![]() ![]() Such as reactions between metal or metal oxide with H2S, precipitation in several liquid medium, reaction between metal and sulfur in closed vessel, chemical vapor deposition (CVD) technique. Several techniques are known for the production of metal sulfides. Transition metal sulfides have wide application area in industry and technology. In this study some of the first row transition metal oxides were transformed to metal sulfides by new solid gas reaction system. The results of this modeling are shown to be in good agreement with complementary characterization methods, like transmission electron microscopy and cyclic voltammetry. Molecular dynamics simulations are shown to be effective in generating realistic structural models and dynamics of an atomic system, and are then used to study the observed features in the powder diffraction pattern.įurthermore, the characterization of a sample of shape controlled Pt nanoparticles is carried out through the use of a developed Debye function analysis routine in an effort to determine the predominant particle shape. It also begins to allow for the incorporation of atomistic simulations into the field of diffraction. This approach allows for the existing theories of diffraction to be tested, and extended, in an effort to improve the characterization of small crystallites. The studied patterns are simulated from atomistic models of nanoparticles via the Debye function. The effects of crystallite size, shape, lattice dynamics, and surface strain are all systematically studied in terms of their impact on the line profiles. This work investigates how different structural characteristics of metal nanoparticles influence the line profiles of the corresponding powder diffraction pattern. Prepared mixtures have been used to demonstrate the very good results that can be obtained with this method.Īccurate statistical characterization of nanomaterials is crucial for their use in emerging technologies. Experimental procedures have been developed for sample preparation and data collection for reference samples and unknowns. This database is used to calculate the weight fraction of each phase in a mixture by fitting its diffraction pattern with a least-squares best-fit weighted sum of selected database reference patterns.The new QXRPD method was evaluated using oxides found in ceramics, corrosion products, and other materials encountered in the laboratory. The analyst builds a reference database of component diffraction patterns, corrects the patterns for background effects, and determines the appropriate reference intensity ratios. To facilitate the use of the new method, menu-driven interactive computer programs with graphics have been developed for the VAX series of computers. The unique approach employed in this method is the utilization of the full diffraction pattern of a mixture and its reconstruction as a weighted sum of diffraction patterns of the component phases. In addition, a detailed analysis of line shapes gives information about physical properties such as the size and shape of the individual crystallites, microscopic strain, and stacking disorder.In the early days of crystallography many simple (and some not-so-simple) structures were solved from x-ray powder diffraction patterns, but the obvious limitations to the number of individual reflection intensities which can be estimated and the increasing sophistication of single-crystal techniques resulted in a decline in the importance of this application in the 1950s and 1960s.ĪbstractA new quantitative X-ray powder diffraction (QXRPD) method has been developed to analyze polyphase crystalline mixtures. From an x-ray pattern of good quality it is possible to determine unit cell parameters with high accuracy and impurity concentrations of 1-5%, so that powder techniques are extremely valuable in phase equilibrium studies and residual stress measurements, for example. Any single-phase polycrystalline material gives an x-ray pattern which can be regarded as a unique “fingerprint,” and modern automated search-and-match techniques used in conjunction with the Powder Diffraction File (maintained by the International Center for Diffraction Data, Swarthmore, PA) allow routine analysis of samples in minutes. It is estimated that there are now about 25,000 users throughout the world, of which about one third are in the United States. X-ray powder diffraction is one of the most widely used techniques by scientists engaged in the synthesis, analysis, and characterization of solids. ![]()
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