Creep of Dispersions of Ultrafine Amorphous Silica in Ice

Abstract

A technique was developed to produce ice containing a fine uniform dispersion of amorphous silica particles. Rates of creep in tension of dispersions with ½- and 1-volume % silica in ice were measured in the temperature range of −22 to −2°C and in the stress range of 4.64–17.8 bar and compared with those of pure ice. The silica dispersion strongly decreases creep in ice, resulting in steady-state creep rates in a 1-volume % dispersion 10–30 times slower than in pure ice. The activation energy for steady-state creep in dispersion-strengthened ice calculated from the temperature dependence of the creep rate is stress dependent with an average value of 97 kcal/mole, 6–7 times that for self-diffusion in pure ice. The steady-state creep rate increases exponentially with stress. This behavior differs from that of metallic coarse-grained dispersion-strengthened materials, in which the creep rate is proportional to a power of the stress and the activation energy is stress independent and equal to that for the self-diffusivity of the matrix metal. It is suggested that this unexpected behavior is due to particle-matrix decohesion in the ice-silica system, which interferes with the normal blockage of dislocation motion by second-phase particles during creep.

Deformation of debris-ice mixtures

“…Other experimental constraints on deformation of ice‐rich debris and dirty ice are no less perplexing. Nayar et al [] studied creep of ice in tension with 0.5–1% silica nanoparticles 0.015 µm in diameter. The addition of particles increased the creep strength by a factor of 10–30 compared to pure ice at temperatures ranging from −22 to −2°C, similar to the effect of dispersoid particles in hardened metal alloys.…”

“…Much of the traditional analysis of ice flow summarized earlier draws extensively from work in metallurgy and materials science [ Nye , ; Weertman , ; Alley , ]. The expected behavior of dirty ice is no exception, in that some of the early investigators interpreted their results within the framework of dispersion‐hardened metals [ Nayar et al, ; Hooke et al, ; Baker , ; Geissler and Croft , ]. Dispersion‐hardening is the process of introducing small amounts of solid impurities into a metal alloy to improve its resistance to creep [ Hart , ; Nabarro and De Villiers , ].…”

Effects of dispersed particulates on the rheology of water ice at planetary conditions

“…The central role of recrystallization in the strain softening of ice discussed earlier and the possible contributions of grain boundary sliding to creep suggest that strengthening well below the Orowan stress may occur due to grain boundary pinning. Our test conditions do not overlap those of earlier experiments on the effects of hard particles on the strength of ice aggregates [Nayar et al, 1971;Hooke et al, 1972;Baker and Gerberich, 1979], so comparisons are difficult. These studies involved unconfined tests at high temperatures (238-271 K) under nominally constant axial stress.…”

Rheological Properties of Water Ice—Applications to Satellites of the Outer Planets

“…Hard particulates of varying size and composition do not have a profound effect on the steady state strength of ice I (Durham et al 1992). Particulates have variable effects at terrestrial conditions where grain boundaries are mobile and brittle fracture occurs (Baker & Gerberich 1979, Hooke et al 1972, Nayar et al 1971, but at cooler temperatures in the ductile field, the effect of particulates is a hardening caused mainly by increased tortuosity of flow paths around particles and viscous drag of flowing ice at particulate surfaces. There is no indication from experiment that hardening by pinning dislocations, as in dispersion hardening (see Durham et al 1992) is an important process in ice I at planetary conditions.…”