[browncoat5871]

I am wondering if people could give me any tips or pointers for a project of mine.  I have to grow a large enough sodium nitrate crystal in order to demonstrate gliding.  I've filtered the sodium nitrate several times to remove any non soluble impurities and formed seed crystals by recrystallizing a small amount twice.  I'm using a closed Erlenmeyer flask in a hot water bath with temperature control and a small jet to move the water around.  I've found that crystals begin to form on the flask at roughly 45°C, but any higher than that and the seed crystal dissolves before it can grow.  I've attempted to use larger seed crystals, but they have too many faces and seem to grow crystals on top of the seed instead of the seed itself growing. 

I know that this is not a very easy crystal to grow, but at this point I don't have a choice but to keep at it.  Any helpful hints or tips would be appreciated.  Thank you. 

[Furanone]

check this out:

https://www.youtube.com/watch?v=FKCS1DvORug

[browncoat5871]

Thanks for the video, but the crystals that they are growing are losing heat at a steady rate.  Sodium nitrate crystals, if you want a large, uniform crystal without nucleation happening in random sites the temperature has to be lowered at steady rates.  Thanks again for the help though.

[Enthalpy]

Semiconductor producers would say: grow your crystal by a Czochralski process
http://en.wikipedia.org/wiki/Czochralski_process
The result will be perfect, but the process is probably more refined than what you want to do.
http://www.chemicalforums.com/index.php?topic=65386.0
further crystallization happens only at the crystal because the controlled conditions (temperature) favour the solid only there.

By the way, I know it's done for molten materials - but dissolved ones may be new.

Since sodium nitrate melts at +308°C, you might try to crystallize the liquid? Not much room before decomposition, though. It enables the easier Bridgeman process
http://en.wikipedia.org/wiki/Bridgman%E2%80%93Stockbarger_technique