Time-resolved powder neutron diffraction study of thermal reactions in clay minerals

Abstract

Thermally induced reactions in three contrasting clay samples have been studied, in situ, using time-resolved powder neutron diffraction. The dehydroxylation of kaolinite was observed in the range 440–600 °C, and the initial stages of mullite formation at 950–1000 °C. A multi-component clay material composed of disordered kaolinite and illite, with excess quartz, known as Etruria Marl, dehydroxylated in the range 400–600 °C and began to recrystallize to mullite at 1000 °C. The quartz–cristobalite phase transition in this material was observed at 1150 °C. An Mg-vermiculite was shown to dehydrate in stages, giving stable hydrates with d-spacings of 14.4, 11.7, 10.3 and 9.4 Å. The vermiculite dehydroxylated at 400–850 °C and began to recrystallize to enstatite at 1000 °C.