Análisis del comportamiento cerámico de arcillas carbonatadas y alumínicas: Variaciones composicionales y en las propiedades físicas con la temperatura de calcinación.

Clay minerals hold significant importance as raw materials due to their diverse applications and, consequently, economic interest. In this study, the behavior of two clays has been analyzed: one illitic–carbonate and the other illitic–kaolinite, mixed in different proportions, 80/20 and 50/50, when fired at temperatures of 900, 1000 and 1100°C. The aim has been to deduce the mineral transformations that occur during high-temperature calcination and assess its influence on certain relevant physical properties, such as density, weight loss, linear shrinkage, both free and forced water absorption and color. For this purpose, samples from each mixture, both in their raw and calcined states, were analyzed using X-ray diffraction and only the calcined samples were analyzed using optical microscopy and field emission scanning electron microscopy (FESEM), in addition to measuring physical properties. The raw samples primarily consist of quartz, illite and kaolinite, and to a lesser extent, feldspars and carbonates in varying proportions depending on the mixture. Calcination causes the disappearance of both illite and kaolinite as well as carbonates, being replaced by quartz, feldspars, diopside-wollastonite, gehlenite, and hematite. From 1000ºC and up to 1100ºC, primarily, a phase with a glassy appearance texture appears, replacing the matrix. The development of a vitreous matrix leads to a progressive homogenization of the mixtures as the temperature increases, transitioning from a heterogenous heterometric texture at 900ºC to a homogeneous homometric texture at 1100ºC. Generally, the observed changes in physical properties are related to both mineralogical and textural alterations. The porosity of both mixtures decreases as the calcination temperature increases and the case of density and linear shrinkage is particularly remarkable, as each mixture displays contrasting behavior. Regarding color variations, it has been observed that both mixtures display a similar behavior as the firing temperature increases, which can be associated with the increase in the hematite content of the mixture.<br /