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Does this make sense ? AS2 corrode lapped aluminum ?

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zoopa_man

zoopa_man

Member
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Joined
May 24, 2001
Location
NY where the cows out number the people
I saw this on a board at the overclockingstore.co.uk site and wonder if there is any truth to this? They seem to sound what there talking about but you know how many "highschool chemists" we have out there. So, to the real chemists, read this and tell me if it makes sense. I'v never heard any warnings of AS2 corroding aluminum.

"Arctic Silver will corrode lapped aluminium. Aluminium is, in fact, a very reactive metal. The reason it's so useful is it's passivation oxide layer on the surface, which once formed prevents further corrosion. Remove this by lapping and put it in contact with silver, and hey presto, galvanic cell! The aluminium then corrodes in preference to the silver (just like zinc galvanising on steel). If you want to lap ally heatsinks, they will need to be passivated before applying AS.
Posted by "Graeme Finlayson" | [email protected]
 
That don't pass the "Hoot Smell Test". The micronized silver particles in AS are relatively passivated by virtue of being suspended in a non-conducting liquid, namely oil. The oil not only passivates the silver by keeping it out of contact with the air, but it also passivates the aluminum for the same reason.

I have seen a reaction occur with copper HSFs where the AS recombines into tiny "flecks" of silver, which adhere to both the core and HS contact area. They have to be removed with a razor blade. Interestingly, this occurs most where the letters are etched into the core. My guess is that the heat, pressure and possibly electro-potential difference between the core and the copper cause this. The longer the time that the AS has been on, the greater the occurrence. If you don't remove these "flecks" they can impede good contact the next time you remount the HSF. They do not wash off with solvent, like the bulk of the AS. You have to pick at them with the razor blade. When they let go, you hear a distinct "tick" sound. I have talked to Nevin about this and we could not explain the phenomenon. Anyone else encounter this? You have to look real close to see them.

Hoot
 
The guy who posed that AS2 will corrode al is talking crud. A few seconds after you have lapped the aluminum the oxide layer will cover it up again. It will be that quick and it will protect the aluminium.
 
This didn't pass my "sniff test" either. Sounded like a "high school chemist" answer to me, that's why I thought I would ask someone who really knows.
Hoot, I have had my AS leave behind a solid like "glaze" on my dd water block. It was between the peltier and waterblock where a lot of heat transfer was taking place. I noticed my temps were up form past months so I took the setup apart thinking it just needed to be "reset" and I found a silvery glaze on a small portion of my DD block. Like you said, I had to pick away at it with a exacto knife and then relap the bottom of my block. Temps went back to where they were when I first did the install so my suspect is that this does effect your temps. It took about four or five months in-between my peltier and DD block for this to occur and it only happened in a small area of the block, not the whole area where contact was being made. It is weird, must be gremlins, the live inside my computer and do funny things like that. They think it's funny I guess. ???
 
*spazzed* (Jul 11, 2001 12:19 p.m.):
Do those "flecks" look like the ones that are left on your hand after using as2?
Click to expand...

No, these are bigger flecks than that and hard like solid silver would be. The biggest i've picked off was the size of a piece of glitter.

Zoopa, your phenomenon is a new one to me. I know that AS gets into ceramic and is a b**ch to get out. Takes a strong solvent to dislodge it, but it sounds like you are describing the same flecks I have observed. I have never had them form into a larger sheet though, but then I rarely have my HSF on for more than a week or two before I'm off on some new experiment. Do you have a digital camera, or access to one? I'd like to see that glaze.

Hoot
 
Lynx (Jul 11, 2001 12:53 p.m.):
The guy who posed that AS2 will corrode al is talking crud. A few seconds after you have lapped the aluminum the oxide layer will cover it up again. It will be that quick and it will protect the aluminium.
Click to expand...

yep yep yep. i am a highschool chemist, but a very good one. I hang out in the chem lab, not the comp lab.
 
Yeah... A lapped HS will get a layer of aluminum oxide anyway because it is in contact with the air... It won't really matter

JigPu
 
Hoot (Jul 11, 2001 10:07 p.m.):

No, these are bigger flecks than that and hard like solid silver would be. The biggest i've picked off was the size of a piece of glitter.

Hoot
Click to expand...

The ones that I've found that really stick to my hand look like as if they were shattered glass or something(really small, seen better in bright light).......take forever to get it off my hands too
 
The aluminium oxide layer only protects against atmospheric corrosion and not against galvanic corrosion. Otherwise how do you explain the mismatch between aluminium radiators and copper waterblocks. It is possible that the micronized silver in AS2 lends a hand in galvanic corrosion as it has an even lower standard reduction potential (+0.8V) compared to copper (+0.15V), ie.more likely to form a galvanic cell than copper with aluminium. If I'm not mistaken, the AS2 site does warn about the potential for AS2 to be electrically conductive. I'm no expert in chemistry but I think this issue warrants more attention. Why don't someone do an experiment with AS and a piece of bare aluminium, leave it for a coupla weeks, and see whether or not it has been tarnished where the AS was applied.
 
