Experimental determination of coexisting iron–titanium oxides in the systems FeTiAlO, FeTiAlMgO, FeTiAlMnO, and FeTiAlMgMnO at 800 and 900°C, 1–4 kbar, and relatively high oxygen fugacity

A synthetic, low-melting rhyolite composition containing TiO2 and iron oxide, with further separate additions of MgO, MnO, and MgO + MnO, was used in hydrothermal experiments to crystallize Ilm-Hem and Usp-Mt solid solutions at 800 and 900°C under redox conditions slightly below nickel–nickel oxide (NNO) to $$\approx 3\,\log_{10} f_{{{\text{O}}_{2}}}$$ units above the NNO oxygen buffer. These experiments provide calibration of the FeTi-oxide thermometer + oxygen barometer at conditions of temperature and oxygen fugacity poorly covered by previous equilibrium experiments. Isotherms for our data in Roozeboom diagrams of projected %usp vs. %ilm show a change in slope at ≈ 60% ilm, consistent with the second-order transition from FeTi-ordered Ilm to FeTi-disordered Ilm-Hem. This feature of the system accounts for some, but not all, of the differences from earlier thermodynamic calibrations of the thermobarometer. In rhyolite containing 1.0 wt.% MgO, 0.8 wt.% MnO, or MgO + MnO, Usp-Mt crystallized with up to 14% of aluminate components, and Ilm-Hem crystallized with up to 13% geikielite component and 17% pyrophanite component. Relative to the FeTiAlO system, these components displace the ferrite components in Usp-Mt, and the hematite component in Ilm-Hem. As a result, projected contents of ulvöspinel and ilmenite are increased. These changes are attributed to increased non-ideality along joins from end-member hematite and magnetite to their respective Mg- and Mn-bearing titanate and aluminate end-members. The compositional shifts are most pronounced in Ilm-Hem in the range Ilm50–80, a solvus region where the chemical potentials of the hematite and ilmenite components are nearly independent of composition. The solvus gap widens with addition of Mg and even further with Mn. The Bacon–Hirschmann correlation of Mg/Mn in Usp-Mt and coexisting Ilm-Hem is displaced toward increasing Mg/Mn in ilmenite with passage from ordered ilmenite to disordered hematite. Orthopyroxene and biotite crystallized in experiments with added MgO and MgO + MnO; their X Fe varies with $$\log_{10} f_{{{\text{O}}_{2}}}$$ and T consistent with equilibria among ferrosilite, annite, and ferrite components, and the chemical potentials of SiO2 and orthoclase in the liquid. Experimental equilibration rates increased in the order: Opx < Bt < Ilm-Hem < Usp-Mag

Nanosynthesis of Iron Based Material for Green Energy

In this work, nanosynthesis of multiple iron-based materials are explored to further their use in green renewable-energy applications. First, the nanosynthesis of the abundant, non-toxic semi-conductor Iron Disulfide (Iron Pyrite, Fool's Gold, FeS2) is investigated. Within these studies, it became possible to tune the shape of the FeS2 nanoparticles easily by modifying injection temperatures and iron precursors. From here, the growth mechanisms of the different shapes were elucidated by examining different time points within the synthesis. It was discovered that the FeS2 did not grow by Ostwald Ripening, but instead by Oriented Attachment. Knowing this, it was possible to not only further the shapes of FeS2 nanoparticles, but also manipulate the size and crystallinity. Focus was then shifted to creating larger micron sized FeS2 crystals. Larger crystals where achieved by a unique FeS nanowire precursor followed by sulfurization. The dominant crystal surface of these crystals could be regulated simply by the time and temperature of the sulfurization. Second, synthetic control of magnetic nanoparticles was examined. A novel synthesis of Iron Palladium (FePd) made possible by interdiffusion of iron into palladium nanocores was identified. Furthermore, a shell of Iron oxide (Fe2O3) could facilely be grown on the FePd nanoparticles, generating a FePd/Fe2O3 core/shell nanoparticle. These FePd/Fe2O3 core/shell particles provided an excellent foundation to create an L10- FePd/&#945;-Fe exchange-coupled nanocomposite that exhibited improved magnetic properties compared to its single phase FePd counterpart. However, the stabilizing ligand used within this FePd synthesis doped into the final nanoparticles, degraded the magnetic properties. iii To overcome the dopant ligand problem, a novel nanoalloy synthetic strategy of Metal Redox was developed. The Metal Redox strategy utilized the inherent reducing power of zero-valent metal sources to create a vast sampling of metal nanoalloys without the need of ligands or excess reducing agents. Stoichiometry of these nanoalloys could be readily adjusted by temperature and explained by simple chemical equilibrium concepts. The Metal Redox methodology was then expanded to shape control and tri-metallic alloys. Finally, the unique MnBi nanoalloy system was created using Metal Redox, making it the first ever reported solution processed formation of this material

