As origens dos elementos residuais (trace element) nas ligas à base de Ni provém basicamente de duas fontes: (1) minérios e (2) sucatas. O controle da concentração destes elementos residuais é muito importante, pois afetam as propriedades mecânicas dessas ligas. Alguns estudos mostram que os elementos Pb e Bi têm um sério impacto negativo nos resultados dos ensaios de fluência das ligas a base de Ni. A presença dessas impurezas causa o aumento da quantidade de cavidades nos contornos de grão que resultam em fracasso prematuro na vida útil desse material. Dessa forma, este trabalho tem como objetivo estudar a cinética da remoção de elementos residuais, tais como Pb e Bi da liga VAT32 através da aplicação de vácuo durante a elaboração da liga. Os resultados obtidos demonstraram que a taxa de remoção dos residuais Pb e Bi no refino a vácuo atingiram percentuais de 99,6% e 96,1% respectivamente. Fatores como volume do cadinho, elevação de temperatura, níveis de vácuo abaixo de 10-4 mbar, limpeza do sistema que compreende câmara e cadinho (residuais de corridas anteriores), contribuem significativamente para as taxas acima descritas. Por outro lado, quanto maior o volume de liga fundida, diminuição de temperatura, vácuo deficiente ou contaminação do sistema, a taxa de remoção de Pb e Bi são prejudicadas. / The origins of trace elements in Ni-based alloys come basically from two sources: (1) minerals and (2) scrap. Control of the concentration of trace elements is very important because they affect the mechanical properties of these alloys. Some studies show that the elements Pb and Bi have a serious negative impact on the results of creep tests of Ni based alloys. The presences of these impurities cause the increase of the number of cavities at grain boundaries that result in premature failure of this material. Thus, this work aims to study the kinetics of removal of trace elements such as Pb and Bi in alloy VAT32 by applying vacuum during the preparation of the alloy. The results showed that the rate of removal of residual Pb and Bi in the vacuum refining reached 99.6% and 96.1% respectively. Parameters such as the crucible volume, high temperature, vacuum levels below 10-4 mbar, cleaning of the system which comprises chamber and crucible (residual from previous races), contribute significantly to the rates described above. Moreover, the higher the volume of molten alloy, low temperature, vacuum system contamination and low vacuum pressure decrease, refining degree of Pb and Bi.

Made available in DSpace on 2014-06-12T18:07:47Z (GMT). No. of bitstreams: 2 arquivo6889_1.pdf: 7133075 bytes, checksum: 488fc74e16a58212dee2e9dbf7f72c2e (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2006 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A presente análise e síntese geográfica versa sobre a relação entre mineração e espaço no município de Pedra Lavrada PB. O princípio do uso do território desse município pela atividade mineira remonta a época da Primeira Guerra Mundial, no entanto, é a partir da segunda metade da década de 1930, e mais enfaticamente no período da Segunda Guerra Mundial, que a forma espacial constituída pela atividade de mineração de pegmatitos ganha importância estratégica mundial, devido à conjuntura de beligerância do período. Esta análise/síntese histórica e geográfica do uso do território do Seridó paraibano com a exploração de minerais, dando ênfase ao município de Pedra Lavrada PB, revela como se deu a constituição e reconstituição dos seus sistemas de objetos e de ações frente à dinâmica econômica mundial, brasileira, nordestina e paraibana, resgatando algumas práticas espaciais características de cada momento de sua feitura. Nesse sentido, o estudo captura as distintas fases mais importantes vividas pelo meio mineiro lavradense e como esses eventos rebatem na conformação da sua geografia, quais sejam: o contexto das duas guerras mundiais responsável pela sua afirmação como lugar produtor de minerais estratégicos, em que toda a produção era destinada ao mercado externo; a fase da consolidação da indústria e da integração do espaço