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Nixie
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Cleaning corroded aluminum and/or epoxy
My computer's watercooling system uses an aluminum heater core from a car as radiator, and the splitter/combiners for distribution I made from a
waterproof epoxy (the kind where you mix two parts and the paste warms up and cures in an hour).
Last month I had run some CLR to clean it out and after flushing with water I put some bleach as well, forgetting it would attack the aluminum. The
CLR could also have caused a problem but I doubt it. Maybe the epoxy was attacked as well, I don't know. But basically flow is significantly reduced
(almost fried my PC; I only noticed there was something wrong when I started getting CRC errors in archives I was compressing and then decompressing).
Looked in the tank and the water is very cloudy--can't see deeper than about 5 cm.
So how do I clean out what I'm assuming are most likely deposits clogging the heater core that came from its aluminum being attacked by the bleach?
But again, I'm not sure it's that and not the epoxy and/or CLR being involved.
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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woelen
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Hmmm.. my PC is nitrogen/oxygen cooled. I use a mix of appr. 80% N2 and 20% O2 (with some argon and trace gasses) for cooling the PC and it works like
a charm 
OK, back to topic. If the problem really is due to Al attacked by bleach, then you could try rinsing it with vinegar, followed by a water-rinse. The
vinegar dissolves any insoluble Al-oxides/hydroxides in the cooling system and as an added bonus it also works as a complexing agent. Use white
vinegar, without all kinds of spices and salt mixed in as well. Also, don't use concentrated acetic acid, just the plain household stuff with max. 5%
acetic acid.
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bio2
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Ice machine cleaner for descaling Aluminum evaporators is hydoxy acetic acid.
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Nixie
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I took apart the whole thing. One of the waterblocks has a gold-plated copper base. The plating had rubbed off (probably due to particulates in the
water), exposing bare copper, and the aluminum near it had corroded, and the whole thing was really clogged. Is there something I can add in the
water to prevent corrosion due to having two different metals in contact with it?
[Edited on 13-4-2008 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Twospoons
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Your best solution is to get a water-block that was not designed by an idiot. Putting dissimilar metals in contact in a wet environment is a recipe
for disaster, unless you include sacrificial anodes. The only thing you could add to water is "nothing" ie use de-ionised water - but it wont stay
that way for long. Getting all the Al parts hard anodised might work, but its going to cost as much as a new waterblock, unless you do it yourself.
Pure glycol might be OK, but cooling perfomance will suffer.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Nixie
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Shortly after my previous post, my hard drive died--and it simply won't spin up now (posting this from the landlady's laptop). Tried the freezer
thing, no good. Now I'm looking for a data recovery company that's not a ripoff, and trying to figure where I'll find the few thousand dollars it
will cost... everything is on that drive, including all my work. I momentarily pondered suicide...
[Edited on 14-4-2008 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Nixie
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Er, just the night before I was about to send it off, I tried it again and gave it a good knock as I powered it on, and it worked. Managed to mirror
it. Phew!
I have a question though--what thermal compound can I use to fill the gap between the hard drive waterblock and the hard drive's uneven surface (on
the circuit board and motor side)? The one that came originally with the waterblock cured to a consistency somewhat softer than silicone and it was
easy to remove. I'd ask the manufacturer what it was but I don't remember who the manufacturer is.
So what can I use? Can't be grease as that doesn't stick well and is kind of runny. Can't be regular epoxy since that turns hard and I wouldn't be
able to remove it. I thought of mixing alumina powder into silicone to make it thermally conductive, but as silicone cures it releases acetic acid
which would corrode the circuit board. So what do I use?
I've also considered immersion cooling for everything, but mineral oil is too much of a mess and it increases capacitance between the closely spaced
CPU pins too much; it also has high viscosity and low heat capacity. Flourinert FC-770 is perfect but I can't afford the thousand dollars per gallon.
Any other suitable dielectric fluid?
