Aims and objectives: The general aim of this study was to determine the personal respiratory exposure and biological monitoring of manganese (Mn) present in welding fumes as well as its neurological influence on welders. The objectives of this study were: (i) to assess the respiratory exposure of welders to Mn present in welding fumes; (ii) to assess the biological Mn load of welders via the use of nail clippings; (iii) to establish possible correlations between respiratory exposure to Mn and its presence in nail clippings, and (iv) to determine the possible difference in finger dexterity and coordination between Mn exposed welders and a control group. Methods: A gravimetrical method was used to determine the respiratory exposure of welders. A cassette containing a 0.8-μm, cellulose ester membrane filter, attached to the side of a welding helmet provided, was connected via a stainless steel fitting to the inside (respiratory zone) of the helmet. Chemical analysis (metal content) of the welding fumes was done according to the NIOSH 7300 method, using Inductively Coupled Argon Plasma, Atomic Emission Spectroscopy (ICP-AES). Nail clippings were collected at the beginning and end of the study to determine the Mn level in the nails in both welders as well as paired controls. The nails were deposited into small, plastic vials and also analysed according to the NIOSH 7300 method. A Perdue pegboard and mirror drawing test was also conducted to determine the influence of Mn exposure on finger dexterity and hand-eye coordination of welders. Results: Mn exposure in the welding fumes did not exceed the occupational exposure limit – recommended limit (OEL-RL) (1 mg/m3) of the Regulations for Hazardous Chemical Substances (RHCS), although two of these exposures exceeded the action level (0.5 mg/m3). No statistical significant correlations were found between the Mn respiratory exposure and the Mn found in the nails of the welders. Mn in the nails of exposed welders was statistical significantly higher (p = 0.003) than that of controls. The only statistical significant differences found in the motor function tests between the controls and welders were the test which was done by using their non-dominant hand in the beginning of the study (p = 0.016) and when the non-dominant hand values were pooled (p = 0.012). The usage of both hands simultaneously showed results that leaned toward statistical significant decrease of the welders compared to the control subjects (p = 0.090). In all these cases the controls inserted more pins than the welders. Only one moderately positive correlation (r = 0.612; p = 0.02) was found between Mn in the welding fumes and the number of errors made in the mirror drawing coordination test done by the welders. Discussion and Conclusions: The Mn in the nails of the control group was significantly lower than the Mn in the nails of the welders. This indicates that Mn respiratory exposure may influence Mn body burden although no correlation between Mn in welding fumes and Mn in nails were found. Nail Mn may serve as a biomarker to determine Mn body burden. Only the use of the non-dominant hand of the control subjects compared to the welders showed a significant decrease in finger dexterity of the welders. The moderately positive association between the Mn in the welding fumes and the number of errors made in the mirror drawing coordination test done by the welders indicates that with an increase in Mn in welding fumes, a decrease in hand-eye coordination will occur. It can be concluded that welders’ finger dexterity and hand-eye coordination may be influenced by the exposure to Mn in the welding fumes. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013

