X-ray Diffraction Profile Fitting Research Articles

Hydration behavior by X-ray diffraction profile fitting of smectite-bearing minerals

Clay mineral hydration and dehydration processes are reversible at temperatures <100 °C and strongly affect wellbore stability, fines migration, permeability, and dispersion of pore pressure. The hydration behavior of smectite-rich material as a function of relative humidity (activity of water, aw, controlled by salinity) and temperature was studied using in situ X-ray diffraction on a material retrieved from coring in the Gulf of Mexico. X-ray diffraction profile fitting was used to explore the competition for water between hydratable phases across a range of relative humidity, 2 % to 90 %, and temperature, 25°C to 95°C, conditions. X-ray diffraction profile fitting employed a modified multi-specimen approach in which proportions of minerals were modelled using Ca-exchanged preparations in air-dried and ethylene glycol solvated states. Across the range of hydration states, the mineral proportions and crystallographic parameters remained constant from the multi-specimen approach and only the number of water layers in hydratable phases varied. Quantitative clay mineralogy showed a natural material with a discrete smectite component and a mixed-layered illite-smectite, both capable of hydration/dehydration. Results of this study showed the discrete smectite component and the mixed-layered illite-smectite hydrated at different rates with discrete smectite up-taking more water at lower relative humidity than the mixed-layered illite-smectite. Over geological time this study highlights the non-static nature of smectite hydration with implications of long-term creep and permeability behavior.

Hydration behavior by X-ray diffraction profile fitting of smectite-bearing minerals in a Plio-Pleistocene mudrock from Eugene Island, Gulf of Mexico

Hydration behavior by X-ray diffraction profile fitting of smectite-bearing minerals in a Plio-Pleistocene mudrock from Eugene Island, Gulf of Mexico

PyXRD v0.6.7: a free and open-source program to quantify disordered phyllosilicates using multi-specimen X-ray diffraction profile fitting

Abstract. This paper presents a free and open-source program called PyXRD (short for Python X-ray diffraction) to improve the quantification of complex, poly-phasic mixed-layer phyllosilicate assemblages. The validity of the program was checked by comparing its output with Sybilla v2.2.2, which shares the same mathematical formalism. The novelty of this program is the ab initio incorporation of the multi-specimen method, making it possible to share phases and (a selection of) their parameters across multiple specimens. PyXRD thus allows for modelling multiple specimens side by side, and this approach speeds up the manual refinement process significantly. To check the hypothesis that this multi-specimen set-up – as it effectively reduces the number of parameters and increases the number of observations – can also improve automatic parameter refinements, we calculated X-ray diffraction patterns for four theoretical mineral assemblages. These patterns were then used as input for one refinement employing the multi-specimen set-up and one employing the single-pattern set-ups. For all of the assemblages, PyXRD was able to reproduce or approximate the input parameters with the multi-specimen approach. Diverging solutions only occurred in single-pattern set-ups, which do not contain enough information to discern all minerals present (e.g. patterns of heated samples). Assuming a correct qualitative interpretation was made and a single pattern exists in which all phases are sufficiently discernible, the obtained results indicate a good quantification can often be obtained with just that pattern. However, these results from theoretical experiments cannot automatically be extrapolated to all real-life experiments. In any case, PyXRD has proven to be useful when X-ray diffraction patterns are modelled for complex mineral assemblages containing mixed-layer phyllosilicates with a multi-specimen approach.

Phase investigation in Pt supported off-stoichiometric iron-platinum thin films

The structural and magnetic phase transformation of Pt/Fe3Pt/Pt films on Si <100> substrates prepared by DC magnetron sputtering is investigated as a function of annealing temperature. Pt diffusion driven low temperature phase transformation from A1 to L10 phase is achieved at 300°C, attaining a very high coercivity of 9kOe. At 300°C, 85% L10 phase transformation is observed using the X-ray diffraction profile fitting. The estimated phase content is also further verified by fitting the demagnetization curve. The underlayer promotes the ordering at lower temperature while overlayer induces growth along (001) preferred orientation. Rutherford back scattering study reveals interlayer diffusion and confirms the desired stoichiometry for L10 phase. The presence of Pt under-overlayer provides the Pt source and further facilitates the Pt diffusion, which makes it effective in promoting the phase ordering at a lower temperature.

