Papers by Keyword: Rietveld

Abstract: Cerium oxide has a high potential to be apply in removing pollutants combustion powders, organic materials from waste water and in the technology of fuel cells. Nickel oxide is an attractive material due to its excellent chemical stability, and their optical, electrical and magnetic proprieties. In this work, CeO₂-NiO systems on molar ratios of 1:1, 1:2 and 1:3 citric metal-acid were synthesized by using Pechinis method. The change in compositions and calcined temperature were studied by different techniques such as: XDR and SEM. It was also done a microstructural study by Rietvelds method, whose routine was designed to run in the Fullprof Suite program, and analyzed by pseudo-Voigt function. It has noticed that the molar ratio between metal-citric acid in the system CeO₂-NiO 1:1, 1:2 and 1:3 has a strong influence on microstructural proprieties, crystallite size and cell micro-deformations and can be used to control these proprieties.

Abstract: Indialite or α-cordierite was synthesized by glass crystallization method using mainly talc and kaolin and with small amount of MgO, Al2O3, SiO2 to compensate the chemical formulation of non-stoihiometric compositions of cordierite. (3MgO.1.5Al2O3.5SiO2). B2O3, P2O5 and CaO was also added to decrease the melting and sintering temperature of cordierite. The glasses were pelletized and sintered from 850oC up to 1050oC. Phase compositions of both heat treated glass was quantified by X-ray powder diffraction data by the Rietveld method using TOPAS Ver 3 software. Result shows that about 60wt% of α cordierite has successfully crystallized at 850oC. Beside secondary phases (forsterite) which come from initial raw materials, phases from grinding media were also presents in the sample. The contamination was considered high since it has reacted with existence phases to form a new phase at higher temperature. Without any contamination from grinding it was expected to obtain more than 90wt% α cordierite using the same composition.

Abstract: A new program to perform fast sequential and parametric whole powder profile refinement of in situ time-resolved powder diffraction data is presented. The program interacts with the launch mode kernel of the total powder pattern analysis software suite Topas® for doing the refinements. The program provides a graphical interface platform, upon which the huge Topas input command files necessary to perform sequential and parametric refinements can be easily prepared and executed. This program requires the user license dongle for Topas academic version 3 or higher.

Abstract: A study of the thermal decomposition sequence of a sample of natural arsenian plumbojarosite has been undertaken using in situ X-ray diffraction. The sample was heated to 900°C using an Anton-Paar heating stage fitted to an INEL CPS120 diffractometer. The data were analysed using a whole-pattern, Rietveld based approach for the extraction of quantitative phase abundances. The instrument configuration used required the development and application of algorithms to correct for aberrations in the (i) peak intensities due to differing path lengths of incident and diffracted beams in the sample and (ii) peak positions due to sample displacement. Details of the structural models used were refined at selected steps in the pattern and then fixed for subsequent analysis. The data sequence consists of some 110 individual data sets which were analysed sequentially with the output of each run forming the input for analysis of the next data set. The results of the analysis show a complex breakdown and recrystallisation sequence including the formation of a major amount of amorphous material after initial breakdown of the plumbojarosite.

Abstract: In the present work the occurrence of surface transformations triggered during chemical and biological leaching of chalcopyrite at 70 °C in basal medium were investigated with the aid of the Rietveld technique. Leaching experiments were conducted in 250 ml shake flasks at 150 rpm, contacting 1 g of a -80 # + 120# chalcopyrite concentrate with 100 ml of iron-free basal medium at pH 1.5 at 70°C. Three different conditions were used: experiment (a) in aerated conditions with basal medium inoculated with Sulfolobus metallicus (4x108 cells/ml); experiment (b) in aerated abiotic conditions; experiment (c) in abiotic conditions under N2 atmosphere. Copper and iron dissolved in solution was analyzed with atomic absorption. Samples of the initial chalcopyrite and the treated samples obtained after 16 days under the various experimental conditions were analyzed by Grazing-Incident X-ray diffraction (GID). The obtained x-ray spectra were then analyzed with the Rietveld refinement technique using the Topas software. Results showed that the initial concentrate consisted mainly of tetragonal chalcopyrite (JCPDS : 37-0471). Chalcopyrite leached under abiotic-anaerobic conditions was crystallographically unaffected. In chalcopyrite leached under aerated abiotic conditions there was evidence of surface texturization showed as preferential orientation to the crystallographical planes ( 3 1 2 ) and (1 1 6). Finally, surface texturization was also observed in chalcopyrite leached under inoculated conditions, but in this case showed as preferential orientation to the crystallographical planes ( 0 2 4 ) and ( 2 2 0). These results give a first evidence of surface texturization phenomena during dissolution of chalcopyrite at 70 °C. They suggest that chalcopyrite dissolution occurs via selective leaching of specific crystallographic planes, and this selectivity is influenced by both the chemical action of oxygen and the microorganism actvity.

