# Melting in air



## Joe Skulan (Mar 26, 2016)

Probably a stupid question, but if a PGM (or any metal) were heated to above the decomposition temperature of all of its oxides, but not so hot that the metal itself vaporized, would it not then be protected from oxidation even if exposed to oxygen?


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## Joe Skulan (Mar 26, 2016)

For example, let's say I wanted to make OsO4 (I know, I know) by passing O2 over hot Os metal. This would work only as long as the Os was under about 500°. Over 500° Os oxides are not stable and thus either would not form at all, or would form and almost instantly decompose back to Os metal and oxygen. Ir should not be able to oxidize above the decomposition temperature of I2O2, about 1100°.


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## Lou (Mar 26, 2016)

This is true and observed in most of these metals.


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## Joe Skulan (Mar 27, 2016)

In theory, then, one could melt Os with an oxy acetylene flame, which is just hot enough. One would warm the metal to ca 600° with an oxygen-poor flame, then burn off the deposited carbon with an oxygen-rich flame, and finally bring the metal to its melting point with a neutral or very slightly oxidizing flame, before cooling the melt under argon. 

But I guess that this would not work in practice. You'd probably get some Os carbonyl or other unwanted compounds, and it may be difficult to transfer enough heat to the Os to actually melt it. And you'd have to work on some extremely refractory and expensive surface, like hafnium nitride.


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## Lou (Mar 27, 2016)

It does not work. The heat density of a torch is much less so only small amounts will be able to be melted. This would be a very bad idea to attempt.

I have melted at most 5 g of Ir into a bead with O2/H2 and it isn't easy.


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