Structure and Martensitic Transformation in NiMnSn Alloy Ribbons with Partial Sn Substitution by Al

The influence of Al substitution for Sn in Ni44Mn43.5AlxSn12.5-x(x= 0, 1, 2, 3) ferromagnetic shape memory alloy ribbons on phase transformation and microstructure evolution is outlined in this paper. Ribbons produced by melt spinning technique showed fully crystalline structure, however non uniform. Energy dispersive spectroscopy microanalysis (EDS) confirmed the average composition of ribbons in accord with the initial alloys. The higher symmetry parent phase was identified with the aid of X-ray diffraction (XRD) as bcc L21Heusler type structure. The unit cell parameters were determined applying the XRD profile fitting method. It was observed that with increase of Al content unit cell parameters and in turn unit cell volume decrease. This may be attributed to the fact that Al has a smaller radius compared to Sn, which it was substituted for. Differential scanning calorimetry (DSC) measurements did not allow to detect the martensitic transformation above -150°C.

Temperature-dependent magnetic and structural ordering of self-assembled magnetic array of FePt nanoparticles

Hexagonal close-packed 2D assembly of monodispersed FePt nanoparticles by the co-reduction method have been synthesised with particles size ~3 nm. The X-ray diffraction (XRD) studies reveal a structural transformation from a chemically disordered faced-centred cubic (FCC) phase to a chemically ordered face-centred tetragonal (FCT) phase with heat treatment. The percentage of phase transformation from FCC to FCT has also been investigated by the XRD profile fitting. Annealing at 750 °C gives 95 ± 1 % FCT phase. The structural transformation was further confirmed by the presence of two superlattice rings corresponding to (001) and (110) by the selected area electron diffraction. Transmission electron microscopy (TEM) shows the grain growth with annealing temperature. High resolution TEM shows the presence of the carbonaceous layer over FePt after annealing. This carbonaceous layer has been investigated by the Raman spectroscopy. Magnetic measurement shows the presence of magnetic hard phase with coercivity of 1 Tesla. The soft/hard compositions have also been investigated by the hysteresis measurements.

Character and Amount of I-S Mixed-Layer Minerals and Physical-Chemical Parameters of Two Ceramic Clays from Westerwald, Germany: Implications for Processing Properties

AbstractThe industrial assessment of ceramic clays commonly consists of the determination of just two parameters, the particle-size distribution and the chemical composition; other parameters may also be important, however. The aim of the present study was to show that a careful determination of the mineralogical phase content provides valuable additional information on the processing behavior of ceramic clays.Two ceramic clays (W1 andW2) from theWesterwald area, Germany, were evaluated as being the same with respect to industrial screening criteria, but showed different processing properties. In order to elucidate the different behaviors, both clays were investigated comprehensively using a multi-method approach combining physical-chemical and mineralogical methods.Different aggregation characteristics for the two clays were revealed by determining the grain-size distribution with and without Na-pyrophosphate as a dispersant. In addition, W1 showed a greater electrical conductivity and soluble-salt concentration which promoted dispersion behavior.The phase content was identified both for bulk materials and for several grain-size fractions by X-ray diffraction (XRD) and Rietveld analysis. The quantitative phase content was crosschecked with the chemical composition by X-ray fluorescence (XRF) analysis. Additional information was gathered by thermal analysis, cation exchange capacity (CEC) measurements, Mössbauer spectroscopy, and optical microscopy. While bulk samples of W1 and W2 showed nearly the same mineralogical and chemical compositions, investigation of the clay-size fractions (0.6–2 μm, &lt;0.6 mm) revealed differences in the composition of the 2:1 layer silicates. The percentages of smectite in the mixed-layer I-S, as well as the amount of kaolinite, discrete illite, and smectite were determined by one-dimensional XRD profile fitting (ODPF). Best-fitting results for W1 were achieved for a physical mixture of an illite-rich I-S mixed-layer mineral (R3 I(0.9)-S) with discrete smectite, whereas W2 was characterized by a greater proportion of smectite in the mixed-layer (R1 I(0.8)-S), without discrete smectite. Based on the different structural features of the swellable clays, a qualitative delamination model for the 2:1 layer silicates during processing of the clays was derived. The model provides a further approach, aside from aggregation characteristics, to help understand the clay-processing behavior, which was found to be different for the two ceramic clays investigated.

