To check if my logging system is working correctly I tried taking a couple photos to calculate a longer term CPM average from the displayed values on the Geiger counter (which hasn't been moved from its usual location)
22:17:34 = 70 counts
22:33:44 = 1576 counts
1506 counts / 970 seconds = 1.55 CPS = 93.15 CPM average
This seems to agree with the general trend shown in the latest values of this graph from the logging system. The daily variations appear to have changed character since I started the tests described in detail in the past few comments, although it can still be coincidental. Ambient temperatures have dropped a bit in the past few days.
Besides this, I've been thinking about what effects would have using KOH electrolyte instead of Na2CO3 as previously suggested.
An immediate effect would likely be that electrode corrosion will ramp up quite a bit. While this is usually an undesirable problem, in my view it would be the opposite here. I expect even more material to get removed at the interface. Furthermore, as the water in the alkaline solution will evaporate in the process and as more is added, locally high (and corrosive) KOH concentrations on the electrode surface should occur in a progressively increasing fashion.
I tried looking at information on the subject of steel and caustic corrosion, and I collected some links.
- Corrosionpedia lists several terms related to generally unwanted phenomena caused by caustic environments which would be caused by using Potassium Hydroxide in my tests
- Caustic Embrittlement (Caustic Cracking)
- Overview of Caustic Stress Corrosion Cracking (Caustic Embrittlement)
- Erosion–corrosion of mild steel in hot caustic. Part I: NaOH solution (paper)
- Corrosion of Stainless Steel by Hot Caustic (article)
- Corrosion in Caustic Solutions
- Stainless Steel and Corrosion