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Anodic Glow Discharge IV

Sodium Potassium Tartrate

     A concentrated solution of sodium potassium tartrate conditioned well up to about 180 volts. This photo shows the dark green glow after about an hour of conditioning. Note the thick lighter green patch in the lower right quadrant of the photo. That's a modification to the oxide surface due to a more intense discharge regime.

After about 180 Volts orange sparkling discharges appeared on the rim and into the center of the anode and were impossible to control. Trying to condition the cell to higher voltage just pushed it into continuous arcing. I decided then to increase the current, and see what would happen after an actual cathode to anode arc was struck. The results were unexpected.

     An arc did form directly between the cathode and anode, and sparging gas bubbles caused the arc to sputter and become unstable.

Due to the volume of gas coming from the cathode, the anode spot was pushed out from under the cathode and began wandering the anode surface. First out to the rim, then pausing for a few moments, then back to the cathode or around the rim. The spot would also merge with the rim and disappear; a new spot immediately forming at the cathode and again being pushed out to wander the anode. The speed of the spot was slow, in the neighborhood of a cm per second. The spot size was about the size of the cathode tip.

     The anode spot shedding process ended with a broad glow covering the anode from cathode to rim, with many colored sparks and flashing. At this point I shut the cell down and examined the surface. The oxide layer was modified by the spots passage, perhaps transformed from boehmite into corundum. I was concerned that the can might be set afire by this discharge! A safer arrangement of the experiment would be necessary to further explore this exotic discharge regime...

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