Chockstone Forum

      Sponsored By
      ROCK
   HARDWARE

Chockstone Photography

Australian Landscape Prints

Chockstone Forum - Gear Lust / Lost & Found

Rave About Your Rack Please do not post retail SPAM.

Author

Carabiner Corrosion

Rupert

12-Jun-2004
11:29:56 AM

I stumbled across this article on carabiner corrosion as it relates to caving - thought you lot might be interested to see it - Some pretty amazing destruction in a relatively short time. Apologies if it has been posted before.

Neil there might be a few candidates here for a gallery like your dodgy bolt collection :)

http://users.skynet.be/sky75112/avalonuk/discov/emotions_corrosion.htm

deadpoint

17-Jun-2004
6:09:57 PM

Yeech

rodw

18-Jun-2004
8:22:41 AM

Makes all those manky carrots look like bombers

shmalec

18-Jun-2004
1:00:14 PM

Whats Zicral?

I don't really find it all that suprising although they are interesting to look at.
There must be high concentrations of some mineral in that cave that is galvanically opposite to the metal in the biners.

deadpoint

22-Jun-2004
2:25:42 PM

Zinc coated aluminium

The Blond Gecko

22-Jun-2004
2:42:37 PM

Well, there's your problem. You don't need any strange minerals in the cave, just a bit of salt water. Aluminium has a higher electrode potential than zinc, so just like with chrome over steel, if you scratch it the aluminium will start to corrode in preference to the zinc. The salt has a dual role - providing a conductive path to complete the circuit, and breaking up the oxide layers on the zinc and aluminium to allow the corrosion to penetrate.

Rupert

22-Jun-2004
3:45:40 PM

I have a faint memory of fixing little metal ('aloominum'?) lumps to the underwater area of a steel boat my stepdad owned years ago. Would this have been to head off the corrosion before it started perhaps?

IdratherbeclimbingM9

22-Jun-2004
4:11:33 PM

Yes.
They are known as 'sacrificial anodes', and the idea is that they corrode/die instead of the supporting structure.
They are fairly commonplace in industrial applications, and often maintenance regimes are timed around their expected 'life'.

The Blond Gecko

22-Jun-2004
5:39:25 PM

Generally magnesium, actually (more reactive than aluminium, and no troublesome oxide layer to worry about).

shmalec

23-Jun-2004
12:46:56 PM

Hey Blondie,

I thought it was the other way around.

Magnesium,
Zinc,
Al,
Steel,
lead,
copper etc

Top of the list is anodic, bottom cathodic. So the zinc coating should "sacrifice" first...which is the way you would want it.

Stretching my high school chem now.... :)

I like the way it kinda looks fibrous.

PS Rupert I'm currently on a job for an american customer and being the groveling subcontractor type company that we are - we have to spell things their way ie aluuuuuuminum!

The Blond Gecko

24-Jun-2004
9:31:20 AM

My apologies - you're entirely correct! Must have been having a sleepy day...

Cool Hand Lock

7-Aug-2004
6:39:13 PM

Aloooominum. Is very reactive and oxidises rappidly. However the oxidised surface forms an in-penitrable layer that limits corrosion to the surface (ie annodised biners: which: have and additive to the oxidising agent for colour). If there is a salt in the rock that exfoliates the oxidised surface the aluminium underneath would oxidise quickly with only the oxygen in the air. Salt would speed this already rapid process. Or there maybe a salt which 'helps' oxygen into the aluminium, causing internal oxidisation.

There are 12 messages in this topic.