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Loss of free sulfuric in hard coat


I have a 542 gal hard coat tank with optimum free sulfuric at 285 g/l and 7.5 g/l oxalic acid ran at about 32 F. I am having trouble with the free sulfuric acid depleting. It appears to decrease more when it is not in use. This bath also absorbs a lot of water? Is this normal for this type of bath? Is there a good way to control this? This tank with go from being 285 g/l on a Friday to 270 g/l on Monday morning. I made a 10 gallon add of sulfuric and only saw and increase of 6 g/l. Also I was wondering if running at idle causes the depletion of the free acid, should we raise the bath to room temp when it is not in use? In contrast, does the bath deplete at a slower rate when in use? If this is so, is there a way to keep it chilled and still maintain the optimum free sulfuric concentration. If anyone can offer any information, it would be greatly appreciated.

Thank you in advance for all advice and information received.

Jenn Wright
- Dayton, Ohio


To dilute that tank solution to its final concentration after the weekend I guess would require at least 30 gals of water.To state that it is absorbing water implies that it is coming from the atmosphere.

30 gallons of water (from air!) is considerable enough to raise it to a noticeable level. We haven't experience this and I suspect another cause that's creating this problem.

Dado Macapagal
- Toronto, Ont

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