TheSamba.com :: View topic - stainless steel and aluminum in coolant expt.

Tue Oct 26, 2010 7:11 pm

Just for fun, and seeing as we all like to theorise but seldom do the experiment, I thought I do a simple test of aluminum and stainless shared coolant, and with the metals electrically connected.

The stainless is 304, the aluminum is 6061. Both samples are 0.125" X 0.750" and immersed in the coolant to approx 2".

The coolant in a 50/50 mix of OAT based coolant and distilled water.

I did a casual buffing of both samples with tripoli, and then degreased. The buffing was to allow any corrosion to be more visible. In the picture, the aluminum is on the right.

the samples are connected by tinned copper wire.

Ambient temp in the lab, I mean the barn, ranges from 7 C to 10 C.

Initial measurements between the unconnected samples in the coolant was, 150 microAmps and 540 milliVolts.

Experiment started at 6:30 pm, pacific time, October 26 2010.

I'll leave it undisturbed for a week or so, then take pics of the metals.

It will be interesting to see if anything happens

alistair

Update:

Nov. 2 1220 hrs - I pulled the metals out of the jar and rinsed off coolant. The aluminum looks pretty good. I don't know if the pic shows it but there is a very slight haze on the surface.

I replaced the coolant with tap water (well water, pretty hard), and set the expt. up again, same conditions as before. Initial readings are:
326 mV and 195 microAmps between the 2 samples.

pic of metals on Nov 2 2010

Update Nov 4 2010

There are a few white "fluffy" deposits on the aluminium sample (none on the stainless). I didn't disturb the set up to take the pic, still in tap water, connected by the wire.

Tue Oct 26, 2010 7:19 pm

maybe I'm wrong but it seems to me since they are connected there wont be any flow? how about hook them up to a battery like another poster suggested checking for a potential in the coolant itself? one sample positive and one negative. or was it you ragner?

from the other thread it seems that the consensus is you need some kind of electrical "leakage" for corrosion to occur?

I just got back from out of town and my van is in storage, but I plan to try the voltmeter test.

Tue Oct 26, 2010 7:26 pm

that seems to be a common misunderstanding. For this specific electrolysis to occur they have to be connected.

Electrons travel in the wire, ions (-OH mainly I think) migrate through electrolyte.

In essence its a battery, and connecting the "terminals" allows current to flow.

We are not talking about stray current electrolysis, but dissimilar metal electrolysis.

in this set up, the more noble stainless steel is the cathode, and the aluminum is the anode. The aluminum will lose electrons (oxidation) and the steel gain electron (reduction)

alistair

Tue Oct 26, 2010 10:54 pm

eagerly awaiting your next report

Tue Oct 26, 2010 11:40 pm

where's that popcorn eating emoticon !?!
:lol:
thanks for setting this up. subscribed now :)

Wed Oct 27, 2010 12:41 am

You should simultaneously run an experiment with no jumper wire between the two electrodes. Might as well show the difference between a bonded and unbonded system while you are at it.

Wed Oct 27, 2010 7:32 am

yes, you are right, I should run a no wire control.

I also should run some at 90 C, and with degassed coolant, and recirculating coolant.

But then again, if the experiment was done perfectly, we wouldn't have anything to argue about.

Its all in good fun :)

alistair

Wed Oct 27, 2010 7:45 am

If there were any doubt that we are all geeks, this removes any doubt. Love it.

Wed Oct 27, 2010 7:54 am

I think you really need to include one more test with the two metals unbonded by wire and not touching each other since that's how we'd set them up in the van if we could.

Wed Oct 27, 2010 8:18 am

This just reenforces the fact I am a Smartass and not at all smart.

This is fun...

Brian.

Wed Oct 27, 2010 9:30 am

ragnarhairybreeks wrote:
It will be interesting to see if anything happens
I don't suppose you've got a sensitive balance lying about? Could be interesting to measure weight loss/gain on the coupons.

By the way, around these parts we shave our breeks and use woad (he said snippily).

WOAD
(to the tune of Men of Harlech) see http://video.google.com/videoplay?docid=1030890399539911654# and http://video.google.com/videoplay?docid=1030890399539911654#docid=-7532792189217637382

Whats the use of wearing braces,
vests and pants and boots with laces?
spats or hats you buy in places
down on brompton road?
Whats the use of shirts of cotton,
studs that always get forgotten?
These affairs are simply rotten
better far is woad.
Woad's the stuff to show men,
woad to scare your foemen!
Boil it to a brilliant blue
and rub it on your back and your ab-do-men.
Ancient briton never hit on
anything as good as woad to fit on
your neck, your knees or where you sit on,
tailors you be blowed!

