I am curious about this, too. All of the information I could find about it is that Sodium Nitrite may explode on heating above 986
°F (530
°C), which, makes sense. Not what you were asking for though. Everything I've found related to storage of SN only states what happens when it's under
heat, not when it's cold.
It says to not "freeze", but I can't find what temperature that would be at. It's advised to keep it at room temperature which is typically around 59 – 77
°F (15 – 25 °C) I believe.
I don't know. I couldn't find anything helpful.
Counting it's a crystalline powder, I would have to assume that it wouldn't freeze too easily. For it to "freeze", it would have to turn into a solid (it's melting point, which in the image above is around 520°F (271°C), and I don't
think it'd turn into a solid around 30
°F. I don't know what happens when you turn it into a liquid though, counting water freezes around 32°F (0°C). You can supercool it, but again, I don't know anything about that.
I'm an idiot who doesn't know what I'm doing. I'm just trying to share what I found very briefly looking around. I'm sure someone smarter than me will correct the record.