Field dependence of carbon electrotransport in gamma iron

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Abstract
The effect of field strength at constant temperature on the effective charge of carbon in gamma iron in electrotransport experiments is determined. At 950 °C the total effective charge is 4.5 for a field of 0.106 V cm−1, rising to a value of 13.6 at approximately 0.028 V cm−1, and falling rapidly at lower fields. Similar results are encountered at 920 and 980 °C; the temperature dependence of the total effective charge is not marked. It is proposed that carbon transport occurs by two processes: vacancy transport, which is activated by a field of approximately 0.028 V cm−1 but is field independent at higher fields, and interstitial transport, the rate of which is proportional to the applied field. The rate of vacancy transport is determined by an activation energy of 42 kcal/mole. The effective charge for purely interstitial carbon electrotransport is strongly temperature dependent; charge values of 2.5, 1.5, and 0.6 were obtained at 920, 950, and 980 °C respectively.
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