Dumb question: Does Magnesium rust?

[Paul-V.]

Sorry for the stupid question, but I actually know little about magnesium. I know about aluminum engines, but nothing about magnesium. I know it's lighter, but softer than alumninum. But does it ever rust or corrode? Thanks.

[rstoll]

Won't rust, will corrode, and it will burn. Back in '74 I worked for a chainsaw manufacturer. The engine crankcases, handles, fan housings etc were made of magnesium.

At the end of each day they would burn off the excess magnesium dust resulting from grinding and such. The prodcedure was to pile up the magnesium behind the factory, a maintenance worker stood about 40 feet away from the pile, lit a railroad flare and threw it onto the pile. It burned so brightly you couldn't look at it.

One drizzly day, when he lit the flare he was burned to death. It seems water and magnesium form a gas that is highly explosive.

Two men were also killed one morning as they ground burrs from parts. A witness to the accident told me they were both wearing blue jeans and jackets. When the mag flashed, the mens clothes were instantly burned away. They died at the scene.

I think they used to make photographic flashbulbs out of magnesium years ago too.

[Zeke]

It's a non-ferrous metal and as such, it corrodes. Very reactive to salt. Pure magnesium is very reactive, period. You might remember in your high school chemistry class that it had to kept submerged in water. Out of water, it cumbusted spontaneously.

Edit: Looks like by the above post, I am wrong about the water. It was kept from the air, I remember that.

[304065]

It was a principal ingredient in the Incendiary Bombs used during WWII.

There's a picture of a 914-6 on Otto's web site- evidently the guy had a fuel line fire which led to the engine burning, and Otto said the magnesium case lit off and it was show time.

[eion]

Originally posted by Zeke914
It's a non-ferrous metal and as such, it corrodes. Very reactive to salt. Pure magnesium is very reactive, period. You might remember in your high school chemistry class that it had to kept submerged in water. Out of water, it cumbusted spontaneously.

Edit: Looks like by the above post, I am wrong about the water. It was kept from the air, I remember that.

Many non-ferrous metals don't corrode (and ferrous metals do - rust) - for example, gold and platinum. Magnesium *reacts* with water to form hydrogen - the explosive gas mentioned earlier - so keeping it under water would be the last thing you'd want to do. It'd be oil it was kept under, but it's not really necessary for magnesium - certainly *really* reactive metals like sodium would be kept under oil. Magnesium does not spontaneously combust on contact with air, otherwise I know a few people who would have some engine problems.

[DonNewton]

And after all these years of being the "fire marshall" on US Navy ships, I thought magnesium burned anarobically. About the only way to get rid of it is to submerge it, and let it burn out. Of course, the fire triangle (heat, fuel, oxygen) must be satisfied for combustion, once magnesium lights off, it does hate to extinguish.

[andrew15]

Hey Zeke914:

I seem to remember that the magnesium we used in science was stable in air but reacted violently with water. I think that it was a spool of thin ribbon, and that we would just rip a piece off and toss into water. Pure SODIUM however was kept in a jar of oil and was dealt with very carefully.

In terms of Magnesium alloy reacting to various stuff- I looked at the engine of a 911 that had been recovered after 12-16 months submerged in a river. It was downstream from a industrial mill of sorts and while the aluminum parts (like the heads) were ok, the Magnesium case showed signs of extreme corrosion. The only texture I can think of is a sea sponge (like you can buy in bath stores). It was pitted very badly and seemed to have been 'eaten' by the river and the chemicals from the mill.


Regards,
Andrew M

[andrew15]

looks like eion beat me to the magnesium / sodium thing.

Regards,
Andrew M

[Paul-V.]

Okay...let's see...used to make incendiary bombs in WWII, explosive reaction with water and/or air (depending on whose take you go with but either one is a pretty common on the planet earth), corrodes like a coral reef when submerged in water, and the METAL can actually catch fire.....Second question I have is, umm...why do I WANT an ENGINE made out of magnesium?

[Zeke]

My batting average is pretty low for the last couple of days, but I'll try again.

Originally posted by Paul-V.
Second question I have is, umm...why do I WANT an ENGINE made out of magnesium?

You don't necessarily. The aluminum TypeIV engine found in the 914 is much stronger than the magnesium TypeI found in the VW bug. And you must have read here on this board how the aluminum 3.0 motor and its evolutions from '78 on is prefferred to the earlier versions which are magnesium.

[beepbeep]

1. Cases are made of magnesium-alloy, not pure magnesium.
2. They are made that way in order to be as light as possible.
3. Magnesium doesn't combust spontaniously and doesn't need to be kept under water (but some other light metals do need to)
4. Magnesium needs oxygen to burn and it burns very hot

[Early_S_Man]

Once 'lit off' ... magnesium will burn under water using the air dissolved in the water, and you can't use water to put out a magnesium fire, because the water just turns into steam ...

Sodium and Lithium react violently with water, but it isn't a 'fire' in any sense of the word, and nowhere as hot as a magnesium fire ... and have to be stored under oil.

Pure Phosphorus can be stored under water or oil, and DOES spontaneously 'catch fire' when exposed to Oxygen or air ... and Phosphorus is used in incindiary bombs (still made today in the Army munitions plant outside McAlester OK) to 'light' the Magnesium component!

[rstoll]

Phosphorus is also used in older domestic kitchen ovens. The capillary on the control thermostat is a real light show if it happens to break.

[TimT]

Im sure many of you will remember from your boy scout days... a block of grayish metal with a flint embedded on the side... you would shave some of the metal onto your kindling.... then strike the flint with the back of your knife....... the metal shaving would ignite...viola!!!!!MAN MAKES FIRE!!!!!!

thats metal block was magnesium


and in technical terms magnesium oxidizes..... rust is a catch all phrase for metal oxidising

[beepbeep]

Uhh...yes, lithium reacts with water...
Silly how you forget all those chemistry lessons...