Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U-Th)/He data patterns from these surfaces and host rock apatite (U-Th)The data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time temperature histories. Temperatures of >similar to 700-1200 degrees C, depending on asperity size, are sufficient to induce 85-100% He loss from hematite within 200 pm of the fault surface. Spatially-isolated, high temperature microtextures imply spatially -variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (M-w approximate to -3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes. (C) 2017 Elsevier B.V. All rights reserved.

Cette thèse a été réalisée dans le cadre d’une cotutelle de thèse (3 ans) Franco-Libanaise entre l’Université Pierre et Marie Curie de Paris et l’Université Libanaise de Beyrouth. Nabil Tabaja a été entièrement financé par le Groupe de Recherche MAPE (Nanosized Porous Materials, Preparation, Advanced Characterization and Environmental Applications) de Beyrouth que nous tenons à remercier. Le but de ce travail était de tester et de valoriser des catalyseurs à base d’oxydes de fer et de ferrites pour la dépollution des eaux par photocatalyse sous lumière visible puis solaire. Les catalyseurs étudiés ont été préparés en employant des silices poreuses en tant que gabarits pour obtenir majoritairement : soit des nanoparticules, NP, d’oxydes de fer ayant cristallisé à l’intérieur des pores des silices (INTERNES, répliquées), soit des nanoparticules ayant cristallisé à l’extérieur des grains de silice et formées lors des traitements d’activation thermiques (EXTERNES). Nous avons employées des techniques faciles à transférer pour obtenir les silices (Chapitre 1). Notre objectif à ce niveau était d’obtenir plus de 50g d’au moins six silices ayant des diamètres de mésopores différents. La variation de ces diamètres s’accompagne de modifications des connections entre les mésopores principaux et des propriétés des surfaces des silices. Différents sels précurseurs de fer (chlorure, nitrate) ou des mélanges de métaux ont été déposées sur les différentes silices obtenues par des techniques de dépôt de type deux solvants (2S). Les échantillons ont été traités thermiquement à 700°C sous air pour obtenir des nanoparticules d’oxydes (Chapitre 2). Nous montrons que, si le diamètre des NP nanorépliquées est en général proche du diamètre des pores des silices initiales, les formes et la dispersion des nanoparticules internes dans les grains de silice dépendent de différents facteurs expérimentaux, des sels précurseurs, des solvants et du type de silice sélectionnée. Nous montrons également que la formation des particules externes est associée au traitement thermique imposé et peut être favorisée en choisissant le bon solvant et le bon sel précurseur pour une silice déterminée. Des premiers tests ayant démontrés un taux de lixiviation important dans le cas de catalyseur au fer, nous avons testé des ferrites de différentes compositions (cations (II) de différentes électronégativités, Ni(II), Co(II), Cd(II), Zn(II) ; cation (III), Cr(III)). Afin de comparer la réactivité catalytique des catalyseurs, deux types de réactions sont introduites successivement. Le premier type de réaction, l’oxydation photocatalytique du méthanol et du formaldéhyde, a été employé à titre fondamental. Dans ce cas, notre objectif était d’étudier la sélectivité de la réaction et d’identifier de façon inambigue quelles nanoparticules présentes dans la formulation des catalyseurs permettent, partant d’une espèce à un seul carbone, d’obtenir des produits à 2 ou plus atomes de carbone (Chapitre III). La seconde réaction, l’oxydation photocatalytique d’un pesticide, a été employée pour démontrer que les catalyseurs peuvent être utiles à titre appliqué. Le pesticide sélectionné a été le carbendazime (Chapitre IV) dont nous avons suivi la décomposition. Ces études n’ont été possibles que grâce à l’emploi de techniques de caractérisation avancées, de type TOC et GC-MS. Les meilleures activités catalytiques ont été analysées en fonction de la présence d’une majorité de NP internes et/ou externes et d’autres espèces plus dispersées et non visibles par DRX. / This thesis was carried out as part of a Franco-Lebanese collaboration thesis (3 years) between the University of Pierre et Marie Curie in Paris and the Lebanese University in Beirut. Nabil Tabaja was fully funded by the Research Group MAPE (nanosized Porous Materials, Preparation, Advanced Characterization and Environmental Applications) Beirut that we thank.The purpose of this study was to test and develop catalysts based on iron oxides and ferrites for decontamination of water by photocatalysis under visible and sunlight. The catalysts studied were prepared by using porous silica as templates to obtain predominantly either nanoparticles, NP, iron oxides having crystallized within the pores of the silica (INTERNAL, replicated), or nanoparticles having crystallized outside the silica grains formed and during the thermal activation treatments (external). We employed techniques easily transferable to obtain silicas (Chapter 1). Our goal at this level was more than 50 grams of at least six silicas having different diameters of mesopores. The change in these diameters is accompanied by changes in connections between major mesoporous silicas and the properties of surfaces. Various iron precursor salts (chloride or nitrate) or metal mixtures were deposited on the various silicas obtained by the two solvents techniques (2S). The samples were calcined at 700 ° C in air to obtain oxide nanoparticles (Chapter 2). We show that, if the diameter of NP nanoreplicated is generally close to the pore diameter of the initial silicas, and forms the dispersion of nanoparticles in the inner silica grain depends on various experimental factors of the precursor salts, solvents and the type of the selected silica. We also show that the formation of particles is associated with the external heat treatment can be promoted and imposed by choosing the right solvent and the right precursor salt for a specific silica. Initial tests have demonstrated an important release rate in the case of iron catalyst, we tested different compositions ferrites ((II) cations of different electronegativities, Ni (II), Co (II), Cd (II), Zn (II) cation (III), Cr (III)). In order to compare the catalytic activity of the catalysts, two types of reactions are successively introduced. The first type of reaction, the photocatalytic oxidation of methanol and formaldehyde was employed as fundamental. In this case, our objective was to study the selectivity of the reaction and identify what way inambigue nanoparticles in the formulation of catalysts allow, starting from a species to a single carbon, to obtain products with 2 or more carbon atoms (Chapter III). The second reaction, the photocatalytic oxidation of a pesticide, was used to demonstrate that the catalysts may be useful as applied. The pesticide was selected carbendazim (Chapter IV) which we have followed the breakdown. These studies have been possible thanks to the use of advanced characterization techniques, type TOC and GC-MS. The best catalytic activities were analyzed according to the presence of a majority of internal and / or external NP and other species more dispersed and invisible by XRD.

