Typewritten Includes bibliographical references.

The clay mineral composition of sediments deposited in the last six oxygen isotope stages in the Gulf of Mexico continental slope was characterized. Smectite and illite were found to be the two major clay minerals of the clay fraction while kaolinite, chlorite and quartz were present in the clay fraction but in less proportions. Variations in clay mineral abundances, especially in the relative abundances of smectite and illite, were identified in relation to climate changes. Smectite was the most abundant mineral in sediments of the current (stage 1) and last interglacial maxima (stage 5) while illite dominates the clay min-eralogy of sediments from the last glacial maximum (stage 2). Relationships between clay mineralogy and physical properties were investigated as well. Significant positive correla-tions were found between Atterberg limits with the smectite content of the bulk sediment and with clay content. However, the relationship with smectite yielded a significantly higher correlation coefficient. Smectite and clay content also affect the natural water con-tent of sediments and its changes with depth.

The objective of this research is the development of a new constitutive model to describe the behavior of cohesive soils under time dependent loading. In the work presented here, the modified SIMPLE DSS model is expanded to account for the effects of strain rate on clays in simple shear conditions. The response of clay soils is highly dependent on the rate of strain for both effective stress path and stress-strain behavior. The undrained shear strength is strongly influenced by strain rate both in monotonic and cyclic simple shear tests. Nevertheless, the few available experimental results cover a very limited range of loading conditions and rates. The existing literature established that the soil response display a unique relationship between shear strength and log scale of strain rate. To include the effects of strain rate, the modified simple effective stress model starts with two assumptions: (1) a specific shear strength corresponds to a specific strain rate in a unique relation; and (2) the effect of strain rate does not change the failure envelope. The proposed model is developed from the original SIMPLE DSS model, based on an effective stress formulation in a reduced stress space, and utilizing concepts related to the framework of bounding surface plasticity. The proposed model evaluationwas carried out comparing model simulations with results of simple shear tests on Boston Blue Clay and San Francisco Young Bay Mud. The model capability is useful especially in strain rate dependent responses for both monotonic and cyclic behavior, including irregular loading and step-changed condition. It was found that undrained shear strength in simple shear is directly related to strain rate effects and the responses in cyclic test show the more rate dependent behavior than those in monotonic test. The proposed model is able to predict the increase in undrained shear strength for higher strain rate.

The purpose of this study was to implement a new, rapid field method to effectively and accurately detect harmful clay minerals in aggregate fines by using the modified methylene blue (MMB) test. The focus of this study was based on existing knowledge that expansive, or swelling, clays can cause performance problems in pavements whose coarse aggregate fraction contains an appreciable amount of clay. It has been shown through various research projects along with pavement sections in the field that have failed due to distresses caused by the presence of a considerable amount of deleterious clay minerals. As part of this study, nearly thirty aggregate sources, mainly throughout Texas, have been collected and tested using the MMB test. These samples also underwent chemical separation in order to determine the amount of clay contained within each sample. A strong correlation between the MMB test and the clay content detected by chemical separation results has been established. In other words, clay-rich samples have been reflected by the results of the MMB test, thus providing evidence of the test’s accuracy in detecting expansive clay minerals. In addition to the quantification of aggregate fines by mineralogy, performance testing using hot mix asphalt (HMA) and Portland cement concrete (PCC) mixes was also conducted. In one phase of the study, known amounts of standard clay minerals were introduced to the mixes, and performance testing was carried out. This was done in hopes of establishing a limit of tolerable amounts of clay in coarse aggregate fines that would not sacrifice concrete performance. In another phase of this study, natural stockpiled aggregates from select quarries throughout Texas known to contain clay minerals in the aggregate fines were used to make Portland cement concrete to see how they performed as the coarse aggregate fraction of the mixes. Through extensive methylene blue and concrete performance testing, the aim was to establish a threshold methylene blue value (MBV) that corresponds with the maximum permissible clay content within the aggregate fines.

No description available.