nacional em que o referido meio passa a se inserir produzindo e beneficiando matérias-primas minerais para diversas indústrias e; o período atual, mostrando os eventos mais recentes responsáveis pela sua dinâmica, bem como a composição técnica-organizacional do seu território que define o seu funcionamento. Na atualidade, esse lugar produtor não figura na cartografia brasileira dos lugares dinâmicos ou luminosos, rápidos, densos em suas camadas técnicas, que são os atrativos para o grande capital, mesmo assim, consegue se inserir nas estratégias de grandes empresas do país e do exterior. Historicamente, o espaço produtor de minerais de Pedra Lavrada PB sempre atendeu a demandas alheias, que foram sempre renovadas ao longo de sua concreção. Assim, atendendo a interesses forâneos e sem comando local, torna-se um espaço alienado

Made available in DSpace on 2014-06-12T23:16:05Z (GMT). No. of bitstreams: 2 arquivo9488_1.pdf: 3754716 bytes, checksum: d57f79de5dffe56d44947a0618a72c11 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Os liquens produzem substâncias que se cristalizam na superfície externa do seu micobionte, funcionando como fotoprotetor. Quando submetidos a diferentes doses e tipos de radiação, estes são estimulados a produzir suas substâncias em quantidades diferenciadas daquelas que produziriam sem a intervenção da mesma. O objetivo desta pesquisa foi quantificar e comparar características químicas (bioprodução do ácido fumarprotocetrarico-FUM, seu principal composto), e fisiológicas (Clorofila Total) em amostras de Cladonia verticillaris (Raddi) Fr., coletadas em dois diferentes ambientes do Nordeste brasileiro, antes e após submissão à radiação gama e ultravioleta. Amostras liquênicas foram coletadas nos municípios de Saloá-PE e Alhandra-PB, locais que apresentam características fisionômicas semelhantes, porém com diferentes altitudes. Amostras de C. verticillaris (12 g) foram submetidas a irradiador gama [Co-60 irradiador, Gammacell 220 Excel, com taxas de dose de 7,795 kGy/h (03/02/2009) para as amostras de Saloá, e 7,144 kGy/h (29/10/2009) para as de Alhandra] nas doses de 0, 10, 50, 100, 500, 1000, 5.000 e 10.000 Gy, e, separadamente, submetidas à irradiação ultravioleta (lâmpada Philips Ultraviolet B 20 W), nas doses de 0, 1, 3, 6, 9, 12 e 15 J/cm2. Após irradiação, foram coletadas amostras de 1,5g do material liquênico e acondicionadas separadamente, para posterior análise. Os resultados indicaram maior produtividade aos 90 dias de experimento, onde amostras de Saloá e Alhandra bioproduziram 1,41 e 2,7 vezes a amostra controle quando expostas a 5000 e 500 Gy, respectivamente. Nas irradiadas com UVB, a bioprodução foi de 2,99 e 3,52 vezes a amostra controle, quando expostas a 9 e 6 J/cm2, respectivamente. A produção de Clorofila total, em todas as amostras expostas à radiação gama ou UVB, apresentou-se inferior as amostras não irradiadas. As amostras de C. verticillaris coletadas em Alhandra, irradiadas com raios gama ou UVB, apresentaram uma maior produtividade de FUM que as provenientes de Saloá. Essa Pesquisa foi realizada no Departamento de Energia Nuclear da Universidade Federal de Pernambuco no período de 2007 a 2011

The Saint-Urbain and Big Island rutile-bearing ilmenite Fe-Ti oxide deposits are located in the composite 450 km² Saint-Urbain anorthosite (1055-1046 Ma, U-Pb zircon) and in the Lac Allard intrusion (1057-1062 Ma, U-Pb zircon) of the 11,000 km² Havre-Saint Pierre anorthosite suite, respectively, in the Grenville Province of Eastern Canada. Slow cooling rates of 3-4°C/m.y. are estimated for both anorthosites, based on combined U-Pb zircon/rutile/apatite and ⁴⁰Ar/³⁹ Ar biotite/plagioclase geochronology, and resulted from emplacement during the active Ottawan Orogeny. Slow cooling facilitated (1) diffusion of Zr from ilmenite and rutile, producing thin (10-100 microns) zircon rims on these minerals, and (2) formation of sapphirine via sub-so lidus reactions of the type: spinel + orthopyroxene + rutile ± corundum → sapphirine + ilmenite. New chemical and analytical methods were developed to determine the trace