Elastic modulus and hardness of muscovite and rectorite determined by nanoindentation

This paper presents the first effort to determine the elastic modulus (E) and hardness (H) of muscovite and rectorite by nanoindentation. Samples were examined under varying maximum load, loading rate,and hold time at the maximum load conditions. The measured E and H values were affected by: (1) numerous giant steps observed in the load-displacement curves, particularly under large loads; (2) maximum load; (3) loading rate: and (4) the hold time at maximum load. The two minerals behaved differently under indentation, owing to the difference in their crystal structure. Rectorite exhibited more highly time-dependent response and had much lower E and H values than muscovite. After correction by removing the giant steps to obtain more accurate E and H values, the dependence of E and H on the maximum load tended to disappear. The corrected values for E, 79.3 +/- 6.9 and 18.3 +/- 4.6 GPa, and H, 5.14 +/- 0.82 and 0.73 +/- 0.17 GPa, for muscovite and rectorite, respectively, were in good agreement with the data published in the literature. This study also demonstrated the importance of choosing appropriate test control parameters in obtaining more reliable E and H values of layered aluminosilicates using nanoindentation. (C) 2008 Elsevier B.V. All rights reserved.