After experiencing a few coolant incompatibilities and issues with
corrosion, I performed these experiements with samples of all materials
in the system. Tap water, distilled water, Water Wetter, and antifreeze
solutions were tested.
Background and Objectives
Wanting to prevent corrosion, electrolysis, and any sort of
biological
growth, I initially used a solution of antifreeze and water as
coolant. A short while later, I noticed that some of the nylon
hose barbs I had used began to turn a bright green, as if they were
absorbing the antifreeze. There were no indications of structural
changes in the plastic, just the color, indicating some sort of
reaction. The next time I drained the reservoir a few months
later, a stringy white polymer had formed, floating on the surface of
the water and being sucked against the grate of the pump inlet. I
was quite sure beforehand that PVC and ethylene glycol were safe, but I
had no real way of knowing the composition of the plastic reservoir,
and the nylon fittings were clearly incompatible. Obtaining a new
polyethylene reservoir and replacing all plastic fittings with brass
has alleviated this issue, but has not addressed possible interactions
of the various metals used.
Mixing different metals in a electrolytic
solutions, such as water, has the potential of causing galvanic
corrosion as one metal serves as an anode for the other. While
the majority of my cooling system are either plastic or copper, some of the older waterblocks I am using are made of aluminum. As such,
the corrosion properties of each have become of particularly keen
interest to me. On more than one occasion, I have found the
slower flowing, more restricted aluminum waterblocks to be clogged with light green precipitates, clearly the result of reaction with soluble copper ions and the aluminum metal. Short of replacing all
aluminum components with a less corrosive material, I have investigated various solutions to minimize this issue of corrosion.
My particular problem has been most throughly studied with respect
to automobile engines, often made of various aluminum and copper
alloys. Typical resolutions involve sacrificial anodes such as
magnesium, applying protective coatings to the easily corroded
components, and addition of additives to the cooling system water to
minimize its electrolytic properties. Antifreeze, largely
composed of ethylene or propylene glycol, while serving a dual purpose of surpressing the freezing point of water, is sold to decrease corrosion. Redline's Water Wetter, a soluble oil, is sold to
minimize corrosion and increase the heat transferring properties of
water. In its essence, they seem to advertise that their product
will reduce the amount of bubbles on hot surfaces, allowing for greater contact with the water. As I am not dealing with extreme temperatures or surfaces above boiling temperatures, I am interested solely in their anti-corrosion properties.
Similar Works
A common topic on the overclocking sites, I have been able to locate a number of references as to which coolants one should use. Unfortunately, the great majority of this information is anecdotal, unsupported by even the loosest of scientific reasoning, or is biased toward achieving the best 'performance', whatever that may infer. As I'm unlikely to blindly accept any so obtained data, I have sought to satisfy my own specific needs with appropriate tests.
Nonetheless, here are a few interesting links I have been able to locate:
Methods
As the objective was to qualitatively estimate the amount of corrosion
in various coolant solutions, roughly equal samples of the various
metals used in the system were combined in each of four solutions,
covered, and let sit. The solutions were kept at room temperature with no agitation. They were analyzed visually, with
scans taken at 11 and 23 days, shown below
Materials
| Sampled Material |
Cooling Component |
| Copper wire/pipe |
Copper piping, waterblocks |
| Steel window screen |
Pump particle filter |
| Galvanized Washer |
Possible pump components, cases in event of leaks |
| Aluminum foil |
Used in place of actual aluminum. May not be representative. |
| Brass screw |
Various hose barbs, fittings |
| Silver Solder |
Unknown |
Solutions
- Tap water
- Distilled water
- Distilled water/Antifreeze
- Distilled water/Redline Water Wetter
Preliminary Results
While the experiment is
still ongoing, the properties of each solution were readily evident
within a matter of days. As can be seen in the photos below, both
the distilled and tap water show significant corrosion of the
galvanized washer as well as the immediately surrounding materials.
While not adequately captured by the scanner, the distilled water
solution contained a significant amount of suspended precipitates,
especially at 23 days. Note that the distilled water aluminum
foil sample happened to have a air bubble and floated, making it
invisible in these scans. The Water Wetter solution showed
corrosion
only of the aluminum foil, something no other solution exhibited.
I am not yet sure what to make of this. The antifreeze has showed
no corrosion to date. Given the plastic incompatibilities
described in the background section above, I'm still reluctant to go
back to antifreeze and currently am running a dilute solution of Water
Wetter while keeping an eye on the aluminum components. I have
experienced no further oxide precipitates or noticeable corrosion thus
far.
11-days
CW from top left: Water Wetter, tap Water, Antifreeze, distilled water.
23-days
CW from top left: Water Wetter, tap water, Antifreeze, distilled water.
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