Characterization of Some Natural Copper samples from the Keweenaw Peninsula of Lake Superior using Electron Microscopy and X-ray Tomography techniques
Abstract
Copper corrosion is of interest to Canada’s Nuclear Waste Management Organization as it relates to their multi-barrier system for nuclear waste disposal in deep geologic repositories. Spent fuel canisters coated with a thin copper layer must persist for up to one million years. Natural copper from the Keweenaw Peninsula in Michigan, USA, has persisted for over 1 billion years and is here characterized to understand copper corrosion over geological time. Copper samples representing three rock types were characterized using optical microscopy, scanning electron microscopy techniques (energy dispersive X-ray spectroscopy and electron backscatter diffraction), and micro-computed X-ray tomography (microCT) to establish a workflow and test suitability for a larger study. Energy dispersive X-ray spectroscopy mapping revealed mineralogy and copper paragenesis. This first application of electron backscatter diffraction showed mm-scale grain size and orientation microstructures such as twins. A 3D microCT model revealed hidden domains of high-density phases (e.g., Ag).