Yes / Mechanical properties of 2-4% manganese PM steels were determined in tension and in bending following laboratory sintering in dry, hydrogen rich atmospheres. Young's modulus determined by an extensometric technique was about 115 GPa; when measured by an ultrasonic method it was about 153 GPa, in accordance with the 'law of mixtures'. The microstructures, significantly devoid of oxide networks, were predominantly pearlitic, but frequently with variability for specimens similarly processed, resulting in appreciable variations in the stresses for macroscopic yielding and fracture. The majority of the experiments were conducted on 3 and 4Mn-0·6C alloys and for these R0·1 was in the range 275-500 MPa, tensile strength (TS) 300-600 MPa, and (apparent) transverse rupture strength (TRS) 640-1260 MPa. Statistical techniques were employed to analyse the data. When careful control of processing was maintained, the Weibull modulus was highest, at about 17, for TS of furnace cooled specimens, and lowest, about 6, for TRS of the rapidly cooled specimens. In order to interpret the significant differences between the TRS and the TS values, both apparently measuring the critical stress for cracking after strains of up to 7%, a two stage normalising technique for TRS was adopted. By taking account of the plastic strains preceding failure, the elastic 'strength of materials' formula was modified to allow true fracture stresses to be calculated. It was also postulated that failure was initiated from a population of flaws of variable size and then the 'normalised' bend strengths, smaller than TRSs, were shown to correspond well with TSs. It is suggested that this combined plasticity correction and Weibull analysis approach, which has a sound scientific basis, should be employed to interpret bend test data in preference to empirical correlations between TS and TRS.

Elevated concentrations of iron (Fe) and manganese (Mn) in drinking water degrade water quality by affecting taste, odor, and color. Under oxic conditions (dissolved oxygen (DO) >2 mg/L), Fe and Mn are rarely present in soluble form in natural waters, as they occur as insoluble, oxidized minerals in sediments. However, the development of low DO concentrations in the bottom waters of some lakes and drinking water reservoirs during thermal stratification can lead to the reduction of oxidized, insoluble Fe and Mn in sediments to soluble forms, which are then released into the water column. In response, many water utilities have installed oxygenation systems to control metal concentrations in situ in drinking water reservoirs. However, previous research has found anoxic (DO < 0.5 mg/L) conditions still develop within sediments, even with operational oxygenation systems, allowing for the reduction and release of soluble Fe and Mn into the water column. To examine the drivers of metal release from sediments into the water column, I conducted sediment flux chamber experiments to directly quantify Fe and Mn fluxes at the sediment-water interface of a small, eutrophic drinking water reservoir (Falling Creek Reservoir, Vinton, VA). The experiments were conducted twice during the 2018 summer stratification period (April 24 – October 21). Using the flux chambers, I measured total and soluble Fe and Mn concentrations under changing oxygen conditions over 10-day periods to calculate fluxes. Throughout the experiments, I monitored DO, oxidation-reduction potential (ORP), temperature, and pH. In addition to the direct measurements, I also estimated metal fluxes using a mass balance method, which relies on measurements of metal inputs and outputs into the bottom waters of the reservoir. Overall, our results showed that fluxes are highly variable during the