Romans came across the channel
all dressed up in tin and flannel
half a pint of woad per man'll
dress us more than these.
Saxons you can waste your stitches
building beds for bugs in britches
we have woad to clothe us which is
not a nest for fleas.
Romans keep your armor,
saxons your pyjama;
hairy coats were meant for goats
gorillas, yaks, retriever dogs and llama.
Tramp up Snowdon with your woad on,
never mind if we get rained or snowed on,
never want a button sewed on --
go it ancient B's!

ps -- none of this is true. See http://www.cyberpict.net/sgathan/essays/woad.htm

Wed Oct 27, 2010 10:00 am

I was also wondering about Stray Current Corrosion and if Vanagons might be susceptible as I understand the effects are substantially greater than Galvanic Corrosion.

http://m.educell.com/cell/div_guide.jsp?guideId=21...ine%20Shop

Could this be a problem in a Vanagon? What would be the potential scenarios? A bad ground? Plugged into 120VAC with a poorly grounded appliance? Can the coil/plug wires induce transients into heads that cause localized pitting? There are a number of sensors in Vanagon water. Do they have any voltage?

"Remember that corrosion occurs at the locations where DC current leaves metal and enters water."
http://www.boatus.com/boattech/MarineCorrosion.htm

"Stray Current Corrosion

Q: If placing two dissimilar metals in an electrolyte creates low-voltage DC current that can wreck unprotected metals in a matter of months, what would happen if all of the current from a boat’s 12-volt batteries were to somehow come in contact with metal?

A: The metal fittings in contact with the bilge water would be in a lot of trouble — and are likely to be wrecked in a few days or even hours.

While less common than galvanic corrosion, stray current corrosion is typically swift and deadly. There have been boats that were sunk when someone carelessly left a battery cable dangling in bilge water. All of the underwater fittings (bronze) were pink and nearly crumbling in only a few days. In other cases, crimped wires in the bilge were “leaking” 12-volt current into the bilge water.

Stray current is one reason DC wires should always be well above bilge water levels. (AC wires must also be kept well away from the bilge! Although they don’t cause corrosion, AC wires in water pose a dangerous shock hazard.)

If a DC wire must be left in the bilge (e.g., mast wires left short at the base), they should be enclosed in a weatherproof junction box to seal out moisture, or individually sealed in heat shrink tubing and secured as high as possible. Liquid electrical tape or corrosion inhibitor sprays can also help to seal terminals from dampness that may infiltrate enclosed junction boxes."
http://www.boatus.com/seaworthy/galvanic/default.asp

Wed Oct 27, 2010 12:21 pm

Oh, Um.... I forgot to empty my bilge in my "87 GL, be right back....

Wed Oct 27, 2010 2:31 pm

rule of thumb, the reaction rate doubles for each 10C temp increase. so heat it up if you want results in a resonable time period.

also note the alloys can play a significant role in corrosion protection. small variations in alloy can make a huge differeance

Wed Oct 27, 2010 3:46 pm

If you have a properly grounded engine and don't have any shorts into the coolant for some very odd reason you aren't going to have a problem with stray current corrosion.

Wed Oct 27, 2010 4:26 pm

agreed about temp and alloys. Problems are:

1. I didn't have a bit of WB engine to use.
2. I don't know what alloy the ss pipes are made of
3. I have a hard time keeping the experiment at elevated temps.

Its really a pretty lame experiment as experiments go. That being said, if I see any kind of corrosion on the aluminum after a week I would take it as a heads up and an indication to do it again with points 1 & 2 covered.

The stray current corrosion is not addressed by this. I'll leave that to others. Where the 2 overlap is in the idea of grounding all metal parts of van. If dissimilar metal corrosion is indicated, then the noble metals should be isolated.

alistair

Wed Oct 27, 2010 4:56 pm

put it in a box with a couple of light bulbs - that will keep it warm

Tue Nov 02, 2010 8:36 am

Hey Al, that's a great idea! Nothing like a little direct knowledge, eh? :)

Randy's point about the cardboard box and the 60 watt light bulb has merit...

Seeya, Jake

Tue Nov 02, 2010 8:47 am

why not suspend your experiment (use small test peieces ) by a wire in the vanagon coolant tank, then drive it around, that will get you the high temps.

look forward to results on this!

Tue Nov 02, 2010 1:18 pm

took pics of metal samples after a week, see original post for pics.

alistair