Does moisture escaping from powders decrease chamber vacuum?

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
2 replies · 2K views
Cleitus
I'm drying some wet powders using vacuum oven and start seeing some condensation on the window after few minutes. The vacuum level stays pretty constant which puzzles me as i thought that the moisture escapes from the powder into the air will increase the chamber pressure or decrease the vacuum. I then put my logger in and found out that the relative humidity (RH) increases even though the chamber is at -0.1 MPa. Since the RH increases, how do i ensure that my powders are completely dry?
 
Physics news on Phys.org
Out of curiosity, how does the RH meter you are using work? Is it supposed to work in vacuum?
 
Well the manual didnt specify whether it works under vacuum. Nevertheless, i went ahead and put it into check whether it logs the temperature and relative humidity. I can see the temperature stays pretty constant at 20˚C but the RH fluctuates depending on when I turn the pump on. At initial pumping, the RH drops and slowly increases after i stopped the pump. RH decreases again when i turned the pump on the second time. Btw, i placed a drop of water in a petri dish as an indicator assuming that when it dries out, my powders are dried.