Papers by Keyword: Rietveld Analysis

Abstract: In the present work on Al-W master alloy for modification of silumina casting alloy was studied. This alloy was characterized by XRD analysis and SEM/EDX methods. The XRD investigations of Al-W sample enabled the identification of Al, Al4W, Al5W phases. The contents of Al4W and Al5W phases are similar and equal 7.6 wt.% and 7.8 wt.%, respectively. SEM and EDS show the microstructure diversification and the shape of Al4W (cubic) and Al5W (oblong) particles in Al-matrix.

Abstract: In the present work, zirconium gadolinium oxide (Gd2Zr2O7) ceramics were prepared by annealing in different conditions and with APS (air plasma sprayed) techniques for thermal barrier coating (TBC) application. Thermal properties, phase transformation, crystal structure and cross-sectional morphologies of these materials were investigated. The thermal behaviour of the material was investigated from room temperature to 1500°C using the differential thermal analysis (DTA). The X-ray diffraction methods were used for the qualitative phase analysis. The structure of the studied samples has been characterized by employing powerful Rietveld’s whole X-ray profile fitting technique using the DBWS 9807a program. The SEM and EDS techniques were used to in the ceramic samples morphology analysis and for their chemical composition, respectively. The research showed that further stages of annealing result in the phase transformation of the parent substances and the main phase Gd2Zr2O7. It was found out that complete phase transformation into Gd2Zr2O7 phase takes place only for the air plasma sprayed sample. The analysis of the morphology of the initial powder revealed the spherical shape of the powder particles, which have a porous internal structure.

Abstract: The fundamental parameters approach (FPA) as implemented in TOPAS is investigated for analyses of conventional X-ray powder diffraction (XRPD) data. The FPA involves the convolution of a series of models, each one constituting an individual contribution to the geometric portion of the instrument profile function (IPF). Parameters within each model are refined by least squares to yield a presumably accurate description of the experiment. If one wishes to interrogate the functionality of said models, a diffractometer wherein the uncertainties in optical character are minimized is required. To this end, a diffractometer was built at NIST which featured conventional divergent beam optics in conjunction with a well aligned, stiff, and accurate goniometer assembly. Initial results indicated that the detector arm was flexing; this problem has been addressed with the fabrication and installation of a new arm and counterweight assembly. Data collected from NIST Standard Reference Material (SRM) 660a, lanthanum hexaboride, are analyzed using the FPA method to yield conclusions on the validity of the models with respect to shape and position of the diffraction profiles.

Abstract: The effect of substitution of zinc into the hydroxyapatite lattice(ZnHA) was evaluated using experimental precipitation studies and with ab initio modelling data. When attempting to introduce zinc into the hydroxyapatite (HA) lattice not all of the zinc is substituted and ICP confirms its presence in the supernatant. Modelling suggests that this is likely to be because of the high formation energy introducing zinc into the pure hydroxyapatite lattice, 4.6 - 4.9eV. In the experimental study it was found that a maximum of 0.61wt% zinc could be substituted into the HA lattice at 10oC with less being substituted at room temperature »22oC. Experimental measurements revealed that the presence of zinc in the lattice decreased the a-lattice parameter and increased the c-lattice parameter. Modelling showed that this was likely to be caused by the movement of the hydroxyl ions away from the c-axis, towards the zinc atoms which were substituted in calcium type II positions. The type II position was shown to be the most stable substitution site.

Abstract: Nanocrystalline CaTiO3 powders doped with Fe2O3 have been prepared using a soft chemical route. Precipitation of CaTiO3 nanocrystals has been studied by monitoring the exothermic peak in their DSC spectra. The crystal growth temperature of the samples depends on the concentration of iron. Surface morphology, crystal structure, optical and electrical properties of the nanostructures are investigated. X-ray diffraction study shows that the as-prepared powders are amorphous in nature and CaTiO3 phase formation starts at around 500 0C. Rietveld analysis revealed that the particle size of iron substituted CaTiO3 is in nanometer range. Optical bandgap of the nanostructures varies from 4.3 to 3.7 eV for the variation of iron concentration from 0.05 to 0.2 mole %.

Abstract: The Zn0.8Co0.2O ceramics were synthesized by the solid state reaction method with the mixture of ZnO and CoO powders. The mixed powders were sintered at 1200 °C and 1300 °C for 4 hours. It was found that the X-ray diffraction patterns of Zn0.8Co0.2O ceramics were similar to that of the pure ZnO one. The crystal structure of Zn0.8Co0.2O ceramics were then determined using the Rietveld full-profile analysis method to indicate a single phase with a wurtzite-like structure. Their microstructures were examined using the scanning electron microscopy. The results showed that their grain sizes were increased with increasing both the sintering temperatures and the doping effect. Moreover, the optical absorption spectra using UV-Vis spectrometer showed that there were several extra absorption bands appearing in the Zn0.8Co0.2O samples. This confirms that Co2+ is substituted Zn2+ in the wurtzite structure.

Abstract: The reaction of a stoichiometric mixture of aluminium isopropoxide and yttrium acetate in 1,4-butanediol (1,4-BG) at 300 °C directly yielded crystalline yttrium aluminium garnet (YAG), while the reaction in ethylene glycol (EG) afforded an amorphous product in which a large amount of EG moieties remained. The latter product exhibited an exothermic peak due to the crystallization of YAG at around 900 °C and single-phase YAG was obtained by calcination at 1000 °C. The YAG sample directly obatained in 1,4-BG had a large unit cell parameter (12.144 Å), whereas the YAG sample obtained by the latter method had a unit cell parameter (12.015 Å) essentially identical with the value (12.01 Å) reported in the JCPDS card. Rietveld analysis indicates that the former crystals had Al vacancies at 24d sites and oxygen vacancies while the latter was essentially free from these vacancies.

Abstract: The solubility of manganese ion in layered perovskite La4Ni3O10 phase was examined and the detailed crystal structure of this phase was discussed. The solid solution of La4Ni3-xMnxO10 was prepared by solid state reaction. The crystal structure of La4Ni3-xMnxO10 was analyzed by powder X-ray diffraction and Rietveld methods. The solid solution for x=0.5 had a orthorhombic system with lattice parameter a=0.5485(0), b=0.5433(6) and c=2.8034(9). In detailed observation of the X-ray diffraction data, some superlattice reflections that were forbidden for a face centered orthorhombic cell were identified. A possible space group Pnnn (no.48) was derived from the reflection conditions.

Abstract: Composite biomaterials based on calcium phosphate ceramic due to their high bioactivity are of interest for biological application and bone tissue repair. Structural and microstructural parameters of inorganic constituent of these materials are very important for the synthesis and characterization of composites. Quantitative and qualitative content, crystallite size of phases, as well as the degree of crystallinity have a great influence on the quality of composites, their application and bone tissue repair. X-ray diffractometry was employed to investigate the components of biocomposite materials, calcium phosphate (CaP) ceramic and poly-DL-lactide-coglycolide (DLPLG) polymer, as well as the biocomposite obtained from the mentioned components. Composite biomaterial was obtained by modified emulsion process. Using the Rietveld refinement, we analyzed CaP as an inorganic component of the composite, whence we have determined structural and microstructural properties of ceramic component of the investigated composite. The results obtained by structure refinement show that calcium phosphate ceramic materials synthesized at room temperature contain hydroxyapatite HAp as a predominant phase. The calculated Ca/P ratio is 1.667. The Rietveld analysis revealed lattice parameters a(Å)=9.4324(7) and c(Å)=6.8785(6) that are in agreement with the theoretical values.