Hoot (Jul 11, 2001 10:07 p.m.):
*spazzed* (Jul 11, 2001 12:19 p.m.):
Do those "flecks" look like the ones that are left on your hand after using as2?
Click to expand...

No, these are bigger flecks than that and hard like solid silver would be. The biggest i've picked off was the size of a piece of glitter.

Zoopa, your phenomenon is a new one to me. I know that AS gets into ceramic and is a b**ch to get out. Takes a strong solvent to dislodge it, but it sounds like you are describing the same flecks I have observed. I have never had them form into a larger sheet though, but then I rarely have my HSF on for more than a week or two before I'm off on some new experiment. Do you have a digital camera, or access to one? I'd like to see that glaze.

Hoot
Click to expand...

Hoot, I could get a digital camera form my friend so I can take some pics for you. The only problem is I just cleaned my setup that had all that shiny stuff on it, so right now it's clean. :( What I can do is write my self a note to take a pic of it the next time I have my setup taken apart.
 
BTW fellas, aluminium oxide vary in translucency from being totally colourless to opaque. A good example of a natural, see-though form of aluminium oxide crystallisation is: Sapphires. What you fellas may have are good, solid flakes of aluminium oxide. Try scratching glass with it...:)
 
cjtune (Jul 12, 2001 09:56 a.m.):
The aluminium oxide layer only protects against atmospheric corrosion and not against galvanic corrosion. Otherwise how do you explain the mismatch between aluminium radiators and copper waterblocks.
Click to expand...

Miscellaneous observations of a non-chemist:

The oxide that metals form in the presence of oxygen varies in its regularity, permeablity and transparency. The normal oxide layer on aluminum and steel is not very protective (even though on aluminum it is extremely hard) , while on gold it is excellent. Aluminum is usually "anodized" to give it good protection; that's why some sinks are yellow, green, or blue. It can also be silvery. Lapping will remove the anodization. Steel can be oxidized to a black form which is quite protective, unlike the red form which seems to actually promote further oxidation.

The ability of water to dissolve substances is amazing, perhaps even aluminum oxide slightly. Practically every material surface on earth contains a bit of water once it is exposed to the atmosphere. Water is readily available in the atmosphere. Also amazing is water's ability to generate ions which can be very reactive and will migrate slowly through protective layers.

Silver slowly forms an ugly, thick black layer in the atmosphere, although this may be mostly a sulfide rather than an oxide. Yes there are sulfur compounds in the air, although not much. Regardless of what they mix silver with in Arctic silver, it can corrode slowly by migration of oxygen or whatever. People think of solid things as impenetrable, but this is seldom the case for thin layers. You can put a dozen coats of polyurethane on a piece of wood, and the wood will still swell up when the humidity goes up and shrink when it goes down. Polyurethane is a pretty tough plastic.

BTW, by design metals which you are likely to buy are seldom a pure form. They are normally alloys. Pure iron, aluminum, silver, and copper are way too soft for most purposes, and corrosion is too much of a problem. "Sterling" silver is NOT 100% silver; it happens to be a good-looking, fairly tough alloy. Aluminum can contain copper. Copper sometimes contains aluminum.
 
CalCoolage (Jul 16, 2001 10:52 a.m.):
cjtune (Jul 12, 2001 09:56 a.m.):
The aluminium oxide layer only protects against atmospheric corrosion and not against galvanic corrosion. Otherwise how do you explain the mismatch between aluminium radiators and copper waterblocks.
Click to expand...

Miscellaneous observations of a non-chemist:

The oxide that metals form in the presence of oxygen varies in its regularity, permeablity and transparency. The normal oxide layer on aluminum and steel is not very protective (even though on aluminum it is extremely hard) , while on gold it is excellent. Aluminum is usually "anodized" to give it good protection; that's why some sinks are yellow, green, or blue. It can also be silvery. Lapping will remove the anodization. Steel can be oxidized to a black form which is quite protective, unlike the red form which seems to actually promote further oxidation.

The ability of water to dissolve substances is amazing, perhaps even aluminum oxide slightly. Practically every material surface on earth contains a bit of water once it is exposed to the atmosphere. Water is readily available in the atmosphere. Also amazing is water's ability to generate ions which can be very reactive and will migrate slowly through protective layers.

