Chondritic meteorites are undifferentiated fragments of asteroids that contain the oldest solids formed in our Solar System. Their primitive, solar-like chemical compositions indicate that they experienced very little processing following accretion to their parent bodies. As such, they retain the best records of chemical and physical processes active in the protoplanetary disk during planet formation. Chondritic meteorites are depleted relative to the sun in volatile elements such as S and O. In addition to being important components of organic material, these elements exert a strong influence on the behavior of other more refractory species and the composition of planets. Understanding their distribution is therefore of key interest to the scientific community. While the bulk abundance of volatile elements in solid phases present in meteorites is below solar values, some meteorites record volatile-rich gas phases. The Rumuruti (R) chondrites record environments rich in both S and O, making them ideal probes for volatile enhancement in the early Solar System. Disentangling the effects of parent-body processing on pre-accretionary signatures requires unequilibrated meteorite samples. These samples are rare in the R chondrites. Here, I report analyses of unequilibrated clasts in two thin sections from the same meteorite, PRE 95404 (R3.2 to R4). Data include high resolution element maps, EMP chemical analyses from silicate, sulfide, phosphate, and spinel phases, SIMS oxygen isotope ratios of chondrules, and electron diffraction patterns from Cu-bearing phases. Oxygen isotope ratios and chondrule fO2 levels are consistent with type II chondrules in LL chondrites. Chondrule-sized, rounded sulfide nodules are ubiquitous in both thin sections. There are multiple instances of sulfide-silicate relationships that are petrologically similar to compound chondrules, suggesting that sulfide nodules and silicate chondrules formed as coexisting melts. This hypothesis is supported by the presence of phosphate inclusions and Cu-rich lamellae in both sulfide nodules and sulfide assemblages within silicate chondrules. Thermodynamic analyses indicate that sulfide melts reached temperatures up to 1138 °C and fS2 of 2 x 10^(-3) atm. These conditions require total pressures on the order of 1 atm, and a dust- or ice-rich environment. Comparison with current models suggest that either the environmental parameters used to model chondrule formation prior to planetesimal formation should be adjusted to meet this pressure constraint, or R chondrite chondrules may have formed through planetesimal bow shocks or impacts. The pre-accretionary environment recorded by unequilibrated R chondrites was therefore highly sulfidizing, and had fO2 higher than solar composition, but lower than the equilibrated R chondrites.Chalcopyrite is rare in meteorites, but forms terrestrially in hydrothermal sulfide deposits. It was previously reported in the R chondrites. I studied thin sections from PRE 95411 (R3 or R4), PCA 91002 (R3.8 to R5), and NWA 7514 (R6) using Cu X-ray maps and EMP chemical analyses of sulfide phases. I found chalcopyrite in all three samples. TEM electron diffraction data from a representative assemblage in PRE 95411 are consistent with this mineral identification. TEM images and X-ray maps reveal the presence of an oxide vein. A cubanite-like phase was identified in PCA 91002. Electron diffraction patterns are consistent with isocubanite. Cu-rich lamellae in the unequilibrated clasts of PRE 95404 are the presumed precursor materials for chalcopyrite and isocubanite. Diffraction patterns from these precursor phases index to bornite. I hypothesize that bornite formed during melt crystallization prior to accretion. Hydrothermal alteration on the parent body by an Fe-rich aqueous phase between 200 and 300°C resulted in the formation of isocubanite and chalcopyrite. In most instances, isocubanite may have transformed to chalcopyrite and pyrrhotite at temperatures below 210°C. This environment was both oxidizing and sulfidizing, suggesting that the R chondrites record an extended history of volatile-rich interaction. These results indicate that hydrothermal alteration of sulfides on the R chondrite parent body was pervasive and occurred even in low petrologic types. This high temperature aqueous activity is distinct from both the low temperature aqueous alteration of the carbonaceous chondrites and the high temperature, anhydrous alteration of the ordinary chondrites.