Clays which exist in formations in the vicinity of injection and disposal wells is a worldwide problem in the petroleum industry. Clays can be categorized as two major groups: swelling clays, which include smectite group clays, and dispersing clays, which include the kaolinite groups of clays. Therefore, two basic damage mechanisms of clay minerals are swelling and dispersion. Both mechanisms cause pore plugging, and thus aggravate hydrocarbon ease of flow. In this thesis, the effect of temperature, injected water chemical composition, pH, and flowrate of the injected fluid were tested experimentally. Clay mineralogy, chemistry, and composition of the exchangeable cations were also examined. The existing theoretical models of evaluation of forces between clay particles and the rock matrix were used to quantify the interactions. Coreflood experiments were conducted to determine the effect of parameters such as variation of temperature, flowrate, pH, presence of various salts in working solution and their concentration. The results obtained from experimental and theoretical work show that clay minerals in sandstone formation are subject to fines migration and can cause a detrimental impact on the reservoir permeability. Every aforementioned factor has its influence on clays behavior and therefore, a degree of fines migration. The work accomplished summarizes and concludes what parameters sensitize clays migration. Moreover, recommendations for formation damage due to fines migration are given. The scope of work presented can be useful for petroleum engineers as well as geologists and clay mineralogists.

Polyimide/clay nanocomposites were synthesized via two processes. The one-step process is a polymer-diffusion process, and the two-step process is a monomer-diffusion/in-situ polymerization process. Effect of clay loading, surfactant, solvent-release, and clays on the structural formation and properties of the hybrids were studied. XRD (X-ray-diffractometer), TEM (transmission electron microscopy), FTIR (Fourier-transform infrared spectroscopy), DLS (dynamic light scattering), TGA (thermo-gravimetric analyzer), TMA (thermo-mechanical analyzer), DMA (dynamic mechanical analyzer), and GPA (gas permeability analyzer) were used for the characterization of the clays and composites. For the effect of clay-loading, it is found that the threshold of clay loading capable of efficiently improving the properties of polyimide (PI) matrix, should be larger than 0.08 ~ 0.31 wt% for the clay with aspect ratio of 200 ~ 50, as judged by the calculation of classical excluded volume argument. For the effect of surfactant, a thermally stable organoclay of 1-methyl-3-octyl-imidazolium chloride modified montmorillonite (8M) displayed the degradation temperature at maximum rate (Td.max) 91 0C higher than that of dodecyl-amine hydrochloride modified montmorillonite (12M). For PI8M hybrid with 5 wt% clay loading, the T10% Loss and Td.max increased 4 0C and 15 0C respectively as compared to that of the neat PI. Besides, two organoclays with improved affinity to solvent NMP (N-methyl-2-pyrrolidone) 18M {octadecylmethyl-bispolyoxylene [15] ammonium chloride modified montmorillonite} and 30B (Methyltallow-bis-2-hydroxyethyl ammonium ion modified montmorillonite) were used to prepare PI/clay nanocomposites. The relative oxygen permeation rate decreased to 0.5 upon the incorporation of these organoclays of 1 wt%, displaying superior improvement on the gas barrier property of polyimide. For the solvent-release effect, the intercalation behavior of the structural formation of PI/clay nanocomposites was studied. The reduction of d-spacing (~1.30 nm) of clay exists in PI/clay nanocomposites even with the case of 1 wt% clay-loading as characterized by XRD and TEM observation. An opposite argument was presented about the explanation to the contraction in galleries of clay with d001~1.30 nm for PI/clay nanocomposites, after the examination of PAA/clay, organoclay/NMP, organoclay, and pristine clay subjected to a specific heating process. We suggest this phenomenon cannot be ascribed to a poly(amic acid) monolayer adopts a flattened conformation is intercalated in the gallery upon thermal elimination of the solvent. And found it is irrelevant to the intercalation of PAA or PI molecules, but is primarily in consequence of the out-flow NMP together with the out-bound surfactants molecules, partial degradation of surfactants, and the re-aggregation of clays induced by the increasing concentration (volume fraction) of clays upon evaporation of NMP. For the effect of different methods of preparation, PI/clay nanocomposites prepared by monomer-diffusion into non-reactive clay (M) process show the higher relative oxygen permeation rate of 0.1, and Td.max of 11 0C as compared to that of hybrids synthesized by polymer-diffusion process. For the effect of different clays, properties of PI/clay nanocomposites prepared by a reactive layered silicic acid of hydrogen-magadiite (H) and nonreactive clay of montmorillonite were studied. The latter displayed a higher Td.max of 7 0C, and the lower relative oxygen permeation rate of 0.07 as compared to the former, demonstrating the better improvement on thermal, and gas barrier properties.

