During the course of this work two fundamental aspects of the electrochemistry of the lead acid battery system have been investigated. The first area of study concerns the respective roles of alpha and beta lead dioxide in the positive plate, and more specifically the interconversion behaviour of the two polymorphs. The second research area concerns the occurence of a passivating layer of lead monoxide between substrate lead and the active material of the electrode. A subject of extreme importance to the lead acid battery manufacturer, since passivating layers of this type are acknowledged as being one of the major failure modes. This work has differed from most before it, in that use has been made of electrodeposits of the two modifications to study both the interconversion products, and the conditions necessary for lead monoxide formation. A survey of some of the recommended methods of preparation for the two forms of lead dioxide has been carried out and compared to the data given in the Powder Diffraction File. X-ray diffraction has been the major investigative tool utilised, and electrodes have been subjected to analysis in both the powder and unground state, after both galvanostatic and potentiodynarnic cycling. Cyclic voltarnmetry was used to study the potentiodynarnic conversion products of deposits swept between the hydrogen and oxygen gas evolution regions in sulphuric acid. The galvanostatic cycling showed that a conversion of alpha lead dioxide to the beta does occur, although evidence for conversion of the beta form to the alpha was not found. The potentiodynamic study revealed that in order for lead monoxide to be formed under deposits of beta lead dioxide, the presence of substrate lead is required beneath a lead sulphate film or membrane. Under these conditions it was discovered that the lead monoxide itself is a precursor to alpha lead dioxide formation.

No description available.

The objectives of this investigation were: 1. To establish calorimetrically the transition temperature for the orthorhombic to cubic transition exhibited by PbF₂ and to determine the enthalpy of this transition. 2. To determine if the solid-solid phase transitions claimed in the literature for PbCl₂, PbF₂, PbBr₂, and PbI₂ were of thermodynamic importance, and if so, to determine the enthalpies of transition. 3. To determine if the discontinuous thermal expansions reported by Hsu for the lead halides were of thermodynamic importance. 4. To obtain reliable heat content data for the lead halides in both the solid and liquid states.

M.Tech. (Minerals Engineering) / This report deals with the feasibility study of a novel concept whereby a lead sulphide concentrate and a solid reductant are reacted with a manganese ore at a temperature of approximately lOOO=C. The manganese oxides are reduced to their lower oxides, which, having a higher affinity for sulphur than lead. scavenge the sulphur from the lead sulphide. A manganese sulphide mane is formed. and liquid lead metal is tapped off. The manganese sulphide mane is then leached with sulphuric acid. After a purification step to remove the base metals from solution, the electrolyte proceeds to an electrolytic manganese metal or manganese dioxide facility where the manganese is recovered. The benefits of this process are fourfold: firstly, lead ores may be beneficiated locally; secondly, the separate and often lengthy processes for the recovery of lead and manganese are combined into a simplified process, thereby reducing the capital expense: thirdly, the Leadman process can be applied to any scale of operation: and fourthly, no 502 is produced. Details of the investigation included the following: a literature survey. a laboratory scale study where the operating conditions were narrowed down, a smelting campaign on a rotary kiln, a mineralogical study, a brief leaching study, a leach liquor purification step and a techno-economic assessment. This study has shown the technical and economical feasibility of the Leadman process. The lead and manganese recoveries were both approximately 93%, with good accountability of all the other elements of interest. Depending on the operating conditions, between 80 and 100 per cent of silver, originally in the galena, was recovered with the lead bullion. The purity of the lead metal produced was good with a lead content of approximately 97 per cent, and low levels of contaminants. It was also shown that the manganese matte produced is suitable for use as feed to an existing manganese electrowinning operation. The techno-economic assessment showed a return of R 3 118/t of Pb, compared with R 939/t and R 240/t for the conventional manganese and lead blast processes, respectively.

