[NewCandle] The role of wicking in electrolyte transportthrough metal foil rolls

[Nick Reiter]

Hi Keith,

Looks like Jones fixed you up with a source for NaOH and KOH... I'd send ya a can of Red Devil, but that would probably be pressing my luck with mail rules, and place me onto more radar scopes than I would care for.

OK, the turn cavities...

I mused on this a few months ago, but have not characterized it anywhere near to my satisfaction.  We know that the rolling process leaves irregular linear straitions on the foil metal, that are an imprint of the texture of the stainless steel mill rolls.  As can be seen in some of my old SEM shots, this leaves something like elongated grooves of irregular dimension and irregular spacing, that are perpendicular to the long axis of the roll, and parallel to the turns of the roll.

This would imply that the most rapid capillary action is likely to be around the turns, and less rapid from bottom to top, in an arrangement such as what you had.  In the case you established, where the bottom inch or so was covered with electrolyte, then one might picture a spiral rising slowly.

Now as to the dimensions of the turn to turn cavities... thats where fun begins and chaos looms, and Nick has nary but a rough guess.  Ideally, the cavities would be defined by the range of what topography on one turn is matched up to the topography on the next turn opposing... irregular valley to irregular peak (least cavity) irregular valley to irregular valley (greatest cavity).  If the surface roughness is defined by Ra, then you'd have a range of anywhere between ~0 and 2Ra.

Now the value for average roughness of kitchen foil - you would suspect that could be an easy to find value; some sort of industry standard.  But if it is, its damned esoteric, because I've only found hints of it, with cited values between 100nm and 2 microns.

N


> It struck me the other day that perhaps the reason you got
> null results
> with your teflon coated foil is that the electrolyte can't
> wick into a foil/teflon sandwich?
> 
> I've yet to see a runaway reaction, but I would certainly
> expect
> it if conditions permit. It's still quite cold here during
> the
> evenings. I don't have vacuum flasks big enough for a full
> roll.
> 
> Speaking of things I don't have; Red Devil Lye has been
> discontinued!
> Apparently a victim of the war on drugs. And it's a good
> thing because
> now there are no longer any meth labs! Yup, they're all
> gone now,
> and former addicts are eating ice cream instead!
> 
> As wonderful and effective as that solution was, it still
> leaves
> us with the problem of getting some lye, short of mail
> order
> and big shipping $$$. We shall see.
> 
> In the ideal reactor, all the leaves of foil should be
> corroded
> equally, or nearly so. Judging by my experiments so far,
> it
> seems possible. What I am wondering about now is how to
> characterize the spacing between the turns of foil. This
> was the principle attraction of the system to you; any
> ideas here? How thick is the fluid layer between turns?
> 
> K.
>