Preliminary studies on sulfuric acid-doped (10 p.p.m.) ice have revealed clear differences between the d.c. conductivity of the grain boundaries and of the lattice (Figure 1). A 1V potential difference was applied to the specimens using thin, spade-like platinum electrodes inserted in the ice. The specimens were incased in a metal box in order to prevent unwanted electromagnetic interference. Two set-ups were used to measure the current. First, the current was sampled at rates as high as 10
6 s
-1 using a fast electromagnetic relay (capable of ramping up the d.c. voltage applied to the specimen rapidly and without oscillations), a signal amplifier (Femto), and a digital oscilloscope. After approximately 0.1 s the sampling rate was reduced to two samples/sec and the current was measured with a Keithley 485 picoammeter connected via a PCMCIA-GPIB+ card to a computer.
The drop in the current as a function of time is presumably due to polarization of the electrodes. This relaxation can provide information on the dielectric properties of ice.
Figure 1: Current as a function of time along a grain boundary and in the lattice in ice doped with 10 p.p.m. H2SO4 after a 1 V d.c. potential was applied through Pt electrodes spaced 10 mm apart.
