Glass ceramic materials of the SiO 2 -CaO-MgO-Al 2 O 3 system: Structural characterization and fluorine effect
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Glass ceramic materials of the SiO2-CaO-MgO-Al2O3 system: Structural characterization and fluorine effect Mitzué Garza-García1, Jorge López-Cuevas2 and Oscar Hernández-Ibarra3 Universidad Autónoma de Coahuila, Escuela Superior de Ingeniería, Blvd. Adolfo López Mateos s/n, C.P. 26800, Nueva Rosita, Coahuila, México. 2 Centro de Investigación y de Estudios Avanzados del IPN, Unidad Saltillo, Carr. SaltilloMonterrey, Km. 13.5, C.P. 25900, Ramos Arizpe, Coahuila, México. 3 Instituto Tecnológico de La Región Carbonífera, Km 120, Carretera 57, Villa de Agujita, Municipio de Sabinas, Coahuila, México. 1
ABSTRACT Glass-Ceramic monoliths of the SiO2-CaO-MgO-Al2O3 system are obtained in this research. Due to its potential dual role as a flux and as a nucleating agent, two CaF2 levels (X = 3 and X = 6 mol.%) are investigated in the parent glass composition. Due to its good mechanical properties, we intend to obtain Diopside-type pyroxene [(Ca)(Mg,Al)(Al,Si)2O6] as the main crystalline phase in the synthesized glass-ceramics. Vickers microhardness (HV), density and type of crystallization are determined in the latter materials. The morphology and size of the Diopside crystals, as well as the crystallized fraction, are determined with the help of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Both materials exhibit surface crystallization with Diopside-type pyroxene phase with acicular morphology homogeneously distributed in the glassy matrix. The specimen with the least amount of added fluorine shows the highest microhardness value, as well as the largest and thickest acicular crystals of Diopside-type pyroxene, the lowest apparent density and the largest crystallized fraction. Our results indicate that CaF2 added in the amounts used by us does not act as nucleating agent, but it does affect the growth of the acicular crystals of the Diopside-type pyroxene phase. This is attributed mainly to the effect of fluorine on the glass structure and properties. The materials developed in this study may be considered as viable alternatives for applications in abrasive and corrosive environments, as well as for substrates for metallic coatings, and for abrasion-resistant floor tiles and other structural applications. INTRODUCTION Glass-ceramics typically contain between 50 and 90 vol.% of crystalline phases, the rest of the materials consists of a residual glassy phase. In comparison with many glasses and ceramics, the glass-ceramic materials have relatively higher mechanical and abrasion strength, as well as higher resistance to the attack by chemical reagents [1]. The properties of these materials depend on the size, morphology, chemical composition and lattice structure of their crystalline phases, as well as on the distribution of the latter in the glassy matrix and on the chemical composition of this phase [1,2]. D.U. Tulyaganov et al. [3] investigated glass-ceramic materials with Diopside-type pyroxene [(Ca)(Mg,Al)(Al,Si)2O6] as the main crystalline phase, plus other secondary crystalline phases. These authors ment
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