Abstract
An icing chamber employing a closed-cycle helium cryostat has been fabricated for Raman microprobe spectroscopy of the icing on electrical transmission cable samples. A thick layer of ice deposited on a cable sample at low temperature (30 K) evaporates gradually under vacuum by increasing the temperature at intervals of 10 K up to 180 K. The Raman spectra of the gradually thinning ice layer obtained in the O-H stretching region reveals the layer-by-layer structure of ice. The study suggests that the structure of the initial ice changes from low-density amorphous ice at low temperatures to high-defect-density polycrystalline ice at higher temperatures. This observation, made for the first time on electrical transmission cable samples, is consistent with the observed phase diagram of bulk amorphous ice.
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