An X-ray investigation of synthetic pyroxenes in the system acmite--diopside-water at 1000 kg/cm2 watervapour pressure

1963 ◽  
Vol 33 (263) ◽  
pp. 625-634 ◽  
Author(s):  
J. Nolan ◽  
A. D. Edgar
Keyword(s):  
Least Squares ◽  
Linear Relationship ◽  
Water Vapour ◽  
Powder Diffraction ◽  
Vapour Pressure ◽  
Water Vapour Pressure ◽  
Ray Method ◽  
X Ray ◽  
Diffraction Patterns

SummaryAn X-ray investigation has been made of synthetic pyroxenes in the system acmite-diopside, crystallized at 750° C and 1000 kg/cm2 water-vapour pressure. Lattice parameters of these pyroxenes have been determined by least squares analyses of powder diffraction patterns and show an approximately linear relationship with composition, plotted as weight per cent. A rapid X-ray method has also been devised for the determination of the compositions of pyroxenes of this series.

Heating device for high temperature X-ray powder diffraction studies under controlled water vapour pressure (0–1000 mbar) and gas temperature (20–200 °C)

2000 ◽  
Vol 15 (1) ◽  
pp. 30-37 ◽  
Author(s):  
Martin Oetzel ◽  
Franz-Dieter Scherberich ◽  
Gernot Heger
Keyword(s):  
High Temperature ◽  
Water Vapour ◽  
Environmental Conditions ◽  
Vapour Pressure ◽  
Water Vapour Pressure ◽  
Gas Temperature ◽  
X Ray ◽  
Temperature Range ◽  
Heating Device ◽  
Dehydration Reactions

In this paper we present a high temperature heating device, working under defined environmental conditions, for a Siemens D500 Bragg–Brentano powder diffractometer. The powder sample is prepared in a flat mould on a metal block consisting either of copper or of platinum depending on the temperature range selected for investigations. Although the heating cell can be used separately under ambient conditions up to sample temperatures of 1000 °C, it is possible to work under defined environmental conditions in the temperature range between 20 and 200 °C and up to a water vapour pressure of 1000 mbar. For that purpose a special cover for the in situ control of temperature and water vapour pressure has been constructed. It is important to note that the three sample conditions (sample temperature, gas temperature, and gas humidity) can be adjusted separately by the user. Current studies have shown that the described X-ray heating device is a powerful tool to study dehydration reactions in the frame of fundamental research as well as to understand industrially relevant processes concerning dehydration reactions and their mechanisms.

Brochantite-2M2 from Pierre Plate Mine, Vizille

2008 ◽  
Vol 23 (3) ◽  
pp. 246-250 ◽  
Author(s):  
Wilson A. Crichton ◽  
Harald Müller
Keyword(s):  
Least Squares ◽  
Powder Diffraction ◽  
Urban Environments ◽  
Powder Xrd ◽  
Secondary Alteration ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

Evidence for the recently described 2M2 polytype of brochantite from X-ray powder diffraction investigation of secondary alteration products of ore material from the Pierre Plate Mine, Vizille, Isère, France is presented. This report is the first to describe the 2M2 polytype from locations outside of Italy and through the use of powder XRD methods. In the procedure used herein, developed in a study by Merlino et al. [Eur. J. Mineral 15, 267–275 (2003)], we have used family reflections, common to both main types of brochantite, as the source of approximate cell parameters from which we obtain positions of characteristic reflections to demonstrate the unique choice of polytype, before final refinement stage. This method demonstrates that the determination of polytype is possible from powder data, for samples typical of both geological and urban environments. Least-squares refined cell parameters for the 2M2 polytype from Pierre Plate are a=12.7409(8) Å, b=9.8371(6) Å, c=6.0109(3) Å, and a=90.135(9)°, constrained in space group P21/n11.

Indexing of Powder Diffraction Patterns

1962 ◽  
Vol 6 ◽  
pp. 1-17 ◽  
Author(s):  
P. M. de Wolff
Keyword(s):  
Powder Diffraction ◽  
Initial Phase ◽  
Complete Solution ◽  
Powder Pattern ◽  
X Ray ◽  
Physical Limit ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Influence Of Impurities

AbstractDespite the advances of the electron mtcrodiflraction technique, the determination of unit cells of microcrystalline compounds still depends in many cases on the interpretation of the X-ray powder pattern. The feasibility of this interpretation depends strongly un the precision of the data, the present-day level of which is far from its physical limit. It could be improved by application of monochromators in diflractometry. Some possible methods are discussed. With regard to interpretation, a survey of existing methods is given (Lipson, Ito, de Wolff, Szoldos). Some of these techniques are suitable for computers, at least in the initial phase of the procedure. This is illustrated by application of a zone-finding program for the complete solution of a given pattern. Finally, the influence of impurities and other disturbing factors is discussed.

