Production and quantification of high-purity mullite at 1600°C from kaolinitic clay and calcined alumina

Abstract

A study is performed to determine the reaction time which is required at 1600°C to obtain mullite from clay with a high content of kaolinite (clay from the La Rioja Province of Argentina) and from a stoichiometric mixture of the clay and calcined alumina of grade Almatis-A2G. The chemical composition of the raw materials was determined and they were studied by x-ray diffraction (XRD) and examined on a scanning electron icroscope (SEM). The materials were then mixed in the stoichiometric proportions 3Al2O3·2SiO2 and pressed at 100 MPa. The pressed specimens were fired at 1600°C in electric furnaces for different lengths of time: 0.25, 0.5, 1, 2, 3, and 5 h. Their density and porosity were determined after they were fired. In the studies performed on the scanning electron microscope and by x-ray diffraction; the crystalline phases were identified by the Rietveld method and the amorphous phases were determined by means of the Le Bail model. The objective was to determine the amounts of primary and secondary mullite that were present and the total mullite content.