MMO corrosion

[kingkama]

I'm new in MMO anode, i connected the two electrode to a 5 v 40 amp Transformer but at the moment i cannot mesure te current amperage, my multimeter signs 2.5 amp but when i connected the direct cable the gas production rise at least double. The electrode are 2" for 6 inch distanced 5 cm, the problem is that a grey Foam started to form on the surface of electrolite, a full 2 liter bowl. Is the grey foam produced by the Distruction of the mmo anode, the catode is the same dimension in titanium mesh.

[Arthur]

You NEED to have a ammeter that reads all the time and remains in circuit all the time.

 

Find the rated current for your electrode and run at 50 to 75% of that. Overcurrent and reverse connection will destroy the electrodes rapidly. Check, ask questions, and check again.

[kingkama]

Thanks for replying, at the end i mesured the amperage, using two wire of the same section of the wire i used for connect the electrodes, so it sign 9 amp, the Dipped part of thw two electrode mesure 12 cm so the areas is 12 x 5 =60 cm2, the max amp before the electrode take damage i 200 mAmp cm2 so 60 x 200 = 12000= 12 Amps so I'm usimg the anode at his 75 %. Are my assumptions correct?

[markx]

Foamy discharge in the electrolyte is quite common during chlorate synthesis. It can stem from the contaminants in water, salt or from the titanium/stainless parts in contact with the cell liqour. As the pH rises during the cell operation a lot of soluble contaminants form hydroxides or other complexes that percipitate out and form the foamy layer. Usually it does not signal a problem within the cell.

But as Arthur already mentioned, you really do need a measurement system that is permanently connected to the cell circuitry. Keeping track of the temperature, current and voltage applied is very important during the synthesis and it allows one to assess the progress. Also if something odd happens to the anode, it can usually be spotted as a change in the current.

[Arthur]

RS Stock No.244-935

Mfr. Part No.R68M-30A-001

BrandHOBUT

or

RS Stock No.244-941

Mfr. Part No.R68M-50A-001

BrandHOBUT

Direct reading DC ammeters ideal for electro chemistry, and cheap enough to leave in circuit all the time.

 

Find a stockist in your country who will sell you one! (rather than a case quantity)

[Arthur]

The issue with clipping a multimeter in and out is the amount that the internal resistance of the meter will actually affect the current that flows.

 

I simply set up a series circuit with lots of fat wire and a 50a meter i series, then clipped the wire shorter til the series resistance just let the right current flow.

 

Remember that you will likely have a 5v (+/- 10% trim) capable of 20+ amps. Do the calculation to see what difference in current will flow if 0.01 ohms is added or removed, it's dramatic!

[kingkama]

Yes I noticed tHe amperage reduction when i used my multimeter to check the current flow, well now i understand why.... Electricity has never been my best, for me this is the discover of a new world... Thanks all for reply.

[Thenupp]

When your electrode is rated for 12A and you run 40A through it, then its no wonder that i will get destroyed that fast

[kingkama]

When your electrode is rated for 12A and you run 40A through it, then its no wonder that i will get destroyed that fast

Yes but I run to 9 A 40 is the max output of the energy source.

[WSM]

I'm new in MMO anode, i connected the two electrode to a 5 v 40 amp Transformer but at the moment i cannot mesure te current amperage, my multimeter signs 2.5 amp but when i connected the direct cable the gas production rise at least double. The electrode are 2" for 6 inch distanced 5 cm, the problem is that a grey Foam started to form on the surface of electrolite, a full 2 liter bowl. Is the grey foam produced by the Distruction of the mmo anode, the catode is the same dimension in titanium mesh.

 

 

If I understand your electrode dimensions correctly, your 2" x 6" anode should demand 23.22 Amps if one matching cathode is used (double the amperes if two cathodes surround the anode).

 

Remember, the anode is connected to the positive lead of the power supply, and the cathode is connected to negative.

 

The comments of the others, to monitor your cell current draw continuously is correct. My preference has been to use inexpensive Chinese digital panel meters, paired with the correct size shunt, wired in series with the power leads. They don't affect the power to the cell in any meaningful way and give highly accurate reads. I've bought many over the past years on eBay.

 

Don't worry about using a large current power supply on your cell. The cell will only use the current it needs, and can't be force-fed more. Voltage, on the other hand, should be controlled to the amount needed and no more.