The goal of this thesis is to investigate the kinetics and amount of SO2 uptake on hematite, which will act as a representative of mineral dust aerosol. The environmental reaction chamber used here will allow the variation of water vapor pressure to examine the effect of relative humidity (RH) on these parameters. The role of a common atmospheric oxidant, ozone, in the uptake process will also be investigated. The results will be presented with emphasis on the role of hematite in mineral dust aerosols as a sink of SO2, and the possible acidification of hematite particles through heterogeneous reaction pathways.

Hematite (α-Fe2O3) is a common, naturally occurring iron oxide, found throughout the earth's crust and atmosphere. Hematite is of interest to the scientific community because it is able to incite a reaction that produces hydrogen gas (H2), which is a form of clean energy (Bora et al., 2013). The composition of hematite in nature is also used to make inferences about conditions on early earth's surface (Guo et al., 2013). Hematite is useful for clean energy production and as an environmental indicator partly because of its apparent stability. However, some evidence suggests that hematite might not be as stable as previously thought. Many iron oxides undergo Fe atom exchange when they come into contact with aqueous Fe(II), as often occurs in nature (Pedersen et al., 2005, Jones et al., 2009, Gorski et al., 2012, Handler et al., 2009). This atom exchange can result in elements and nutrients being taken up or released from the iron oxides as they recrystallize (Frierdich & Catalano, 2012, Cwiertny et al., 2008, Boland et al., 2014). Although atom exchange has not been directly shown in hematite, it has been demonstrated that trace metals are released from hematite in the presence of aqueous Fe(II), implying that exchange may be occurring (Frierdich et al., 2011). Here, we directly demonstrate Fe atom exchange between hematite and aqueous Fe(II). This work provides knowledge concerning the surface chemistry of hematite that has important implications for clean energy production and the environment.

