Kaolinite and dickite behaviour after deformation by compaction and shear

The structural changes produced on commercial powdered kaolin deformed by compaction and shear was investigated by X-ray diffraction (XRD), low temperature FTIR, differential thermal analysis and thermogravimetry (DTA/TG). Kaolin is composed by 40% of well orderered kaolinite, 18% of dickite and 42% of quartz. The deformation was induced through a specifically built planetary ball milling working in a controlled thermodynamic environment at room temperature and at a vacuum of 0.13 Pa (10-3 Torr). In this controlled environment the mechanical apparatus induces simultaneous compaction and shear stress to the material. Kaolin samples were milled for 1, 5, 10 and 20 hours. The deformation treatment produces a kaolinite structural order decrease, from a low-defect kaolinite to a high-defect kaolinite according to the AGFI index determined by XRD. An index to evaluate the changes produced on dickite was determined following a fitting procedure. The results indicated that dickite is apparently less affected by the deformation than kaolinite. A structural order was defined by FTIR and the results were correlated with AGFI results.