Browsing by Subject "X-ray diffraction"
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Item Geochemistry and high-resolution chemostratigraphy of the Haynesville Formation, East Texas(2015-05) Bitar Nehme, Rita Abdo; Rowe, Harry; Fisher, W. L. (William Lawrence), 1932-; Kerans, CharlesThe Upper Jurassic Haynesville Formation of East Texas and Louisiana is an organic-rich calcareous mudrock that is Kimmeridgian in age. It underlies the less calcareous Bossier Shale, and it overlies the Smackover Formation limestone. The Haynesville has low permeability, but a relative high porosity, compared to other mudrock formations. Mudrocks are the most common sedimentary rock and some of the most challenging to study, analyze and understand. Despite having a homogeneous appearance on a macroscopic scale, mudrocks often have high variability in facies and composition on the microscopic scale and elemental level. Many studies and methods have been developed to identify facies and stratigraphic variations in mudrocks. A complete understanding of these variations is valuable to comprehend paleoenvironments, paleoclimate and paleoceanographic conditions. Mudrocks studies are also beneficial to shale exploration because these formations, which have a high hydrocarbon content, can be targeted by oil and gas companies for exploration and production. Geochemical methods, chemostratigraphy in particular, will be used in this thesis to complement core description, petrophysical studies and sedimentological studies. This thesis focuses on acquiring chemostratigraphic data from X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) measurements to identify elemental and mineralogical variations in the T. W. George core, from the Haynesville Formation in Harrison County, Texas. The data are linked to core description and are analyzed using Hierarchical Cluster Analysis (HCA) to acquire a better understanding of the paleoceanographic conditions and depositional environments that controlled the sediment deposition of the Haynesville Formation. The Haynesville Formation comprises a Ca-rich lower Haynesville, a more Ca-rich upper Haynesville, and underlies the Si-rich and Ca-poor Bossier. The dominant condition during deposition is anoxic/euxinic in the lower Haynesville becoming dysoxic in the upper Haynesville and more oxygenated in the Bossier Formation. The greenhouse climate of the Late Jurassic led to the deposition of strata yielding petroleum source rocks such as the Haynesville Formation that today have great economic value. Thus, studying the Haynesville has both academic and economic importance.Item Nineteenth century concrete in Seguin, Texas: construction materials & techniques(2014-08) Hunter, Sarah Beth; Gale, Frances R.; Holleran, MichaelThis investigation centers on early concrete technology used in Seguin, Texas, during the mid-19th century. Over the course of fifty years, more than ninety concrete structures were built in Seguin. Over the last century, these have dwindled to twenty extant structures. Much of the previous Seguin concrete era research has focused on the historical narrative and architectural description. This study aims to answer questions that previous research has not — it investigated the raw materials used in making Seguin’s concrete. The results provide new information about the Seguin concrete structures, providing guidance for their long-term maintenance. The materials analysis uses instrumental techniques such as scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction to determine the chemical composition and crystalline structure of the cement binder from several extant structures in Seguin. Gathering both qualitative and quantitative data for the binder allowed us to identify the raw materials used in the concrete and better understand the construction methods. Studying the materials and methods increased our understanding of these historic structures and will inform future preservation efforts.Item Strengthening Mechanisms of Sputtered Copper, Cobalt and Their Nanocomposites(2014-04-28) Liu, YueLow energy planar defects such as twin boundaries have been employed to strengthen materials effectively with insignificant loss of the conductivity and ductility. High density growth twins can be formed in low stacking fault energy (SFE) metals, such as copper (Cu) and silver (Ag). However, low SFE metal cobalt (Co) received little attention due to the complex coexistence of hexagonal close-packed (HCP) and face-centered cubic (FCC) structure. The focus of this research is to identify the strengthening mechanisms of planar defects such as twin boundaries, stacking faults, and layer interfaces in epitaxial FCC/HCP Co, and Cu/Co multilayers. Our studies show that epitaxial Cu/Co multilayers with different texture have drastic different mechanical properties, dictated by the transmission of partial vs. full dislocations across layer interfaces. Furthermore the mechanical properties of epitaxial Co are dominated by high density stacking faults. Moreover, by applying advanced nanoindentation techniques, such as thermal-drift corrected strain-rate sensitivity measurement, the mechanical properties including strain-rate sensitivity is accurately determined. By using in situ nanoindentation under transmission electron microscope (TEM), we determined deformation physics of nanotwinned Cu, including detwinning, dislocation-twin interactions and work hardening. This project provides an important new perspective to investigate mechanical behavior of nanostructured metals with high density stacking faults.Item X-ray study of III-Nitride epitaxial layers(2007-12) Akula, Aditya K; Nikishin, Sergey A.Group III-Nitride semiconductors are currently under extensive investigation as promising materials for optoelectronic, high-temperature, and high-power devices due to properties such as large direct band gap, high thermal stability, and strong inter-atomic bonds. The performance of III-Nitride epitaxial devices depend heavily on their structural quality. Thin epitaxial semiconducting films usually contain high density of structural defects and a high degree of mosaicity; the III-Nitrides in particular have these properties due to the lack of a natural substrate. In this thesis we study the mosaic nature of III-Nitride epitaxial layers and their characteristics like tilt angle, twist angle, interdependence factor (m). We also discuss methods to accurately determine the density of edge and screw dislocations in an epitaxial film. In the latter part of the thesis we show the effect various growth parameters have on the structural and electrical properties of GaN: Mg, grown by MOCVD. The data for the study of GaN:Mg epitaxial layers was obtained using a high resolution X-ray diffractometer (XRD). Methods discussed earlier in the thesis were employed on the data to analyze critical structural information of the thin GaN films, with an ultimate aim of improving their electrical, structural, thermal and optical properties.