In situ high temperature X-ray diffraction study of illite

Abstract Despite extensive researches, many aspects of the structural transformation that occur in illite on heating remain unclear. This study concentrates on samples from a mine located in Wenzhou, Zhejiang Province, China to supplement data obtained by previous investigators. In situ high temperature X-ray diffraction (HTXRD), infrared spectroscopy (IR), field emission scanning electron microscope (FESEM) and electron microprobe (EMP) analysis were used to record the characterization of the raw material. XRD pattern showed the illite sample was primarily in 2M 1 polytype. The phase transition from illite into dehydroxylated phase started at about 525 °C in static air and at about 550 °C in vacuum, and from dehydroxylated phase into mullite occurred at above 1100 °C. These lattice parameters of illite (RT – 1100 °C) and mullite (1125–1150 °C) both in static air and in vacuum were refined. The variations of illite lattice parameters with temperature (°C) were therefore well described. Thermal expansion coefficients of illite (RT – 1100 °C) were determined. In situ high temperature X-ray diffraction study revealed four stages during heating: expansion, dehydroxylation, post-dehydroxylation and mullite stages.