Effect of Temperature and Potassium Chloride Impurity on the Relative ⟨10(1)over-bar0⟩ Tilt Grain Boundary and Surface Free Energies in Ice

The ratio of the grain boundary free energies relative to the surface free energies gamma(gb)/gamma(s) can be determined by measuring the root angles of the grooves formed at the intersection of the grain boundary with the free surface. The grooves were copied by plastic replicas, and the topographic details were revealed with a laser confocal 3D microscope. Values of gamma(gb)/gamma(s) were determined for high purity and potassium chloride doped ice bicrystals annealed at -5 and -18 degrees C. The studied samples were a10 (1) over bar 0o/Psi tilt grain boundaries with Psi between 10 and 180 degrees. The used KCl concentrations were 1 and 10 mu mol/l, and the conductivity of the pure ice was 0.3 mu S. a10 (1) over baro/60 degrees grain boundary relative energies were also determined for different grain boundary inclinations. All the gamma(gb)/gamma(s) obtained values were analyzed and compared using the CSL (coincidence site lattice) theory. For pure samples annealed at -18 degrees C, an important variation of gamma(gb)/gamma(s) with the grain boundary inclination was found. In general, a remarkable correspondence between CSL planar density Gamma and gamma(gb)/gamma(s) was observed. Results also showed that the increase of temperature and the impurity changes significantly gamma(gb)/gamma(s).