Determination of Mean Crystallite Dimensions from X-Ray Diffraction Peak Profiles: A Comparative Analysis of Synthetic Hematites

Mario Crosa1, Valter Boero1 and Marinella Franchini-Angela2
1 Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali-Chimica Agraria, Università di Torino, via Leonardo da Vinci 44, I-10095 Grugliasco (Torino), Italy
2 Dipartimento di Scienze Mineralogiche e Petrologiche, Università di Torino, via Valperga Caluso 35, I-10125 Torino, Italy
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Abstract: X-ray diffraction (XRD) profile analysis of eight synthetic hematite samples was performed to identify the best parameters for determining the apparent mean crystallite dimension (D) and, consequently, surface area. The samples are comparable to soil hematite with respect to crystallinity. The procedure included: a) deconvolution of the XRD peaks to Gauss and Cauchy components and subtraction of the instrumental profile, b) determination of D from full-width at half-maximum, integral breadth, and integral breadth measurements of the Cauchy component, and c) comparison of deduced surface areas with those obtained by the N2-BET adsorption method. As expected, D values are strongly influenced by the broadening parameters. An appropriate selection of peaks is required to obtain size values along the crystallographic axes a (hkl: 110, 300) and c (hkl: 104, 116) and to calculate reliable surface areas. Using the Cauchy component of the above peaks, the calculated surface areas compared well with those measured by the N2-BET adsorption method.

Key Words: BET • Hematite • Iron Oxides • Mean Crystallite Dimension • Powder X-ray Diffraction • Surface Area • XRD

Clays and Clay Minerals; December 1999 v. 47; no. 6; p. 742-747; DOI: 10.1346/CCMN.1999.0470608
© 1999, The Clay Minerals Society
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