Quantitative X-ray Diffraction Data Research Articles

Quantitative Mineral Mapping of Drill Core Surfaces II: Long-Wave Infrared Mineral Characterization UsingμXRF and Machine Learning

AbstractLong-wave infrared (LWIR) spectra can be interpreted using a Random Forest machine learning approach to predict mineral species and abundances. In this study, hydrothermally altered carbonate rock core samples from the Fourmile Carlin-type Au discovery, Nevada, were analyzed by LWIR and micro-X-ray fluorescence (μXRF). Linear programming-derived mineral abundances from quantified μXRF data were used as training data to construct a series of Random Forest regression models. The LWIR Random Forest models produced mineral proportion estimates with root mean square errors of 1.17 to 6.75% (model predictions) and 1.06 to 6.19% (compared to quantitative X-ray diffraction data) for calcite, dolomite, kaolinite, white mica, phlogopite, K-feldspar, and quartz. These results are comparable to the error of proportion estimates from linear spectral deconvolution (±7–15%), a commonly used spectral unmixing technique. Having a mineralogical and chemical training data set makes it possible to identify and quantify mineralogy and provides a more robust and meaningful LWIR spectral interpretation than current methods of utilizing a spectral library or spectral end-member extraction. Using the method presented here, LWIR spectroscopy can be used to overcome the limitations inherent with the use of short-wave infrared (SWIR) in fine-grained, low reflectance rocks. This new approach can be applied to any deposit type, improving the accuracy and speed of infrared data interpretation.

Rock type based poroperm and continuous permeability predictions in a tight gas formation

Porosity from log response such as density provides a continuous representation of pore volume as function of depth in a well, which can be calibrated with core analysis data. Obtaining a continuous log of permeability is not as straightforward as there is yet no means of logging permeability. While DST-derived permeability values are useful in calibrating dynamic models, they only represent an average value over the radius investigated by the test and will not readily correlate to permeability values derived from core especially where there are lateral and vertical permeability variations within the reservoir. It is, however, possible to obtain a depth-continuous permeability estimate by deriving a free regression algorithm known as the poroperm transform function, which defines how the permeability varies as a function of porosity. Such correlations are typically derived empirically from overburden corrected core-derived porosity and permeability data. General porosity-permeability trends are far too scattered to be of use. However, far tighter porosity-permeability trends can be obtained by use of rock typing to identify suitable analogues. The following study highlights how microstructural rock-tying can be used to improve permeability prediction in a set of tight gas sandstone wells. Scanning electron microscopy (SEM) and quantitative X-ray diffraction (QXRD) data were obtained from >200 tight gas sandstone samples from the Southern North Sea for which porosity and permeability measurements had previously been conducted. The SEM and QXRD data were used to derive microstructural and mineralogical rock types respectively. Samples from each rock-types occupy different but overlapping positions on porosity-permeability cross plots. Exponential functions were fitted to porosity-permeability data for each rock type and then applied to the porosity values from wire-line log data to derive continuous permeability estimates. The log porosity curves-being the independent variables of the respective functions, were validated by core observation to avoid error propagation. Continuous permeability curves that honour mineralogical variation were obtained by the use of microstructural rock typing.Key words: Porosity, Permeability, Rock-typing, Poroperm, Microstructural, Mineralogical.

Enhanced Crystal Growth Kinetics in Cation-Doped Sr0.7Bi2.3Ta2O9Ferroelectric Thin Films

Sr 0.7 Bi 2.3 Ta 1.7 Ti 0.3 O 9 (SBTT) and Sr 0.7 Bi 2.3 Ta 1.7 Zr 0.3 O 9 (SBTZ) ferroelectric thin films were fabricated through partial substitution of Ta 5+ ions in Sr 0.7 Bi 2.3 Ta 2 O 9 (SBT) and crystal growth kinetics of ferroelectric Aurivillius phase was analyzed and compared for each thin film. Quantitative X-ray diffraction (Q-XRD) analyses were performed on each thin film isothermally heated in the range of 730-760°C at 10°C intervals for different time periods. Activation energy and Avrami exponent values for Aurivillius crystal growth were determined by employing Johnson-Mehl-Avrami (JMA) isothermal kinetic analyses to the Q-XRD data. A reduction of ∼51 and ∼82 kJ/mol in activation energy was observed for the SBTT and SBTZ, respectively, which plays a major role in enhancing the crystal growth kinetics of SBTT and SBTZ thin films. A possible mechanism for the reduction in activation energy values was discussed based upon the ionic bond strength difference. The Avrami exponent values were determined as ∼1.0 for SBT, SBTT, and SBTZ thin films, indicating one-dimensional crystal growth with a diffusion-controlled mechanism at a decreasing nucleation rate.

Lithium sorption to Yucca Mountain tuffs

The Li ion has been used as a reactive tracer in field tests performed in the saturated and unsaturated-zone in volcanic tuffs at Yucca Mountain, Nevada. Lithium sorbs weakly by cation exchange and permits field-scale testing of laboratory-based predictions of reactive-solute transport. A series of laboratory studies show that Li sorption is nonlinear and varies with lithology in the different horizons of the tuff. In particular, both Li sorption and Li-specific cation-exchange capacity vary as functions of tuff mineralogy, and can be predicted given quantitative X-ray diffraction data. These results indicate that Li sorption is dominated by clay and zeolite minerals, and that sorption coefficients can be predicted given mineralogic analysis results.

Mechanical alloying of cobalt and boron powders

Mechanical alloying was performed on elemental cobalt and boron powders in the atomic ratio Co 67B 33. The process was monitored by X-ray diffraction spectra taken at regular time intervals. The progressive lowering of the crystalline peaks' intensity accompanied by the formation of an amorphous halo was observed; in the final stages peaks due to crystalline t-Co 2B began to emerge. With the exception of the time scale, the evolution of the system was similar to that of a previous preparation carried out under different energy conditions. The structure functions and radial distribution functions were calculated from quantitative X-ray diffraction data taken near complete sample amorphization to follow the details of the milling process at these stages.

Structure of the D phase. II

Abstract Results are presented of a Fourier analysis of quantitative X-ray diffraction data obtained from a D phase single crystal, the structure of which has previously been shown to possess primitive cubic symmetry. The Fourier analysis method determines the distribution of electron density in the crystallographic unit cell from the intensities and phases of the Bragg reflections. Diffraction data provide no information on the phase factors, and the Fourier method is therefore practical only when the structure is centrosymmetric, as is shown to be the case for the D phase, since the phase factors are then either 0 or π. It is shown that there are essentially only four physically reasonable solutions for the electron density distribution. The physical interpretation of these models is discussed in terms of molecular packing in the unit cell.

Chain conformation in the collagen molecule

Quantitative X-ray diffraction data have been collected from stretched kangaroo tail tendon and used to test models for the conformation of the polypeptide chains in the collagen molecule. The magnitude of the unit twist of the molecular helix was estimated to be 107.1 ° ± 0.6 °, which is close to the value expected for a helix with ten units in three turns. The intensity data were used to carry out a linked-atom least-squares refinement of models based on two possible interchain hydrogen bonding schemes suggested by Rich & Crick (1955, 1961). No stereochemically acceptable solution could be found for the hydrogen bonding scheme of model I, but a stereochemically satisfactory solution was found for the scheme of model II which gave a crystallographic R factor of 0.272.