coolant system corrosion

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following from the recent thread on this topic, it seems there are some fundamental misunderstandings out there that need to be cleared up.
the first thing to understand is where corrosion comes from in the first
place. very simply, it comes down to electrolysis. remember when you made a battery in school with a strip of zinc, a strip of copper and a lemon? well, that works because of the difference in electrode potentials between the two metals, and the presence of an accommodating electrolyte.
in car cooling systems, you have different metals used, iron, aluminum, copper, etc., and you have an electrolyte, the fluid in the cooling system. [there is more than that, but i'm simplifying for illustration]. so, that's going to lead to corrosion!!! how do you stop it?
basic methods:
1. remove the electrode potential difference as much as possible - use an aluminum radiator with an aluminum block for example.
2. passivate the materials as much as possible - slows thing down.
3. use a non-electrolytic coolant fluid.
used together, all these work well and cooling systems can last many years with no obvious or at least, minimal degradation.
but what are the practical realities?
a. people tend to introduce electrolytes into their cooling system - the use of tap water being the prime example. not great, but it's life. and cars don't last forever.
b. use of the above can in fact cause some passivation. for example, buildup of calcium carbonate in a cooling system can slow down corrosion rates since it interferes with electron flow. but it also interferes with heat transfer, a strongly negative and unwanted side-effect. again, not great, but it happens. indeed, as a passivation strategy, silicates were use as a corrosion inhibitor in cheap antifreeze for this reason - it passivated the system by coating it. [but it also coated and ruined pump seals]
c. when, inevitably, a cooling system treated as above becomes too inefficient and fails and a radiator is replaced, the new radiator can fail rapidly afterwards. why?
this last seems to be the big problem that's confusing, even to experienced and otherwise very knowledgeable vehicle techs, and it seems it's being misattributed to use of de-ionized water as antifreeze dilutant.
how can this be? because there is essentially no difference between distilled and de-ionized, and certainly not for this application.
let's go back to what we know from the above:
electrolysis. electrode potentials for copper, iron and aluminum are ranked in that order. iron is more active than copper, but aluminum is more active than iron.
if you have an iron engine block, and a copper rad, even if you use a coolant full of electrolytes, the dissolution takes place primarily in the most active component, the iron. and with some considerable thickness of iron to eat through, you're really not going to notice any problems most of the time.
so why did the new radiator fail?
most new radiators are aluminum. so, as we learned above, now it will be the one that corrodes, not the iron. and, this aluminum is /real/ thin.
but we just used de-ionized water - didn't that cause the problem? nope - there's no difference between that and distilled. not true de-ionized anyway. some products are sold as producing "de-ionized" water, but they're mis-described, and are merely water softeners, not de-ionizers. [and their product is highly corrosive].
remember that this is a repair of an existing system? well, that engine is full of years of corrosion product. you didn't care about it before, but now, unless your new antifreeze contains sufficient concentration and efficacy of corrosion inhibitors, all those products are going to re-equilibrate back into the coolant and become an electrolyte and provide the means for the corrosion to start. did we use a chemical de-scaler or coolant flush as part of the replacement? then magnify this effect even further because those chemicals are very aggressive and very hard to completely remove.
bottom line: if we want to avoid surprises like this, we need to understand the principles of what's happening.
i. replace like with like wherever possible. your system reached something close to an equilibrium as it stood before. if you change that, and complete electron flow reversal like swapping a copper radiator for aluminum on an iron engine block will do that, is about the worst thing you can do.
ii. use the best quality antifreeze with a decent corrosion inhibitor package. don't use "filtered" or recycled crap.
iii. consider very carefully before using a chemical flush of the system. no matter how you try, chemicals will remain on the metal surfaces and come back out into the new coolant fluid to act as electrolyte and facilitate corrosion. in extreme cases, it may be better to use them than have a system full of scale that's overheating, but if doing so, observe #i above. personally, i recommend leaving flush chemicals alone in aluminum systems unless you have no other choice. [use of decent coolant/dilutant will usually avoid all need for this though.]
iv. use high quality replacement parts! internal passivation and corrosion resistance varies. cheap stuff is cheap for a reason!
v. understand what's going on. don't misattribute a failure to the wrong cause [for this application, there is no difference between distilled and true de-ionized]. you'll spend a bunch of money and you'll have the same problem coming back again and again.
vi. don't mistake the difference between de-ionized and softened water.
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I thought I would find some issues with you here, but your points are not at all bad.
"Electrolysis" is a catch-all word that people use instead of electrochemical explanations.
It is not an all inclusive term.
Galvanic corrosion often occurs when metals of two unlike redox potentials are connected with an electrolyte as the external current path.. Basically what you said, but a little more detailed.
Electrolysis may also take place when corrosion currents occur from sources other than galvanic contacts.
Corrosion inhibitors CAN reduce corrosion enormously by modifying the surface matrix on a metal, in contact with an electrolyte.
Triple distilled water (or GOOD deionized water) can be a wise choice instead of tap water that may be laden with a plethora of minerals.
Aluminum is a strange one. When properly anodized, it can be relatively corrosion resistant. When that film is broken, aluminum is not worth a darn as a corrosion resistant metal.
Worthwhile post, Jim
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On 06/08/2010 03:04 PM, hls wrote:

