Quantification of phases with partial or no known crystal structures

2006 ◽  
Vol 21 (4) ◽  
pp. 278-284 ◽  
Author(s):  
Nicola V. Y. Scarlett ◽  
Ian C. Madsen
Keyword(s):  
Crystal Structures ◽  
Rietveld Method ◽  
Amorphous Material ◽  
Internal Standard ◽  
Crystalline Phases

Quantification of mixtures via the Rietveld method is generally restricted to crystalline phases for which structures are well known. Phases that have not been identified or fully characterized may be easily quantified as a group, along with any amorphous material in the sample, by the addition of an internal standard to the mixture. However, quantification of individual phases that have only partial or unknown structures is carried out less routinely. This paper presents methodology for quantification of such phases. It outlines the procedure for calibration of the method and gives detailed examples from both synthetic and mineralogical systems. While the method should, in principle, be generally applicable, its implementation in the TOPAS program from Bruker AXS is demonstrated here.

Determination of the crystallized fractions of a largely amorphous multiphase material by the Rietveld method

2001 ◽  
Vol 34 (2) ◽  
pp. 114-118 ◽  
Author(s):  
X. Orlhac ◽  
C. Fillet ◽  
P. Deniard ◽  
A. M. Dulac ◽  
R. Brec
Keyword(s):  
Rietveld Method ◽  
Amorphous Material ◽  
Effective Means ◽  
Site Occupancy ◽  
Internal Standard ◽  
Ceramic Materials ◽  
Contrast Effects ◽  
Crystalline Phases ◽  
Cell Parameters ◽  
High Level

The Rietveld method has proved to be a very effective means to characterize and quantify the crystalline phases and the amorphous phase in glass ceramic materials using X-ray powder diffraction data. The technique was applied to a borosilicate glass of the type used for high-level nuclear-waste containment, in order to measure the proportions of the crystallized phases after heat treatment and, thus, to qualify the thermal stability of the glass. Six crystalline phases were analysed in this way in an almost entirely (>95 wt%) amorphous material after adding a known proportion of an internal standard (TiO2). The quantitative analyses were corrected to allow for microabsorption effects resulting from grain-size and absorption-contrast effects. In addition to the quantitative data, unit-cell parameters and site-occupancy refinements revealed solid-solution and substitution phenomena in the crystal.

scholarly journals QUANTIFICAÇÃO DE MULLITA PROVENIENTE DE RESÍDUOS DE CAULIM DA REGIÃO AMAZÔNICA: USO DO MÉTODO DE RIETVELD

Química Nova ◽  
2020 ◽  
Author(s):  
Marlice Martelli ◽  
Eric Mochiutti ◽  
João Lima ◽  
Roberto Neves
Keyword(s):  
Rietveld Method ◽  
Internal Standard ◽  
Amazon Region ◽  
Synthesis Process ◽  
X Ray Diffraction ◽  
Crystalline Phases ◽  
X Ray ◽  
Mineral Phases ◽  
Precursor Material ◽  
Quantitative Analyses

QUANTIFICATION OF MULLITE FROM KAOLIN WASTES FROM THE AMAZON REGION: USE OF THE RIETVELD METHOD. Mullite is used to obtain a refractory material, there are several factors that influence the synthesis process of mullite: the preparation of the mixture, the precipitation and the reaction of SiO2 and Al2O3. For the synthesis of mullite, samples of kaolin processing residues were used as precursor material, because it presents SiO2 and Al2O3 in its composition. This work aimed to identify, by X-ray diffraction, and quantify the mineral phases present in samples of kaolin processing residues from the Amazon region calcined at 1300, 1400 and 1500 ºC, using the Rietveld method. The method allowed the refinement of the complex crystalline structures and was applied to the data supply for quantitative analyses with satisfactory results of good accuracy. The results of the quantification of crystalline and non-crystalline phases (with internal standard) in the samples calcined at 1500 ºC presented approximate values of mullite (62%), cristobalite (32%) and non-crystalline phases (6%), for both samples, indicating that the refinement model applied is optimal. These results obtained from the quantification of the phases by the method of Rietveld are presenting coherent and satisfactory values, in comparison with the theoretical ones by the phase diagram Al2O3 and SiO2

Problems and Solutions in Quantitative Analysis of Complex Mixtures by X-Ray Powder Diffraction

