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Aluminum block vs copper block

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August 17, 2010 12:28:49 AM

aluminum block vs. copper block

i have an aluminum radiator and i'm out of budget if im going to purchase a new copper rad and my recent water block is copper. would it be better if im going to go for an aluminum water block? so that there would be no issues about dissimilar metal reactions.

i need your opinion guys
August 17, 2010 5:16:27 AM

having different metals isnt going to be a big problem unless you dont have any anti corrosive mix in your coolant. i made my own loop and i have...copper waterblock, copper rad, and brass fittings. no corrosion yet that ive seen.
August 17, 2010 6:52:51 AM

copper and brass are somewhat similar. how about aluminum and copper or brass?
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August 17, 2010 6:55:12 AM

any anti corrosive mix? or im gonna use only plain distilled water? my stock setup uses anti corrosive mixture but still ends up on the copper block with blue rusts.
a c 190 K Overclocking
August 17, 2010 8:05:11 AM

Thats verdigris, you'll always get that where copper and moisture meet
Moto
August 17, 2010 10:46:58 AM

any suggestions? reactions?
a b K Overclocking
August 17, 2010 2:52:25 PM

09rodney17 said:
any anti corrosive mix? or im gonna use only plain distilled water? my stock setup uses anti corrosive mixture but still ends up on the copper block with blue rusts.


Is the bluish rust on the outside or inside of the block? If it's on the outside of the block, it's simple oxidation of copper when exposed to the oxygen in air in the presence of water and means that you have a small leak or had one at one point in time. If it is on the inside of the block, it means you have a lot of galvanic corrosion occurring (see below) and need to rehab your loop.

09rodney17 said:
copper and brass are somewhat similar. how about aluminum and copper or brass?


Galvanic corrosion deals with the difference in the reduction potential of the metals in the loop and the amount of electrolytes in the liquid coolant (see here for more information.) Brass is mostly copper and a little zinc, so the difference in electrode potential between copper and brass is very small and you will get an insignificant amount of galvanic corrosion. Aluminum has quite a different electrode potential than copper and brass, so you will get significant corrosion if you do not take steps to address the flow of electrons in the liquid. Using a sacrificial anode of something even more reactive than aluminum would work- I'd pick zinc or magnesium alloy. However, that would still lead to a buildup of Mg or Zn on the copper block. You could also use commercial automotive coolant at a relatively high concentration like 25% to limit corrosion, but you'd still have some. The best thing to do is just to use one metal in your loop.
August 17, 2010 3:13:59 PM

MU_Engineer said:
Is the bluish rust on the outside or inside of the block? If it's on the outside of the block, it's simple oxidation of copper when exposed to the oxygen in air in the presence of water and means that you have a small leak or had one at one point in time. If it is on the inside of the block, it means you have a lot of galvanic corrosion occurring (see below) and need to rehab your loop.



Galvanic corrosion deals with the difference in the reduction potential of the metals in the loop and the amount of electrolytes in the liquid coolant (see here for more information.) Brass is mostly copper and a little zinc, so the difference in electrode potential between copper and brass is very small and you will get an insignificant amount of galvanic corrosion. Aluminum has quite a different electrode potential than copper and brass, so you will get significant corrosion if you do not take steps to address the flow of electrons in the liquid. Using a sacrificial anode of something even more reactive than aluminum would work- I'd pick zinc or magnesium alloy. However, that would still lead to a buildup of Mg or Zn on the copper block. You could also use commercial automotive coolant at a relatively high concentration like 25% to limit corrosion, but you'd still have some. The best thing to do is just to use one metal in your loop.



so you mean that if im going to use alum, rad then im going to use alum blocks? or copper rad and copper blocks?
a b K Overclocking
August 17, 2010 3:33:50 PM

09rodney17 said:
so you mean that if im going to use alum, rad then im going to use alum blocks? or copper rad and copper blocks?


Yes.
August 17, 2010 7:09:25 PM

i got 50/50 antifreeze and distilled in my loop. i also have an algae killer from the local pet shop and it kills any nasties in my loop =) its ghetto but it works
a c 324 K Overclocking
August 18, 2010 8:53:47 PM

You'll want copper, anyway. I don't have the stats on-hand, but there is a significant difference in the amount of heat copper can displace and remove over aluminum. Let me see if I can find it on the Google...

http://arstechnica.com/civis/viewtopic.php?f=7&t=811894&start=40
(found another forum that gives a decent explanation without too much overbearing science-speak)
a b K Overclocking
August 19, 2010 1:35:30 AM

rubix_1011 said:
You'll want copper, anyway. I don't have the stats on-hand, but there is a significant difference in the amount of heat copper can displace and remove over aluminum. Let me see if I can find it on the Google...

http://arstechnica.com/civis/viewtopic.php?f=7&t=811894&start=40
(found another forum that gives a decent explanation without too much overbearing science-speak)


The thermal conductivity of copper is higher than aluminum, so this means that copper is a bit better at carrying heat from the CPU to the liquid than aluminum. However, it's also a lot heavier and a lot more expensive than aluminum. The increased weight of copper is why it generally is only used in small, low-profile heatsinks and water blocks.

However, don't confuse thermal conductivity with specific heat. Specific heat is how much heat a certain amount of a substance can absorb. That's very important when talking about cooling fluids, but you really do not care much about how much heat the heatsink itself can absorb. The heatsink will reach a steady-state temperature ("come up to temp") fairly rapidly, and then the temperature of the CPU is only dependent on how well the heatsink conducts heat away from the CPU and dissipates it.
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