Atomistic long-term simulation of heat and mass transport

We formulate a theory of non-equilibrium statistical thermodynamics for ensembles of atoms or molecules. The theory is an application of Jayne's maximum entropy principle, which allows the statistical treatment of systems away from equilibrium. In particular, neither temperature nor atomic fractions are required to be uniform but instead are allowed to take different values from particle to particle. In addition, following the Coleman-Noll method of continuum thermodynamics we derive a dissipation inequality expressed in terms of discrete thermodynamic fluxes and forces. This discrete dissipation inequality effectively sets the structure for discrete kinetic potentials that couple the microscopic field rates to the corresponding driving forces, thus resulting in a closed set of equations governing the evolution of the system. We complement the general theory with a variational meanfield theory that provides a basis for the formulation of computationally tractable approximations. We present several validation cases, concerned with equilibrium properties of alloys, heat conduction in silicon nanowires and hydrogen desorption from palladium thin films, that demonstrate the range and scope of the method and assess its fidelity and predictiveness. These validation cases are characterized by the need or desirability to account for atomic-level properties while simultaneously entailing time scales much longer than those accessible to direct molecular dynamics. The ability of simple meanfield models and discrete kinetic laws to reproduce equilibrium properties and long-term behavior of complex systems is remarkable

Application of statistical and decision-analytic models for evidence synthesis for decision-making in public health and the healthcare sector

With the awareness that healthcare is a limited resource, decision-makers are challenged to allocate it rationally and efficiently. Health economic methods of evidence synthesis for decision-making are useful to quantify healthcare resource utilisation, critically evaluate different interventions and ensure the implementation of the most effective or cost-effective strategy. The nine studies included in the present cumulative doctoral thesis aim to demonstrate the capability of statistical and decision-analytic modelling techniques to inform and support rational healthcare decision-making in Germany. Five studies apply statistical modelling in analyses of public health and health economic data. They show that the developed models are valuable instruments for examining patterns in the data and generating knowledge from observable data which can further be used in devising disease management and care programs as well as economic evaluations. Further, two health economic evaluations, which adopt the decision-analytic-modelling approach, show that decision-analytic modelling is a powerful tool to represent the epidemiology of infectious and non-infectious diseases on a population level, quantify the burden of the diseases, generalise the outcomes of clinical trials, and predict how the interventions can change the impact of the diseases on the health of the population. Additionally, two literature reviews examine the application of decision-analytic modelling in health economic evaluations. The first study reviews and empirically analyses health technology assessments by the German Institute for Medical Documentation and Information and demonstrates that the application of decision-analytic models improves the evidence produced for policy-making in the healthcare sector in Germany. The second systematic review focuses on methodological choices made in constructing decision-analytic models and explains how critically the structural and parametrical assumptions can influence the final message of the economic evaluations and shows that building a validated, reliable model as well as the transparent reporting is of high priority in facilitating the communication and implementation of the most cost-effective course of action. Overall, the present thesis shows the relevance and advantage of the application of models in synthesising evidence for decision-making. The included studies contribute to the current and future development of the methods used to address the problems of health economic efficiency. Further advances in the computational modelling techniques and data collection, from one side, will ease the decision-making process, but, from another side, will require increasing competence and understanding within the decision-making bodies

Multi-length scale 5D diffraction imaging of Ni-Pd/CeO2-ZrO2/Al2O3 catalyst during partial oxidation of methane

A 5D diffraction imaging experiment (with 3D spatial, 1D time/imposed operating conditions and 1D scattering signal) was performed with a Ni–Pd/CeO2–ZrO2/Al2O3 catalyst. The catalyst was investigated during both activation and partial oxidation of methane (POX). The spatio-temporal resolved diffraction data allowed us to obtain unprecedented insight into the behaviour and fate of the various metal and metal oxide species and how this is affected by the heterogeneity across catalyst particles. We show firstly, how Pd promotion although facilitating Ni reduction, over time leads to formation of unstable Ni–Pd metallic alloy, rendering the impact of Pd beyond the initial reduction less important. Furthermore, in the core of the particles, where the metallic Ni is primarily supported on Al2O3, poor resistance towards coke deposition was observed. We identified that this preceded via the formation of an active yet metastable interstitial solid solution of Ni–C and led to the exclusive formation of graphitic carbon, the only polymorph of coke observed. In contrast, at the outermost part of the catalyst particle, where Ni is predominantly supported on CeO2–ZrO2, the graphite formation was mitigated but sintering of Ni crystallites was more severe

