An oxyfuel cutting torch was biased with a positive DC voltage relative to steel and copper work pieces, and ion currents were seen to flow due to ions generated chemically in the flame and at the work surface. A repeatable 150% rise in these currents occurs over steel at a surface temperature around 1050°C. Equally strong intermittent spikes appear over clean and corroded steel samples alike. They are are easily removed by a median value filter, and are believed to be due to small reacting particulates. Tests in which salt was deliberately deposited on the steel surface produces a signal similar in shape, but exaggerated in magnitude to those currents supposed to be from other surface impurities.

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