Phase Changes in the Heating Process of a Mixture of Halloysite and Potassium Iodide

Abstract

Studies on the heating process of a mixture of halloysite and potassiu m iodide were carried by TG-DTA, X-ray powder diffraction and mass spectrometry. Halloysite reacts with potassium iodide at its dehydroxylation temperature (-500°C) to generate H20, HI and H2I2. Halloysite (1.0 mol) react with up to 2.2 mol of potassium iodide completely. When above 2.4 mol of potassium iodide is added to 1.0 mol halloysite, excess potassium iodide me lt at 667°C and then evaporate completely below 800°CC. Among potassium halides (KC1, KBr, KI) the largest reaction with halloysite is potassium iodide. A mixture of 2.0 mol of potassium iodide and 1.0 mol of halloysite forms kaliophilite (KAlSia, ) at 1090°CC. The kaliophilite decomposes into leucite (KA1Si206) and corundum (Al203) after above one hour of heat treatment at 1300°C, as the following reaction.
4 KAlSiO, ₂ KA1Si₂0₆ + Al₂0₃ + K₂0
Considering decrease of K20 content and weight loss in heated products, it may be concluded that K20 evaporate at this temperature. When quartz is added to a mixture of 2.0 mol of potassium iodide and 1.0 mol of halloysite, kaliophilite once produced reacts with quartz at 1300°C to form only leucite.