Dielectric properties of ice containing ionic impurities at microwave frequencies

The relative complex dielectric permittivities of ice containing ionic impurities have been measured at 5 GHz with the cavity resonator method in the temperature range -80 to -2 degrees C. The contained impurities are NaCl, HNO3, and H2SO4, and the impurity concentration of the samples was between 10(-5) and 10(-3) M (molarity). The dielectric loss of ice increased with the increases in temperature and contained impurity concentration. The sharp increase in dielectric loss values of ice containing NaCl, HNO3, and H2SO4 was observed immediately above the eutectic points -21, -43, and -73 degrees C, respectively. The change shows that the liquid phase of the contained impurity is formed in ice above the eutectic point. A microscope observation showed that the liquid phase in the ice sample occurs at triple junctions as veins and at grain boundaries as lens-shaped inclusions, and 90% of the liquid existed as lens inclusions. We discuss the possible mechanisms which govern the dielectric loss of ice containing impurities by the change of the volume fraction and impurity concentration of the liquid phase inclusions with the temperature.