Sodium in Dry Air

[jqavins]

Apropos of nothing, does anyone happen to know if the oxide layer that forms on sodium is mechanically stable, passivating the metal beneath, as happens with aluminum? Or does it flake off or otherwise allow oxidation to continue through the volume of the metal? Note, I'm specifying dry air.

After a bit of Googling, I'm thinking I might have to just try it. But first I thought I'd ask the nerdiest bunch of nerds I know.

 

[tsmith1315]

We have a little bit, but there’s no dry air down here to try that out!

 

[Johnly]

It doesn't self-passivate and will form a porous oxide layer that will allow continued oxidation.

 

[prfesser]

Can only describe my experience with small amounts of sodium. The oxide layer will come off, not as easily as rust generally does from iron, more easily than aluminum oxide flakes off.

Used to do sodium fusions---drop or two of unknown organic compound on a molten small-pea-sized piece of sodium. Usually not as exciting as you might think...though once in a while.... I usually scraped the sodium reasonably clean. Took a little scraping but wasn't too hard to remove most of the oxide.

 

[SolarYellow]

I reckon there are very few places on earth where the air can be considered dry in context of sodium metal being exposed.

 

[Funkworks]

Metallic sodium in a starring role. The narrator uses "tarnish" to describe the oxyde layer.

 

[jqavins]

I reckon there are very few places on earth where the air can be considered dry in context of sodium metal being exposed.

Except inside a small box with plenty of desiccant., which is what I would have used had I decided to try it. But now I don't have to.

The random thoughts wandering around my head went like this: what if I needed an oxygen free box for some process or other. I could use a nitrogen or argon purge, but I'd want an oxygen getter as well. Now, if the process is hot and some H₂O and CO₂ won't hurt, then even a bit of shredded paper would do, but what if I want it to work at room temperature, or gaseous products would be a problem. Maybe sodium would work? Honestly, if there was any stage in the train of thought before that, like why I was thinking about oxygen getters at all, I don't even remember what it was.

Thanks.

 

[OverTheTop]

What about granules that can adsorb the O2? We use them in a PSA (pressure-swing adsorption) nitrogen generator.

 

[Funkworks]

What about granules that can adsorb the O2? We use them in a PSA (pressure-swing adsorption) nitrogen generator.

I'm pretty sure metallic sodium would also react with O2 in dry air. It would just take longer. But the warmer it is, the faster the reaction.

 

[OverTheTop]

I'm pretty sure metallic sodium would also react with O2 in dry air. It would just take longer. But the warmer it is, the faster the reaction.

Yep.
https://en.wikipedia.org/wiki/Arrhenius_equation
But the nitrogen generator granules are less fire-prone
You also get to remove the oxygen that has adsorbed on the granule surfaces, and re-use them.

 

[cautery]

I reckon there are very few places on earth where the air can be considered dry in context of sodium metal being exposed.

Southern Sinai desert at night when the winds switch to come FROM the desert. So hot and dry that folks sleep outside on the roof.

I can come up with a couple more but you wouldn't want to go there to do Na experiments.

 

[Grog6]

Cesium, uranium, and Plutonium are way more pyrophoric. Thankfully, those are hard to come by.
l

 

[teepot]

Our humidity here is usually single digit in the summer. In my house right the humidity is too low to measure.

 

[jqavins]

Cesium, uranium, and Plutonium are way more pyrophoric. Thankfully, those are hard to come by.
l

And of course, I didn't want something too pyrophoric. It would need to be just pyrophoric enough. Cesium and rubidium crossed my mind and were rejected. Maybe potassium wouldn't be too aggressive. Lithium is a wimp.

 

[Johnly]

You might want to look for calcium turnings.