Les travaux présentés dans cette thèse portent sur la synthèse et la caractérisation structurale et physico-chimique de composés sulfures à propriétés thermoélectriques. Un intérêt a été porté sur plusieurs familles de composés sulfures avec pour objectif le développement et/ou l’optimisation des performances thermoélectriques de ces composés.Un premier composé binaire, TiS2, a été élaboré par mécanosynthèse suivi d’une étape de densification par Spark Plasma Sintering (SPS). Les caractérisations structurales ont démontré un effet du processus d’élaboration sur la microstructure ainsi que sur la stœchiométrie du composé. Ce procédé induit une réduction considérable de la conductivité thermique mais aussi électrique du matériau ne permettant pas d’optimiser la figure de mérite du composé. Un second composé a ensuite été développé selon deux voies de synthèses (conventionnelle et mécanosynthèse), le composé ternaire Cu4Sn7S16. Il a été mis en évidence que ce composé semi-conducteur possède une structure complexe qui favorise une conductivité thermique intrinsèquement faible. Les propriétés thermoélectriques ainsi que l’influence de la non-stœchiométrie sur ce composé ont été rapportées. Enfin les composés CuCoxTi2-xS4 et Cu26V2Sn6S32 ont été au cœur des derniers résultats présentés. Ces composés présentent des propriétés de transport plus métalliques propices à l’obtention de facteurs de puissance plus élevés que dans composé Cu4Sn7S16. D’une part, l’élaboration du matériau et l’influence du taux de Co sur le transport électronique ont été discutées sur le composé CuCoxTi2-xS4. D’autre part, l’élaboration par la mécanosynthèse ainsi que les conditions de densification ont été reliés aux propriétés de transport du composé Cu26V2Sn6S32. Une amélioration significative des performances thermoélectriques de ce dernier a été rapportée.Ces différentes études ouvrent des perspectives intéressantes dans l’élaboration et l’optimisation des composés sulfures en vue d’applications industrielles. / The work presented in this thesis focuses on the synthesis and the structural/physicochemical characterizations of sulfide compounds with thermoelectric properties. Several families of sulphide compounds have been studied with the aim of developing and/or optimizing their thermoelectric performances.A binary compound, TiS2, was synthesized by mechanical alloying followed by a densification using Spark Plasma Sintering (SPS). The structural characterizations have revealed the effect of the elaboration on the microstructure and stoichiometry of the compound. This process induces a considerable reduction in the thermal and electrical conductivity of the material which hindered the optimization of the figure of merit. The ternary compound Cu4Sn7S16 was then developed according to two synthetic routes (conventional and mechanical alloying). It has been demonstrated that this semiconductor compound has a complex structure which promotes an intrinsic low thermal conductivity. The influence of the non-stoichiometry on the thermoelectric properties has been reported. Finally, the CuCoxTi2-xS4 and Cu26V2Sn6S32 compounds were the last interesting results presented. These compounds show metallic transport properties with high power factors. The synthesis and the influence of the Co content on the electronic transport properties have been discussed on the CuCoxTi2-xS4 compound. The effect of mechanical alloying and densification conditions were related to the transport properties of the Cu26V2Sn6S32 compound. Substantial improvement of the thermoelectric performances as reported.These various studies open interesting perspectives for the development and optimization of sulfide compounds for industrial application.

