Strengthening polycrystalline ice with SiO$_2$ nanoparticles

The paper presents the results of ice strengthening by means of ultrafine silica nanoparticles introduced to distilled water prior to its crystallization. Stable SiO$_2$ particles suspensions with concentrations ranging from 0.003 to 5 wt.%. have been prepared, and nanoparticles size distribution and zeta potential have been monitored in them. Both values remain almost constant for a week. Concentration dependences of maximal stress, Young's modulus and inelastic deformation at and after reaching peak stress in uniaxial compression test have been studied. The highest rate of change with the particles concentration for these properties is between 0.01 and 1 wt.%. while beyond the above range the concentration sensitivity is much weaker. The strongest effect of silica concentration is on inelastic deformation, and the weakest effect is on Young's modulus. Concentration sensitivity of the properties has been estimated by the power index of the best fitted power function for each of the property. Dependence of strength upon average grain size, that diminishes sixfold with growing concentration, is well approximated by power function also, but with negative power index -1/2. Additive constant in this dependence is found to be much lower than the strength of large grain pure ice and is close to zero within experiment accuracy. Hence, the strength of studied polycrystalline ice and ice composites is limited by the nucleation and subsequent propagation of Griffiths cracks with characteristic length proportional to average size of ice grain.