Studies of Metal-Organic Polyhedra: Synthesis and Applications in Gas Storage and Separation

Metal-organic polyhedra (MOPs) are a class of porous materials, comprised of metal ions and organic ligands, which form discrete cage-like structures. Possessing large internal void volumes, the physical and chemical properties of MOPs can be tuned by appropriate selection of the metal and organic building units. The work presented in this thesis investigates the application of MOPs to environmentally significant gas storage and separation. The first chapter introduces MOPs as an emerging class of promising materials and discusses their historical development since the first examples of synthetic supramolecular structures. As microporous materials, MOPs demonstrate strong interactions with small molecules giving them promise as a medium for selective gas adsorption. These attributes are of interest in the areas of H2 storage and the capture of CO2. As such, Chapter 1 discusses the benefits and challenges of utilising porous materials in these areas. Chapter 2 presents synthetic routes to MOPs containing both internal and external functionalisation by modifying both the metal nodes and the organic components which constitute the supramolecular structure. Presented herein are the first permanently porous examples of this class of materials to incorporate two different metal elements into a single paddlewheel unit in a controlled manner. These bimetallic MOPs demonstrate a strong binding affinity as well as an impressive volumetric capacity for H2 gas furthering development of a suitable H2 storage solution. Chapter 3 explores the decoration of MOPs with various external functionality and the effect these motifs have on MOP packing in the crystalline matrix. The synthesis of several new organic pro-ligands and subsequent MOPs is also detailed within. A method of modelling single crystal X-ray diffraction data is described that provides insight into the interactions between MOP structures which are dominated by the chemistry of the MOP exteriors. The tendency of these large structural entities to reduce porosity is further studied using X-ray diffraction data and computational methods. The work in Chapter 4 focuses on the use of MOPs in a composite system rather than as a singular material. By combining MOPs with a highly permeable polymer, poly[1- (trimethylsilyl)-1-propyne] (PTMSP), a series of mixed matrix membranes are synthesised for application in separating N2 and CO2 gases, a challenge of global significance from both an environmental and economic perspective. The compatibility of these constituents is shown to have a significant impact on the physical properties as well as the gas separation performance of the resulting composites.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

Crystallization of primitive basaltic magmas at crustal pressures and genesis of the calc-alkaline igneous suite: experimental evidence from St Vincent, Lesser Antilles arc

International audienceNear-liquidus crystallization experiments have been carried out on two basalts (12.5 and 7.8 wt% MgO) from Soufriere, St Vincent (Lesser Antilles arc) to document the early stages of differentiation in calc-alkaline magmas. The water-undersaturated experiments were performed mostly at 4 kbar, with 1.6 to 7.7 wt% H2O in the melt, and under oxidizing conditions (ΔNNO = −0.8 to +2.4). A few 10 kbar experiments were also performed. Early differentiation of primitive, hydrous, high-magnesia basalts (HMB) is controlled by ol + cpx + sp fractionation. Residual melts of typical high-alumina basalt (HAB) composition are obtained after 30–40% crystallization. The role of H2O in depressing plagioclase crystallization leads to a direct relation between the Al2O3 content of the residual melt and its H2O concentration, calibrated as a geohygrometer. The most primitive phenocryst assemblage in the Soufriere suite (Fo89.6 olivine, Mg-, Al- and Ti-rich clinopyroxene, Cr–Al spinel) crystallized from near-primary (Mg# = 73.5), hydrous (∼5 wt% H2O) and very oxidized (ΔNNO = +1.5–2.0) HMB liquids at middle crustal pressures and temperatures from ∼1,160 to ∼1,060°C. Hornblende played no role in the early petrogenetic evolution. Derivative HAB melts may contain up to 7–8 wt% dissolved H2O. Primitive basaltic liquids at Soufriere, St Vincent, have a wide range of H2O concentrations (2–5 wt%)

Using Core-Shell Nanocatalysts to Unravel the Impact of Surface Structure on Catalytic Activity:

