No description available.

Seven distinctly different museum-quality concretionary morphotypes of elongate, spheroidal, banded, botryoidal, columnar, rosette, and speleothem in regolith at two small sites at the base of the Meski Plateau near Erfoud, Morocco are described. Although most are isolated hand samples, the largest concretions are meter-sized blocks. Not one sample resembles any surrounding outcrop or bedrock. The barite rosettes formed first via periodic mixing of Ba2+/SO42- saturated solutions. They provided nuclei for cyclical precipitation-based concentric concretion development. The speleothem formed via precipitation from a carbonate-saturated solution in a large void within porous sandstone. The sand concretions formed when calcite precipitated around grains in unconsolidated quartz sands with cyclic fluctuation of Ca2+/CO32- saturated ground water. Petrographic analyses, stable isotope data, sample morphology, coupled with light and scanning electron microscopy indicate that microbial processes induced the periodic cement precipitation that produced the unique concretions.

Differential thermal analysis le a dynamic process for observing the thermal decomposition of reacting sub- stances, The heart of the equipment for this process is a vanadium steel sample holder approximately two inches in diameter and one inch thick. Two wells, approximately one inch apart, serve as holders for the sample and reference material. Inserted in the bottom of each well is a thermo- couple of platinum, platinum-rhodeus. Attached to the thermocouples is an amplifier and a recorder.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2020. / This dissertation presents the results of the ab-initio based computational studies of spinel lithium manganese oxide (LiMn2O4) bulk, surfaces, and the adsorption of an organic electrolyte, ethylene carbonate. The spinel LiMn2O4 is one of the most promising cathode materials for Lithium-ion batteries because of its affordability, nontoxicity, and improved safety compared to commercially used LiCoO2. However, it also suffers from the irreversible capacity due to the electrolyte-cathode interactions which lead to manganese (Mn) dissolution. Using the spin-polarized density functional theory calculations with on site Coulomb interactions and long-range dispersion corrections [DFT+U−D3−(BJ)], we investigated the bulk properties, surface stability and surface reactivity towards the ethylene carbonate (EC) during charge/discharge processes. Firstly, we explored the structural, electronic, and vibrational bulk properties of the spinel LiMn2O4. It was found that the bulk structure is a stable face-centred cubic structure with a bandgap of 0.041 eV and pseudo-gap at the Fermi level indicating electronic stability. Calculated elastic constants show that the structure is mechanically stable since they obey the mechanical stability criteria. The plotted phonon curves show no imaginary vibrations, indicating vibrational stability. To study the charge/discharge surfaces, we modelled the fully lithiated and the partially delithiated slabs and studied their stability. For the fully lithiated slabs, Li-terminated (001) surface was found to be the most stable facet, which agrees with the reported experimental and theoretical data. However, upon surface delithiation, the surface energies increase, and eventually (111) surface becomes the most stable slab as shown by the reduction of the plane in the particle morphologies. Finally, we explored the surface reactivity towards the ethylene carbonate during charge/discharge processes. The ethylene carbonate adsorption on the fully lithiated and partly delithiated facets turn to enhance the stability of (111) surface. Besides the strong interaction with the (111) surfaces, a negligible charge transfer was calculated, and it was attributed by a large charge rearrangement that takes place within the surfactant upon adsorption. The wavenumbers of the C=O stretching showed a red shifting concerning the isolated EC molecule

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No description available.

Yes / Fouling on heat transfer surfaces due to scale formation is the most concerned item in thermal desalination industry. Here, a dynamic fouling model is developed and incorporated into the MSF dynamic process model to predict fouling at high temperature and high velocity. The proposed dynamic model considers the attachment and removal mechanisms in the fouling phenomena with more relaxation of the assumptions such as the density of the fouling layer and salinity of the recycle brine. While calcium sulphate might precipitate at very high temperature, only the crystallization of calcium carbonate and magnesium hydroxide are considered in this work. Though the model is applied in a 24 stages brine recycle MSF plant, only the heat recovery section (21 stages) is considered under this study. The effect of flow velocity and surface temperature are investigated. By including both diffusion and reaction mechanism in the fouling model, the results of the fouling prediction model are in good agreement with most recent studies in the literature. The deposition of magnesium hydroxide increases with the increase in surface temperature and flow velocity while calcium carbonate deposition increases with the increase in the surface temperature and decreases with the increase in the flow velocity.

