Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 144-152).

Thesis (M.Sc.)--Aberdeen University, 2008. / Title from web page (viewed on March 9, 2009). Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Jack C. Lee. Vita. Includes bibliographical references.

The purpose of this study is to understand mineral diagenesis authigenic mineral and the effect of climate on mineral of Pleistocene-Holocene sediment deposits in the Southern Kenya Rift. Lake Magadi unique geologic settings are characterized by extreme alkalinity and high silica activities. The mineralogical analysis was achieved by X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) applications. The bulk mineralogy (quartz, halite, calcite) is the same on all localities due to similar volcaniclastics compositions throughout the Kenya Rift Valley. The clay mineralogy significantly differ among the groups of sample localities. The differences reflect different tectonic settings and ambient climate regime. In humid climate at higher elevation detrital clay minerals are abundant (feldspars, phillipsite). At lower elevation like Lake Magadi, the clay fractions dominated by authigenic minerals (zeolites and silicate minerals found with zeolites). These results show the potential of clay minerals as terrestrial climate proxies.

Novel solutions to offset thermal degradation of polyamide-6 (PA-6) and organoclay (organically modified layered silicates) nanocomposites during melt compounding have been investigated. In this research, a novel chain extender (Joncryl ADR 3400) has been used to improve thermal stability of PA-6 and PA- 6/organoclay nanocomposites during melt compounding. The materials were compounded using a linear twin extruder and various laboratory scale mixers. The effects of organoclay and chain extender were studied using both processing methods. In order to replicate large scale production used in industry, a comprehensive plan of experimental work was carried out under different processing conditions (extrusion temperature and screw speed), organoclay and chain extender loading using a linear twin screw extruder. Rheology, mechanical and thermal properties were analysed and selected samples were also characterised by TEM and FTIR. Process induced degradation of PA-6 during the melt compounding was found to have significant influence on the rheological and mechanical properties. Rheological and mechanical characterisation clearly showed showed that incorporation of the chain extender minimised thermal degradation of PA-6 and nanocomposites during melt processing. Visual analysis of selected nanocomposites using TEM confirmed that chain extender increased the dispersion of nanoclays in the PA- 6 matrix. The crystallinity of the PA-6 was slightly affected by addition of organoclay and chain extender. The samples obtained by linear twin screw extrusion showed higher rheological properties than the samples from laboratory scale mixers suggesting better mixing and less thermal degradation during extrusion.

La carbonatation minérale est une technique alternative de capture et stockage du CO2 anthropique. L'abondance des matériaux carbonatables sur terre en fait une solution à fort potentiel. En particulier, la carbonatation directe en voie aqueuse a été présentée dans la littérature comme la voie la plus intéressante d'un point de vue énergétique pour la carbonatation minérale ex-situ, à la condition que les cinétiques naturellement lentes de dissolution des silicates magnésiens en phase aqueuse puissent être accélérées de plusieurs ordres de grandeur. Cette thèse étudie en détail les verrous et mécanismes de cette réaction en présence d'additifs organiques tels que l'oxalate, connus pour leur capacité à accélérer la dissolution des silicates magnésiens. Dans un premier temps, la carbonatation en voie aqueuse sans additif d'une olivine modèle est étudiée de manière à mettre en évidence la nature des phénomènes limitants. Ensuite le travail se concentre sur l'étude du rôle de l'additif oxalate à travers des essais spécifiques et une analyse fine de la phase solide. Il est démontré que pour différentes concentrations de suspension et sous 20 bar de CO2, cet additif conduit à la formation de complexes aqueux stables du magnésium avec l'oxalate et à la précipitation de MgC2O4,2H2O (glushinskite), qui empêchent toute précipitation quantitative de magnésite. La simulation géochimique complète du système a été réalisée et a permis d'expliquer les résultats des essais par un mécanisme de dissolution à grain rétrécissant. L'extension de l'étude à un autre silicate (harzburgite) et à d'autres ligands organiques accélérateurs de la dissolution des silicates tels que le citrate et l'EDTA n'a pas non plus permis d'obtenir la formation quantitative de carbonate, à cause d'une forte complexation en phase aqueuse du Mg extrait du minerai. Ces travaux remettent en doute la perspective de développement d'un procédé industrialisable de minéralisation du CO2 en présence d'additifs organiques. / Mineral carbonation is an interesting option for mitigation of anthropogenic CO2 emissions. Direct aqueous mineral carbonation has been presented by many as a promising strategy for ex-situ mineral carbonation, on the basis that organic additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. This thesis discusses and extends the current understanding of this process through geochemical modelling and detailed solid characterization. First, mineral carbonation is investigated in water alone, without additives, in order to understand and quantify the actual limitations of the process with specific magnesium silicate ores. Dissolution kinetics being critical with this process, the role of disodium oxalate as a dissolution accelerating agent is thoroughly examined with olivine, through dedicated experiments and comprehensive analysis of both solid and liquid phases. Under 20 bar of CO2, and irrespective of the conditions used, it is found that the formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of precipitating significant amounts of magnesium carbonate. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model. Other promising ligands from a dissolution perspective, namely citrate and EDTA, were also investigated. Contrary to oxalate, these do not form any solid by-products with magnesium, and yet they do not produce better carbonation results. The results and findings from this work cast strong doubts about the possibility of developing a viable direct aqueous mineral carbonation process using organic salts.