A standardless X-ray diffraction method for the quantitative analysis of multiphase mixtures. II. Application to non-infinitely thick samples

2002 ◽  
Vol 35 (5) ◽  
pp. 600-605 ◽  
Author(s):  
Eva T. Gomez ◽  
Teófilo Sanfeliu ◽  
Jordi Rius
Keyword(s):  
Quantitative Analysis ◽  
Least Squares ◽  
Powder Diffraction ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
Absorption Coefficients ◽  
Airborne Particulates ◽  
X Ray ◽  
Experimental Values

In 1987, Rius, Plana & Palanques [J. Appl. Cryst.(1987),20, 457–460] devised an X-ray powder diffraction method based on the `least-squares' determination of calibration constants using only the diffracted intensities and the calculated absorption coefficients of the components. This method was developed for `infinitely thick' samples, a condition which is seldom met by airborne particulates because of the small amount of material normally available. Since the analysis of such samples may become one of the principal applications of the method, this condition represents a serious limitation. The simplest way to overcome this limitation is by correcting the measured intensities. This can be done either by direct measurement of the sample transmission, or alternatively, by using refined transmission values. In the latter case no experimental values are necessary. With the help of some test calculations, the viability of both possibilities has been explored.

DETERMINATION OF THE CRYSTAL STRUCTURE OF ERBIUM TITANATE, Er2Ti2O7, BY X-RAY AND NEUTRON DIFFRACTION

1965 ◽  
Vol 43 (10) ◽  
pp. 2812-2826 ◽  
Author(s):  
Osvald Knop ◽  
François Brisse ◽  
Lotte Castelliz
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Infrared Spectrum ◽  
Least Squares ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
X Ray ◽  
X Ray Scattering ◽  
Pyrochlore Type

The crystal structure of erbium titanate, Er2Ti2O7, has been shown by X-ray and neutron powder diffraction to be of the cubic pyrochlore type, with ao = 10.0762 ± 6 Å. Least-squares isotropic refinement based on resolved single reflections gave x(O2) = 0.4200 ± 10 and R = 2.25%. Ionic and neutral X-ray scattering factors gave practically identical results. The six equal Ti—O2 distances in the distorted coordination octahedron of the Ti atom are 1.955 ± 5 Å. The two short (apparent) Er—O distances are 2.1815 ± 5 Å (Er—O1) and 2.471 ± 8 Å (Er—O2). The infrared spectrum of the titanate in the region 1 600 to 250 cm−1 shows features similar to those encountered in the spectra of other simple oxygen compounds of titanium.

Deconvolution of instrument andKα2contributions from X-ray powder diffraction patterns using nonlinear least squares with penalties

2018 ◽  
Vol 51 (1) ◽  
pp. 112-123 ◽  
Author(s):  
Alan A. Coelho
Keyword(s):  
Least Squares ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Nonlinear Least Squares ◽  
Penalty Functions ◽  
Instrument Function ◽  
X Ray ◽  
Emission Profile ◽  
Fourier Techniques ◽  
Diffraction Patterns

A new deconvolution method, tolerant of noise and independent of knowing the number of Bragg peaks present, has been developed to deconvolute instrument and emission profile distortions from laboratory X-ray powder diffraction patterns. Removing these distortions produces higher-resolution patterns from which the existence of peaks and their shapes can be better determined. Deconvolution typically comprises the use of the convolution theorem to generate a single aberration from instrument and emission profile aberrations and then the Stokes method to deconvolute the resulting aberration from the measured data. These Fourier techniques become difficult when the instrument function changes with diffraction angle and when the signal-to-noise ratio is low. Instead of Fourier techniques, the present approach uses nonlinear least squares incorporating penalty functions, as implemented in the computer programTOPAS-Academic. Specifically, diffraction peaks are laid down at each data point with peak shapes corresponding to either expected peak shapes or peak shapes narrower than expected; a background function is included. Peak intensities and background parameters are then adjusted to obtain the best fit to the diffraction pattern. Rietveld refinement of the deconvoluted pattern results in background parameters that are near identical to those obtained from Rietveld refinement of the original pattern. Critical to the success of the deconvolution procedure are two penalty functions, one a function of the background parameters and the other a function of the peak intensities. Also of importance is the use of a conjugate gradient solution method for solving the matrix equationAx=b.

scholarly journals Born out of Fire and Ice: Polymorph Studies of the Antiviral Famciclovir

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 129
Author(s):  
Liana Vella-Zarb ◽  
Ulrich Baisch
Keyword(s):  
Variable Temperature ◽  
Chemical Properties ◽  
Crystal Form ◽  
X Ray Diffraction ◽  
Crystal Forms ◽  
X Ray ◽  
Physical Chemical ◽  
Diffraction Patterns ◽  
Crystalline Forms

There is much interest and focus on solid forms of famciclovir. However, in spite of the abundance of reported differences in oral bioavailability, compressibility, and other physical–chemical properties of the various crystal forms of this drug, very little precise structural analysis is available in the literature to date. The form used in the commercial formulation is the anhydrous form I. Patents and patent applications report three different anhydrous crystalline forms on the basis of unindexed powder diffraction patterns. Single-crystal and variable-temperature X-ray diffraction experiments using the commercially available anhydrous form of famciclovir were carried out and led not only to the crystal structure determination of the anhydrous form I, but also to discovery of a new crystal form of anhydrous famciclovir from powder data.

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