Papers by Keyword: Rietveld Method

Abstract: In this work were investigated the systems-NiO_x-CoO_1-x-Al₂O₃ using X-ray diffraction of the powder, which identified and quantified to phase in the sample was performed through the Rietveld method. The insertion of nickel oxide in the system obeyed the proportions of molar fraction of 0,05, 0,30, 0,50, 0,70 and 0,95 (x). Analyses were realized on samples which were treated at the temperature 1773K. From the results of refinement of spinel phase structure, was analyzed the relationship between lattice parameter refinement and the substitution of Co⁺² ion by Ni⁺²ion in the structure. The electrical resistivity dc was observed as a respect to temperature and the results appears a decrease of resistivity when were simultaneously increased the temperature. It was observed that the conduction mechanism was the same in all samples and the results for activation energy, characterized like electron hopping, it due exchange setting the ion Co⁺² D Co⁺³.

Abstract: Metal-ceramic composites are recently being used as electrode materials in solid oxide fuel cell (SOFC), which have received much attention as alternative energy sources. In this work cermets of Cu-Ni-Ag/Y₂O₃ were synthesized with different quantities of Ni and Ag. Various samples were prepared from pure precursors by conventional powder metallurgy processing and sintered at 800°C. The characterization by differential scanning calorimetry (DSC) and thermal gravimetric analyze (TGA) indicate that the presence of Y₂O₃ could increase the corrosion resistance of the metallic copper alloys. The copper crystalline structure presents internal strengths and possibly crystallites with different cell parameters due to the effect of thermal and mechanical treatments in presence of Y₂O₃. The highest electrical conductivity and highest hardness were obtained for the composition with 5% Y₂O₃ and 5% nickel, which increases the hardness and could contribute to the higher conductivity through a precipitation mechanism.

Abstract: Some samples of La2/3(Ca(1-x)Znx)1/3MnO3 （x = 0, 0.2, 0.4, 0.6, 0.8, 1.0） were prepared by solid-state reaction method at 1623K. The crystal structures of the compounds were studied by X-Ray Diffraction(XRD). All the samples are orthorhombic structure (Pnma), the symmetry has no obvious change with the increase of Zn atom content x. The crystal lattice constants, Mn-O bond length and Mn-O-Mn bond angle varied with the different Zn content, analyzed by the Rietveld method.

Abstract: In this work, the precursors zinc nitrate hexahydrate and zinc chloride were used to synthesize zinc oxide (ZnO) nanocrystals, applying a simple solochemical technique. ZnO rod-like nanostructures were successfully obtained by chemical reaction between NaOH and zinc nitrate hexahydrate at 90 °C. The sample formed by chemical reaction between NaOH and zinc chloride at 90 °C showed the ZnO phase mixed with the Zn5(OH)8Cl2•H2O phase. Only after thermal treatment at 500 °C for 3 hours, the conversion of Zn5(OH)8Cl2•H2O in ZnO was achieved. The samples prepared with different precursors were characterized by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. Rietveld analysis to the X-ray diffraction data indicated that ZnO nanocrystals obtained have hexagonal wurtzite structure and nanometric-sized crystallites.

Abstract: Quantitative X-Ray diffraction (QXRD) combined with the Rietveld refinement method allows direct determination of crystalline phase content of cement and its hydrates. However, relatively precise results need the correction of proper internal standards and the use of matched peak profile functions with masterly refinement strategies. The aim of this paper is to research and discuss effects of these factors on the quantitative phase analysis results. For this purpose, different internal standards and peak profile functions with corresponding refinement strategies were attempted in experiments and refinements. The results indicate that Al₂O₃ as internal standard is more suitable for cement and its hydrates than ZnO, and the better peak profile function is CW function 2 rather than function 3 in GSAS.

Abstract: This paper has put forward a high-temperature quantitative X-ray powder diffraction analysis method for the determination of an isothermal section of a ternary system in comparison with a conventional method. In a three-phase region of the isothermal section at 1150 °C of Cu₂O(CuO)-Al₂O₃-SiO₂ pseudo-ternary system, the compositions of the solid phase points of three system points are determined according to the quantitative analysis of the crystalline phases in the samples carried out by Rietveld method. Then the liquid phase point of the three-phase region is determined according to the crosspoints of the tie lines of every pair of system point and solid phase point. The precisions of the analytical results have reached to be 0.1 ~ 5.0 %. By comparison, a good result is obtained for the determination of the liquid phase point of the three-phase region in the isothermal section at 1150 °C when the analytical results of high-temperature RQA analysis are used in determination of the isothermal section of the pseudo-ternary system.

Abstract: Tin oxide material (SnO2) is synthesized in nano scale range and is characterized. The refined X-ray intensity data was obtained from the Reitveld method. The electron density of nano SnO2 is determined using MEM (Maximum Entropy Method). Using one, two and three dimensional MEM maps, the bonding within the atoms is clearly understood. The particle size of SnO2 is also analyzed using XRD and SEM.

Abstract: Industrial applications of partially stabilized zirconia (PSZ) has increased substantially recently, considering its excellent thermal stability, strength and ionic conductibility. Its main application includes oxygen sensors and fuel cells. In this work zirconia ceramic powder is produced by Pechini process, mixing citric acid and ethylene glycol, adding yttrium and zirconium precursors. All the process was carried out with complete agitation. The obtained powder after this procedure is heat treated at 650°C during two hours. Characterization was performed by infra-red spectroscopy, x-ray diffractometry and quantitative analysis by Rietveld Method. The results show tetragonal and monoclinic phases, with nanometric crystallite.

Abstract: The yttria-stabilized zirconia (YSZ) is used in a great variety of applications, for example, electrolytes of solid oxide fuel cells and oxygen sensors. In the study of YSZ, the particle size powders and sintering processes are important to define the final properties of the zirconia products. The objectives of this work were to determine the phases and the crystalline size using X-Ray Diffraction (XRD) data and the Rietveld Method (RM) of the YSZ powders obtained by chemical synthesis based on the Pechini method. It was used ZrOCl2.8H2O and Y(NO3)3.5H2O as precursors reagents. After calcination at 550oC during 24 hours, the powder was analyzed by XRD and scanning electronic microscopy (SEM). From XRD and using Rietveld method were verified that there is only cubic phase with lattice parameter a = 5.1307(1) Å and the space group Fm3m. Due to substitution of the Zr atoms in the Y atoms sites, there were vacancies in 17.72 % of O atoms sites. However, the percentage of substitution of Zr atoms in Y atoms sites in the structure not was determinate because the curves of atomic scattering of them are very similar. Using Scherrer equation and considering anisotropy effect, the average crystalline size was determinate: 10,43 nm (c axis) and 10,39 (b axis). This spherical symmetry also observed for SEM.

Abstract: Ceramic materials have properties defined by their chemical and micro-structural composition. The quantification of the crystalline phases is a fundamental stage in the determination of the structure, properties and applications of a ceramic material. Within this context, this study aims is the quantitative determination of the crystalline phases of the ceramic materials developed with addition of mineral coal bottom ash, utilizing the X ray diffraction technique, through the method proposed by Rietveld. For the formulation of the ceramic mixtures a {3,3} simplex-lattice design was used, giving ten formulations of three components (two different types of clays and coal bottom ash). The crystalline phases identified in the ceramic materials after sintering at 1150oC during two hours are: quartz, tridimite, mullite and hematite. The proposed methodology utilizing the Rietveld method for the quantification relating to crystalline phases of the materials was shown to be adequate and efficient.