Introduction: Lead metal toxicity in children is a major public concern internationally. In South Africa, January 2006 was the date set for the complete phase-out of leaded petrol, a well known major source of environmental lead contamination. Analysis was conducted to describe the distribution of blood in children, to establish proportions of children with elevated blood lead levels (unacceptable blood lead levels of ≥ 10 μg/dl) and to establish factors associated with elevated blood lead levels using data collected in 2007, one year after the phase-out of leaded petrol. Methods and Materials: An analytical cross-sectional secondary data analysis was conducted on a survey dataset from the Environment and Health Research Unit of the Medical Research Council, South Africa. The primary sampling unit (cluster) was defined as primary schools. Data on first grade children from 13 schools from three suburbs of Cape Town – Woodstock (eight schools), Hout Bay (three schools) and Mitchell’s Plain (two schools) – were analyzed using a survey method, calculating design-based robust standard errors. Different weights were applied to schools in the suburbs which formed the stratification variable. The outcome variable was defined as blood lead levels < 10 μg/dl or ≥ 10 μg/dl. A number of background characteristics – health and diet, housing and social aspects – were investigated; odds ratio measurement was calculated and reported. Results: A total of 532 children were included in the analysis, representing a weighted total of 1 744 children. The children’s weighted mean age was 7.40 years (95% CI 7.39 to 7.41). The geometric weighted mean blood lead level was 5.27 μg/dl (95% CI 5.08 to 5.46). The weighted proportion of children with BLLs ≥ 10 μg/dl was 11.81% (95% CI 8.78 to 15.72); in Woodstock it was (21.0%). In the multivariable logistic regression, several factors were independently associated with higher odds of having BLLs ≥ 10 μg/dl, including use of gas for cooking OR 3.24 (95% CI 2.34 to 4.48) p <0.0001; houses in need of major repairs OR 7.81 (95% CI 1.59 to 38.33) p = 0.017; attending a crèche/preschool OR 15.23 95% CI (3.40 to 68.29) p = 0.003; Others included use of buses or taxis, which increased the odds of a child having a BLLs ≥ 10 μg/dl compared to walking to school by 5.20 times (95% CI 3.00 to 8.99) p < 0.0001 and children who were living in flats (OR 5.55, 95% CI 3.76 to 8.18, p < 0.0001) or in informal/shack dwellings (OR 2.09, 95% CI 1.06 to 4.12, p = 0.037) were at greater odds of having a blood lead ≥ 10 μg/dl than if they lived in free-standing houses. The following factors offered protection against elevated BLLs: Using private cars to transport children to school offered 0.83 lower odds of a child having elevated lead levels (OR 0.17, 95% CI 0.09 to 0.31, p < 0.0001) compared to walking to school, use of plastic water pipes OR 0.60 (95% CI 0.44 to 0.82) p = 0.005 and, domestic cleaning practices, such as cleaning floors with a wet mop (rather than a dry broom) reduced the odds of having blood lead levels ≥ 10 μg/dl by 0.88 (OR 0.12, 95% CI 0.10 to 0.15, p < 0.0001). Conclusion and Discussion: This analysis indicated that the distribution of blood lead appears similar that determined in the leaded petrol era. The proportion of children with elevated blood lead levels in a Cape Town study was still high. Multiple factors were associated with BLLs ≥ 10 μg/dl. Some factors were protective. The implementation of the phasing out of the leaded petrol should be critically monitored to determine the time period before observing a reductive effect. Preventive measures targeting removal of non petrol sources of lead from the school and home environments should be considered as important.

Thesis advisor: Jeremy D. Shakun / The Arctic is one of the fastest warming regions on the planet. Currently, much of the Arctic is covered by permafrost, which contains approximately 1,700 gigatons of organic carbon. Permafrost thaw could release a substantial amount of this carbon as greenhouse gases into the atmosphere through microbial decomposition, potentially dramatically amplifying anthropogenic warming. However, the risk of permafrost thaw is uncertain, with models exhibiting a wide range of possibilities. Assessing the stability of permafrost during past interglacial periods enables evaluation of the sensitivity of permafrost to warming. Cave mineral deposits (speleothems) in areas currently covered with permafrost can act as a proxy for past permafrost thaw, as liquid water is one criterion for speleothem growth and thus speleothem deposition implies thawed ground conditions. Previous uranium-thorium (U-Th) dating of speleothems (n=73) from a wide range of latitudes and permafrost zones across the southern Canadian Rockies, Northwest Territories, and northern Yukon indicate that most of these formations exceed the U-Th dating limit of 500 ka. In this study, I apply uranium-lead (U-Pb) geochronology to several of these speleothems to extend the record of speleothem growth further back in time. Results include a U-Pb age of 412.8 ± 1.3 ka that replicates a previous U-Th age of 415.0 ± 11.5 ka, demonstrating the reliability of the U-Pb methodology. Additionally, U-Pb ages on six other speleothems are determined to be 876 ± 9 ka, 1501 ± 31 ka, 1570 ± 66 ka, 2046 ± 106 ka, 7636 ± 184 ka, and 7697 ± 185 ka. Further application of this technique could result in long records of past permafrost thaw and Arctic terrestrial climate extending back millions of years. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

