Mechanical properties of kaolinite ‘macro-crystals’

Abstract

The mechanical properties of a rare sample of kaolinite macroscopic crystals were evaluated using instrumented indentation. The crystals were also characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy before and after heat treatment at 1100°C. The results are explained in terms of the fracture process occurring in the layered structure of kaolinite, and of the effect of roughness on the hardness and elastic modulus. Data analysis using One-way ANOVA (p < 0.05) showed that the values of hardness and elastic modulus obtained are statistically homogeneous. Before heat treatment, the sample was composed essentially of kaolinite, with hardness of 42 MPa and elastic modulus equal to 1.3 GPa. After calcination at 1100°C, the sample keeps its layered habit and consists of amorphous metakaolinite. The hardness increases to 360 MPa and the elastic modulus increases to 6.9 GPa.

Acknowledgements

The authors would like to thank CAPES for the financial support, Prof. Dr. Gerhard Lagaly (University of Kiel, Germany) for kindly providing us with the rare kaolinite samples from his private collection and Centro de Microscopia Eletrônica – UFPR for the electron microscopy facilities.