The Earth’s large continental ice sheets contain a variety of naturally-occurring impurities, both soluble and insoluble. Understanding how these impurities affect the rheology, intrinsic thermodynamic properties, and fate of these ice sheets is not well understood. To investigate the effects that trace amounts of sulfuric acid (H2SO4) have on the flow and ductility of polycrystalline ice, a series of mechanical tests were conducted from -6°C to -20°C using laboratory-prepared specimens of polycrystalline ice doped with 1-10 ppm of H2SO4. Parallel tests were also performed on identical, but undoped specimens of polycrystalline ice. Mechanical testing included constant-load tensile creep tests at an initial stress of 0.75 MPa and compression tests at constant displacement rates ranging from 1x10-6 s-1 to 1x10-4 s-1. Post-mortem microstructural analyses were performed using cross-polarized light thin section imaging, X-ray computed microtomography, Raman spectroscopy, and scanning electron microscopy. Mechanical testing results showed that the H2SO4-doped specimens of ice exhibited accelerated creep rates in tension and a reduced peak stress in compression, when compared to the undoped ice. From the microstructural analyses, it was found that H2SO4-doped specimens typically demonstrated a greater mean grain size, an earlier onset of brittle behavior, and an aqueous phase of H2SO4 in the grain boundaries and triple junctions of the ice, when compared to their undoped counterparts. These results suggest that even trace amounts of H2SO4 can become significantly concentrated in the grain boundaries and triple junctions of the ice, which was observed to alter both the mechanical properties and microstructural characteristics of the ice. Current research efforts are focused on the effects of H2SO4 on the densification of laboratory-prepared specimens of polar firn.

How sulfuric acid affects the mechanical behavior and microstructural properties of polycrystalline ice

2019 Fall National Meeting

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