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Abstract Physical chemistry and microstructure of polyimide / clay nanocomposites were investigated in this study. Diffusion of diamine monomers into the clay gallery prior to polymerization was carefully controlled in order to demonstrate the physical constraint during the formation of the nanocomposites. In addition, diamines with different chemical reactivity were employed to show the effect of chemical reaction on the resultant composites. The microstructure and morphology were identified with X-ray diffraction (XRD) and transmission electron microscopy (TEM), while thermal gravimetric analysis (TGA) was performed to demonstrate the thermal stability of the composites. XRD and TEM results indicate that the final properties and microstructure of the PI / clay nanocomposites were profoundly affected by both the diffusion and chemical reactivity of the monomers prior to the formation of polyamic acid and the subsequent thermal imidization had almost no effect. It should be emphasized that diffusion and chemical reactivity of the monomers are highly competitive. An exfoliated or intercalated nanocomposites can be formed only with a low-reactivity diamine and long enough diffusion time; this ensures polymerization was taken place within the clay gallery. On the other hand, a PI / clay blend is formed with insufficient diffusion time and high diamine reactivity. Under this circumstance, nearly all monomers were captured outside the clay gallery and a homo-polyimide was formed independent of clay. These results were consistent with observations from TGA. The maximum degradation temperature (Td) of the nanocomposite increased with increasing diffusion time; Td of the nanocomposites with low-reactivity 1,3-phenylenediamine was 30oC greater than the nanocomposites with high-reactivity 4,4¡¦-oxydianiline.

Abstract Organically modified montmorillonite by a long chain alkylammonium surfactant was used to prepare polyimide/clay nanocomposites in this study. Several attempts were made in an effort to achieve fully exfoliated nanocomposites. These included the one-step method, two-step method and in-situ polymerization method. At the same time, the effects of polyimide structures and clay contents were studied. Two dianhydrides and two diamines were used to prepare polyimide/clay nanocomposites via the two-step method. The polyimide/clay nanocomposites with various clay contents from 1.5 ~ 10 wt % were prepared via the two-step method too. The structure of polyimides and the dispersion level of clay were identified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Thermogravimetric analysis (TGA) was performed to demonstrate the thermal stability of the nanocomposites. TGA and XRD results indicate the surfactants are intercalated into the layers of clay. FTIR results indicate the all polyimides in the nanocomposites are formed successfully. XRD results indicate the BPDA-ODA/clay nanocomposite within 3 % by weight of clay via the two-step method is shown to have the best dispersion level of clay. These results are consistent with observations from TGA. The temperature at 10 % by weight loss of the nanocomposite is 31 ¢J greater than that of pure BPDA-ODA. The formation mechanism of polyimide/clay nanocomposites via the two-step method can be described by three distinct steps. A polyamic acid/clay mixture with an exfoliated morphology is first formed. A portion of solvents and intercalated surfactants are then either degraded or expelled from the clay gallery under thermal imidization, resulting in a reduced gallery height of 1.32 nm. On the other hand, portion of the clay layers show an exfoliated morphology due to the effective surfactant and polyimide molecules. As a result, a partially exfoliated polyimide/clay nanocomposite is obtained.