element concentrations and Hf isotopic compositions of Ti-based oxides. Rutile is a magmatic phase in the deposits with minimum crystallization temperatures of 781°C to 1016°C, calculated by Zr-in rutile thermometry. Ilmenite present in rutile-free samples has higher Xhem (hematite proportion in ilmenite), higher high field strength element concentrations (Xhem = 30-17; Nb = 16.1-30.5 ppm; Ta 1.28-1.70 ppm), and crystallized at higher temperatures than ilmenite with more fractionated compositions (Xhem = 21-11; Nb = 1.36-3.11 ppm; Ta = <0.18 ppm) from rutile-bearing rocks. The oxide deposits formed by density segregation and accumulation at the bottom of magma reservoirs, in conditions closed to oxygen, from magmas enriched in Fe and Ti. The initial ¹⁷⁶Hf/¹⁷⁷ Hf of rutile and ilmenite (Saint Urbain [SU] = 0.28219-0.28227, Big Island [BI] = 0.28218-0.28222), and the initial Pb isotopic ratios (e.g.²⁰⁶Pb/²⁰⁴ Pb: SU = 17.134-17.164, BI = 17.012-17.036) and ⁸⁷Sr/⁸⁶ Sr (SU = 0.70399-0.70532, BI = 0.70412-0.70427) of plagioclase from the deposits overlap with the initial isotopic ratios of ilmenite and plagioclase from each host anorthosite, which indicates that they have common parent magmas and sources. The parent magmas were derived from a relatively depleted mantle reservoir that appears to be the primary source of all Grenvillian anorthosite massifs and existed for --600 m.y. along the margin of Laurentia during the Proterozoic. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This study was conducted to investigate the capacity of Cynodon nlemfuensis (star grass) to accumulate lead (Pb) and cadmium (Cd) and develop metal uptake models for sandy soils receiving treated sewage from domestic and industrial sources. The study area comprised a non-polluted area and an adjacent area that received treated sewage from Harare’s Firle Wastewater Treatment Plant for over 30 years. Measured soil properties, total Pb and Cd in soils and grass and past records of Pb and Cd in treated sewage were analysed. Growing grass in a greenhouse in pots with previously non-polluted soils amended by single and mixed Pb and Cd salts and irrigated with treated sewage tested the uptake capacity of star grass. Yields, soil bio-available and grass Pb and Cd levels were measured and used to develop models for estimating critical soil and grass concentrations at which productivity declines. In the field, star grass grown in 10m x 10m plots in the non-irrigated and irrigated areas, received varying amounts of treated sewage over 11 months. Soil bio-available and grass metal contents were measured and used to develop field-based models to predict Pb and Cd content in star grass. Star grass had a high Pb and Cd extraction capacity, making it unsuitable for pasture if grown on polluted soils. Correlation between total Pb and Cd in soils and grass was insignificant (p<0.05). Logarithm-based models of log10 bio-available soil levels and log10 grass metal levels provided the best-fit regression models for Pb and Cd predictions in grass. Toxicity levels of Pb and Cd that were derived for star grass from pot-based models were higher than levels recommended for pasture. Toxicity occurred without visible signs on grass, making it difficult to recognise toxicity without testing. The field-based uptake models predicted safe bio-available limits for pasture on sandy soils. The co-presence of Pb and Cd resulted in increased Cd uptake but did not significantly affect Pb uptake. Star grass can accumulate more than 1 mg/kg of Cd at total soil Cd levels of less than 1 mg/kg, suggesting that the soil limit may be too high for a sandy soil. / Thesis (PhD (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

