CONICET | Buscador de Institutos y Recursos Humanos

Kaolin is a natural clay with kaolinite as the main crystallographic phase. The importance of this clay is related to its influence in ceramics, materials science, and mineralogy. The industrial use of kaolinite requires thermal treatments, so it is interesting to understand how metakaolin is formed during the thermal activation of this clay and also to know what are the physics and chemistry mechanisms behind its production [1]. These mechanisms are complex and according to theliterature there is not a general agreement on which is the rate-controlling step in the reaction, and on the atomic arrangement of metakaolinite [2].In this work it is studied the beginning of the dehydroxylation process using calculation methods based in Density Functional Theory. Four systems that combine vacancies of an OH group and a H atom in the kaolinite unit cell were proposed, considering each one as a possible first step in the reaction. Using the open source package Quantum ESPRESSO [3], the structure of each system was optimized and its energy was analyzed after the optimization. The results were compared between them and with the literature. After that, one system was chosen as the most compatible with the physical process, and its properties were analyzed. The X-ray diffraction pattern, the vibrational normal modes, and the electronic density of states were also studied and compared with those calculated for kaolinite.The predicted properties were also compared to experimental data, obtained from a well-crystallized kaolinite (KGa-1) and a national one (Sur de Río Blanco).The obtained results help to elucidate the beginning of the metakaolin production process and also help to understand the differences between the four proposed systems. The promising results encourage further analyses using the same theoretical-experimental methodology in order to continue the study of the transformation of kaolinite towards its dehydroxylated form.