Analysis of electrochemical disintegration process of graphite matrix

The electrochemical method with ammonium nitrate as electrolyte was studied to disintegrate the graphite matrix from the simulative fuel elements for high temperature gas-cooled reactor. The influences of process parameters, including salt concentration, system temperature and current density, on the disintegration rate of graphite fragments were investigated in the present work. The experimental results showed that the disintegration rate depended slightly on the temperature and salt concentration. The current density strongly affected the disintegration rate of graphite fragments. Furthermore, the content of introduced oxygen in final graphite fragments was independent of the current density and the concentration of electrolyte. Moreover, the structural evolution of graphite was analyzed based on the microstructural parameters determined by X-ray diffraction profile fitting analysis using MAUD (material analysis using diffraction) before and after the disintegration process. It may safely be concluded that the graphite disintegration can be ascribed to the influences of the intercalation of foreign molecules in between crystal planes and the partial oxidation involved. The disintegration process was described deeply composed of intercalate part and further oxidation part of carbon which effected together to lead to the collapse of graphite crystals.

Advances in characterization of soil clay mineralogy using X‐ray diffraction: from decomposition to profile fitting

SummaryStructural characterization of soil clay minerals often remains limited despite their key influence on soil properties. In soils, complex clay parageneses result from the coexistence of clay species with contrasting particle sizes and crystal chemistry and from the profusion of mixed layers with variable compositions. The present study aimed to characterize the mineralogy and crystal chemistry of the &lt;2 μm fraction along a profile typical of soils from Western Europe and North America (Neo Luvisol). X‐ray diffraction (XRD) patterns were interpreted using: (i) the combination of XRD pattern decomposition and indirect identification from peak positions commonly applied in soil science; and (ii) the multi‐specimen method. This latter approach implies direct XRD profile fitting and has recently led to significant improvements in the structural characterization of clay minerals in diagenetic and hydrothermal environments. In contrast to the usual approach, the multi‐specimen method allowed the complete structural characterization of complex clay parageneses encountered in soils together with the quantitative analysis of their mineralogy. Throughout the profile, the clay paragenesis of the studied Neo Luvisol systematically includes discrete smectite, illite and kaolinite in addition to randomly interstratified illite‐smectite and chlorite‐smectite. Structural characteristics of the different clay minerals, including the composition of mixed layers, did not vary significantly with depth and are thus indicative of the parent material. The relative proportion of the &lt;2 μm fraction increased with increasing depth simultaneously with smectite relative proportion. These results are consistent with the leaching process described for Luvisols in the literature.

Proportion and dispersion of rhombohedral sequences in the hexagonal structure of graphite powders

Using the Phase Matrix Method, we derive a calculation scheme giving the analytical form of the intensity diffracted by graphite crystallites containing rhombohedral stacking faults. The physical model accounts for all possible types of interstratification of the hexagonal and rhombohedral forms in graphite. The relevant statistical parameters are the proportion of the rhombohedral phase, its “dispersion” within the hexagonal structure and the average number of graphene layers in the crystallites. A mean-squares refinement program allows calculation of the (10ℓ) diffraction profiles and the X-ray data reduction into physically meaningful statistical parameters. In the case of powdered materials, the parameters describing the rhombohedral phase are found to depend on the material origin and on its preparation process. Reducing the grain size by milling always increases the proportion of the rhombohedral phase whereas its dispersion in the hexagonal structure can significantly vary, depending upon both raw material type and milling conditions. X-ray diffraction profile fitting also evidenced the fact that compacting a powder of crystallites in which the two phases are segregated (coexistence of large rhombohedral and hexagonal crystallographic domains) leads to the destruction of the large domains constituting both phases and results in strong inter-mixing of the two crystalline forms.