Petrophysical properties are fundamental to understanding fluid flow processes in hydrocarbon reservoirs. Special Core Analysis (SCAL) routinely used in industry are time-consuming, expensive, and often destructive. Alternatively, easily available thin section data is lacking the representation of pore space in 3D, which is a requisite for generating pore network models (PNM) and computing petrophysical properties. In this study, these challenges were addressed using a numerical SCAL workflow that employs pore volume reconstruction from thin section images obtained from confocal laser scanning microscopy (CLSM). A key objective is to investigate methods capable of 2D to 3D reconstruction, to obtain PNM used for the estimation of transport properties. Representative thin sections from a well-known Middle-Eastern carbonate formation were used to obtain CLSM images. The thin-sections were specially prepared by spiking the resin with UV dye, enabling high-resolution imaging. The grayscale images obtained from CLSM were preprocessed and segmented into binary images. Generative Adversarial Networks (GAN) and Two-Point Statistics (TPS) were applied, and PNM were extracted from these binary datasets. Porosity, Permeability, and Mercury Injection Porosimetry (MIP) on the corresponding core plugs were conducted and an assessment of the properties computed from the PNM obtained from the reconstructed 3D pore volume is presented. Moreover, the results from the artificial pore networks were corroborated using 3D confocal images of etched pore casts (PCE). The results showed that based on visual inspection only, GAN outperformed TPS in mimicking the 3D distribution of pore scale heterogeneity, additionally, GAN and PCE outperformed the results of MIP obtained by TPS on the Skeletal-Oolitic facies, without providing a major improvement on more heterogeneous samples. All methods captured successfully the porosity while absolute permeability was not captured. Formation resistivity factor and thermal conductivity showcased their strong correlation with porosity. The study thus provides valuable insights into the application of 2D to 3D reconstruction to obtain pore network models of heterogeneous carbonate rocks for petrophysical characterization for quick decision. The study addresses the following important questions: 1) how legacy thin sections can be leveraged to petrophysically characterize reservoir rocks 2) how reliable are 2D to 3D reconstruction methods when predicting petrophysical properties of carbonates.

Modern microbialites provide the opportunity to explore the influences of biology on microbialite formation and understand how biosignatures can be preserved in these structures. In this study, we compared δ13Ccarb values from nodule and surface biofilm carbonates on microbialite structures across depths and locations throughout Pavilion Lake to evaluate whether variable light exposure produced limitations to biosignature formation. At depths below 21 m, vertical profiling of δ13Ccarb across colour transitions of surface biofilm on microbialite structures was performed to identify spatial arrangement of autotrophic and heterotrophic biosignatures. Finally, preservation of the photosynthetic biosignature over time was investigated by collecting carbonates beneath the microbialite surface. These investigations were performed in order to better characterize the factors controlling biosignature formation, distribution, and preservation within Pavilion Lake.Decreasing trends of δ13Ccarb with depth across study sites indicated that attenuated sunlight in the water column is likely the primary control on biosignature formation. Below 21 m, photosynthetic enrichments representing biosignatures on microbialite surfaces were reduced and recorded δ13Ccarb values that fell within the predicted equilibrium range. Biosignature loss is suggested to result from the relative proportions of autotrophic and heterotrophic processes changing at depths and producing average δ13Ccarb values. Variability of where biosignatures are lost on the microbialite surface indicated that the spatial extent of photosynthetic communities producing enrichments is potentially influenced by variable incidences of light at these depths. Although no definitive biosignatures of heterotrophy were identified, several interfaces were identified where the balancing proportions of autotrophic and heterotrophic processes influenced by light variability potentially mediate biosignature loss. Decreasing trends of δ13Ccarb beneath the microbialite surface and estimates of past microbialite growth rates indicated that surface biosignatures are lost within 100 – 400 years. It is suggested that infilling processes overprint enrichments and deplete δ13Ccarb values due to heterotrophic abundance below the microbialite surface. This is supported by an isotopic mass balance that predicts smaller inputs of heterotrophically-depleted DIC are required to sufficiently overprint δ13Ccarb enrichments. These results concluded that the photosynthetic biosignature identified in Pavilion Lake is short-lived and mitigated by biological processes. / Thesis / Master of Science (MSc)

<p> Concretions in a zone about 4 m. below the Tichenor Limestone formed just below the sediment water interface. Their growth was initiated about an organic-rich fossil cluster and was probably completed before they were more than 5 to 8 m below the sediment surface. Chemical products of organic decay, notably bicarbonate ions and ammonia, diffused outward, raising the pH and precipitating calcite from connate waters already nearly saturated with respect to calcium carbonate. These conclusions derive from the shape of the concretions, from their relation to the enclosing shales, and from their overall structure , particularly the position of pyritic fossil clusters. The relative volumes of soluble material (calcite) in the concretions are consistent with relative pore volumes through the upper 5 m. of recent, fine-grained, clayey sediments. The postulated genetic sequence agrees with recent work on carbonate diagenesis. Restriction of the concretions to discrete layers was most probably due to a widespread comnbination of high rates of organic productivity, high rates ·of sedimentation, and low rates of water circulation, that lasted a short period of time and resulted in the rapid burial.of much undecomposed organic material. </p> / Thesis / Master of Science (MSc)