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|Type:||Artigo de periódico|
|Title:||Phase Transition In Barium Chlorate Monohydrate|
|Abstract:||The dehydration of barium chlorate monohydrate is investigated as the monoclinic fully hydrated Ba(ClO3)2·H2O modification is transformed into the orthorhombic face centered (ofc) fully anhydrous Ba(ClO3)2. The underlying structural changes were followed, both on single crystal and powdered samples, as a function of their degree of dehydration using a combination of several experimental techniques which included Raman and infrared spectroscopy, x-ray diffraction, thermogravimetry, and thermodifferential analysis. The dehydration process gets thermally activated at T∼85°C and the transition seems to proceed through intermediate steps, where the two phases coexist with a gradual dominance of the ofc phase as the temperature increases. The role of the loss of the water of crystallization in the process is clarified and the experimental results are interpreted by invoking a two-step mechanism for the accomplishment of the structural changes within the crystal. This comprises random nucleation and growth of clusters of vacancies, left by the exit of H2O molecules, which up to a certain critical size can retain the original crystal structure, followed by a sudden onset of the phase transition within each of the overcritically sized clusters. As this process goes on, the concentration of clusters increases and the transition gets further enhanced by cluster-cluster interactions. © 1978 American Institute of Physics.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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