AKICOLJ question

[philmophlegm]

OK, bear with me on this, because it will sound like a stupid question.

Whenever you see a lorry carrying scrap metal, the lorry trailer that carries the scrap will always be rusty. This seems to be the case even if the trailer is new and even if the lorry tractor is new and shiny.

Why is this? Is rust somehow contagious?

Comments

[miss-next.livejournal.com]

Yes. Yes, it is. I am not sure of the exact chemistry of the thing, but what I think happens is that rust is autocatalytic. That is to say, if you've got some rust, it will help to facilitate the formation of more rust if there is any untarnished metal in the vicinity. And that is why, if you're painting a metal surface that has any rust on it, you have to be very sure to remove all the rust first (except with some modern paints which are specifically formulated to stop the process). It's not just because rust makes the surface of the metal flaky; it's because, even if the paint remains intact, the rust will spread underneath it.

[philmophlegm.livejournal.com]

That makes some sort of sense. "Autocatalytic"...

[wellinghall.livejournal.com]

That's pretty much what I was going to say. Unfortunately, I stopped studying chemistry 29 years ago, so I've forgotten any additional detail I might once have known.

[wellinghall.livejournal.com]

And hence the reason why the sensible haulier will only ever use his oldest, rustiest trailer to carry scrap metal.