The bean plant anthracnose is caused by fungus Colletotrichum lindemuthianum (Sacc& Magnus) Scribner, which is considered one of the main diseases that attacks the culture, which might cause losses and final productivity decrease and one of the most used alternative of control is the chemical and genetic induction of resistance. The use of silicon in agriculture presents many benefits, such as: decrease of toxicity by metals, relief of saline stress and lack of water, increase of resistance to strong winds, increase of resistance to pathogens and insects, among others. Thus, the present paper has the aim of evaluating the effect of silicon as inductor of resistance to anthracnose in bean plant, by using different sources in the seeds’ coating. It was used four sources of silicon: ash of carbonized rice hull, dust of rock commercial product Potenccy® , the commercial product Supa Sílica, Agrichem® and the commercial product Silicon SiO2, Rigrantec®. It was conducted two experiments: in experiment 1 it was tested the silicon sources applied in seeds of culture IPR Graúna, susceptible to anthracnose, through sanitary and physiological evaluation of seeds and it was carried out the histological analysis of seedlings and tegument of the seeds to detect the presence of silicon. The silicon source which presented the best answers to the anthracnose control, in experiment 1, was used in experiment 2, that was performed in the field, with two cultures of bean susceptible to anthracnose (IPR Graúna and IPR Uirapuru), where it was assessed the emergency and symptoms in the seedlings. It was possible to identify silicates in the primary leaves of bean seedlings, deriving from silicon source Silicon SiO2, Rigrantec®. The application of silicon reduces the negative effect of inoculation with Colletotrichum lindemuthianum in bean seeds. / A antracnose do feijoeiro é causada pelo fungo Colletotrichum lindemuthianum (Sacc & Magnus) Scribner, sendo considerada uma das principais doenças que atacam a cultura, podendo ocasionar perdas e diminuição da produtividade final e uma das alternativas de controle mais utilizadas é a indução química e genética de resistência. O uso do silício na agricultura apresenta vários benefícios, tais como: diminuição de toxidez por metais, alívio do estresse salino e da falta de água, aumento da resistência a ventos fortes, aumento da resistência a patógenos e insetos, entre outros. Diante disso, o presente trabalho tem como objetivo avaliar o efeito do silício como indutor de resistência à antracnose do feijoeiro, utilizando diferentes fontes no recobrimento de sementes. Foram utilizadas quatro fontes de silício: cinza de casca de arroz carbonizada, pó de rocha produto comercial Potenccy®, o produto comercial Supa Sílica, Agrichem® e o produto comercial Silicon SiO2, Rigrantec®. Foram conduzidos dois experimentos: no experimento 1 foram testadas as fontes de silício aplicadas em sementes da cultivar IPR Graúna, suscetível a antracnose, através da avaliação sanitária e fisiológica das sementes, e foi realizada a análise histológica das plântulas e do tegumento das sementes para detectar a presença de silício. A fonte de silício que apresentou as melhores respostas para o controle da antracnose, no experimento 1, foi utilizada no experimento 2, que foi realizado em campo, com duas cultivares de feijão suscetíveis a antracnose (IPR Graúna e IPR Uirapuru), onde foram avaliadas a emergência e sintomas nas plântulas. Foi possível identificar silício nas folhas primárias de plântulas de feijão, somente para o tratamento com silício oriundo do produto comercial Silicon SiO2, Rigrantec®. A aplicação de silício reduz efeito negativo da inoculação com Colletotrichum lindemuthianum nas sementes de feijão.

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