stratification period, with some periods having positive fluxes (release of metals from sediment to the water column) and some with negative fluxes (return of metals from the water column to sediment). The metal fluxes are highly sensitive to redox conditions in the water column, sediment-water interface and sediments. Metal fluxes measured using the chambers are 91-105% higher than those estimated using the mass balance method. This difference supports result of previous work that the flux chamber method likely provides maximum values of metal fluxes as the isolated chamber water does not allow for mixing with the bottom waters. In contrast, because the mass balance method relies on water column data, results are affected by mixing and biogeochemical reactions that can remove metals from the water column; thus, flux estimates using this method likely reflect minimum values. However, when used together, these two methods provide a useful tool for constraining metal fluxes under different redox conditions and highlight the importance of measuring ORP in addition to DO. The results of this study can be used by water utilities to improve the effectiveness of engineered oxygenation systems and water quality management practices related to iron and manganese. / Master of Science / In many drinking water reservoirs, elevated concentrations of metals, such as iron (Fe) and manganese (Mn), pose a challenging water quality problem. Elevated metal concentrations affect taste, color, and odor in drinking water and can be expensive to treat for. The presence of Fe and Mn in water is influenced by the oxygen concentrations in the water. When oxygen levels in the water are high, Fe and Mn are not soluble in water. However, when the oxygen levels in water are low, Fe and Mn can be released from soils, sediments and rocks into water and can thus pose a concern for drinking water quality. Many water utilities have installed systems to increase oxygen concentrations in drinking water reservoirs with the goal of maintaining low levels of metals in water supplies. However, previous research has shown that even when oxygenation systems are operational, Fe and Mn can still be released into water from the reservoir’s bottom sediments. To examine the factors that contribute to the release of metals from the sediments into the water column, I measured the rate of release of Fe and Mn from the sediments into the water column at a local drinking water reservoir (Falling Creek Reservoir, Vinton, VA). I conducted the experiments twice during summer 2018 using chambers that isolated the water immediately above the sediments. During the experiments, I monitored how Fe and Mn concentrations changed over time under different oxygen conditions. In addition to the measurements, I also used a mass balance method using water column data to estimate the metal release. Overall, results showed that release rates are highly variable during the summer months, with some periods having positive rates (releasing metals from sediments into the water column) and some with negative rates (returning metals from the water column to sediment). The metal release rate are highly sensitive to oxygen conditions in the water column, at the sediment-water interface and in the sediments. When used together, these two methods provide a useful tool for constraining metal release rates under different oxygen conditions. This research will help drinking water plant managers to improve the effectiveness of oxygenation systems and water quality management practices related to Fe and Mn. Additionally, this research will help improve the water quality for residents and can be applied to other lakes and reservoirs where metal concentrations are elevated.