Thesis advisor: Udayan MohantyThe high surface area and atomic-level tunability offered by nanoparticles has defined their promise as heterogeneous catalysts. While initial studies began with nanoparticles of a single metal assuming thermodynamic shapes, modern work has focused on using nanoparticle composition and geometry to optimize nanocatalysts for a wide variety of reactions. Further optimization of these refined nanocatalysts remains difficult, however, as the factors that determine catalytic activity are intertwined and a fundamental understanding of each remains elusive. In this work, precise synthetic methods are used to tune a number of factors, including composition, strain, metal-to-metal charge transfer, atomic order, and surface faceting, and understand their impact on catalysis. The first chapter focuses on current achievements and challenges in the synthesis of intermetallic nanocatalysts, which offer long-range order that allows for total control of surface structure. A particular focus is given to the impact of the synthetic approach on the activity of the resulting nanoparticles. In the second chapter, multilayered Pd-(Ni-Pt)x nanoparticles serve as a controlled arena for the study of metallic mixing and order formation on the nanoscale. The third chapter controls the shell thickness of Au@PdPt core-alloyed shell nanoparticles on a nanometer scale to isolate strain at the nanoparticle surface. In the fourth chapter, the synthetic approaches of chapters two and three are applied to catalysis. In totality, the work presented here represents a brick in the foundation of understanding and exploiting structure-function relationships on the nanoscale, with an eye toward the rational design of tailored nanocatalysts.Thesis (PhD) — Boston College, 2020.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

The Effect of Principal Elements on Defect Evolution in Single-Phase Solid Solution Ni Alloys

The objectives of this thesis are: firstly, to investigate the effect of increasing chemical complexity on radiation-induced defect evolution (both in voids and dislocation loops) in Ni based single-phased concentrated solid solution alloys (SP-CSAs). SP-CSAs typically contain two to five elements in high or equiatomic concentrations. The compositionally complex but structurally simple features of SP-CSAs make them great candidates in studying irradiation-induced defect interactions. This was done by first performing a study on SP-CSAs in a single elevated irradiation temperature, and followed by testing the dose and temperature dependence of radiation tolerance of these alloys. Secondly, to understand the role of increasing alloy concentrations on defect migration mechanisms with Ni-xFe (x=up to 35%) binary alloys. Thirdly, to understand the effect of alloying elements on radiation-induced microstructural evolution with pure Ni and Ni-20X (X=Fe, Cr, Mn and Pd) binary alloys. Most of the tested samples were irradiated with 3.0 MeV Ni2+ ions at 500℃ up to damage levels of 60 dpa at peak dose. A combination of Transmission electron microscopy (TEM) was used to characterize the microstructure evolution of irradiated CSA samples, emphasizing void swelling and dislocation loop formation. As a result, void swelling decreased while the growth of dislocation loops was suppressed with increasing chemical complexity of an alloy in general. The exceptions were attributed to the difference in CSAs melting temperature. Two interstitial migration mechanisms; 1D and 3D mode, were proposed to explain the qualitative observation of defect distributions throughout the irradiation depth. The suppression on void swelling and delay of dislocation loop growth were attributed to the relatively localized 3D migration mode, which enhanced defect recombination in the main irradiated region. The transition of 1D to 3D mode for interstitials was quantitatively analyzed in Ni-xFe binary alloys using the mean free path of interstitial clusters. In the study of varying irradiation temperatures, the equiatomic Ni-based high entropy alloys (HEAs) have demonstrated superior swelling resistance than Ni-based medium entropy alloys (MEAs) over three homologous temperatures of irradiation. In NiCoFeCrMn, an order of magnitude increase on swelling was observed with increasing temperature, but the swelling performance was still comparable to ferritic steels. Between the two HEAs studied, alloying with Pd was found to have a stronger suppression effect on void and dislocation loop growth than alloying with Mn. This was attributed to the higher lattice distortion observed in NiCoFeCrPd than in NiCoFeCrMn. No significant increase was observed on the equilibrium vacancy concentration as the number of alloying components increased. In the study of Ni-20X, it was found that the average size of defect clusters decreased as the solute atomic volume size factor increased. Oversized magnetic solutes can act as strong trapping sites for interstitials and suppress the growth of dislocation loops. The average dislocation loop size in Ni-20Fe was four times larger than Ni-20Pd (atomic volume factor is 10.6% and 41.3%) but an order of magnitude lower in density. Overall, the alloying effect on defects is more significant in concentrated binary alloys than in dilute binary alloys, due to the concentration difference of alloying atoms and the interstitial dominant migration mechanisms in the main irradiated region. Furthermore, this study demonstrated that similar results on swelling resistance can be achieved in HEAs and well-designed binary alloys with increased concentration or atomic volume factor of alloying elements.PHDNuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149968/1/taiyang_1.pd