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Galvanic corrosion: theoretical prevention idea.

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UberBlue

Completely NUTS
Joined
Apr 20, 2002
Location
Huffing Water Wetter
When placed in an electrolyte, different metals/alloys assume different corrosion potentials. It is this potential difference that is the driving force for galvanic current flow. The less noble material in the galvanic couple will become the anode and will undergo accelerated corrosion. There are several things done to reduce this effect, such as the addition of various corrosion inhibitors (Dex-cool, Zerex, Water Wetter, ect.) to commonly used distilled water used by most of us in our water-cooling systems.

galvanic_1.JPG


As we all know, pure distilled water is the best medium for heat transfer. The addition of said additives will lower the performance of pure water. How much of a performance hit is dependant on the water/additive ratio. I personally would like to find a way to prevent galvanic corrosion without taking a performance hit.

What I am proposing is to counter the potential difference with an equal and opposite potential via a DC power source and potentiometer.

Measure the electrical potential with a multimeter, then tweak the potentiometer until the meter reads zero.

galvanic_2.JPG


I have a feeling our systems are electrically dynamic due to variations in the metal, oxidation, and water chemistry. If this were so, it would require constant tweaking of the potentiometer to maintain a zero potential, and could lead to huge problems if left unattended for long periods of time. These problems could include increased rates of corrosion, electrolysis of the water leading to Hydrogen-build up, and leaks due to added pressure associated with Hydrogen build-up.

To remedy this, an active feedback loop consisting of a voltage control unit and a voltmeter could be utilized to constantly and automatically measure, and correct for, any deviations from zero potential.

galvanic_3.JPG


Of course all of this is mostly speculation, and not very practical. The reason I posted this is I'm looking for either confirmation or disproval of my idea, based on factual information, not speculation, and the little details that I have overlooked that could make this completely pointless.

I realize it will be practically impossible to completely eliminate galvanic corrosion with the above method. I would be happy if it could limit galvanic corrosion to the same levels as corrosion inhibitor additives.
 
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Got hosting. ;) There are forum members that will host the images for you if you email them.

EDIT: theforumisdown has been giving pics on and off here lately that read:

"theforumisdown uploader is not available for this site..."

I saw it earlier with modenaf1's post, hopefully their server is just hiccuping and they aren't growing tired of the abuse, err, use at our forums.
 
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Are you talking about causing a short between the anode and the cathode? If so I connected a wire from my water block (copper) to my radiator (aluminum) and it did drop the voltage reading on my meter to almost zero.

The only thing I realized is even with the short created the chemical reaction will still occur within the system and cause corrosion. So I just went with a larger concentration of Antifreeze coolant to prevent it.
 
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IdreamofDSl said:
Are you talking about causing a short between the anode and the cathode? If so I connected a wire from my water block (copper) to my radiator (aluminum) and it did drop the voltage reading on my meter to almost zero.

The only thing I realized is the even with the short created the chemical reaction will still occur within the system and cause corrosion. So I just went with a larger concentration of Antifreeze coolant to prevent it.

And hopefully removed the wire...
 
The basic idea is correct.
The corrosion process is just redox process similar to one used in a car battery. So basically you talking about 'charging' up the system and keeping it at that level at all times. Typical schematics for a car charger with input/output adjusted according to specs would be a suitable starting point in building a prototype.
On related note, just how much of a performance hit does one take depending on the ratio of water to acme inhibitor?
 
walkerIV said:
The basic idea is correct.
The corrosion process is just redox process similar to one used in a car battery. So basically you talking about 'charging' up the system and keeping it at that level at all times. Typical schematics for a car charger with input/output adjusted according to specs would be a suitable starting point in building a prototype.

Well... Upon further reading, it turns out that galvanic corrosion is actually pretty rare in the water-cooling community, and other corrosion processes are mistakenly identified as such. IE pitting in aluminum. Chloride ions love to breakdown the protective aluminum oxide layer that forms.


walkerIV said:

On related note, just how much of a performance hit does one take depending on the ratio of water to acme inhibitor?

I don’t remember the exact number, but I do remember being appalled at just how crappy a 25% concentration of polyethelenegloycol can be.


It'
 
I apologize in advance if the following is already known to you. I would like to address certain points concerning water additives.

Very few people in watercooling community need to run glycol additives per se. The primary purpose of those is to broaden the working range of temperatures, ie lower the freezing point and elevate the boiling point. Again very vew systems out there work below 0 degrees celsius and none, I hope, reach boiling point.
Industrially available glycol mixtures do contain about 5% corrosion inhibitors by weight. According to:
http://www.process-cooling.com/CDA/...ures/BNP__Features__Item/0,3674,82904,00.html

minimum concentration of those glycol additives in water is 30% for the inhibitors to reach practically usefull concentration. Note also that they strongly advise against usage of auto antifreeze.


You are right to note that glycol lowers overall heat capacity of the system in our typical w/c temperature range. Some useful graphs can be seen here:
http://www.jcna.com/library/tech/tech0011.html

The most informative ones are towards the bottom of the page with temperature vs. time curves. The heat capacity of the system can be approximated by area under the curve between in the desired temperature range. IMHO typical range for w/c is between 0 and 200 for all practical comparisson purposes.

To summarize:
- stay away from glycol (antifreeze) unless subject to temperatures below freezing point of water

- surfactant (surface tension reducer) is the best way to improve heat capacity (dish soap is a surfactant)

- other useful additives should include corrosion inhibitor, antibacterial components and ,if surfactant is used, foam supressor

- "Water Wetter"(tm) and the likes are the mixtures of surfactants, corrosion inhibitors and foam supressors ( note that not one selfrespecting bacteria would live in such neighborhood)

- Someone should do a test already plotting heat capacity vs. concentration of WW

- my posts tend to turn to formal reports
 
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