thank you. difficult to condense major scientific principles into just a few paragraphs.
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On 06/09/2010 07:18 AM, hls wrote:

[accessible] further reading:
http://www.eetcorp.com/antifreeze/antifreeze-faq.htm
http://answers.google.com/answers/threadview/id/591732.html
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wrote in message

Not being a chemist, I solved this quandary by simply following the specific directives of the engineers that designed my engine and/or its OEM fluids. I decided that they are quite likely to know best exactly what will prevent my engine's cooling system from corroding. And you know what? The advice I've followed has been spot-on.
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On 06/10/2010 09:59 AM, Tegger wrote:

what do those engineers say for the conditions under which to check the oil level on an integra?
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I am sure they know what is best, but I am not sure that they always specify what is best. DexCool, IMO, was not necessarily the great inhibitor package it was cracked up to be, and I am sure there were political reasons for its choice as much as, if not more than, performance reasons.
Sometimes a company "buys into" a certain technology, and they push it (until it pushes back).
Especially during the warranty period, there is some wisdom in using what the manufacturing company specifies.
Like we have discussed in previous oil threads, coolant packages are not usually accompanied with hard scientific data that would let you know what the actual performance criteria are. Lots of testimonial and hype, but seldom any hard data.
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Not to you, no. Not to you.
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Yes, I want data, not testimonial and hype. Nothing wrong with that, now, is there?
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On 06/18/2010 12:50 PM, hls wrote:

it's not "hard", but it's more informative than normal "hype"...
http://www.eetcorp.com/antifreeze/antifreeze-faq.htm
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At one point, several years ago, I worked on formulation and testing of this type of corrosion inhibitive packages, as well as others. That is why I keep singing the song of wanting data.
We actually bought the DexCool package and used it for bulk glycol deliveries. It wasnt so very great, but it was ****biofriendly**** which is what the customer wanted.
It was not a matter of "not invented here".
There is often a tradeoff when trying to field ecologically "green" materials. Usually they dont work as well as the optimum technology that can be formulated, but there is money to be made with them on the market.
People are often afraid of "those dangerous chemicals" without knowing what they are and what dangers, if any, are involved.
Thanks for the link
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On 06/18/2010 01:17 PM, hls wrote:

can you share any links to the testing you did?

