Measurement of mineral elastic modulus through nanoindentation

Abstract

Minerals are the main component of Earth’s crust and mantle. For our planet, the data we have on the Earth’s interior are obtained from the measurement of seismic wave velocity. Measurement in laboratory of mineral’s elastic properties are vital for the understanding of seismic information. The method we used here to determine mechanical properties of mineral is nanoindetation also called depth sensing indentation (DSI). DSI is a reliable and fast testing method to determine mechanical properties of materials, it relies on the relationship between elastic modulus and loading and unloading displacement data. Conventional DSI is directly indent on mineral surface which may cause the form of crack owing to high stress concentration caused by indenter tip. The unloading slope is called stiffness which describe the extent to resist deformation, formed crack and defects would lower the stiffness compared to expected value and lead to smaller elastic modulus. In order to eliminate the effect of crack and other defects, a chromium film is deposited on mineral sample. The elastic modulus of mineral can be obtained without penetrating into it, since the set penetration depth would be the thickness of deposited film. This is started from the model developed by Bo Zhou and Bart Prorok, which could be used to deal with film substrate system, and method developed by Yan Chen and Bart Prorok, which shows good results for measuring modulus for brittle material. Minerals are chosen for samples due to its representativeness of brittle material and inaccurate modulus results measured so far. Scanning Electron Microscope (SEM) was used to determine film thickness after deposited, Z-P model and Chen-Prorok method was employed to obtain substrate modulus form raw data.