Sciencemadness Discussion Board

Help finding epoxy to seal mmo anodes in housing

Ramdough - 5-8-2011 at 12:11

I am building a membrane electrolysis cell for making sodium hypochlorite from salt water. The cell housing will be PVC and I have some titanium mmo expanded sheets. The cell will have slight water pressure on it due to the water height in my brine tank.

Anyone have any suggestions for sealing to the mmo coating? I plan on running the sheared edge of the mmo out of the PVC cell an epoxying the gap so that only the mmo coating is in liquid.

Thanks in advance.

Anyone there?

Ramdough - 9-8-2011 at 03:52

I am sure someone her has some ideas. I was considering Scotchweld 2216 grey or tan. I have used it before with some success with bonding to titanium. All of the electrode assemblies that I have seen use a white looking epoxy. Anyone know what that white epoxy is?

hissingnoise - 9-8-2011 at 05:40

Hypochlorite is prepared by electrolysis without the use of a membrane.
Cells shouldn't be pressurised as hydrogen is evolved during the oxidation.
Electrodes should be closely spaced for efficiency.
Cell temperature should be kept low to prevent chlorate formation and the cell can be an open container because little chlorine will escape.
And sealing with glue shouldn't be necessary . . .

dann2 - 9-8-2011 at 07:36


I have used stuff from the car accessory shop. It is polyester resin and it is used in conjunction the fiber glass to fix car panels.
The polyester resin is mixed with some hardner. It seems to stand up well to Chlorate cells. It also wets the MMO well and forms a good seal. Its a viscous liquid that pours easily (like molasses)

Ramdough - 9-8-2011 at 07:47

Quote: Originally posted by hissingnoise  
Hypochlorite is prepared by electrolysis without the use of a membrane.
Cells shouldn't be pressurised as hydrogen is evolved during the oxidation.
Electrodes should be closely spaced for efficiency.
Cell temperature should be kept low to prevent chlorate formation and the cell can be an open container because little chlorine will escape.
And sealing with glue shouldn't be necessary . . .



The system I am building uses a membrane. The the brine solution is fed to only one electrode while pure water and sodium hydroxide is fed to the other. The products of chlorine and sodium hydroxide are combined later outside of the cell. This allows me to make sodium hypochlorite without adding brine to my product. Also the electrodes should stay cleaner.

I need an epoxy because the cell will be below my brine tank and will have hydrostatic pressure on it.

hissingnoise - 9-8-2011 at 08:28

Quote:
The products of chlorine and sodium hydroxide are combined later outside of the cell. This allows me to make sodium hypochlorite without adding brine to my product.

The reaction of chlorine with alkali in the cold; Cl<sub>2</sub> + 2NaOH -> NaCl + NaCLO + H<sub>2</sub>O produces NaCl, obviously, so your cell would seem a waste of time and effort when you can buy ordinary bleach which contains only hypochlorite and alkali.
Using a membrane is self-defeating . . .
Evolved H<sub>2</sub> must be allowed to escape, so a closed
cell is out of the question . . .
I think you should further familiarise yourself with the reactions involved.


Ramdough - 9-8-2011 at 12:18

The system is centered around a membrane cell. One side takes in brine solution and produces chlorine which is used later. The other chamber produces sodium hydroxide. In a separation chamber, hydrogen gas is vented off. .....

I am duplicating a comercially available system that works. I could try to sketch it out, but not today.

What I am trying to find out is how to seal the edges of my mmo material that have been sheared.

hissingnoise - 9-8-2011 at 13:01

A diagram would certainly help, or better, a link to the system you're intent on replicating . . .


dann2 - 9-8-2011 at 13:51


"What I am trying to find out is how to seal the edges of my mmo material that have been sheared."

If you are worried about the Ti metal being attacked where there in no MMO, (at the sheared edges) fear not. Thats what Valve metals are all about. They will form a self protecting Oxide coat if exposed to the electrolyte (as an Anode).
They are 'self sealing', 'self healing' or whatever you like to call it.
Dann2

Xenoid - 9-8-2011 at 15:07

I would stay away from epoxies and other glues for sealing MMO electrodes, they always breakdown eventually!

Spot weld some bent Ti straps to the MMO and use Ti bolts (possibly with "O" rings) through the walls of the container. Ti bolts are available from some bike shops, engineering shops and online (Google).

I discussed this in detail in the following thread on making a salt water chlorinator for a swimming pool.

http://www.sciencemadness.org/talk/viewthread.php?tid=16144

Ramdough - 10-8-2011 at 08:11

Quote: Originally posted by hissingnoise  
A diagram would certainly help, or better, a link to the system you're intent on replicating . . .




Patent 1

And

Patent 2


I am not exactly copying either of these. I am using the concepts to make something I think is better.

Please feel free to comment now that it is more clear what I doing.

Most people on this forum probably know more about electrolysis than me, so I appreciate any help. My expertise is making things. A friend of mine has a full machine shop and a welder. I plan on making my system with all parts outside of the tank so that it is easier to service them. I have an arduino with Ethernet that I plan to interface to an orp and Ph sensor as well. I hope monitor the whole system through my home server.

I hope that is enough info to get the wheels spinning.

From what you all are saying, I am thinking I might either do the spot welded sheet metal approach or just tig weld a hex head bolt to the mmo sort of like patent 1.

Does anyone have any input on the design of the chamber that combines the chlorine and sodium hydroxide?

Thanks in advance

Anyone there?

Ramdough - 15-8-2011 at 08:56

Just checking to see if anyone has any comments on my last post.

I appreciate the help from the group.

magnus454 - 20-8-2011 at 15:45

JB weld or Polyester resin (bondo resin)

Ramdough - 20-8-2011 at 18:18

From what I learned on this forum, I no longer plan on using epoxy.

I still would appreciate help with the design of the chamber that mixes the chlorine gas with the sodium hydroxide.

I am thinking of a design similar to a co2 down flow type system like those used in aquariums.

Any thoughts?