Making EBSD on water ice routine

Abstract

Electron backscatter diffraction (EBSD) on ice is a decade old. We have built upon previous work to select and develop methods of sample preparation and analysis that give >90% success rate in obtaining high-quality EBSD maps, for the whole surface area (potentially) of low porosity (<15%) water ice samples, including very fine-grained (<10 μm) and very large (up to 70 mm by 30 mm) samples. We present and explain two new methods of removing frost and providing a damage-free surface for EBSD: pressure cycle sublimation and 'ironing'. In general, the pressure cycle sublimation method is preferred as it is easier, faster and does not generate significant artefacts. We measure the thermal effects of sample preparation, transfer and storage procedures and model the likelihood of these modifying sample microstructures. We show results from laboratory ice samples, with a wide range of microstructures, to illustrate effectiveness and limitations of EBSD on ice and its potential applications. The methods we present can be implemented, with a modest investment, on any scanning electron microscope system with EBSD, a cryostage and a variable pressure capability. Lay description: Electron backscatter diffraction (EBSD) provides a way generating quantitative microstructure: detailed maps of the distribution of crystal orientations. EBSD of ice is valuable in understanding how the microstructure of ice relates to its physical properties and in constraining the processes (deformation, grain growth, recrystallization, change of crystal form, etc.) that have generated the ice microstructures. EBSD of ice can help us understand terrestrial ice systems, ice on the moons of outer planets and ice in engineering and bioscience. We detail the methods of sample preparation and analysis that make EBSD on water ice samples, including very fine-grained (<10 μm) and very large (up to 70 mm by 30 mm) samples, routine. We use experiments and modelling to ensure that warming during preparation has not modified sample microstructures significantly. We show EBSD results from laboratory ice samples, with a wide range of microstructures, to illustrate effectiveness and limitations of EBSD on ice and its potential applications. Journal compilation