 

As far as what you're seeing in your cell (color, etc.), more information will help to analyse what's going on. Do you have photos of the setup and materials used?

 

WSM

[kingkama]

If I understand your electrode dimensions correctly, your 2" x 6" anode should demand 23.22 Amps if one matching cathode is used (double the amperes if two cathodes surround the anode).

 

Remember, the anode is connected to the positive lead of the power supply, and the cathode is connected to negative.

 

The comments of the others, to monitor your cell current draw continuously is correct. My preference has been to use inexpensive Chinese digital panel meters, paired with the correct size shunt, wired in series with the power leads. They don't affect the power to the cell in any meaningful way and give highly accurate reads. I've bought many over the past years on eBay.

 

Don't worry about using a large current power supply on your cell. The cell will only use the current it needs, and can't be force-fed more. Voltage, on the other hand, should be controlled to the amount needed and no more.

 

As far as what you're seeing in your cell (color, etc.), more information will help to analyse what's going on. Do you have photos of the setup and materials used?

 

WSM

Wow I thinked max amperage was 200 mha cm2 so max 15 amp.

[Arthur]

It doesn't hurt to run an electrode at down to 50% of nominal power, BUT at 50% over nominal the life is going away as you watch..

[SeaMonkey]

That is true indeed. The surfaces of the Anodes are somewhat

porous. It is within those pores that the bubbles of Chlorine form.

With moderate formation and expansion of bubbles the erosion

forces are not too destructive, but when the bubbling becomes

violently vigorous the bubbling pressure of the gas becomes quite

erosive and is capable of breaking small particles of the Anode free

while slowly destroying it.

 

This breakdown is particularly visible with Graphite Anodes but the

same erosion will occur, albeit more slowly, on MMO Anodes which

are driven too hard.

Edited June 27, 2020 by SeaMonkey

[Arthur]

The catch being that and eroded graphite surface is still graphite, BUT an eroded MMO surface has no more MMO, it's just metal.

 

Commercially there will be a balance between cost of erosion and cost of electrode change down time and production rate. On an amateur basis the MMO is not expensive but usually hard to find (ebay?) so preserving the electrode surface by operating at less that commercial current per area may have some value to each user.

[WSM]

Speaking of MMO corrosion, the greatest hazard I'm aware of to an MMO on titanium anode, is fluorine. Soluble fluorides in the electrolyte will permanently destroy the anode within a day, in a running cell.

 

Fluorides eat titanium with extreme prejudice, causing separation of the MMO from the base metal and destroys the anode.

 

Make sure there are NO fluorides in your cell, if titanium in any way plays a part in your system.

 

WSM

Edited June 30, 2020 by WSM

[WSM]

Speaking of MMO corrosion, the greatest hazard I'm aware of to an MMO on titanium anode, is fluorine. Soluble fluorides in the electrolyte will permanently destroy the anode within a day, in a running cell.

Fluorides eat titanium with extreme prejudice, causing separation of the MMO from the base metal and destroys the anode.

Make sure there are NO fluorides in your cell, if titanium in any way plays a part in your system.

WSM

 

 

When in doubt, use distilled or deionized water to make your electrolyte. It's cheap insurance for protecting your expensive MMO and CP titanium electrodes.

 

WSM

[WSM]

The comments of the others, to monitor your cell current draw continuously is correct. My preference has been to use inexpensive Chinese digital panel meters, paired with the correct size shunt, wired in series with the power leads. They don't affect the power to the cell in any meaningful way and give highly accurate reads. I've bought many over the past years on eBay.

WSM

 

 

The photo below shows one such setup from several years ago:

 

 

I used a PVC electrical box to contain the Voltage and Amperage meters, which afforded some protection for the delicate electronics. These meters are useful and very accurate, plus easy to read in the LCD versions. I payed roughly $10 US each and they perform flawlessly for the most part. The ammeter requires a shunt to run in parallel with the negative power lead to the cell.

 

Check them out on eBay or possibly Amazon.

 

I haven't used an analog ammeter since my very first setups over a decade ago. The digital meters work very well and cost much less, plus have a wide range of current reading options.

 

Best regards,

 

WSM

Edited July 11, 2020 by WSM