Rietveld quantitative amorphous content analysis

Abstract

A procedure for Rietveld quantitative amorphous content analysis (RQACA) is outlined, in which the effects of systematic errors in the powder patterns are studied. The method derives the amorphous content from the small overestimation of an internal crystalline standard in a Rietveld refinement of an appropriate mixture. Of several standards studied, Al2O3 gave the best results. The statistical analysis of standard mixtures with a known amount of amorphous content indicated that this is a precise and accurate tool. It enables the measurement of the amorphous content with an accuracy close to 1%. Sample preparation and Rietveld analysis need to be optimized in order to minimize the systematic errors. The analysis of samples with phases displaying strong preferred orientation effects gives very high errors in the amorphous content. Samples with different absorption coefficients have also been studied in order to evaluate the importance of microabsorption. This plays an important role but it can be adequately corrected if the absorption coefficients of the standard and the sample are not very different. RQACA has been applied to tricalcium silicate, C3S, which is the main component of Portland cement. The average amorphous content of C3S, after microabsorption correction using two standards of higher and lower absorption coefficients, was found to be 19%.

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration

“…X-ray powder diffraction (XRPD) is an appropriate technique to identify, quantify and characterize the crystalline phase(s) involved in the hydration reactions. The application of Rietveld methodology [26] to XRPD data in order to obtain quantitative phase analyses (QPA) has been demonstrated for anhydrous cement materials [27][28][29][30][31], including the quantification of the amorphous fraction by adding a suitable standard [32]. Attempts to quantify the hydration processes of cements using XRPD and the Rietveld method have also been published in the last few years [33,34].…”

Efecto de la microestructura sobre la bioactividad de dos materiales vitrocerámicos del sistema CaSiO₃ – ZrO₂

“…Los difractogramas fueron refinados con el programa GSAS (16) usando para la forma de los picos la función pseudo-Voig (17) con la corrección de asimetría de Finger et al (18). El análisis cuantitativo de la fase amorfa se realizó, utilizando α-Al 2 O 3 como estándar interno, siguiendo el protocolo establecido por De la Torre et al (19), lo que permite su determinación con un error menor del 1%.…”

Rietveld Quantitative Analysis of Buen Retiro Porcelains

“…This compound was overestimated in all previous refinements, indicating that it has a negligible amorphous content. 17 So, we assume in this study that the Al 2 O 3 standard is free from amorphous phases. Additionally, Al 2 O 3 displays little preferred orientation, which dramatically increases the errors of the analyses; it has small (lower than 1 m) grain size, which helps to obtain accurate intensities as enough particles diffract in any direction; and the peak shape is easy to model.…”

“…Therefore, the standard phase fraction will be overestimated. The procedure relates the amorphous phase content to the overestimation of the crystalline 17 However, it should be pointed out that the overall amorphous content determined by this method includes every minor crystalline phase not defined, all nondiffracting fractions such as vitreous phases, grain-boundary regions, and intrinsic defects, etc. So, the binding glassy fraction in a porcelain must be slightly lower than the overall amorphous content that can be determined from RQACA.…”