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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bio2
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Try the red high temperature silicone.
Works for me and cures faster than RTV.
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Nixie
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Didn't find that but they had GE Silicone II which gives off methanol and ammonia instead of acetic acid while curing. I assume that wouldn't hurt a
PCB or semiconductors in plastic packages?
I tried mixing this curing silicone 2:1 with thermal silicone grease. It still cured, but I don't know how much I can lower the ratio before it
stops, I think not much. I'd rather just mix in alumina powder, but I don't know how to make it. If I make say aluminum chloride by dissolving
aluminum foil in hydrochloric acid, can then I make the oxide by heating or something?
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Nixie
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Anyone? How do I make alumina?
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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497
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Mix up some thermite.
Heating any aluminum compound really hot in air should do it.
Why alumina though? I wouldn't think that would work as well as something like copper powder. Or is there a reason that wouldn't work?
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Nixie
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Copper powder is electrically conductive. I need a thermally conductive electrical insulator.
I have beryllia but it's way too hard and I can't crush it into powder (not to mention protect my lungs).
[Edited on 23-4-2008 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Nixie
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BTW, for another project entirely, can I use a cheap aquarium pump to circulate Fluorinert (FC-770)? It's not viscous, but it's almost twice as dense
as water. Or maybe I'd need two pumps in series to get proper operation?
[Edited on 24-4-2008 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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Nixie
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What mesh alumina should I use? Can I use superfine (6000 grit) like this?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=23022...
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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497
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An aquarium pump should work fine for that.
And I believe the finer it is the more thermally conductive it is (at least I think thats the case with sand). The finer stuff will also conform
better to the surface of the metal.
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Twospoons
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For the silicone I suggest Dow Corning 3140. It is intended as an encapsulant for electronics - so no corrosion risk. It is quite liquid (like
honey, pourable), so it should take quite a heavy alumina loading before it becomes unfeasibly stiff.
I don't think it will matter too much how fine the alumina is - the biggest factor in overall performance will be the total thickness of the interface
between circuitry and heatsink.
Silicone sticks like shit to a blanket - don't expect to be able to remove it easily.
http://www.bergquistcompany.com/tm_gap_pad_list.cfm would solve all your problems.
Helicopter: "helico" -> spiral, "pter" -> with wings
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ShadowWarrior4444
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I should note that there are thermally conductive adhesives specifically designed for this purpose available from most computer supply stores. A web
search may identify what they are, and a quick scan of the MSDS should give the exact components, should you wish to make your own.
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Nixie
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I already checked local computer stores but didn't find anything. They have thermal adhesives but they cure to a hard substance that cannot be
removed. I need something that cures to no harder than RTV silicone.
Anyway, I already ordered the alumina.
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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ShadowWarrior4444
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| Quote: | Originally posted by Nixie
I already checked local computer stores but didn't find anything. They have thermal adhesives but they cure to a hard substance that cannot be
removed. I need something that cures to no harder than RTV silicone.
Anyway, I already ordered the alumina. |
Hmmm, I wonder if Ethylene Vinyl Acetate mixed with alumina would work. EVA is a thermoset plastic, so I am uncertain whether it will hold up to the
heat, but it certainly has the consistency you are looking for. (It is ostensibly used to make shoe soles and hot glue.)
Another interesting procedure is given here using a mix of adhesive and grease: http://www.d-silence.com/feature.php?id=259
Another note--your original grease was likely this:
"Ceramic-based thermal grease has generally good thermal conductivity and is usually composed of a ceramic powder suspended in a liquid or gelatinous
silicone compound, which may be described as 'silicone paste' or 'silicone thermal compound'. The most commonly used ceramics and their thermal
conductivities (in units of W/m•K) are:[1] beryllium oxide (218), aluminum nitride (170), aluminum oxide (39), zinc oxide (21), and silicon dioxide
(1). Thermal grease is usually white in color since these ceramics are all white in powder form."
