[jasongnome]

Purely for demonstration purposes I'm trying to do a long term demo with some of my students.

We were talking about tin allotropes and put some white tin (Philip Harris, granulated, 99.5% purity) in the freezer. Just the freezer compartment of a fridge. The aim is for it to undergo tin pest and turn into gray tin.

It's been there for nearly a year and there's very little change so far. On the very bottom of the sample, where it's touching the bottom of the glass beaker it has dulled, but not as much as I'd expected.

I've done some research and impurities in tin inhibit the process, unfortunately, the stock bottle doesn't list the impurities, it just gives the percentage.

Does anyone know of any way I can cheat to speed up the process? I know that once it's started it's supposed to speed up by itself as grey tin catalyses the process.

[AWK]

Check liquid nitrogen.

http://iweb.tms.org/pbf/jom-0106-39.pdf

[Arkcon]

The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation.

-- https://en.wikipedia.org/wiki/Tin_pest

Your freezer isn't cold enough.  Its just that simple.  A household freezer is 'supposed' to be -20 C.  We have a laboratory freezer rated for -20 C, its always at -18 C, until its opened, and then it can be anywhere until -12 C, when it alarms.  The guy who bought it gets defensive whenever someone brings it up.  But facts are facts.

Now, getting a tiny amount of germanium, the tiniest crystal, and melting it into the tin ingot.  Now that's cool.  But is it cheating?  I dunno.

[jasongnome]

Check liquid nitrogen.

http://iweb.tms.org/pbf/jom-0106-39.pdf

That's actually encouraging. It says in that article that at the temperature I have got in the freezer it will take over a year to see effects. It's been in about a year now, so we may see effects in the next few months. I did tell them when we put it in that it would be a VERY long experiment...

I wish I could source liquid nitrogen here, but at the moment it's eluding me. The problems of living in a small island country.

[jasongnome]

The transformation is slow to initiate due to a high activation energy but the presence of germanium (or crystal structures of similar form and size) or very low temperatures of roughly −30 °C aids the initiation.

-- https://en.wikipedia.org/wiki/Tin_pest

Your freezer isn't cold enough.  Its just that simple.  A household freezer is 'supposed' to be -20 C.  We have a laboratory freezer rated for -20 C, its always at -18 C, until its opened, and then it can be anywhere until -12 C, when it alarms.  The guy who bought it gets defensive whenever someone brings it up.  But facts are facts.

Now, getting a tiny amount of germanium, the tiniest crystal, and melting it into the tin ingot.  Now that's cool.  But is it cheating?  I dunno.

Possibly, but it's doable, I should be able to get hold of germanium on eBay. Thanks.