Originally Posted by Falanx (Post 15004786)

Iron, nickel, cobalt and gadolinium are the four elements that are ferromagnetic at room temperature. Bear in mind that paramagnetic materials can be attracted to a magnet, too, and there's bloody hundreds of them, including liquid oxygen.

Originally Posted by Falanx (Post 15004786)

Iron, nickel, cobalt and gadolinium are the four elements that are ferromagnetic at room temperature.

Originally Posted by ftwelder (Post 15008183)

Nickel? Oxygen? Really now?. :)

I have no argument but would a magnet really attract to liquid oxygen?

That spot rot tool is pretty neat.

Originally Posted by Italuminium (Post 15009572)

Another high school maxim busted! But since Stan came up with that awesome tool, could it (or a different version which can measure to a finer degree) be used as a way to tell tubing apart, or are the main kinds of tubing used too much alike in this department?

Originally Posted by Italuminium (Post 15009572)

Another high school maxim busted! But since Stan came up with that awesome tool, could it (or a different version which can measure to a finer degree) be used as a way to tell tubing apart, or are the main kinds of tubing used too much alike in this department?

Originally Posted by Falanx (Post 15009584)

Yep, seen it done. You pour out enough LOX into a boiling tube to chill and fill it, so there's no losses, suspended from something like a bench clamp with a bit of string and bring a strong magnet near it, it will pull towards the magnet. Oxygen is a diatomic gas, with a double bond, so that's four valence electrons used up between two atoms. That leaves two unbonded pairs of electrons on each atom (oxygen is 1s2,2s2,2p2 = 6, but a full 1 and 2 shell is 8 electrons). And unbonded pairs give fun electric behaviour, like paramagnetism. There's hundreds, if not thousands of compounds and materials with paramagnetic behaviour, just because certain electron configurations allow for it.



With iron and iron alloys specifically, magnetism is a function mostly of how much body centred (alpha- and delta- ferrite, or alpha- or epsilon- martensite) crystal there is there. Austenite does have a Curie point, but it's so far below zero you're essentially never going to see it, and some austenitic steels are metastable, so they transform to martensite long before they get that cold anyways. A magnet would give you some feel for how much of various crystal structures you had in your sample, but 50% martensite-50% ferrite is basically the same no matter what it's composition (within reason*), and the same for x% austenite-y% ferrite-z% martensite microstructures.

* Discounting strange alloys with huge amounts of cobalt, aluminium, tungsten, nickel and carbon, 'cause they were bred for magnetism and pretty much suck at being engineering alloys.

Originally Posted by bsektzer (Post 15072961)

FWIW, gaseous oxygen is paramagnetic too. There are medical oxygen analyzers that use this property to determine the % of oxygen in a gas sample.