The effects of H (sub 2) SO (sub 4) on the mechanical behavior and microstructural evolution of polycrystalline ice

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 H (sub 2) SO (sub 4) have on the flow and ductility of polycrystalline ice, a series of mechanical tests were conducted at -6, -10, -12.5, and -20 degrees C using laboratory-prepared specimens of polycrystalline ice doped with 1-15 ppm of H (sub 2) SO (sub 4) . Parallel tests were 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 with initial strain rates ranging from 1 X 10 (super -6) to 1 X 10 (super -4) s (super -1) . It was found that H (sub 2) SO (sub 4) -doped specimens of ice exhibited faster creep rates in tension and significantly lower peak stresses in compression, when compared to the undoped ice. Postmortem microstructural analyses were performed using cross-polarized light thin section imaging, X-ray computed microtomography, Raman spectroscopy, and electron backscatter diffraction. These analyses showed that H (sub 2) SO (sub 4) -doped specimens had a larger grain size at strains < or =15%, and an earlier onset of microcracking at lower strain rates than the undoped ice. Strain-induced grain boundary migration was found to be the predominant mechanism of recrystallization in both doped and undoped specimens. Further, an aqueous phase of H (sub 2) SO (sub 4) was found to exist at the grain boundaries and triple junctions of the doped ice, which is thought to have significantly contributed toward its reduced viscosity.

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