O cinturão Fíngoè é uma unidade tectônica do Supercontinente Gondwana Oeste composta por rochas supracrustais formadas há aproximadamente 1.33 Ga. Essas rochas são portadoras de mineralizações de Au, Cu, Zn, Pb e Fe. Com cerca de 150 km de comprimento, e orientado WSW-ENE, este cinturão estende-se desde o Monte Atchiza a oeste até cerca de 30 km para leste da vila de Fíngoè no norte de Moçambique e consiste de uma extensa variedade de rochas metassedimentares e metavulcânicas. O cinturão Fíngoè apresenta especialização metalogenética para Au e Cu, que já foram explotados no passado em diversos locais. Muitos destes registros estão associados com magnetita e malaquita. Atualmente trabalhos de prospecção e pesquisa mineral têm sido realizados pela empresa de mineração African Queen Mines Ltda, através do projeto denominado de King Solomons, localizado na parte central do mesmo. A geologia da área abrangida pelo prospecto Mankombiti, mostra uma predominância de rochas carbonáticas, granitos e gabros. As rochas carbonáticas são consideradas importantes na gênese de depósitos tipo skarn e depósitos de substituição de metais de base e Au devido à sua natureza fortemente reativa. Os dados geocronológicos realizados neste trabalho indicaram uma idade precisa para a rocha intrusiva granítica associada à mineralização de 1079,1 ± 8,2 Ma, que poderia ser a idade da formação do skarn e consequentemente desta mineralização. Entretanto a idade obtida para o processo de alteração hidrotermal que afetou o gabro, na ordem de 657 ± 36 Ma e a idade modelo Pb-Pb sugerida pelo modelo de Stacey e Kramers (1975) para a calcopirita da mineralização principal de 725 Ma, sugerem que a mineralização, do prospecto Mankombiti é neoproterozóica. Para melhor entendimento dos processos que estiveram envolvidos na formação deste depósito skarn, duas hipóteses são consideradas: (i) poderia ser admitida a presença de corpos graníticos intrusivos em 700 Ma, situados em profundidade, que não foram ainda caracterizados, como responsáveis pela fonte de calor necessária, (ii) pode ser admitida ocorrência de um evento distensional em 700 Ma que produziria um adelgaçamento da litosfera e a consequente ascensão da astenosfera, produzindo uma elevação do fluxo térmico gerando os fluidos mineralizantes necessários. / The Fíngoè belt is a tectonic unit of West Gondwana Supercontinent, comprised of supracrustal rocks formed at approximately 1.33 Ga. These rocks are carriers of Au, Cu, Zn, Pb and Fe mineralization. With about 150 km long and oriented WSW- ENE, this belt extends from west of the Atchiza Mount to about 30 km east of the Fíngoè village in the north Mozambique, and consists of an extensive variety of metasedimentary and metavolcanic rocks. The Fíngoè metallogenic belt provides specialization for Au and Cu, which have been exploited in the past in various locations. Many of these records are associated with magnetite and malachite. Currently, the prospecting and mineral exploration have been conducted by the African Queen Mines Ltd mining company, through a project called the King Solomons, located in the central part of it. The geology of the studied area shows a predominance of carbonate rocks, granites and gabbros. The carbonate rocks are considered important in the genesis of the skarn deposits type and deposits of replacement for base metals and Au due to its highly reactive nature. The geochronological data performed in this work indicate a precise age of the 1079.1 ± 8.2 Ma for the intrusive granitic rock associated with mineralization, which could be interpreted as the age of the skarn and consequently of the mineralization. However the age obtained for the hydrothermal alteration that affected the gabbro at about 657 ± 36 Ma and the Pb-Pb model age suggested by the model of Stacey and Kramers (1975) for primary chalcopyrite mineralization at 725 Ma, suggesting that the mineralization of the Mankombiti prospectus was developed during the Neoproterozoic time. For understanding the processes that were involved in the skarn-type mineralization processes, two hypotheses are here considered: (i) could be admitted the presence of i ntrusive granitic rocks at 700 Ma, situated in depth, which have not yet been characterized, as responsible for the heat source required, (ii) may be admitted occurrence of an extensional event at 700 Ma to produce a thinning of the lithosphere and the uplift of the asthenosphere, producing high thermal flows generating the mineralization fluids.

