X-ray powder diffraction (XRD) in combination with the Rietveld method was used to evaluate the proportion of crystalline and amorphous (glassy) phases in fly ashes produced in pulverized-coalcombustion (PCC) power plants. The quantification of amorphous phases through the Rietveld method is most usually carried out i) by using an internal standard or ii) by using a poorly-crystalline phase to ...

This paper shows a simple procedure for the quantification of industrial and laboratory samples of Ammonium Sulphate-Nitrate fertilizers (ASN) based on a Rietveld fit from X-ray powder diffraction profiles. The Rietveld fit is performed by means of the structural models of the double salts 2NH4NO3·(NH4)2SO4 and 3NH4NO3·(NH4)2SO4, previously reported by the authors. The proposed method demonstra...

ReO2 presents two crystalline variants, with monoclinic and orthorhombic structures. The former is metastable and irreversibly transforms to an orthorhombic structure above 460oC. The structure of the latter was determined from studies on monocrystalline samples, whereas for the monoclinic variant there are no single crystals available so far. It was found only one monoclinic variant and the st...

To refine amorphous structures like crystalline ones is impossible. This statement needs now some reconsideration in the case of silica glass. Starting with a microstrained crystalline model deriving from the α-carnegieite structure, atomic coordinates refinements by the Rietveld method prove to be possible. The study credibility is supported by the simultaneous fit of neutron and X-ray diffrac...

Displacement of the specimen surface from the instrument rotation axis in reflection optics diffractometry introduces bias into the measured Bragg peak positions thereby causing systematic shifts in the 2θ-dependent Rietveld parameters. Specimen transparency also results in 2θ-bias, which tends to mimic that from specimen displacement. The authors have investigated the influence of specimen dis...