesis were investigated, namely, the abilities to produce avenacinase and to oxidize manganese. Avenacinase, an avenacin detoxifying enzyme, was associated with Gga pathogenicity for oats but this enzyme is not important in Ggt pathogenicity for wheat. Manganese oxidation was also correlated with Ggt virulence. In this study, avenacinase-like genes were discovered in Ggt and Ggg and manganese oxidation was confirmed for Ggt, Gga, and Ggg. All isolates of Ggt except isolate ATCC 28230 were manganese oxidizers. Ggg and Gga isolates could oxidize manganese but their precipitation patterns were not as intense or closely correlated with mycelial growth as for Ggt. Pathogenicity assays on oats for Ggt, Gga, and Ggg isolates confirmed that Ggt isolates could not cause disease on oats aside from occasional slight root damage. Root weight was reduced for oat seedlings inoculated with Gga isolates. Comparison of partial sequences of avenacinase-like genes from Ggt and Ggg showed strong homology to that of Gga (94.8% identity to Ggt and 94.6% identity to Ggg). However, the Ggt gene was more closely related to that of Ggg (99.2% identity) than to Gga. DNA restriction endonuclease polymorphisms of the genes supported DNA sequencing information and revealed that there were variations within the genes among Ggt, Gga, and Ggg. Variety-specific electrophoretic patterns were obtained when the genes were digested with <I>Hae</I>III. Ggt, Gga, and Ggg upstream (5') variety-specific primers and a downstream (3') universal primer were designed from the avenacinase and avenacinase-like DNA sequences. PCR amplification with Ggt-, Gga-, and Ggg-specific primers generated fragments of 870, 617, and 1,086 bp, respectively. Each 5'-specific primer showed high specificity for its own DNA template in mixed populations of DNA templates. The optimized PCR procedure was sensitive to DNA template concentration as low as 100 pg. Genomic DNA of sixteen Ggt isolates, seven Gga isolates, and five Ggg isolates were tested. Although all Ggt isolates were originally isolated from wheat, seven isolates produced Ggg-specific fragments. This result corresponded well with <I>Hae</I>III DNA polymorphisms, pathogenicity assay, and manganese oxidizing ability. All but one Gga isolates produced the variety-specific fragment. Ggt- and Gga- specific products were generated from Gga isolate RB-W. Although Ggg-specific fragments were produced from all Ggg isolates, non-specific products were also observed from isolates that were not from wheat origin suggesting some genetic variations due to host ranges. Additionally, no non-specific amplification was obtained from any closely related fungi such as <I>Gaeumannomyces</I> <I>cylindrosporus</I> or <I>Phialophora</I> spp. The test developed in this study is the first test capable of identification of Ggt, Gga, and Ggg in a single PCR tube with a basic PCR protocol. The test is rapid and specific. Interpretation of results is simple and conclusive based on differences in size of each variety-specific fragment. / Ph. D.