1987 ◽  
Vol 31 ◽  
pp. 295-308 ◽  
Author(s):  
David L. Bish ◽  
Steve J. Chipera
Keyword(s):  
Quantitative Analysis ◽  
Amorphous Materials ◽  
Rietveld Method ◽  
Internal Standard ◽  
Preferred Orientation ◽  
Complex Mixtures ◽  
Calibration Data ◽  
Cell Parameters ◽  
Amorphous Phases ◽  
Standard Data

AbstractIn spite of the wide availability of automated diffractometers and advanced data reduction software, numerous traditional problems still exist that make highly precise and accurate quantitative analyses of complex mixtures difficult. The problems include particle statistics, primary extinction, microabsorption, preferred orientation, overlapping and broad reflections, variation in standard data with composition, availability of pure standards, and detection of amorphous and trace phases. Our analyses of rocks use the matrix flushing method on < 5μm particle-size material mixed with a 1.0-μm corundum internal standard to minimize the first four effects. Integrated intensities are used, and we employ several peaks from each phase whenever possible. We overcame overlap problems through iterative calculations using integral, multiple peaks or with profile refinement. Use of observed and calculated diffraction patterns for every phase enables us to predict the effects of composition and preferred orientation on RIRs. This allows us to correct for these effects if reference intensity ratios (RIRs) are known as a function of composition and orientation. Detection of amorphous phases is a significant problem, and standard mixtures reveal that amounts of amorphous components below 30% are difficult to detect. The poor detection limit and the nature of the diffraction band from amorphous phases make internal standard or spiking methods the best approach for analyzing samples containing amorphous materials. The Rietveld method of quantitative analysis has the potential to minimize all of the above problems. This method requires a knowledge of the crystal structures of all component crystalline phases, but no calibration data are necessary, structural and cell parameters can be varied during the refinement process, so that compositional effects can be accommodated and precise cell parameters can be obtained for every phase. Since this method fits the entire diffraction pattern and explicitly uses all reflections from every phase, complex, overlapped patterns can be easily analysed. In addition, this method presents the opportunity to correct for preferred orientation and microabsorption during data analysis.

Quantitative Analysis of Cement-Based Materials and Sulfate Attack Products by XRD-Rietveld Analysis

2013 ◽  
Vol 357-360 ◽  
pp. 1362-1369 ◽  
Author(s):  
Hua Li ◽  
Jia Ping Liu ◽  
Wei Sun
Keyword(s):  
Quantitative Analysis ◽  
Calcium Hydroxide ◽  
Rietveld Method ◽  
Internal Standard ◽  
Rietveld Analysis ◽  
Sulfate Attack ◽  
Practical Significance ◽  
Cement Pastes ◽  
Cement Based Materials ◽  
Mixed Samples

XRD-Rietveld method has been adopted for quantitative analysis of phases in cement powder, phases in mixed samples of cement and pure calcium hydroxide, and sulfate attack products in cement pastes, based on the TOPAS software. The results show that, Rietveld analysis values show good agreement with the actual levels of mixed samples, and the accuracy degree of Rietveld method is at least as well as that of TG/DSC method which is commonly used in quantitative analysis of calcium hydroxide. By adding appropriate internal standard substance, XRD-Rietveld analysis method can be effectively used in quantitative analysis of sulfate attack products in cement-based materials. This work has practical significance on the study of sulfate attack of cement-based material.

Semi-Quantitative XRD Analysis of Fly Ash Using Rutile as an Internal Standard

1988 ◽  
Vol 32 ◽  
pp. 569-576 ◽  
Author(s):  
A. Thedchanamoorthy ◽  
G.J. McCarthy
Keyword(s):  
Fly Ash ◽  
Error Analysis ◽  
North American ◽  
Intensity Ratio ◽  
Limit Of Detection ◽  
Internal Standard ◽  
Xrd Analysis ◽  
X Rays ◽  
Fly Ashes ◽  
Crystalline Phases

AbstractXRD analysis of fly ash was quantitated using the Reference Intensity Ratio (RIR) method and rutile (TiO2) as an internal standard. Rutile RIR's for 15 of the crystalline phases commonly observed in North American fly ash were determined. Error analysis on the various steps in quantitation indicated that precision ranged from ±10% of the amount present for phases that diffract x-rays strongly to ±21% for weakly diffracting phases. Limit of detection in the mostly glassy fly ashes ranged from 0.2% for lime, the most strongly diffracting phase, to 3.5% for weakly diffracting mullite. Accuracy evaluated with a simulated fly ash was within the limits established by precision, but in actual fly ash samples, accuracy will be a function of the match between the crystallinity and composition of the analyte and the analyte standard. Overlaps among peaks of some of the important phases require intensity proportioning; for this reason, the method is best described as semi-quantitative.

