Sciencemadness Discussion Board

MMO gap distance

hyfalcon - 9-8-2013 at 03:04

I'm putting together a chlorate cell using a full piece of lasered's MMO anodes. I've read and read and I'm not seeing anything to tell you what kind of a gap to leave between your anode and cathode. I've got a constant current/voltage bench top power supply that I can push up to 200A out of so having enough power to push the reaction isn't going to be a problem. I just need to know how much to "gap" my electrodes.

Xenoid - 9-8-2013 at 14:33

Well, for an amateur cell it's not really important!

In commercial cells and pool chlorinators they use spacings of as little as 5 mm. This is to achieve maximum efficiency. Less voltage is required for a given current flow because the resistance of the cell is less. Thus less power is used and running costs are lower. If you use spacings as small as this you will require some sort of rigid supports to ensure the electrodes don't short circuit accidentally.

A home cell is going to require at least 3.5 V to operate, so most people would adjust the electrode spacing to give the required current. This is a good procedure if you have a fixed voltage supply like a computer power supply for example (5.0 V). Just adjust the spacing to give 5, 10, or 20 A - whatever suits your size of cell.

Just remember that for a given cell there is a limit to how much current you can pass through it, generally governed by it's physical size and the cooling procedure used. Be careful of thermal runaway, as the cell becomes warmer it conducts better and hence more current flows, etc. etc. until it starts boiling!

I have used spacings of as little as 5 mm (pool chlorinator assemblies) and up to several cm in bigger cells (5 and 10 liter). I have always been able to adjust the current to a suitable level using a variac or an adjustable power supply.

ElectroWin - 9-8-2013 at 15:37

and any less than that 5 mm and you will find bubbles of gas begin to hinder flow of liquids, which require agitation.

hyfalcon - 9-8-2013 at 16:16

I've got .22" thick HDPE to use for spacers to keep the electrodes apart. If I was going to need more space then that, I was going to stack 2 pieces of the HDPE together but if I can get away with just one layer of it that would be great. It figures out to about 5.5mm so I should be good to go. I'm going to use a slightly narrower titanium mesh and run it in a loop around both sides of the MMO with the HDPE spacers to keep them from touching. I figure about 150cm2 one sided on the anode.

Everything should fit nicely into a 5 gallon bucket.
[Edited on 10-8-2013 by hyfalcon]

[Edited on 10-8-2013 by hyfalcon]

morganism - 13-8-2013 at 14:21

i just posted this up as a sonic sensor.
might be a good feedback mechanism for efficiency too....

hyfalcon - 14-8-2013 at 02:51

Sounds like a nightmare of wiring. It would not be very home user friendly I would think.