Sciencemadness Discussion Board

Which material is suitable for working with hot H3PO4?

guy - 11-12-2006 at 20:28

It attacks glass and most metals. Does it attack aluminum or copper?

Baphomet - 12-12-2006 at 04:46

What about a crucible made of a refractory material like Al2O3?

Organikum - 12-12-2006 at 09:36

Teflon. Several kinds of SS steel - the steel once passivied is mostly resistant against the acid.

unionised - 12-12-2006 at 11:00

Copper should be OK in the strict absense of oxygen. Aluminium might be a bit violent.
Al2O3 certainly should react, but it might be slow enough not to matter.
Aluminium phosphate is used as a ceramic but I think it might not stand up to the free acid.

Baphomet - 13-12-2006 at 04:18

I like the Aluminium Phosphate idea. Just guessing but would the phosphate ions suppress the donation of protons from the acid due to being the same as the acid's anion?

unionised - 14-12-2006 at 11:16

Actually, I suspect that you would get a whole mess of Al salts with
PO4---
HPO4--
H2PO4-
and lots of other things all of which would reduce the melting point of the AlPO4 untill it all turned into a liqid mess.
OTOH, I have't tried it; just don't try it with anything expensive first.

BromicAcid - 14-12-2006 at 16:01

To some extent this question was tackled in the thread on making polyphosphoric acids as dehydrating agents:

http://www.sciencemadness.org/talk/viewthread.php?tid=4409

Eclectic - 15-12-2006 at 06:45

Well, after reading through the post linked to above, It doesn't look like anyone has actually tested an alumina crucible to see if a surface layer of AlPO3 forms and protects the rest of the crucible.

Chloric1's breakage was likely due to thermal stress.