Exposure to excess manganese via drinking water raises concerns due to potential for adverse neurological impacts, particularly in children. Manganese is ubiquitous in US groundwaters above the SMCL = 0.05 mg/L. Manganese is an essential nutrient, but exposures to elevated manganese have neurotoxic effects. Chapter 2 focuses on human senses\' ability to detect manganese in drinking water. Findings indicate human senses cannot be relied upon to detect excess Mn(II) in drinking water. Mn(IV) is easily visually detected, but cannot be tasted at 10 times the SMCL. Chapter 3 is an assessment the ability of an ultrasonic humidifier to expel drinking water impurities in aerosols. The quality of the water used to charge the humidifier reservoir affects the composition of elements in the aerosols and condensate. Findings indicate condensed humidifier aerosols contain 85% of elements present in the reservoir water for a variety of water types if there is no precipitation. Waters with high concentration of hardness or iron formed precipitates that decreased the concentrations of these metals in the aerosols causing variable results for other elements that were initially present at < 1mg/L in the charge water. This indicates that humidifiers could be a source of inhalation exposure for source water contaminants. / Master of Science

Medium-manganese steels (5-12 wt%) are candidates for third-generation advanced high strength steel (AHSS). Potential applications for these steels are centered around the automotive industry due to their combination of high tensile strength, high tensile ductility, and low alloying cost. Previous studies at VT have been primarily focused on the effect of chemistry on mechanical properties with only a minor emphasis on microstructure. This led to a detailed investigation into the effect of carbon content on the microstructure of Fe8Mn2AlSiC alloys. Six different chemistries with carbon contents of 0.30, 0.34, 0.39, 0.44, 0.49 and 0.52 wt% were produced at the Kroehling Advanced Materials Foundry. After a variety of heat treatments, the samples were characterized using x-ray diffraction (XRD), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), optical microscopy, and hardness testing. This thesis will discuss how the microstructure and hardness of these medium manganese steels is influenced by the carbon content. / Master of Science / This research will be used to help design steel alloys that might one day be used in automotive applications. These steels need to be tough and ductile so they can absorb impact without fracturing. This is especially important in the event of a car crash, in which the steel needs to deform without breaking and causing injury to the driver or passenger. In order to achieve such qualities today, expensive elements are often added to the steel which increases cost. Medium manganese steels hope to alleviate this issue by providing a less expensive alternative with similar deformation properties. The properties of steel can be correlated with its microstructure, and more specifically, the different phases that make up the microstructure. These phases give rise to the macroscopic properties that make steel so useful. Microstructure can be controlled through chemistry and through thermomechanical processes. This research focuses on the effects of carbon and on heat treatments. This research is unique in that it keeps the chemistry consistent between all of the samples, making the effect of carbon or of the heat treatment identifiable. A total of six different carbon contents were tested over eight different heat treatment conditions. After creating the samples, the hardness was measured. The samples were then characterized to understand the microstructure. The results of this research showed there is a direct connection between heat treatment and chemistry to the microstructure.

M.Tech. (Operations Management) / Total Quality Management is a management philosophy embracing all activities through which the needs and requirements of customers and the objectives of the organisation are satisfied in a cost effective way through a drive for continuous improvement. Kaizen is a Japanese philosophy and is defined as a process of continuous improvement. It reflects a common-sense, low-cost approach to managing an organisation. A literature review was undertaken on the subjects of Total Quality Management (TQM)principles and Kaizen philosophy and a TQM model was developed for the cellhouse at Manganese Metal Company basedon information from literature review. The cellhouse is part of an organisation that has ISO 9002 accreditation and produces electrolytic manganese metal for customers world-wide. The quality assurance system defines guidelines for producing a quality product, on time and conforming to the required product specifications. The model is designed to complement current quality control philosophy and provide guidance for maintaining and improving the quality assurance programme. All cellhouse employees will be actively involved in participating in a process of improvement on an ongoing basis.

This dissertation describes the determination of the equilibrium constant for the reduction of ferrous oxide by manganese to yield manganese oxide and iron. The experimental work was carried out over the temperature range of 1650°C to 1870°C. The results from the present work were combined with reliable published data to give what is considered to be the best relationship between the equilibrium constant and the temperature. The difference between this study and previous work on this topic is the radically new experimental approach. While previous workers used crucible techniques to achieve equilibrium for their system and standard wet chemical analysis, the method used here involved levitation melting and analysis by the electron probe micro-analyser. / Thesis / Master of Engineering (ME)

