Effect of pressure on kaolinite nanomorphology under wet and dry conditions : Correlation with other kaolinite properties

The objectives of this investigation were to evaluate the change produced by isostatic pressure on nanomorphology of kaolins and to determine the effect of the presence or absence of water during these experiments. Nanomorphology was evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM), including roughness measurements by AFM height data. Nanomorphological changes were compared with variations in other kaolins properties as particle size distribution, fractal dimension, specific surface area and kaolinite structural order by X-ray diffraction (XRD).Nanomorphology changed by confined pressure, but the behaviour was different if the compaction was performed in the absence or presence of water. During pressure dry kaolinite crystals gradually lost their pseudohexagonal morphology, edges were rounded and books and vermicular stacks were fractured and distorted. On the contrary, kaolinite morphology did not show any change under wet conditions by SEM and TEM. AFM revealed less irregular edges of kaolinite crystals and a low amount of deformed crystals.In general, isostatic pressure in dry conditions increases roughness whereas in wet conditions roughness decreased (on average by 40 mass%). The nanomorphology changes of kaolinite were inversely correlated with the variation of the structural order as determined by XRD. The specific surface area decreased under pressure treatment especially in wet conditions.