Effect of Gradual Substitution of CaO by SrO in Glass-Ceramic Materials of the System SiO 2 - Al 2 O 3 - CaF 2 - RO (R =
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Effect of Gradual Substitution of CaO by SrO in Glass-Ceramic Materials of the System SiO2 - Al2O3 - CaF2 - RO (R = Ca, Mg, Sr) M. Garza-García1, J. López-Cuevas2, C.A. Gutiérrez-Chavarría2, N. Piedad-Sánchez3, E. Camporredondo-Saucedo3, O. Hernández-Ibarra4 1 Universidad Autónoma de Coahuila, Escuela Superior de Ingeniería, Nueva Rosita, Coahuila, México. 2 Centro de Investigación y Estudios Avanzados del IPN, Unidad Saltillo, Coahuila, México. 3 Facultad de Metalurgia. Universidad Autónoma de Coahuila, Monclova, Coahuila, México. 4 Instituto Tecnológico de Estudios Superiores de la Región Carbonífera, Coahuila, México. ABSTRACT The density, Vickers microhardness and crystallization fraction of glass-ceramic materials synthesized from parent glasses are determined in which CaO is gradually substituted by SrO. The chemical composition (in mol.%) of the parent glasses is 54SiO2-(23-X)CaO-12MgO5Al2O3-6CaF2-XSrO, where X is the employed CaO substitution level (X = 0, 3, 6 and 9 mol.%, with X = 0 corresponding to the reference material). In order to determine the type of crystallization occurring in the glass-ceramic samples, as well as the crystalline phases formed in them, these are characterized by both Scanning Electron Microscopy (SEM/EDS) and X-Ray Diffraction (XRD). Independently of the CaO substitution level employed, the glass-ceramics show the formation of a solid solution corresponding to diopside-type pyroxene, with chemical formula Ca(Mg,Al)(Al,Si)2O6, as a single crystalline phase. The synthesized glass-ceramic materials with the reference composition show the highest Vickers microhardness and crystallization fraction, as well as the lowest density. INTRODUCTION Glass-ceramic materials are obtained through the controlled crystallization of a parent glass, involving the separation of a crystalline phase from the glass. The final properties of these materials are determined by the size, morphology, composition, properties and distribution of the crystals dispersed in the glassy phase [1]. Diopside (CaMgSi2O6) is a pyroxene mineral belonging to the single chain group of the inosilicate family, with a simple crystalline structure in which the SiO4 tetrahedra are linked to each other by two oxygen atoms forming a relatively seemingly endless chain. The basic structural group is Si2O6 with silicon to oxygen ratio of 1:3. The most common crystalline morphologies presented by diopside are needle and dendritic. Diopside is also characterized by high twinning, which constitutes an energy-absorbing mechanism. Thus, a glass-ceramic material is strengthened, getting high hardness and resistance to fracture, if it has diopside within its crystal structure [2]. On the other hand, it is known that SrO improves some properties of glasses, such as their hardness and abrasion resistance. SrO also increases the brightness and ease of polishing of glasses and it is used too in the glazing of traditional ceramics, preventing the formation of bubbles during the firing process of the frit [3]. Thus, a glass-ceramic material havin
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