Electrical double-layer formed at the interface between an electrode and an electrolyte has been a topic of innumerable studies. The electrical interface plays a crucial role in kinetics, mechanisms and applications in variety of electrochemical reactions. The electrical double-layer and electron-transfer reactions lead to many important applications of electrochemistry, which include energy storage devices, namely, batteries, fuel cells and supercapacitors. Electrochemical supercapacitors can withstand to higher power than batteries and deliver higher energy than the conventional electrostatic and electrolytic capacitors. A supercapacitor can be used as an auxiliary energy device along with a primary source such as a battery or a fuel cell for the purpose of power enhancement in short pulse applications. Among the various materials studied for electrochemical supercapacitors, carboneous materials, metal oxides and conducting polymers received attention. Among carboneous materials, various forms of carbon such as powders, woven cloths, felts, fibers, nanotubes etc., are frequently studied for electrochemical supercapacitors. Low cost, high porosity, higher surface area, high abundance and well established electrode fabrication technologies are the attractive features for using carboneous materials. However, specific capacitance (SC) of these materials is rather low. These electrodes store charge by electrostatic charge separation at the electrode/electrolyte interface. Electronically conducting polymers are interesting class of materials studied for supercapacitor application because of the following merits: high electronic conductivity, environmental friendliness, ease of preparation and fabrication, high stability, high capacitance and low cost. Polyaniline (PANI), polypyrrole and polythiophene are studied in this category. Transition metal oxides have attracted considerable attention as electrode materials for supercapacitors because of the following merits: variable oxidation state, good chemical and electrochemical stability, ease of preparation and handling. Hydrated RuO2 prepared by sol-gel process at low temperature has a specific capacitance as high as 720 F g-1 due to solid state pseudo faradaic reaction. However, high cost, low porosity and toxic nature limit commercialization of supercapacitors using this material. MnO2 is attractive as it is cheap, environmentally benign, its resources are abundant in nature and also it is widely used as a cathode material in batteries. An early study on capacitance behaviour of MnO2 was reported by Lee and Goodenough. Amorphous hydrous MnO2 synthesized by co-precipitation method exhibited rectangular cyclic voltammogram in various aqueous alkali salt solutions. A specific capacitance of 200 F g-1 was reported. Following this report, several reports appeared on capacitance characteristics of MnO2. According to the charge-storage mechanism reported, a specific capacitance of 1370 F g-1 is expected from MnO2. However, this value can be obtained in practice only when the mass of MnO2 is at the level of a few micrograms per cm2 area. At such a low thickness range, the utilization of the active material is high. As thin layers of MnO2 are uneconomical for practical capacitors, studies with a mass range of 0.4-0.5 mg cm-2 have been extensively reported. At this mass range, a maximum specific capacitance of about 240 F g-1 has been obtained. With an increase in mass per unit area, the specific capacitance of MnO2 decreases. The problem associated with low values of specific capacitance of thick layers of MnO2 is the following. The MnO2 deposits or coatings generally do not possess high porosity and the electrolyte cannot permeate into the coating. Only the outer layer of the electrode is exposed to the electrolyte. Consequently, the electrochemical utilization of the material decreases with an increase in thickness. Nevertheless, utilization of thick layers of the active materials is preferable for obtaining capacitance as high as possible in a given volume and area of the electrodes. Indeed, it would be ideal if specific capacitance of MnO2 is improved from its presently reported value of 240 F g-1 to a value equivalent to that of RuO2.xH2O, namely, 720 F g-1. In view of this, attempts are made to enhance specific capacitance of MnO2 by electrochemical deposition in presence of surfactants. Nanostructured MnO2 synthesized by inverse microemulsion route is also studied for electrochemical supercapacitors. The effect of crystallographic structure of MnO2 on the capacitance properties, studies on electrochemical deposition of MnO2 in acidic and neutral medium using electrochemical quartz crystal microbalance and capacitance characteristics of MnO2-polyaniline composites are also described in the thesis. Chapter 1 briefly discusses the importance of electrochemistry in energy storage and conversion, basics of electrochemical power sources, importance of MnO2, different synthetic procedures for MnO2 and its applications in energy storage and conversion in particular for electrochemical supercapacitors. Chapter 2 provides the experimental procedures and methodologies used for the studies reported in the thesis. In chapter 3, the