Along those lines, one that is not based on Silicone: http://www.arcticsilver.com/arctic_alumina.htm
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Nixie
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Alumina is only 18 W/m•K according to another source. Perhaps the powdered form has a different property :?
Still, it will be good enough for the application, since the heat is not high density. Beryllia is wonderful but it cannot be bought on eBay, or many
other places for that matter. If anyone knows where I can get my hands on either small thin tiles (to use as insulators on power semiconductors), or
powder, kindly let me know.
By the way, I'm wondering if thermal conductivity of a mixture is simply a weighted average of the conductivity of the constituents? I have a bunch
of these tiles: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=38002...
It says 95% alumina and 5% CrO3, the latter being about 4x as conductive as the alumina. So then it would seem to make almost no difference as an
additive, no?
[Edited on 2-5-2008 by Nixie]
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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not_important
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That's not a simple mixture, it's actually a solution of Cr2O3 in Al2O3 = ruby. As you increase the chromium doping the colour goes from pink to red
to a dark purple, and it begins to become electrically conductive.
These are likely doped enough that the thermal conductivity has increased but not enough to really affect the electrical conductivity.
I know someone who made lightly doped alumina for use in ceramics by ball milling Al(OH)3 with a small amount of Cr2O3, then firing the mix at cone
11. When cooled they washed it with bisulfite solution to remove any loose higher oxides of chromium, and had a pink powder.
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Nixie
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I got the alumina powder. It is extremely fine. I had to wet it with a bit of methanol and silicone lubricant before being able to mix it in. The
RTV silicone holds about 1:1 mix by volume (I know it's stupid to measure powders by volume but I was testing with smaller amounts than I could
weigh). I'm wondering, is there anything else I can add to improve thermal conductivity than the alumina allows? I didn't find any aluminum nitride
powder on eBay, or know of a source in the country.
BTW, if someone can supply me with beryllia powder I'll pay good money for it.
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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not_important
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You tend to pay beryllia powder with your health, it's real nasty stuff.
AlN powder:
http://www.nanoamor.com/inc/sdetail/1830
note that it slowly reacts with moisture.
Boron nitride
http://www.reade.com/Products/Nitrides/Boron-nitride-powder-(BN).html
Some forms of diamond have high thermal conductivity. I've been told, but do not have any hard data, that this hold true for the diamond grit used in
shaping and polishing gemstones. This grit can be had with particle sizes smaller than a micron.
http://www.inlandlapidary.com/user_area/gritchart.asp
The problem with mixing a good thermal conductivity material with a poor one is the the high conductivity particles are going to be isolated by the
matrix. This is illustrated by silver loaded thermal grease, which has about 1/200 the thermal conductivity of silver an 10X the thermal conductivity
of the basic grease. Silver's conductivity is around 400-430, AlN and BeO are half that, Al2O3 is 1/10, diamond 2x to 5x.
Loading up the mix so the thermal conductor is the majority material might boost the aggregate conductivity but the mechanical strength might suffer.
The best thermal mating compounds reach 7 W/mK or so, far below that of metals and less than a quarter of alumina.
This might interest you, it addresses the limits of effectiveness of thermal compounds - less impact than you might think.
http://www.overclockers.com/articles662/
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Nixie
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The "less impact" is due to the very thin layer of thermal paste used. I'm working with very thick layers, in some areas more than a centimeter, so a
small difference matters.
However, this gives me an idea. I could add layers of aluminum I cut from a sheet to shapes to fill in some of the thickness.
\"Good is a product of the ethical and spiritual artistry of individuals; it cannot be mass-produced.\" --Aldous Huxley
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not_important
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I can't see the hard drive generating that much heat, compared with a CPU. The increased thermal resistance is likely to offset any gain from the
cooling block, it would be better just to increase airflow across the drive.
I suppose you could try diamond dust, might start a new trend.
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