Video Extras 5: The Reef Transcript

2 nails

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Follow Mike as he grapples with the corrosive effects of seawater, as part of the BBC/OU's programme website for Rough Science 5

Kate	Now then Michael B.
Mike	Yeah.
Kate	Can I make a little observation.
Mike	Yeah.
Kate	You're looking a little bit smug
[LAUGHTER]
Kate	Have you solved your corrosion problem?
Mike	I have. You realise - yeah, no - I was worried about the corrosion of the trip wire. So I did a little experiment last night. I look a nail like that.
Kate	Mmm. Mmm-huh.
Mike	And I just left it bobbing up and down in seawater.
Kate	Yeah.
Mike	Like our tripwire will be.
Kate	Yeah.
Mike	And look how it's rusted! Just overnight.
Kate	That's amazing, how much -
Mike	It's rusted.
Kate	Really has, hasn't it?
Mike	So we did need to worry about corrosion.
Kate	Yeah.
Mike	Now there are several ways you can stop that corrosion happening.
Kate	Yeah.
Mike	You could coat the wire in zinc, and that's - this screw is coated in zinc. It's galvanised.
Kate	Right, yeah.
Mike	You see.
Kate	It hasn't rusted at all no.
Mike	No, that's been in salt water overnight. Nothing.
Kate	So are you proposing to cover the trip wire in zinc?
Mike	[LAUGHS] No we don't have the resources to do that, no.
Kate	No.
Mike	But there's an even smarter way of dealing with corrosion. What we use is a bit of magnesium. It is more reactive than the iron in the nail. And it will react with the oxygen in the air.
Kate	Yeah.
Mike	It will corrode and it sacrifices itself for the iron. And you can see, you compare these two, they've been in salt water for the same amount of time. But this one has been connected up to magnesium and you can see, no corrosion.
Kate	That's extraordinary. So basically, the magnesium takes all the flack, if you like, instead of the iron.
Mike	That's right. It sacrifices itself for the sake of the iron.
Kate	So how are you going to build magnesium into the system? Does that mean you're going to now have to find metres and metres of the stuff?
Mike	We only need to put a little bit in and not many people know this, but a lot of pencil sharpeners are made of magnesium. The body of that is magnesium, so we just put that in, the appropriate point in…
Kate	What you just hang a pencil sharpener?
Mike	Yeah.
Kate	Within the system?
Mike	Yeah …
Kate	And that will do it?
Mike	It will stop our, our tripwire corroding. Er, strange but true. It's electro-chemistry.
Kate	Phew!