effect of surface active agents, namely, sodium dodecyl sulphate (SDS) and Triton X-100 added to the electrolyte during electrodeposition of MnO2 on Ni substrate on capacitance properties is presented. Electrocrystallization studies show that MnO2 nucleates instantaneously under diffusion control and grows in three dimensions. The potentiodynamically prepared oxide provides higher specific capacitance than the potentiostatically and galvanostatically prepared oxides. Specific capacitance values of 310 and 355 F g-1 obtained for MnO2 electrodeposited in the presence of 100 mM SDS and 10 mM Triton X-100 are higher than the oxide electrodeposited in the absence of surfactants. Surfactant molecules adsorbed at the electrode/electrolyte interface alters structure of double-layer and kinetics of electrodeposition. Smaller particle size, greater porosity, higher specific surface area and higher efficiency of material utilization are the factors responsible for obtaining higher specific capacitance. Extended cycle-life studies indicate that the superior performance of MnO2 due to surfactants is present throughout the cycle-life tested. Chapter 4 pertains to electrochemical supercapacitor studies on nanostructured α-MnO2 synthesized by inverse microemulsion method and the effect of annealing. As synthesized nanoparticles of MnO2 was found to be in α-crystallographic structure with particles less than 50 nm size. Nanoparticles exhibited rectangular cyclic voltammograms between 0 and 1 V vs. SCE in aqueous 0.1 M Na2SO4 at sweep rates up to 100 mV s-1 due to the short diffusion path length. On annealing at different temperatures, a mixture of nanoparticles and nanorods with varying dimension is noticed. Specific capacitance of 297 F g-1 obtained during initial cycling decreases gradually on extended cycling. The capacitance loss is attributed to the increase in the resistance for intercalation/deintercalation of alkali cations into/from MnO2 lattice. MnO2 crystallizes into several crystallographic structures, namely, α-, β-, γ-, δ- and λ-structures. As these structures differ in the way MnO6 octahedra are interlinked, they possess tunnels or inter-layers with gaps of different magnitudes. Because capacitance properties are due to intercalation/deintercalation of protons or cations in MnO2, only some crystallographic structures, which possess sufficient gap to accommodate these ions, are expected to be useful for capacitance studies. The effect of crystal structure of MnO2 on its electrochemical capacitance properties is also included in chapter 4. Specific capacitance of MnO2 is found to depend strongly on the crystallographic structure, and it decreases in the following order: α ≅ δ > γ > λ > β. A specific capacitance value of 240 F g-1 is obtained for α-MnO2, whereas it is 9 F g-1 for β-MnO2. A wide (~ 4.6 Å) tunnel size and large surface area of α-MnO2 are ascribed as favorable factors for its high specific capacitance. A large interlayer separation (~7 Å) also facilitates insertion of cations in δ-MnO2 resulting in SC close to 236 F g-1. A narrow tunnel size (1.89 Å) does not allow intercalation of cations into β-MnO2. As a result, it provides very small SC. In Chapter 5, capacitance characteristics of PANI synthesized using (NH4)2S2O8, nanostructured MnO2 (α- and γ-form) and also PANI-MnO2 composites are presented. Morphology of PANI synthesized resembles the morphology of the MnO2 used as the oxidant. Electrochemical capacitance properties of PANI and composites are studied in a mixed electrolyte of 0.1 M HClO4 and 0.3 M NaClO4 between 0 and 0.75 V vs. SCE. Specific capacitance of 394 F g-1 is obtained for PANI synthesized using γ-MnO2. Chapter 6 describes the electrocatalytic behaviour of Mn3[Fe(CN)6]2 synthesized by ion-exchange reaction between MnSO4 and K3[Fe(CN)6] and the effect of annealing on its electrochemical capacitance properties. As prepared Mn3[Fe(CN)6]2 and also the sample heated at 100 oC exhibit redox couple in 0.1 M Na2SO4 electrolyte, corresponding to Fe(CN)64-/Fe(CN)63- present in the matrix. Mn3[Fe(CN)6]2 samples annealed at 150 oC and above decompose to oxides of manganese and iron, and hence exhibit capacitance characteristics in 0.1 M Na2SO4 electrolyte. A maximum specific capacitance of 129 F g-1 is obtained for Mn3[Fe(CN)6]2 annealed at 300 oC. Electrochemical quartz crystal microbalance (EQCM) investigations of kinetics of electrodeposition of MnO2 in acidic and neutral media, and capacitance behaviour are presented in chapter 7. Oxidation of Mn2+ to MnO2 is characterized by an anodic cyclic voltammetric peak both in acidic and neutral media. During the reverse sweep, however, reduction of MnO2 into Mn2+ occurs in two steps in the acidic medium and in a single step in the neutral medium. From EQCM data of mass variation during cycling, it is observed that the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from acidic medium owing to different crystallographic structures. Reversible insertion/deinsertion of hydrogen in to the layers of δ-MnO2 is observed in hydrogen evolution region. Details of the above studies are described in the thesis.

No description available.

Call number: LD2668 .T4 1930 C64

Call number: LD2668 .T4 1961 B88