Abstract: Induction of an apatite-forming ability on a 100% Y2O3-ZrO2, 100% Al2O3, and 80/20 and 20/80 wt% of zirconia-alumina (Y2O3-ZrO2-Al2O3) composite polycrystals via chemical treatment with 5M H3PO4 have been investigated. The chemical treatments produced Zr-O surface functional groups, which are known to be effective for apatite nucleation in simulated body fluid. It’s believed that Al-OH surface functional groups are not effective for apatite nucleation. I this work was shown that apatite nucleates in substrate of alumina treat and untreated chemically. This implies that Al- OH functional groups are effective for apatite nucleation.

Abstract: Wet gel obtained by sol-gel technique was dried in supercritical CO2 to prepare hydrated form of magnesium oxide. Calcination at 723 K under vacuum yielded nanocrystalline MgO aerogel. Structure studies were performed by X-ray diffraction, scanning and transmission electron microcopies. Electron microscopy images reveal rough, unfolded and ramified structure of solid skeleton. Specific surface area SBET was equal to 238 m2/g. X-ray pattern reveals the broadened diffraction lines of periclase, the only crystalline form of magnesium oxide. The gamma crystallite size distribution was determined using FW 5 4 / 5 1 M method proposed by R. Pielaszek. The obtained values of and σ (measure of polydispersity) of particle size parameters are equal to 6.5 nm and 1.8 nm, respectively, whereas the average crystallite size estimated by Williamson-Hall procedure was equal to 6.0 nm. The obtained at Rietveld refinement Rwp, and S fitting parameters equal to 6.62% and 1.77, respectively, seem to be satisfactory due to the nanosize of MgO crystallites and because of the presence of amorphous phase.

Abstract: Structure parameters of minerals in human bone, bioapatite, are very important for biomaterials. In situ micro-XRD and Rietveld structure refinement were used to extract subtle structure information of human ribs. Rietveld refinement testified that lattice parameters, crystallite size and microstrain for cortical and cancellous bones were significant difference. Anisotropic crystallite sizes of human rib showed preferential growth of apatite along c-axis and the graded variation at radial direction of bone axis. The variations of the subtle structures of bioapatite, such as, P occupancy and P-O2 bond length, as well as distortion index of P-O tetrahedron, demonstrated the tendency of mineralization and the content of CO3 2- in human ribs.

Abstract: This paper presents a new method to separate interfering spectra obtained in wavelength dispersive x-ray fluorescence spectrometry (WDXRF). This method permits improved results to be obtained, compared to conventional analytical results and enables the determination of chemical species of the same element without chemical separation. This is done by separation of the spectra due to electronic transitions of the valence electrons. The Rietveld method [11] overcomes the problem of superimposed peaks of the species present in the specimen and simultaneously enables determination of the species and does not require standard specimens and calibration curves. This signifies a marked improvement in comparison to other techniques. Specimen surface preparation to obtain spectra is a critical stage and its effects can be minimized by using Rietveld refinement, which permits the determination of intensity relationships of superimposed peaks with the aid of mathematical models. This establishes the basic conditions to obtain more accurate results in quantitative analysis. In the determination of chemical species, it is possible to separate, for example, Cr (III) and Cr (IV), with almost 100% superimposition.

Abstract: The aim of the work was to prepare an overview about the microstructures present in high-speed steel, focused on the crystallography of the carbides. High-speed steels are currently obtained by casting, powder metallurgy and more recently spray forming. High-speed steels have a high hardness resulting from a microstructure, which consists of a steel matrix (martensite and ferrite), in which embedded carbides of different crystal structure, chemical composition, morphology and size, exist. These carbides are commonly named MxC, where M represents one or more metallic atoms. These carbides can be identified by X-ray diffraction considering M as a unique metallic atom. In this work, it is discussed, in basis of the first principles of physics crystallography, the validation of this identification when it is considered that other atoms in the structure are substitutional. Further, it is discussed some requirements for data acquisition that allows the Rietveld refinement to be applied on carbide crystallography and phase amount determination.