Deformation stacking fault probability and dislocation microstructure of cold worked Cu–Sn–5Zn alloys by x-ray diffraction line profile analysis

Plastically deformed (hand-filed) Cu–Sn–5Zn ternary alloys with Sn concentrations 1, 2.5, and 5wt% are investigated. Microstructural parameters are studied in terms of x-ray diffraction profile fitting analysis. It is observed by Dey et al. [Acta. Mater. 53, 4635 (2005)] that the change in stacking fault probability (α) with Sn concentration for ternary Cu–Sn–5Zn alloys is similar to Cu-based binary alloy (Cu–Sn) system but behaves in a different manner from Cu–1Sn–Zn ternary alloy systems. The crystallite size distribution is broader for alloy with 1wt% Sn and becomes narrower with increasing Sn concentration. Value of dislocation density (ρ) is of the order of 1015m−2 and shows a compositional dependence. Type of dislocation is found to be predominantly screw; ⟨100⟩-type dipoles may also be present in the cold-worked alloys. The dislocation arrangement is found to be more correlated in case of 1wt% Sn compared to other alloys of higher Sn concentration. The stacking fault energy (γ) is obtained from modified Reed-Schramm equation and is of the order of 20mJm−2 with no significant compositional dependence.

Structural properties of Fe 50Co 50 nanostructured powder prepared by mechanical alloying

Mechanical alloying of high purity elemental powders in a planetary ball mill (Fritsch pulverisette 7) was used to prepare nanocrystalline Fe and equiatomic FeCo powders. Morphology changes, structural properties and local iron environment variations have been investigated by Scanning Electron Microscopy, X-ray diffraction and 57 Fe Mössbauer spectrometry. X-ray diffraction profile fitting, reveals the Co allotropic transformation from fcc to hcp form at the early stage of milling. The milling route implies diffusion of hcp-Co into α (Fe) leading to the formation, after 12 h, of the bcc-FeCo solid solution with a lattice parameter close to a = 0.2861 nm and a grain size of about 12 nm. The analysis of the evolution of the hyperfine magnetic field distribution, indicates that the disordered bcc-FeCo solid solution is formed after 12 h of milling, through the interdiffusion of Fe and Co elemental powders. The average hyperfine magnetic field of the bcc-FeCo solid solution ( B = 35 T) suggests that the disordered Fe 50Co 50 system is formed.

Determination of structural disorder degree using an XRD profile fitting procedure. Application to Czech kaolins

Diffractions of (02, 11) band are very sensitive to the structural defects in kaolinite structure. Therefore, the empirical relation based on weighting peak intensity ratio of 0 2 0, 1 1̄ 0, and 1 1 1̄ (1 1̄ 1̄) reflections was used to estimate the degree of disorder in kaolinite samples collected from different Czech Republic kaolin deposits. X-ray diffraction (XRD) profiles taken from <5 μm fraction of kaolinite samples were used for determination of peak intensities I(1 1̄ 0), I(1 1 1̄), I(1 1̄ 1̄), I(0 2 0) and full width at half maximum (FWHM) values using profile fitting and decomposition procedure. The weighting intensity ratio index (WIRI) WIRI=1− exp{−[w 1I(1 1 ̄ 0)+w 2I(1 1 1 ̄ )+w 3I(1 1 ̄ 1 ̄ )]/[w 4I(0 2 0)]} was calculated. The w 1, w 2, w 3, and w 4 weight values are the reciprocal values of FWHM for 1 1̄ 0, 1 1 1̄, 1 1̄ 1̄, and 0 2 0 reflections, respectively. According the WIRI values (theoretically ranging from 0 to 1), three groups of kaolinite samples can be recognized: (I) one sample with high degree of structural order (0.70<WIRI<1.00), (II) two samples with medium degree of structural order (0.40<WIRI≤0.70), and (III) five samples with low degree of structural order (0.00<WIRI≤0.40). The WIRI values obtained were compared with Hinckley (HI) and Aparicio–Galán–Ferrell (AGFI) indices and very good relations were found between them.

A Gaussian–Hermite polynomials function for X-ray diffraction profile fitting

In recent years, several profile-shape functions have been successfully used in X-ray powder diffraction studies. Here, a new profile function for approximating the X-ray diffraction peaks is proposed. This model, based on a Gaussian function multiplied by a correction factor in the form of a series expansion in Hermite polynomials, can be employed in the cases where there are peak asymmetries. The function has been tested by using samples of α-Al2O3and 9-YSZ (yttria-stabilized zirconia), yielding generally satisfactory results.