Silver slowly forms an ugly, thick black layer in the atmosphere, although this may be mostly a sulfide rather than an oxide. Yes there are sulfur compounds in the air, although not much. Regardless of what they mix silver with in Arctic silver, it can corrode slowly by migration of oxygen or whatever. People think of solid things as impenetrable, but this is seldom the case for thin layers. You can put a dozen coats of polyurethane on a piece of wood, and the wood will still swell up when the humidity goes up and shrink when it goes down. Polyurethane is a pretty tough plastic.

BTW, by design metals which you are likely to buy are seldom a pure form. They are normally alloys. Pure iron, aluminum, silver, and copper are way too soft for most purposes, and corrosion is too much of a problem. "Sterling" silver is NOT 100% silver; it happens to be a good-looking, fairly tough alloy. Aluminum can contain copper. Copper sometimes contains aluminum.
Click to expand...

Miscellanoues observations of a chemist :)

Thanks for the extra info but you haven't quite hit the nail on the head yet: can Arctic Silver 2, given it's close proximity to the unanodized aluminium (alloy) of a heatsink, degrade it or/and itself by corrosion to the point that it impedes heat transfer from the CPU core to the heatsink/ambient, all within a period of just weeks or months into its use?
Me thinks that this happens, that ionic/electronic diffusion does happen through the aluminium oxide layer and the suspension for micronised silver in AS2. Otherwise, how does one explain the flecks of glaze-like stuff? It could be the oxide layer, after growing too thick, becomes easier to flake off -there will be internal stresses on the oxide layer itself it's too thick. Someone should get info on the thermal conductivity of a aluminium oxide layer and calculate the rate of oxide film growth due to galvanic corrosion. See whether that appreciably adds to the C/W of the heatsink in its estimated lifetime of service.

BTW, aluminium and its alloys can be given thicker oxide layers for protection against atmospheric (either by direct rxn with oxygen or gaseous reduction) and I think aqueus corrosion as well, in acid baths as an alternative to anondizing. I'm not sure though, how impermeable a layer of aluminium oxide is to gaseous as well as ionic diffusion. One thing for sure is that the layer is hard and does not come off easily unless under the action of strong acids or alkalis or....lapping.

In addition to being in such close contact with each other, the aluminium is also under stress from the mounting clips/bolts. Stress corrosion can occur with the higher-stressed regions being anodic relative to the less stressed regions.

AS2 a faulty product?
 
well I am intrigued, giving my chemistry a call tomorrow. Will reply with her answer.
 
HA! I removed my Alpha 6035 HS with Arctic Silver II as the thermal compound, wiped it clean, and lookee there, exactly what you are talking about. BUT, (this is the cool part) THE IMAGE ON THE COPPER IS THE CODES ON THE DIE OF MY PROCESSOR. Cool, huh? My Alpha says 'Duron' on it. Bet yours doesn't. :)
 
In order to have corrosion three conditions must be met:
1) there must be an electrical potential.
2) there must be a path between the metals.
3) there must be an electrolyte present.

If any one of these conditions are not met then corrosion will not take place.

The silicone oil is an insulator, not an electrolyte.

All the metal-based thermal compounds (silver, copper, and aluminum) can form the micro-thin foil under certain conditions. It is where the soft metal particles in the compound have been fused together by pressure. Only way to totally avoid it under all circumstances is to make the compound with an oxide of a metal, i.e. zinc oxide or aluminum oxide. Unfortunately, the best metal oxides have less than 1/10 the thermal conductivity of silver. Fortunately, the metal foil can only form where an excessive gap existed between the two mating surfaces (I.e. a flat heatsink on a concave processor or a processor with excessively deep laser etching.) and the small bits of pure fused metal are excellent thermal conductors.

Nevin
 
Nevin, what exactly makes an electrolyte an electrolyte and an insultor an insultor? Water (pure) is a pretty good insulator, but yet under high enough potential differences, it'll break down and electrical charges get to pass. Some goes for air when you see lightnings or when someone uses an arc-welder. I think this applies too to the silicone grease suspension for AS2 despite the obvious fact that it isn't an ionic solvent. Insulation also depends on dimensions than just material type -very much like heat transfer. I don't think electrolytes even play a role in galvanic corrosion -needs no difference in ionic types or ionic concentration in any half cell so its just there to complete a circuit.

Very interesting fact there you brought up about the fusing of soft metals and the use of oxides. Could there be a reason that THE standard thermal interface material (don't just think of the pink gunk) produced is the obiquitous white zinc-oxide/silicone grease paste? Could the Arctic Silver guys have tried to sell us a way to reach for the sun and WE are now realising the folly of buying wax wings? Stay tuned....

One more thing, due to thermal stresses (hotter parts of metal bodies expand more than the cooler parts), a heatsink's bottom would tend to concave towards the CPU core than concave outwards. But usually this is nullified by the super-strong mounting clips and the CPU core and heatsink bottom maintains nearly full contact.
 
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