No / To interpret nitrogen sintering of chromium and manganese steels without the formation of deleterious oxides, but with manganese and carbon the formation of deleterious oxides, but with manganese and carbon modifying the local microclimate, the role of the volatile Mn and modifying the local microclimate, the role of the volatile and Mn carbothermic reactions were considered. carbothermic reactions were considered. Reduction of Cr Reduction of Cr 2 2 O About 3 3 by Mn vapour by Mn vapor is always favourable. is always favorable. CO is an effective reducing agent, however, whereas CO is an effective reducing agent, however, whereas at atmospheric pressure it will reduce FeO at730°C, temperatures some at atmospheric pressure it will reduce FeO at730 ° C, temperatures some 500 and 700°C higher, ie above those for conventional sintering, are 500 and 700 ° C higher, ie above those for conventional sintering, are necessary for reducing Cr necessary for reducing Cr 2 2 O About 3 3 and MnO, respectively. and MNO, respectively. Accordingly partial Accordingly partial pressures must be considered and the sintering process is modelled at a pressures must be considered and the sintering process is modeled at a conglomerate of several surface oxidised alloy particles surrounding a pore conglomerate of several surface oxidised alloy particles surrounding a pore with graphite present and a tortuous access to the nitrogen-rich atmosphere with graphite and present a tortuous access to the nitrogen-rich atmosphere containing some water vapour and oxygen. containing some water vapor and oxygen. The relevant partial pressures The relevant partial pressures were calculated and reduction reactions become thermodynamically were calculated and reduction reactions become thermodynamically favourable from 200°C. favorable from 200 ° C. Kinetics, however, dictates availability of CO and Kinetics, however, dictates availability of CO and the relevant reactions are the water-gas, C + H the relevant reactions are the water-gas, C + H 2 2 O = CO + H O = CO + H 2 2 from 500°C from 500 ° C and the Boudouard, C + CO and the Boudouard C + CO 2 2 = 2CO, from 700°C. = 2CO, from 700 ° C. Discussion of sintering Discussion of sintering mechanisms is extended to processing in semi-closed containers, also mechanisms is extended to processing in a semi-closed containers, also possessing specific microclimates.

Magnetic Structure of antiferromagnetic Mn₂P₂O₇ at 4.2º K has been established by neutron diffraction from a powder specimen. The magnetic unit cell is found to be the same size as the chemical unit cell. The spins are arranged in ferromagnetic sheets with the moments in each sheet aligned antiferromagnetically relative to its adjacent sheets. Neutron diffraction results in regard to the critical temperature (13±3)º K, and the spine being at an angle of 23º from the a-axis in the a-c plane have been found consistent with the ones obtained by Fowlis, Atkinson, Choh and Stager by susceptibility and NMR studies on the material. However, to confirm the angle with some precision, more work, probably with a single crystal, will be required. / Thesis / Master of Science (MSc)

<p> The oxidation kinetics of iron-manganese alloys with manganese contents up to 60 w/o exposed to carbon dioxide-carbon monoxide atmospheres at 1000°C have been determined as a function of gas composition by a gravimetric technique. The experimental conditions were chosen in order that the product of the reaction between metal and oxidizing atmosphere would be a single-phase oxide scale.</p> <p> The main objective of this study was to determine the oxidation characteristics of iron-manganese alloys. It has been found that the rate of oxidation of alloys up to 12% manganese at the early stages is limited by interfacial reaction control and later by diffusion processes in the oxide scale. Oxidation rates of alloys containing more than 27% manganese are entirely controlled by diffusion in the oxide scales. The experiments show that the linear oxidation rate is independent of alloy composition. On the other hand, the rate of parabolic oxidation becomes lower with increasing manganese content in the alloy.</p> <p> The results from gravimetric measurements and chemical analyses have been interpreted by a model for the diffusion of iron and manganese through the wustite scale. The phenomenological equations from this theoretical approach have enabled calculations of self-diffusion coefficients for iron and manganese and the concentration of defects in the FeO-MnO solid solution as a function of MnO content. The calculated defect concentrations are compared with theoretical models assuming different types of defect structures.</p> / Thesis / Master of Engineering (MEngr)

<p> The magnetic structures of antiferromagnetic manganese pyrophosphate and copper pyrophosphate have been determined by single crystal neutron diffraction techniques. More detailed features of the magnetic structure have been determined by nuclear magnetic resonance (NMR). A discrepancy between previous NMR measurements on Mn2P2o7 and the single crystal neutron measurements was resolved by postulating a low temperature crystallographic phase transition. Information about the dependence of the transferred hyperfine interaction upon the separation of the relevant ions is obtained for Cu2P2o7 from the NMR data and from previously determined deviations from a higher symmetry phase. The origin of the magnetic anisotropy energy in Cu2P2o7 is discussed. </p> / Thesis / Doctor of Philosophy (PhD)