1) Frequent water changes accelerate some type of corrosion, from what I've read. So, it seems that it is a common myth that people believe than "cleaner" (fresher) distilled water will keep corrosion in check. Obviously, certain corrosion sources, like algal growth, will be inhibited by frequent water changes but that's not the only source — leading us to:
2) Dissolved oxygen causes corrosion. Water systems with very low dissolved oxygen can last much longer.
3) Distilled water alone will cause corrosion.
4) Silver coils need chlorine in the water to be effective.
article said:
Copper and Silver Ionization
Ionization indicates the electrolytic generation of copper and silver ions in cooling tower water. If properly managed, copper and silver ion concentrations at 20 to 30 µg/L and 10 to 15 µg/L,respectively, can be effective to kill bacteria in the systems. The ions assist in the control of bacterial populations in the presence of a free chlorine residual of at least 0.2 mg/kg. It should be noted that in hard water systems, silver ion concentrations is difficult to maintain due to build-up of scale on the electrodes, and the high concentration of dissolved solids precipitating the silver ions out of solution. For both hard and soft water, the ionization process is pH sensitive and it is difficult to maintain silver ion concentrations above pH 7.6. It is not recommended to adopt ionization in systems having steel or aluminum heat exchanger since deposition of the copper ion and subsequent galvanic corrosion is significant.
link
5) Glycol has to be above 20% concentration or it will be degraded by biological activity.
Daryl Hartwick said:
In the case of glycol loops, verifying that the glycol concentration is more than 20% is critical. At levels less than this (for chilled and out of service hot loops), rapid biological degradation of either ethylene or propylene glycol to an assortment of organic acids and intermediate products, will take place.
Source: Water Treatment In Closed Systems — ASHRAE Journal. Darrell Hartwick is the technical marketing manager with Eclipse Chemical Company in Baie D’Urfé, Quebec.
6) Even inhibited propylene glycol removes more metal from the copper surface than distilled water. See attachment 1.
7) Benzotriazole (BTA), tolyltriazole, and napthotriazole are effective corrosion inhibitors for copper. Only BTA is readily soluble in room temperature distilled water.
information about napthotriazole, which may be the strongest inhibitor:
link 1
link 2
IBM said:
Benzotriazole (BTA) is mixed with the deionized (DI) water to a concentration of 1000 parts per million by weight.
8) Molybdate should be added for loops with aluminum and/or steel in them. I don't know how much of a threat steel jet plates pose without molybdate.
9) A study involving the preservation of copper artifacts said BTA must be combined with MTA for the best corrosion prevention.
10) Potassium iodide can enhanced BTA's anti-corrosive action but it must be used in a precise ratio and isn't worth the trouble. Some used iodine in their loops to function as a biocide. It seems too difficult to control the concentration over time to make it worthwhile.
study said:
The mixture of 0.1M BTA with 0.01M KI in deionised water increased the efficiency of BTA, whilst in other cases the mixture accelerated corrosion. When a higher concentration of BTA was used, the presence of KI did not cause any significant effect in the process.
11) Silicates are used in some auto antifreezes but might be abrasive and cause sludging. I doubt they're needed in our loops, or desirable.
12) Be careful with OAT/HOAT auto antifreezes if they have 2-EHA, which can rots seals.
13)
article said:
Metal oxides are generally not very good conductors, in fact, most are dielectrics and hence non-conductors.
14) Triazole inhibitors inhibit the action of silver, making silver of questionable use when combined with them. The silver's biocidal action would be potentially nullified and the azole would be bound to the silver, nullifying it, too. This seems to be why EK, for instance, says it's super-important to rinse one's loop very thoroughly if one has used some other coolant and why silver coils are bad news.
15)
forum post said:
A conservator's study found that the only solution that stopped corrosion of their copper samples was a combination of benzotriazole (.1M) and AMT (.01M) in ethanol. The water-based version had some corrosion, although that combination was better than BTA alone. They didn't test tolyltriazole nor napthotriazole.
AMT is 2-amino-5-mercapto-1,3,4-thiadiazole
One possible reason for AMT's usefulness in that study is that it's better at removing chloride than BTA. The artifacts contaminated with chloride would have reduced BTA's effectiveness, thus making the addition of AMT helpful. I don't think chloride is going to be an issue in our loops unless people try to use chlorine with silver. It seems clear that the silver coil is a bad idea.
AMT and chloride:
link
article said:
Most metals, including copper and aluminum, form thin metal oxide film layers when exposed to air for even a brief time -- this is what makes a new penny turn dull after a few days or weeks. These oxide layers are so thin however that for all practical purposes they do not interfere with the conductivity across such layers.
So, you don't want an oxide (corrosion) layer on your block's fins, or anywhere else that's exposed to the fluid. This is where having a thin layer of anti-corrosive, like BTA, comes in. It prevents the oxide layer from forming. However, some oxide layer formation may be unavoidable unless the parts were prepared in an oxygen-free environment and dipped in triazole. Dipping in triazole is apparently a fairly common practice but the protective layer can be worn away if the fluid used by the buyer isn't correct. It should have triazole in it to keep the protective layer renewed.
16) Ethylene glycol would be the better choice, versus propylene, for heat transfer and biocidal action — if not for its toxity. It has a vapor pressure. It should slowly evaporate as far as I know. I have read that even "closed" loops suffer from fluid evaporation so some of the chemicals added to water in coolants may be an inhalation issue. This doesn't merely apply to ethylene glycol. As for glycol, one must ask oneself if anti-freezing is a quality that is important for a room temperature loop.
17) How much is the efficiency of premade PC watercooling coolants negatively impacted by the desire for aesthetic qualities, like dye and UV "reactivity"? Is there a coolant on the market that maximizes both thermal transfer and longevity, while ignoring aesthetics? For instance, opaque coolants can include titanium and/or zinc oxides. These serve no positive function for thermal transfer. Instead, they do the opposite, by replacing water volume.
18) This looks like a typical formulation that will offer good reliability for non-aluminum loops:
Accepta said:
Potassium hydroxide, 5–15%
Sodium Molybdate, 5–15%
Benzotriazole, <5%
Borax 5–25%
Accepta 2542 is a high performance molybdate - borate based water treatment corrosion inhibitor scientifically formulated to offer excellent corrosion control for the protection of steel, copper and brass in water systems.
High performance corrosion inhibitor for steel, copper and brass
Minimises unwanted microbiological system growth
Borax is very abrasive, though, so it should always be fully-dissolved in water. The hydroxide and borax are used to elevate/buffer the pH. At low pH, pitting is a problem. At too-high a pH, scaling is a problem.
Note the second attachment which compares corrosion rates between water, uninhibited glycols, and inhibited glycols. Not also how the first one says that glycol is apparently only needed when there is the need for its anti-freeze function.