This dissertation describes my efforts in the Nuckolls lab to expand synthetic methods of wet-chemistry superatom synthesis, superatom surface ligand and core modification, and assembly of superatoms into materials with useful, cumulative properties. This work builds off of previous work from the Nuckolls lab describing photolabile ligand substitution and use of this technique to covalently bind superatoms to form various materials such as polymers and weaved sheets. This work will focus on the Chevrel-type M₆E₈L₆ metal-chalcogenide cluster Co₆Se₈, modification of its outer stabilizing ligands, and fusion of its core with other Co₆Se₈ superatoms to form fused dimers. Chapter 1 consists of a review of background material that forms a foundational basis for this work. The field of superatoms and superatomic materials will first be covered to contextualize this work in the field at large. Then, the prior work on wet-chemistry synthesis of Co₆Se₈ superatoms with replaceable, photolabile carbonyl (CO) ligands will be discussed. Finally, previous dimensionally-controlled assembly of materials using these carbonylated superatoms will be covered. Chapter 2 consists of the discovery of a masking carbene ligand generated from trimethylsilyl diazomethane (TMSD) and its use to create a new, electronically-coupled superatom dimer species (Co₁₂Se1₆(PEt₃)₁₀) that shows evidence of quantum confinement akin to nanoparticles and nanoparticle assemblies. Chapter 3 consists of new ligand substitution and methods to synthetically functionalize the fused dimer introduced in Chapter 2. The reactive carbene-ligated cluster is used to add new functional groups that were previously inaccessible to these cobalt-selenide clusters. New multi-carbene clusters are demonstrated as well as the use of site-differentiated clusters to form functionalized fused dimers from bis-carbonyl clusters. Chapter 4 consists of an investigation of the carbene cluster and insights that may be used in the future to finally expand cluster fusion into a chain. A reversible bridging of the carbene ligand based on temperature and oxidation state is analyzed experimentally and computationally. This information is used to synthesize a series of new carbene clusters which are used to try and assemble electronically-coupled, fused Co₆Se₈ superatomic materials.

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Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaf 69. / by Alfred Olu Agunloye. / M.S.

This investigation showed that a single bacterium was capable of sulfide oxidation in exposed ore bodies. This single bacterium was isolated and characterized. It exhibited different characteristics than any previously known organism. It was found to be a chemosynthetic autotroph. An optimum nutrient concentration was determined for pyrite oxidation. The nutrient concentration was determined for pyrite oxidation. The nutrient contains only a source of phosphate and nitrogen. Urea was found to be a better source of nitrogen than ammonium sulfate which had previously been used. The effect of various organic compounds on the oxidation of pyrite was observed. Glucose and sucrose showed no affect. Acetone slightly inhibited the oxidation. Benzene almost completely stopped the reaction. Kerosene showed no effect if the surface of the nutrient solution was not covered completely. It was found that a bacterium of the same type as that isolated in this investigation is responsible for sulfide oxidation at a location in Mexico. Thus, the oxidation of sulfides by bacteria is not a unique occurrence but is believed to occur wherever proper conditions are present.

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No description available.

