Rietvelda Analysis Research Papers - Academia.edu (original) (raw)

In the quest to develop a green cement composite with the lowest possible carbon footprint and the highest possible use of industrial by-products, an experimental investigation was undertaken, replacing 100% of ordinary portland cement. This paper presents the results of an experimental program to develop a zero-cement composite, incorporating 2.5, 5, and 7.5% nanosilica, 72.5, 70, and 67.5% fly ash, 25% ground granulated blast furnace slag (GGBFS), and hydrated lime used as a cement additive at 10 and 15% of the total supplementary cementitious material. Compressive strength tests were undertaken to study the mechanical properties of mortar samples of various mix designs. In addition, scanning electron microscopy, thermogravimetry, and X-ray diffraction were undertaken in conjunction with quantitative phase analysis to investigate the various physicochemical changes taking place within the cement matrix and to formulate strategies for its further development. The results demonstrate that the addition of nanosilica and hydrated lime to low calcium/high-volume fly ash and GGBFS blend can help in achieving an environmentally friendly zero-cement composite without the need of any heat treatment. The optimum content of nanosilica was found to be 5%. With the further increase in nanosilica content, although the pozzolanic reaction and the resulting C–S–H/C–A–S–H gel formation increases, it also increases the microcracking within the cement matrix, resulting in the reduction in compressive strength at both 7 and 28 days of curing. The siliceous hydrogarnet formed as a result of the pozzolanic reaction of amorphous silica (FA, GGBFS, NS), with the calcium aluminate present in GGBFS, shows very poor crystallinity with no visible peak reflection in X-ray diffraction data. The formation of siliceous hydrogarnet increases with the increase in amorphous nanosilica, but decreases with the increase in hydrated lime content.

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- Scanning Electron Microscopy, XRD, TGA, Rietvelda Analysis

The structural, vibrational, magnetic and dielectric properties of polycrystalline BiFeO3 and Bi0.95Pr0.05FeO3 are investigated by combining X-ray diffraction, Raman scattering spectra, magnetometry and dielectric measurements. Structural symmetry with rhombohedral R3c phase is revealed for both parent and 5% Pr substitution at Bi site, serving no chemical pressure and causes no structural transition from R3c to any other phase is identified from x-ray diffraction patterns and Raman scattering spectra. The shifting of phonon modes towards higher frequency side is attributed to lower atomic mass of Pr ion as compared to Bi ion. The magnetic measurements at room temperature indicate that Pr substitution induces ferromagnetism and discerns large and non-zero remnant magnetization as compare to pristine BiFeO3. Both dielectric permittivity and loss factor of Bi0.95Pr0.05FeO3 strongly decreases with increased frequency. Significant role of hopping of oxygen ion vacancies in Bi0.95Pr0.05FeO3 is inferred from modulus spectra and ac conductivity analysis.

The effect of high energy ball milling on the hematite for milling periods of times ranging from 1 to 48 h
was investigated by Rietveld analysis based on XRD patterns and Mössbauer spectroscopy. An expansion
of the unit cell parameters was observed. Both Scherrer method and Rietveld analysis show an evident
decrease of the grain size with the increase of the milling time. Moreover, some dependence of the lattice
parameters on the grain size was observed. Mössbauer spectroscopy measurements reveal that there
are two kinds of particles which co-exist in the sample: nanostructured and micrometric hematite. The
magnetic hyperfine field is affected by the grain size.

- by Mohamed Abdellah Lemine
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- XRD, Rietvelda Analysis, Ball Milling, Iron Oxides Nanoparticles

(Ba,Ti)-precursor complexes, important for the production of advanced BaTiO3 perovskite-type materials, undergo structural transformations and complex reactions during their thermal decomposition. Based on XRD phase analysis, combined with Rietveld refinement of crystal structure data, and on IR analysis, the intermediate formation of calcite-type BaCO3 is evidenced, which can be explained by the stabilization of this metastable modification in the form of an oxycarbonate phase down to room temperature. Two possible processes, leading to such an oxycarbonate, are discussed: (i) partial substitution of CO32− by O2− in the anionic sublattice, and (ii) topotaxial formation of calcite-type structural domains of BaCO3 by templating with oxygen-deficient titanates, resulting in the oxide–carbonate intergrowth structures.

- by Roberto Köferstein
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- Rietveld refinement, Perovskites, Infrared spectroscopy, BARIUM TITANATE