Dielectric Losses in Supercooled Pore Water at a Frequency of 34 GHz

We present the results of measuring the coefficient of specific attenuation in supercooled water in the pores of silica gel at a frequency of 34 GHz in the temperature range from +20°C to −190°C. It is shown that in moistened silica gel with nanosized pores, noticeable radiation losses occur down to a temperature of about −100°C. This is due to the presence of a certain amount of liquid water in the pore space. Part of the water, which is strongly bound with the surface of the pores, does not freeze at temperatures down to −136°C, at which vitrification takes place. The properties of the other fraction, which is weakly bound with the surface are close to that for the volumetric water, i.e., it crystallizes completely on being cooled down to the critical temperature −(38–45)°C, which is determined by the properties of the surrounding medium. Absorption of the electromagnetic radiation in supercooled water captures in pores should be allowed for, e.g., in the problems of radiation transfer in an atmospheric moistened aerosol, especially in the millimeter wavelength band.