Important reactions in the environment often occur at the interface between a mineral surface and aqueous phase. Reactions occurring at this interface often control the uptake or release of harmful components resulting in the geochemical cycling of elements in the environment. Additionally, minerals are commonly used in the remediation of contaminated areas, where similar chemistry occurs at their interfaces. Thus, studies of the chemistry of these interfaces are essential to our understanding of complex environments. Many of these processes are controlled by electron transfer reactions between adsorbates and the mineral interface, and it is here where this research presented will concentrate. The studies in this thesis key in on redox chemistry on various environmentally relevant iron minerals, including ferrihydrite, pyrite, and amorphous iron sulfide. A large portion of this body of work is dedicated to the understanding of the surface mediated reaction between chromate (Cr(VI)) and arsenite (As(III)). Both of these species are present in the environment and are detrimental to human health. Using in- and ex-situ experiments we have monitored the coupled redox transformation of Cr(VI) and As(III) to chromite (Cr(III)) and arsenate (As(V)). Quantum mechanical modeling was used to support the experimental studies of this novel redox chemistry. The reaction was monitored in situ, using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), on the surface of the iron oxyhydroxide, ferrihydrite, at various solution pH values by following vibrational modes unique to Cr(VI), As(III), and As(V). At pH < 9 we observed an initial growth of Cr(VI) vibrational modes due to adsorption, followed by the simultaneous decrease in Cr(VI) vibrational modes and increase in As(V) vibrational modes. Ex situ analysis of the reaction products via X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) indicated that there was an increase in the percentage of reaction products as the pH decreased. Quantum mechanical calculations were completed to model the reaction of Cr(VI) and As(III) on the ferrihydrite surface by analyzing differences in geometric and electronic structural changes and thermodynamic preferences. The results indicate that Cr(VI) and As(III) adsorbed physically separated from each other is not only thermodynamically favorable but results in changes in As(III)-Fe and Cr(VI)-Fe atomic distances, towards those characteristic of As(V)-Fe and Cr(III)-Fe. Thus a mechanism where electron transport occurs through bulk states is plausible. Additionally, natural bond order analysis reveals a redistribution of electron density away from the Cr(VI) atomic center upon adsorption, indicating probable changes in Cr(VI) reduction potential. The electrochemical reduction of Cr(VI) on three surfaces, ferrihydrite, titanium dioxide, and aluminum oxides, indicate that Cr(VI) reduction potential is surface dependent, an observation that has significance for redox chemistry in the environment. The interaction of ferric, Fe(III), with iron sulfide surfaces (during and after coal mining activities) contributes to the detrimental environmental problem known as acid mine drainage (AMD). We investigated whether Fe(III) chelating siderophores could be used to suppress the oxidation of iron sulfide surfaces and the resulting AMD chemistry. The exposure of the iron sulfide, pyrite, to the siderophore, desferrioxamine B (DFOB) at initial pH values of 3, 6, and 8 under oxic conditions showed a significant decrease in the rate of dissolution of pyrite: decreases of 43.7%, 37.5% and 78.4%, respectively. An even greater decrease in pyrite oxidation was observed when DFOB was present in anoxic conditions, specifically 56.1%, 74.4% and 91.5%, at pH 3, 6 and 8, respectively. We further compared the rate of dissolution between DFOB and another siderophore, enterobactin, which is a stronger chelator of Fe(III). The presence of enterobactin suppressed pyrite oxidation more than DFOB, consistent with the contention that inhibiting the interaction of Fe(III) with pyrite will decrease the oxidation of the mineral. We also analyzed the exposure of the pyrite surface to DFOB using ATR-FTIR, to determine if any surface chelation occurs. We found that when Fe(III) is present on the pyrite surface, DFOB adsorbs to the surface via hydroxamate groups, similar to the aqueous phase spectra of DFOB-Fe(III) complex. In contrast the spectra do not exhibit hydroxamate vibrational modes when Fe(III) was not initially present on the pyrite surface and in this circumstance the spectra resembled that of aqueous phase unchelated DFOB. Taken together the results showed that siderophore inhibited pyrite oxidation by chelating Fe(III) present on the pyrite surface and in solution. Finally, the reduction of NO(g) to NH3/NH4+ with amorphous iron sulfide (FeS) was studied. The exposure of NO gas to a suspension of FeS solid resulted in the conversion of 2.3% NO(g) to the reaction product ammonia (NH3), which was found to grow over time, while the exposure of NO(g) to water (in the absence of mineral) resulted in no NH3 formation. Additionally, we completed in situ analysis of NO exposure to FeS as a function of water concentration using ATR-FTIR. The exposure of NO to an aqueous paste of FeS or a FeS film (with adsorbed H2O), resulted in the adsorption of NO to the FeS surface and the subsequent production of NH3, as indicated by N-H vibrational modes. In contrast, the removal of all water, via thermal desorption from the film, resulted in the adsorption of NO but did not show vibrational modes consistent with the formation of NH3. We conclude that the presence of H2O, as a source of protons, and a FeS surface, as a source of electrons, results in the transformation of NO to NH3 via a heterogeneous reaction. This result has important implications towards remediation of NOx gases and mechanisms of prebiotic synthesis of NH3. In summary, the research presented expands our understanding of redox reactions at mineral interfaces in the environment. The work herein aims to inform and aid in the development of remediation methods for arsenic and chromium, the formulation of methods to inhibit the production of acid mine drainage, and develop our understanding of toxic NOx gas reduction on surfaces. / Chemistry

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 95-99. / by Simon Muir Peacock. / M.S.