The crystallographic and magnetic properties of manganese oxides belonging to the Ruddlesden Popper (RP) series, described by the formula A_n+1B_nO_3n+1, are presented. Compounds having n = 2, 3 and ∞ are discussed in Chapters 3, 4 and 5, respectively, their properties being studied by powder X-ray and neutron diffraction, SQUID magnetometry and magnetotransport measurements. In Chapter 3 (A₃B₂O₇) it is shown that Sr_2-xNd_1+xMn₂O₇ (0 ≤ x ≤ 0.5) and Sr₂PrMn₂O₇ exhibit colossal, negative magnetoresistance (CMR) below 150K. The zero field resistivity signal is reduced by 2-3 orders of magnitude in a field of 14T, at ~4.2K. The compounds Sr₂HoMn₂O₇ and Sr₂YMn₂O₇ show no significant magnetoresistance. In contrast to the tetragonal Sr,Nd and Sr,Pr compositions, these compounds show a symmetry lowering to space group P4₂/mnm, and spin glass freezing on the Mn sublattice at ~20K. Chapter 4 (A₄B₃O₁₀) focuses on A- and B-cation substitutions in the parent compound Ca₄Mn₃O_10-δ. Substitution of Ca by Sr yields Sr₄Mn₃O_10-δ, an orthorhombic (Cmca) compound, composed of trimers of face sharing octahedra. The magnetic susceptibility of this sample is interpreted in terms of direct and indirect antiferromagnetic (AFM) Mn-Mn exchange interactions. The orthorhombic (Pbca) RP phase Ca_3.95La_0.05Mn₃O_10-δ has a magnetic transition at ~114K, suggesting that the antiferromagnetic groundstate, with associated weak ferromagnetism arising through the Dzyaloshinsky-Moriya interaction observed in Ca₄Mn₃O_10-δ, is preserved on introduction of a fraction of La³⁺ dopant cations. Ca_3.95La_0.05Mn₃O_10-δ displays CMR at 4K, with the resistivity signal reduced to 18% of the zero field value, in 14T. B-cation substitution yields Ca₄Mn₂TiO_9.93, an orthorhombic (Pbca) RP phase in which the Mn:Ti cation distribution, deduced from the combined results of anomalous dispersion X-ray experiments and neutron diffraction studies, is 59.8%(2.6):40.2%(2.6) and 70.1%(1.3):29.9%(1.3) across the 4b and 8c octahedral sites, respectively. Neutron diffraction studies at 5K show the presence of only short range magnetic interactions in this insulating material, the resistivity of which is reduced by just 10% at 75K in 14T. Chapter 5 (ABO₃ or A₂BB'O₆) describes the mixed B-cation phases, La₂GaMnO₆ and Nd₂GaMnO₆, containing Mn³⁺, 3d⁴ cations. Both are cation disordered, orthorhombic (Pnma) materials, and Nd₂GaMnO₆ exhibits a static, cooperative Jahn-Teller (JT) distortion. La₂GaMnO₆ contains a relatively higher proportion of dynamic, cooperative JT distortions, and as such exhibits isotropic ferromagnetism at 5OK and 5K (2.80(5)μ_B per Mn aligned along y at 5K), predicted by the 'quasistatic hypothesis', which describes the correlation between electron spin configurations of neighbouring JT cations. The magnetic structure of Nd₂GaMnO₆ at 5K and 1.7K is modelled as 'A_X F_Y G_Z' for the Mn sublattice, and 'F_γ' for the Nd sublattice, using Bertaut's notation, resulting in competing ferromagnetic and antiferromagnetic superexchange interactions on the Mn sublattice along the [010] direction of the unit cell. Both materials are highly insulating and neither displays CMR, with resistivity values in each being reduced to just 96% of the zero field value at 200K, in a field of 14T.

No description available.

Graduation date: 1987

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.

Manganese furnace dust is made up of volatiles and fine particles of the raw materials collected from the off-gas during smelting of manganese alloys. Impediments to the recycling of the manganese furnace dust back to the ferroalloy furnaces are handling due to the presence of tar, and the potential accumulation of zinc in the furnaces, which can cause irregularities in their operation. The aim of the thesis was to establish conditions for zinc removal from the dust and assess the feasibility of the dust recycling in the Tasmanian Electrometallurgical Company sinter plant. Major findings are: - Manganese furnace dust taken from the settling ponds contained water, carbonaceous materials (tar), and metal oxides. The carbon content of the dried furnace dust was about 20% and the average manganese and zinc contents were 33.4 and 1.29%, respectively. Moisture content was 30-60%. - The tar components were aliphatic hydrocarbons and polyaromatic hydrocarbons, their derivatives, and sulphur- and oxygen-containing compounds with a wide range of carbon number (15-28) and boiling point (230-530oC). Light hydrocarbons were not detected. - If manganese furnace dust was recycled to ferroalloy furnaces through the sintering plant, the overall zinc input had increased by 51-143%. Sustainable utilisation of manganese furnace dust should include enhanced zinc removal. - Reduction of zinc oxide from manganese furnace dust pellets started at 800oC. Zinc oxide was reduced to zinc vapour by tar in the dust. Temperature and gas atmosphere were key parameters affecting the zinc removal from the dust. The zinc removal rate increased with increasing temperature and was close to completion at 1100oC. - Optimal conditions for removal of zinc from the furnace dust include: temperature in the range 1000-1150oC, inert gas atmosphere and furnace dust fraction in the furnace dust-manganese ore mixture above 60%. - Zinc removal in the processing of manganese furnace dust in the sinter plant was low because of zinc reoxidation in the sinter bed. This makes the sinter plant unsuitable for recycling of the dust. More suitable conditions for utilisation of manganese furnace dust exist in the rotary hearth furnace, which development is recommended for further study.

Thesis (Ph. D.)--State University of New York at Binghamton, Multidisciplinary Program in Materials Science and Engineering, 2007. / Includes bibliographical references.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 2003. / Includes bibliographical references (leaves 285-292).

Thesis (PH. D.)--University of Chicago, 1918. / "Private Edition Distributed by the University of Chicago Libraries, Chicago, Illinois." "Reprinted from the Journal of Industrial and Engineering Chemistry, Vol. 11, No. 4, 1919." Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains viii, 46 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 43-45).