Chemistry of rusting

There are inconsistencies between the two charts. Your chart suggests that aluminum would protect both zinc and iron, and that iron would protect cadmium. Lange's chart suggests that zinc and cadmium will protect iron, and that zinc will protect aluminum.
Cadmium has been used as a sacrificial or galvanic plate for steel in the past, and aluminum outboard motors have zinc tabs below the waterline to protect the aluminum body, and maybe the aluminum boat it's attached to.
Reply to
Don Foreman
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That sounds sensible. I tried putting a 60 W light bulb inside a power supply I'm trying to protect. It dropped the relative humidity from 71% to 44%.
No. I have various rough and smooth parts on my desk. Quite a variety, and they sit there a long time as they're either trial parts or parts I screwed up.
That could very well be a factor. Some of the stuff I noticed significant rust on was in a cardboard box.
That's possible too, although I've seen stuff get very dusty in some buildings without a trace of rust. I guess it's a combination of factors.
Best wishes,
Chris
Reply to
Christopher Tidy
Maybe at that warm room temp - a micro-mist or out gassing oils might coat the steel. Also, in the shop it likely dews. Temp drops below the dew point ? In the house it is above the dew point - you two make it so else you get clammy. Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member
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Reply to
Martin H. Eastburn
Aha. That doesn't matter.
Muriatic acid fumes permeate right through polyethylene bottles.
Chlorine outgassing from pool chemicals vents from and permeates through containers.
Very tiny concentrations of these gases from storing such materials in an enclosed space will initiate and greatly accelerate any metal corrosion.
Reply to
Richard J Kinch
Can't help it Don. Both charts are out of the same reference.
Steve
Reply to
Steve Smith
I didn't get in on the original thread but my simple answer is: A condensing environment makes the difference. Inside the house, the temperature doesn't vary very much. Outside it does. When the sun goes down, the humidity goes up. The parts cool off. Water vapor condenses on the part and there you go.
Pete Stanaitis ---------------------
Steve Smith wrote:
Reply to
spaco
Grinding dust will really make things rust.... Do you grind things in your shop ???
Reply to
kbeitz
Grinding dust will really make things rust.... Do you grind things in your shop ???
Reply to
kbeitz
Grinding dust will really make things rust.... Do you grind things in your shop ???
Reply to
kbeitz
Grinding dust will really make things rust.... Do you grind things in your shop ???
Reply to
kbeitz
Grinding dust will really make things rust.... Do you grind things in your shop ???
Reply to
kbeitz
Someone mentioned grease or oil. Remember that oil floats on water. If you oil it, the oil will float away eventually.
Pete Stanaitis ------------------
Steve Smith wrote:
Reply to
spaco
Go figure. Beats me, I'm no electrochemist.
Reply to
Don Foreman
In 8th grade shop in 1965, we were shown a film that explained sacrificial Zinc anodes, and showed them being welded to ships.
Then they showed the rusting process and a tiny square of steel acting as the sacrificial anode for a tiny square of steel next to it. Then the roles reversed between the squares.
My parents garage has had tools for 50 years with no rust. It has a wall in common with the house and a concrete floor.
My tractor shed with a dirt floor could rust a tool over night.
I have been covering the mill and the lathe with a sheet to keep moisture from condensing. If I find rust, I rub it off with oil and a fine stone. Then I wipe it off and re oil it.
I have been buying rusted up lumps at with tools inside at garage sales. I have been putting the tool in a jar of brine made with vinegar and salt and putting the jar in the microwave. The rust foams and falls off. Then I rinse, dry, and oil the tool. I enjoy this process as an end in itself with well made tools and guns.
Sometimes the rust is a raised hard scab, and I have to break it with a welding hammer and do the brine over again.
I salvaged a pair of wire cutters this way this week end. I got them at a garage sale.
When I was 3 years old, I found my father's wire cutters in a pile of leaves, all rusted frozen. I rejuvenated them with oil and elbow grease.
Reply to
Clark Magnuson
The data you see are half cell potentials under standard conditions where the concentration of the cation is 1N. You can't assume that what you see in the real world is the same as shown in the tables. In addition complexing agents such as chloride or ammonia e.g. can shift some of these potentials drastically.
Differences of a few hundredths of a volt are within experimental error and shouldn't be used to conclude that one metal will displace another.
The tables "suggest" perhaps to a metallurgist but not to a chemist that aluminum will protect a lot of metals in the table. The chemist will realize that the oxide coating on aluminum will be part of the equation and one shouldn't jump to conclusions.
The aluminum in the outboard and the boat probably gets more protection from the adherent oxide layer than any sacrificial anode.
Reply to
Unknown
I agree that the process is enjoyable, but there is something just plain *unpleasant* about a tool that is pitted from rust. Totally subjective, of course, and YMMV.
Bob
Reply to
Bob Engelhardt
The two charts are simple enough.
One - the first simply states the one that is more negative than the other - or higher on the chart takes the hit, lower less or none. And that tells the story...
If one has a copper bottom boat and puts a Magnesium bar against it - expect -2.34V-(-.34) = -2.00V differential and the most negative takes the hit. The higher number shows the intensity of the hit.
Now Iron and Cadmium are very close. -.44 - (-.4) or a -.04 difference for a nominal hit. So Cad plate on Iron bolts won't corrode the bolts. (notice the direction of subtraction...)
as to the other chart - it simply groups 'good' stuff together. The active indicates that the metal has not been passivated with Nitric or Critic acids. e.g. 18-8 steel won't by itself corrode to death even when still active.
Also - 18-8 touching 304(passivated) and/or with 18-8-3 (passivated).
I'm not a chemical Engineer, but a Physicist and Practicing Engineer and senior management.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member
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Reply to
Martin H. Eastburn

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