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I wish I could. It is held within the company in my laboratory notebook archives, and in reports to the customer (Statoil Norway). That is where a lot of technology is "hidden" and it is why it is so hard to access.
A lot of this is not patented, but is disclosed so as to be able to prove prior art. A patent is just a clue to the competitor as to what you are doing.
I do hold some patents, but we were encouraged not to patent.
We tested both with linear polarization resistance instruments(where applicable) , and with prepared metal coupons of all the typical metals and alloys that would be encountered within a system. The coupons were evaluated by weight loss, surface condition and matrix, embrittlement tests, etc.
Tests were done with and without oxygen for extended periods, as you would encounter in cooling systems from time to time.
Short term tests often give promising results, but as the system ages, as it would in application, some of the inhibitor components decompose, are precipitated, or are otherwise deactivated.
Aluminum is perhaps the hardest nut to crack. Once it starts corroding, it is hard to stop. Organic acid technology didnt seem to be too good for this, compared with the industry standard silicates.
Pinhole, crevice, and other very locallized modes of corrosion sometimes take a while to show up in testing, leading one to think that the system is well protected. But in time, when the inhibitor package allows it to happen, failures can be rapid and catastrophic even though most of the system looks pristine.
We introduced, by the way, the first biodegradable nontoxic corrosion inhibitor to the North Sea area. It was good, but not great, but beat everything else in the market, and is still being sold.
These coolant packages are used not only in automobiles but in coolants for industrial applications of many types.
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On 06/18/2010 02:15 PM, hls wrote:

doesn't that mean systems should be flushed and replenished?

but silicates can wreck pump seals - something very well documented.

that's what you get when you have differing electrode potentials. materials quality is crucial to that since not only do you have to worry about potentials from one material to another, but you can have non-homogeneous materials with strongly different potentials for different phases within it.

i would imagine this field continues to be actively researched.
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Without a doubt.'

One of the worst problems I have seen from silicates has nothing to do with seals. The crap can plug radiators SOLID with silica. Silica cannot be removed by simple flushing or acid flush. This happens when you use formulations with too much silicate, or use water containing magnesium or other ions which are not compatible with silicate.
I dont doubt that, if overdone, silica excesses in the system can and will damage seals, bearings, etc.
If you dont overdo with silicates, they dont really cause much of a problem. To wit, the hybrid organic acid technology (HOAT) was an improvement of the DexCool systems, using some lower concentrations of silicates.
You know, of course, that silicone greases are nothing more than silicone oils, viscosified or gelled with fumed silica.. So it depends upon the form of the silica whether they are highly abrasive or not. Sand is a bitch.. fumed silica is not so problematic. Both are silica
If you are going to use sodium silicate, there is no way chemically to prevent them from decomposing to silica, of some form or another. It happens no matter what you do, with time.
But if you control the concentration, you can make them liveable. AFAIK, nothing protects aluminum like silicate.
"We" are currently considering looking into some phosphate chemistry, but at this point there is no real commercial interest, and therefore nobody to pay the bills.
By the way, "we" are manufacturers, for whom I still consult.
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On 06/19/2010 05:25 PM, hls wrote:

some, not all - there are still silicone greases with lithium stearate soap thickeners. dow's molykote 33 for example.

indeed.
well, i think the 10-year performance spec for whatever it is in honda oem coolant fill is pretty damned worthy. i doubt it's a silicate given honda's dire warnings about them in their tsb's.

interesting chatting with you. thank you.
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On 6/18/2010 9:50 AM, hls wrote:

Looking for hard data of this type in a Usenet group is probably wrong on a couple of levels. A trade journal would be a better place to start, or would it? :-)
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Some industries are more open than others. Occasionally you will find articles in some trade journals, or in the periodicals of associations like the National Association of Corrosion Engineers.
I suppose that companies which market coolants either think we are too stupid to appreciate test data, or it is a practice that they really dont want to get started.
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On 6/18/2010 11:58 AM, hls wrote:

Unfortunately, most of us are too stupid to appreciate test data, you're not, but that doesn't matter much anyway because it's not in the best interest of the companies that market coolants to release hard data that has not been spun to favor their products. That's the breaks.
Hearing aid companies have all kinds of schemes to reduce noise and increase comprehension of their products. The dirty little secret is that the people selling hearing aids don't know what their products are really doing because all that info is proprietary and closely guarded.
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