As origens dos elementos residuais (trace element) nas ligas à base de Ni provém basicamente de duas fontes: (1) minérios e (2) sucatas. O controle da concentração destes elementos residuais é muito importante, pois afetam as propriedades mecânicas dessas ligas. Alguns estudos mostram que os elementos Pb e Bi têm um sério impacto negativo nos resultados dos ensaios de fluência das ligas a base de Ni. A presença dessas impurezas causa o aumento da quantidade de cavidades nos contornos de grão que resultam em fracasso prematuro na vida útil desse material. Dessa forma, este trabalho tem como objetivo estudar a cinética da remoção de elementos residuais, tais como Pb e Bi da liga VAT32 através da aplicação de vácuo durante a elaboração da liga. Os resultados obtidos demonstraram que a taxa de remoção dos residuais Pb e Bi no refino a vácuo atingiram percentuais de 99,6% e 96,1% respectivamente. Fatores como volume do cadinho, elevação de temperatura, níveis de vácuo abaixo de 10-4 mbar, limpeza do sistema que compreende câmara e cadinho (residuais de corridas anteriores), contribuem significativamente para as taxas acima descritas. Por outro lado, quanto maior o volume de liga fundida, diminuição de temperatura, vácuo deficiente ou contaminação do sistema, a taxa de remoção de Pb e Bi são prejudicadas. / The origins of trace elements in Ni-based alloys come basically from two sources: (1) minerals and (2) scrap. Control of the concentration of trace elements is very important because they affect the mechanical properties of these alloys. Some studies show that the elements Pb and Bi have a serious negative impact on the results of creep tests of Ni based alloys. The presences of these impurities cause the increase of the number of cavities at grain boundaries that result in premature failure of this material. Thus, this work aims to study the kinetics of removal of trace elements such as Pb and Bi in alloy VAT32 by applying vacuum during the preparation of the alloy. The results showed that the rate of removal of residual Pb and Bi in the vacuum refining reached 99.6% and 96.1% respectively. Parameters such as the crucible volume, high temperature, vacuum levels below 10-4 mbar, cleaning of the system which comprises chamber and crucible (residual from previous races), contribute significantly to the rates described above. Moreover, the higher the volume of molten alloy, low temperature, vacuum system contamination and low vacuum pressure decrease, refining degree of Pb and Bi.

The transition from the end of the Ordovician to the beginning of the Silurian Period is characterized by the glaciation of the Gondwana paleocontinent, eustatic sea level change, a perturbation to the global carbon cycle and one of the ve major mass extinctions of the Phanerozoic Eon. Due to signi cant sea level fall, the Ordovician-Silurian (O-S) boundary is often marked by hiatus and exposure in the shallow marine geologic record (e.g., Copper et al. [2013]). Two locations that host stratigraphic succession close to the boudary are Anticosti Basin of Quebec (Canada, e.g., Desrochers et al. [2010]), and the carbonate mounds of the Siljan ring district (Dalarna County, Sweden, e.g., Ebbestad et al. [2015]). The exact timing and dynamics of the glaciation and mass extinction are yet to be understood. Similarly, the interplay between those events and the carbon cycle perturbation are still unclear. As a result, there is a serious need for radiometric age constraints in this crucial part of the Paleozoic Era. The acquisition of more radiometric dates, achieved in this study, aims to address the present dearth of absolute dates close to the boundary. The dates produced in this study represent the first modern geochronologic constraints on the O-S boundary, leveraging the development of the EARTHTIME initiative and the latest U-Pb dating techniques that have improved accuracy and allowed for dating of single zircon crystals at <=0.1% precision level. Here I present two new U-Pb zircon ages obtained via bentonite dating. The first bentonite, 443.61+-0.52 Ma (2, including analytical, tracer calibration and decay constant uncertainties) was collected from the base of the Lousy Cove Member, Ellis Bay Formation (Anticosti Island, Quebec, Canada). The second one, 443.28+-0.50 Ma (including analytical, tracer calibration and decay constant uncertainties) comes from a karstic void within the Boda Core Facies of the Boda Formation (Dalarna County, Sweden). U-Pb geochronology (chemical abrasion, isotope dilution, thermal ionization mass spectrometry: CA-ID-TIMS) on single zircons was used to obtain these ages. These results are the closest radiometric ages to the current O-S boundary (compared to any time constraints in the 2012 Geologic Time Scale) and allow to signifcantly reduce the uncertainty of the current age boundary (443.8+-1.5, Cohen et al. [2018]). Furthermore these absolute ages have been used to make models that explore drivers of Earth system change, such as an end-Ordovician global carbon cycle perturbation. / Graduate / 2022-07-07

