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oai:docta.ucm.es:20.500.14352/605452024-07-22T18:15:35Zcom_20.500.14352_14col_20.500.14352_21

Caracterización de la solución sólida Na2(C03,S04) A 550°C López De Andrés, María Sol Marcos Pascual, Celia Cocaño Blanco, Susana García Martínez, O. Prieto Rubio, Manuel Although it is known that unlimited solid solution exists for the high temperature polymorphs Na2S04 (1)and α-Na2C03 , the phase relationships and the variation of crystallographic parameters for different compositions are not studied. Na2S04 has four well established modifications, but only the high temperature modification Na2S04 (1) (Pб3/mmc), stable above 237°C, forms extended solid solution series with Na2C03. At the other extreme, Na2C03 shows three polymorphs and a rather complicated transition behaviour, being the hexagonal phase α-Na2C03 (Pб3/mmc)stable at T > 489°C. In this paper, the crystallographic parameters were determined at 550°C for different solid solution compositions. The study was carried out by X ray diffraction in a high temperature powder camera. The diffraction patterns show a continuous evolution through the entire compositional range. Crystalline spacings and cell parameters decrease as the sulphate content decreases. This fact and the unusual unlimited S04=-C03= substitution can be explained by the orientational disorder of tetrahedral and triangular groups. Theoretical powder diffraction diagrams, calculated assuming this orientational and substitutional disorder, show a good fit with the experimentalresults. 2023-06-20T21:03:02Z 2023-06-20T21:03:02Z 1996 book part 8460552705 https://hdl.handle.net/20.500.14352/60545 spa open access Univ. Oviedo, Vicerrectorado de Extensión Universitaria