A Rietveld tutorial—Mullite

2009 ◽  
Vol 24 (4) ◽  
pp. 351-361 ◽  
Author(s):  
James A. Kaduk
Keyword(s):  
Crystal Structure ◽  
Chemical Composition ◽  
Rietveld Method ◽  
Amorphous Material ◽  
Thought Processes ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Bulk Chemical ◽  
The Common ◽  
Variable Stoichiometry

The crystal structure of the mullite in a commercial material was refined by the Rietveld method using laboratory X-ray powder diffraction data. In this one refinement, most of the common challenges—including variable stoichiometry (partially occupied sites), multiple impurity phases, amorphous material, constraints, restraints, correlation, anisotropic profiles, microabsorption, and contamination during grinding—are encountered and the thought processes during the refinement are described step-by-step. Interpretation of the refinements includes bulk chemical analysis, chemical composition of the mullite, assessment of the geometry, bond valence sums, the displacement coefficients, crystallite size and microstrain, comparison to similar structures to assess chemical reasonableness, and the nature of the amorphous phase.

Entropy changes and structural implications for crystalline phases of pyrazine

1979 ◽  
Vol 57 (23) ◽  
pp. 3056-3060 ◽  
Author(s):  
Robert K. Boyd ◽  
John Comper ◽  
George Ferguson
Keyword(s):  
Crystal Structures ◽  
Phase Ii ◽  
Adiabatic Calorimetry ◽  
Heat Capacities ◽  
Unit Cell ◽  
Phase Iii ◽  
Point Symmetry ◽  
Crystalline Phases ◽  
Spectroscopic Evidence ◽  
X Ray

Molar heat capacities of crystalline pyrazine have been measured by adiabatic calorimetry in the range 20–40 °C and interpreted to show that in the crystal structures of phases II and III half the molecules must be disordered. Together with previous X-ray studies, this allows possible structures for phase II and phase III to be deduced. Of the eight molecules in the phase III unit cell, four are disordered over two sites so that the point symmetry is effectively mmm; the remaining four molecules have 2/m symmetry and are not disordered. This structure is consistent with the available spectroscopic evidence. It is likely that the phase II structure is closely related to the phase III structure, for example by the molecules with 2/m symmetry adopting a slightly different orientation.

Cristobalite-Related Phases in the NaAlO2–NaAlSiO4 System. I. Two Tetragonal and Two Orthorhombic Structures

1998 ◽  
Vol 54 (5) ◽  
pp. 531-546 ◽  
Author(s):  
J. G. Thompson ◽  
R. L. Withers ◽  
A. Melnitchenko ◽  
S. R. Palethorpe
Keyword(s):  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structure Type ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Modulation Wave ◽  
Wave Approach ◽  
The Ideal

The crystal structures of five new cristobalite-related sodium aluminosilicates with four different structure types from the system Na2−x Al2−x Si x O4, 0 ≤ x ≤ 1 [Na1.95Al1.95Si0.05O4, P41212, a = 5.2997 (6), c = 7.0758 (9) Å; Na1.75Al1.75Si0.25O4, Pbca, a = 10.4221 (11), b = 14.264 (3), c = 5.2110 (5) Å; Na1.65Al1.65Si0.35O4, P41212, a = 10.3872 (7), c = 7.1589 (8) Å; Na1.55Al1.55Si0.45O4, Pbca, a = 10.385 (1), b = 14.198 (3), c = 5.1925 (6) Å; Na1.15Al1.15Si0.85O4, Pb21 a, a = 10.214 (2), b = 14.226 (7), c = 10.308 (1) Å], have been refined by the Rietveld method from X-ray powder diffraction data. Plausible starting models were derived for the x = 0.05, 0.25 and 0.45 structures by analogy. Starting models for the x = 0.35 and 0.85 structures, with previously unreported structure types, were derived from a modulation wave approach based on distortion of the ideal C9 structure type and assuming regular SiO4 and AlO4 tetrahedra.

Sign in / Sign up

Export Citation Format

Share Document