abstract: Establishing the timing of impact crater formation is essential to exploring the relationship between bolide impact and biological evolution, and constraining the tempo of planetary surface evolution. Unfortunately, precise and accurate impact geochronology can be challenging. Many of the rock products of impact (impactites) contain relict, pre-impact phases that may have had their isotopic systematics completely reset during the impact event, only partially reset, or not reset at all. Of the many isotopic chronometers that have been used to date impactites, the U/Pb zircon chronometer (ZrnPb) seems least susceptible to post-impact disturbances, and ZrnPb dates are typically much more precise than those obtained using other chronometers. However, the ZrnPb system is so resistant to resetting that relict zircons in impactites often yield dates that reflect the igneous or metamorphic ages of the target rocks rather than the age of the impact itself. The present study was designed to answer a simple question: is there a straightforward sample collection and analysis strategy for high-accuracy ZrnPb dating of an impact structure if the impactites collected from it may contain inherited zircons? To study this, ZrnPb dates were determined for impactites from a single crater with a well-constrained impact age: the West Clearwater Lake impact structure, located at Lake Wiyâshâkimî, Québec, Canada. The amount of ZrnPb resetting and the mechanisms responsible for resetting varied amongst the samples. Each sample characteristically contained either: newly crystallized zircons from the impact melt ("neocrystalline"), relict zircons ~50-100% reset, or, relict zircons ~0-50% reset. The variably reset relict zircons define a discordia line from ~2700 Ma to ~286 Ma – consistent with the ages of the target rock and the impact, respectively (Schmieder et al., 2015a; Simard, 2004). ZrnPb measurements from the neocrystalline zircons provided a new preferred impact age of 286.64 ± 0.35 Ma (2σ), a ~10x improvement in precision. The characteristics of the West Clearwater ZrnPb data vary between samples yet become easily interpretable as a whole, showing that efforts to measure robust, precise impact ages benefit from strategies that prioritize applying multiple analytical techniques to multiple types of impactite from the same crater. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

Indiana University-Purdue University Indianapolis (IUPUI) / Tills from major ice streams (Institute, Foundation, Academy, Recovery, and Slessor) of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a provenance tool to better understand ice stream dynamics. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks, and 12 samples of offshore till. Grains were analyzed by LA-ICPMS at the University of Arizona (n=5447). Relative probability U-Pb age density plots of till in moraines along the Institute Ice Stream have dominant Grenville (1070 Ma) and secondary Ross/Pan-African peaks (560 Ma, 630 Ma). The Foundation and Academy show prominent Ross/Pan-African peaks (500-530 Ma and 615-650 Ma). The Recovery transports zircons with prominent 530 Ma and 635 Ma peaks along the southern margin, and 1610 and 1770 Ma along the northern margin. The Slessor carries zircons with prominent populations at 1710 Ma and secondary 2260-2420 Ma. U-Pb ages in zircons from offshore till samples show a general trend of fewer Mesozoic ages from west to east. The western most core, PS 1423, has dominant Jurassic populations while cores 1197 and 1278 have a high proportion of early Ross/Pan-African ages relative to Grenville ages. The similar zircon age distributions between PS 1278 and the Foundation Ice Stream tills suggest that the Foundation switched to an easterly flow path around Berkner Island (BI) at some point during the LGM. In the eastern Weddell Sea (PS 1400), there was a near absence of Proterozoic zircon age populations carried by the Slessor and northern side of the Recovery. Another unexpected find was a lack of Grenville ages in PS 1423 relative to the Institute tills. The U-Pb data in this study provides a basis for two possible LGM ice flow reconstructions. In the first, the Institute flowed west around the unnamed isolated bedrock highs, deposited tills between PS 1423 and PS 1197, providing a westerly flow path around BI for the Foundation. In the second, the Institute flows over the subglacial topography and deposited till closer to PS 1197, forcing the Foundation east around BI.