No description available.

Rationale: The rate of acquisition of drug self-administration may serve as a predictor of later drug-taking behavior, possibly influencing vulnerability to initiate drug use. Objectives: The present study examined the effects of perinatal (gestation/lactation) lead exposure on adult rates of acquisition of intravenous (i.v.) heroin self-administration and cocaine self-administration using an automated procedure that included both Pavlovian and operant components. Methods: For Experiment 1, female rats were gavaged daily with 0 or 16 mg lead for 30 days prior to breeding with nonexposed males. Metal administration continued through pregnancy and lactation and was discontinued at weaning (postnatal day [PND] 21). Animals born to control or lead-exposed dams received indwelling jugular catheters as adults and subsequently were tested daily in a preparation where sessions included an initial 3-hr autoshaping period followed by a 3- hr self-administration period. During autoshaping, heroin (.018 mg/kg) infusions were paired with the extension and retraction of a lever when a lever press was not made for 15 sec, while infusions occurred during self-administration only when a lever press was executed (FR-1). The criterion for acquisition was a 2-day period during which a mean of 10 infusions/session occurred during self-administration. Animals were given 35 days to reach criterion. Results: Findings from Experiment 1 showed the proportion of rats meeting the lever-press response criterion for heroin when tested as adults was lower among lead-exposed animals. In Experiment 2, cocaine (.20 mg/kg) was presented to animals that underwent the same metal-exposure regimen, surgical procedures and methods with variations only in the number of infusions that were automatically administered during the Pavlovian component. Criterion for cocaine acquisition was a mean of 50 infusions over a two-day. In Experiment 2, a greater proportion of leadexposed animals reached the criterion for cocaine acquisition. Conclusions: Developmentally lead-exposed animals showed a decrease in vulnerability to initiate drug-taking behavior when presented with heroin in the adult phase, relative to controls. In contrast, developmentally lead-exposed animals showed an enhanced vulnerability to reach the criterion for cocaine self-administration. Clinical relevance of developmental exposure to lead and the attendant vulnerability to self-administer drugs of abuse is discussed.

The interaction and orbital energy levels of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules on a Pb/Si(111) 1x1 substrate have been investigated. A Si(111) sample was annealed to form the 7x7 configuration. 1.5 monolayer of Pb was evaporated onto the surface, which was then annealed. 0.5 monolayer of PTCDA was applied to the substrate through molecular beam epitaxy (MBE). The surface configuration of the substrate was monitored step by step by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Scanning tunneling spectroscopy (STS) was used to pinpoint the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules. It was found that the PTCDA molecules formed a herringbone pattern on the substrate. The PTCDA electronic energy levels corresponding to the HOMO and the LUMO were obtained. From these values the energy gap between these orbitals, the molecular bandgap of PTCDA on Pb/Si(111) 1x1, was determined.

The extent of BiInO3 substitution in the perovskite system xBiInO3-(1-x)PbTiO3 and the corresponding raise in the Curie temperature were investigated using thermal analysis, X-ray diffraction and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x=0.20, with a corresponding Curie temperature of 582C. Phase-pure tetragonal perovskite was obtained for x less than 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD) by crushing after calcining, dry pressing and firing. Sol-gel fabrication resulted in nano-sized tetragonal or pseudo-cubic perovskite particles, which after two-step firing, resulted in a tetragonal perovskite microstructure at as high as (x=0.25) 98.2% of TD.