The recent momentum in energy research has simplified converting solar to electrical energy through photoelectrochemical (PEC) cells. There are numerous benefits to these PEC cells, such as the inexpensive fabrication of thin film, reduction in absorption loss (due to transparent electrolyte), and a substantial increase in the energy conversion efficiency. Alpha-hematite ([U+F061]-Fe2O3) has received considerable attention as a photoanode for water-splitting applications in photoelectrochemical (PEC) devices. The alpha-hematite ([U+F061]-Fe2O3) nanomaterial is attractive due to its bandgap of 2.1eV allowing it to absorb visible light. Other benefits of [U+F061]-Fe2O3 include low cost, chemical stability and availability in nature, and excellent photoelectrochemical (PEC) properties to split water into hydrogen and oxygen. However, [U+F061]-Fe2O3 suffers from low conductivity, slow surface kinetics, and low carrier diffusion that causes degradation of PEC device performance. The low carrier diffusion of [U+F061]-hematite is related to higher resistivity, slow surface kinetics, low electron mobility, and higher electro-hole combinations. All the drawbacks of [U+F061]-Fe2O3, such as low carrier mobility and electronic diffusion properties, can be enhanced by doping, which forms the nanocomposite and nanostructure films. In this study, all nanomaterials were synthesized utilizing the sol-gel technique and investigated using Scanning Electron Microscopy (SEM), X-ray Diffractometer (XRD), UV-Visible Spectrophotometer (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR), Raman techniques, Particle Analyzer, Cyclic Voltammetry (CV), and Chronoamperometry, respectively. The surface morphology is studied by SEM. X-Ray diffractometer (XRD) is used to identify the crystalline phase and to estimate the crystalline size. FTIR is used to identify the chemical bonds as well as functional groups in the compound. A UV-Vis absorption spectral study may assist in understanding electronic structure of the optical band gap of the material. Cyclic voltammetry and chronoamperometry were used to estimate the diffusion coefficient and study electrochemical activities at the electrode/electrolyte interface. In this investigation, the [U+F061]-Fe2O3 was doped with various materials such as metal oxide (aluminum, Al), dichalcogenide (molybdenum disulfide, MoS2), and co-catalyst (titanium dioxide, TiO2). By doping or composite formation with different percentage ratios (0.5, 10, 20, 30) of aluminum (Al) containing [U+F061]-Fe2O3, the mobility and carrier diffusion properties of [U+F061]-hematite ([U+F061]-Fe2O3) can be enhanced. The new composite, Al-[U+F061]-Fe2O3, improved charge transport properties through strain introduction in the lattice structure, thus increasing light absorption. The increase of Al contents in [U+F061]-Fe2O3 shows clustering due to the denser formation of the Al-[U+F061]-Fe2O3 particle. The presence of aluminum causes the change in structural and optical and morphological properties of Al-[U+F061]-Fe2O3 more than the properties of the [U+F061]-Fe2O3 photocatalyst. There is a marked variation in the bandgap from 2.1 to 2.4 eV. The structure of the composite formation Al-[U+F061]-Fe2O3, due to a high percentage of Al, shows a rhombohedra structure. The photocurrent (35 A/cm2) clearly distinguishes the enhanced hydrogen production of the Al-[U+F061]-Fe2O3 based photocatalyst. This work has been conducted with several percentages (0.1, 0.2, 0.5, 1, 2, 5) of molybdenum disulfide (MoS2) that has shown enhanced photocatalytic activity due to its bonding, chemical composition, and nanoparticle growth on the graphene films. The MoS2 material has a bandgap of 1.8 eV that works in visible light, responding as a photocatalyst. The photocurrent and electrode/electrolyte interface of MoS2-[U+F061]-Fe2O3 nanocomposite films were investigated using electrochemical