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 Post subject: Copper Coolers & Oxidation
PostPosted: Mon Mar 03, 2003 9:20 pm 
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Joined: Mon Mar 03, 2003 7:54 pm
Posts: 2
Location: Enterprise, KS
If I don't live at the seahore, nor in a high
pollution environment, nor even in one that
often sees high humidity, do I need to be
concerned about oxidation on a copper HSF?

Are the fins on "Cu" HSFs even pure Cu, or are
they alloys less susceptible to oxidation?

If copper is a concern, and the supplier doesn't
offer gold-plating, is it practical to get the
local chrome shop to gold plate it for me?

Background:

I'm planning a PC build for later this year,
most likely an AMD Barton in the +2GHz class.
Since my current 1GHz Tbird is already quite
noisy enough, acoustic emissions reduction
is a goal.

As I consider candidate HSFs, the leaders in
the quiet category all seem to be copper types,
like the SLK-900.

I've already given up on copper-bottomed
cookware, and I'm wondering what a copper cooler
looks like (and performs like) after a
couple of years.

Observations:

Thermally speaking, excluding diamond (!),
the perfect material to use for heatsink fins
would be pure silver, but nobody uses it
(at least, not unprotected).

Why isn't silver used for fins?

Because it would oxidize within hours, and
rapidly lose its edge over the materials people
DO use, like copper, gold(plating) and aluminum.

But copper oxidizes eventually, as the older
pennies in your pocket attest.


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 Post subject:
PostPosted: Mon Mar 03, 2003 9:45 pm 
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Joined: Sun Feb 16, 2003 3:37 pm
Posts: 371
Location: S. Illinois
You pose a good question, but I would tend to think that the copper darkening would not really have much of an effect on the cooling capacity.. Even if it did begin to darken/oxidize, most likely within a couple of years you will probably have moved on to another style processor or H/S and it wouldn't be worth worrying about..

I have an Zalman ZM15-Cu which is mounted on a GeForce2 GTS-V in a secondary system, and it's been on there about 15 months now and pretty much looks as shiny as a brand new penny :)


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 Post subject:
PostPosted: Mon Mar 03, 2003 9:58 pm 
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SPCR Reviewer

Joined: Sun Aug 11, 2002 3:26 pm
Posts: 3998
Location: Phoenix, AZ
In general, no, you don't need to worry about the copper oxidizing. Copper doesn't rust through like iron does, it only forms a layer a few microns thick, then it stops. Aluminum and Silver do the same thing. (It's because their oxides aren't water soluble)

Although the copper oxide isn't as good a conductor as pure copper it's too thin on the fins to make a difference. The only place you worry about it is on the contact surface between the CPU and the heatsink. Most good copper heatsinks come with a piece of tape over that area to keep the copper from oxidizing before you mount it. Once mounted the thermal grease protects the copper.

Gold plating a copper heatsink is a bad idea. It will most likely actually reduce the cooling power, not improve it. In the process of gold plating layers of nickel and chromium are laid down first to improve the adhesion of the gold. Both of them have lower thermal conductivity than copper or gold, so the heat gets trapped by them inside the copper.


Silver isn't used for heatsinks for one very simple reason.....It's wicked expensive!

This topic has been discussed here before, a couple of times in fact:



http://forums.silentpcreview.com//viewtopic.php?t=3201
http://forums.silentpcreview.com//viewtopic.php?t=2977

(Try the search feature)

_________________
Senior Contributing Writer, SPCR


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 Post subject:
PostPosted: Sat Mar 08, 2003 3:11 pm 
"The only place you worry about it is on the contact surface between the CPU and the heatsink. Most good copper heatsinks come with a piece of tape over that area to keep the copper from oxidizing before you mount it. Once mounted the thermal grease protects the copper. "

That's correct, if air can't get to it nothing will happen. As I run bare copper wire to my speakers I have removed the wire on occaision and found it just as shiny as when it was installed. The stuff exposed to air is a bit darker, and it took quite a while.

Youi'll discover the real problem with HO train sets, brass (a copper mix) oxidizes and doesn't conduct electricity well.


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