Thermal and structural properties of Ca-rich Montmorillonite mechanically deformed by compaction and shear

Abstract This research work reports on the thermal and structural properties of powdered Ca-rich montmorillonite induced by mechanical deformation, which involves simultaneous compression and shear in a controlled thermodynamic environment. X-ray powder diffraction (XRPD), infra-red (FT-IR) and thermal analyses (TG-DTG-DTA) were employed for structural and thermal characterization. Mechanical deformation performed up to 20 h induces significant physical and structural changes to Ca-rich montmorillonite as a function of time, leading to a progressive compaction and agglomeration of particles, reduction of crystallinity and an increase of microstrain, which affects both the tetrahedral and octahedral layers. Thermal analysis of the deformed samples has indicated a loss of structural OH at a temperature which is well below the classical dehydroxylation temperature of the undeformed Ca-rich montmorillonite. This is a consequence of the disordered and defective structure (produced by the mechanical treatment), which requires a lower energy to induce the dehydroxylation of montmorillonite. Also the formation of mullite produced by heating montmorillonite at high temperature is affected by the mechanical treatment. The deformed samples yielded mullite with a faster kinetics at a lower temperature compared to their original counterparts (1155 instead of 1270 °C).