techniques. The MoS2 material could help to play a central role in charge transfer with its slow recombination of electron-hole pairs created due to photo-energy with the charge transfer rate between surface and electrons. The bandgap of the MoS2 doped [U+F061]-Fe2O3 nanocomposite has been estimated to be vary from 1.94 to 2.17 eV. The nanocomposite MoS2-[U+F061]-Fe2O3 films confirmed to be rhombohedral structure with a lower band gap than Al-[U+F061]-Fe2O3 nanomaterial. The nanocomposite MoS2-[U+F061]-Fe2O3 films revealed a more enhanced photocurrent (180 μA/cm2) than pristine [U+F061]-Fe2O3 and other transition metal doped Al-[U+F061]-Fe2O3 nanostructured films. The p-n configuration has been used because MoS2 can remove the holes from the n-type semiconductor by making a p-n configuration. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as the n-type and ND-RRPHTh as the p-type deposited on both n-type silicon and FTO-coated glass plates. The p-n photoelectrochemical cell is stable and allows for eliminating the photo-corrosion process. Nanomaterial-based electrodes [U+F061]-Fe2O3-MoS2 and ND-RRPHTh have shown an improved hydrogen release compared to [U+F061]-Fe2O3, Al-[U+F061]-Fe2O3 and MoS2-[U+F061]-Fe2O3 nanostructured films in PEC cells. By using p-n configuration, the chronoamperometry results showed that 1% MoS2 in MoS2-[U+F061]-Fe2O3 nanocomposite can be a suitable structure to obtain a higher photocurrent density. The photoelectrochemical properties of the p-n configuration of MoS2-α-Fe2O3 as n-type and ND-RRPHTh as p-type showed 3-4 times higher (450 A/cm2) in current density and energy conversion efficiencies than parent electrode materials in an electrolyte of 1M of NaOH in PEC cells. Titanium dioxide (TiO2) is known as one of the most explored electrode materials due to its physical and chemical stability in aqueous materials and its non-toxicity. TiO2 has been investigated because of the low cost for the fabrication of photoelectrochemical stability and inexpensive material. Incorporation of various percentages (2.5, 5, 16, 25, 50) of TiO2 in Fe2O3 could achieve better efficiencies as the photoanode by enhancing the electron concentration and low combination rate, and both materials can have a wide range of wavelength which could absorb light in both UV and visible spectrum ranges. TiO2 doped with [U+F061]-Fe2O3 film was shown as increasing contacting area with the electrolyte, reducing e-h recombination and shift light absorption along with visible region. The [U+F061]-Fe2O3-TiO2 nanomaterial has shown a more enhanced photocurrent (800 μA/cm2) than metal doped [U+F061]-Fe2O3 photoelectrochemical devices.

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

The study aimed at investigating the chemical composition and microstructure of raw iron ore from the deposits in Muko area (south-western Uganda). The quality of this iron ore was evaluated to establish its suitability to serve as a raw material for iron production. Samples were taken from the six hills of Muko ore deposits and tests carried out to establish their composition and properties. X-ray diffraction and scanning electron microscopy were employed in the investigation and chemical analysis performed to determine the compounds constituting the ore. The quality of this ore was compared to generalized world market standards and ores from other nations. It was found that Muko ore is a rich hematite grade with Fe content above 65%. It has little gangue (&lt;6% SiO2 and 3-4% Al2O3) and low contents of the deleterious elements (P ~ 0.02% and S &lt; 0.006%), which correspond to acceptable levels for commercial iron ores. / <p>QC 20130531</p> / Sustainable Technology Development in the Lake Victoria Region

No description available.

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Thesis (Ph. D.)--University of New South Wales, 2005. / Also available online.