XAS and XRD structural study of nickel electrode materials (Part I) and FTIR quantitative analysis of mineral mixtures (Part II).

摘要

This dissertation contains two parts. The first part presents a study of the structure of nickel electrode related materials. The second part presents a study of FTIR quantitative analysis of mineral mixtures.; Part I. Nickel electrode model compounds have been studied with X-ray Absorption Spectroscopy (XAS) and powder X-Ray Diffraction (XRD). The position and shape of the nickel k-edge in the x-ray absorption spectra provide information about the nickel oxidation states. In situ measurement allows the observation of the maximum oxidation state, 4+, only in the presence of oxidant. A unique calibration curve has been obtained by combining the results of XANES (X-ray Absorption Near-Edge Spectroscopy) with those of chemical titration. This curve can be used to calculate the nickel oxidation state of nickel electrode materials whose k-edge position is known. The previously proposed point defect containing structural model allows interpretation of the variation in oxidation state of these materials. Therefore, these oxidation state results further substantiate the validity of this structural model.; EXAFS (Extended X-ray Absorption Fine Structure) spectra of model compounds have been analyzed. The Ni-O and Ni-Ni distances have been determined. The variation of the K-edge position and the Ni-O distance as a function of nickel oxidation state has been established. The Ni-O distance decreases with increase in nickel oxidation state in a non-linear fashion. The origin of the third well-resolved peak appearing in the Radial Structure Function (RSF) has been identified. The Ni-Ni distances obtained from experimental powder XRD patterns are in excellent agreement with those from EXAFS. Combined with XRD powder pattern calculation, the powder XRD data can still provide structural information for disordered materials. The new identify of a phase previously observed in failed nickel electrodes has been confirmed by comparison of the experimental powder XRD pattern and a simulated XRD pattern.; Part II. Fourier Transform Infrared (FTIR) spectroscopy has been used to perform quantitative analyses of well core samples from oil fields. A suite of standard minerals has been collected, and a standard mineral FTIR spectral matrix suitable for the analysis of oil field samples has been built. The sample preparation method for FTIR quantitative analysis has been developed. The Linear Baseline Subtraction Procedure (LBSP) has been developed. A Non-Negative Least Squares algorithm, combined with the LBSP, has been successfully used to quantitatively analyze the oil well mineral samples with FTIR. The silica phase transformation (opal-A to opal-CT to quartz) has been successfully monitored using FTIR analysis for two oil wells.