Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Freeze drying Phosphoric acid

  1. Oct 14, 2015 #1
    Hello all.
    I have carbonaceous material soaking in Phosphoric acid. I'd like to anneal it under an inert environment to activate the carbon. One method used in literature involved freeze drying the mixture and annealing it as is, as opposed to filtering or centrifuging the mixture. However, I am limited to a regular household freezer and a vacuum chamber. Does anyone have recommendations on how to achieve this with specialty tools?
  2. jcsd
  3. Oct 19, 2015 #2
    An update.
    I built a small size vacuum chamber and placed the Phosphoric acid soaked material in a petri dish inside the chamber. After pumping the air out, I place the chamber in the freezer. After 24 hours there was build up of sublimated vapor in the chamber, so I pumped that out one more time and replaced the chamber in the freezer.
    This is likely to fail. Here my opinion on why drying this into a powder would not work using this method: Freeze drying requires a continuous suction to extract the phosphoric acid vapors out of the chamber. This is would likely not happen using my contraption as my suction is not continuous and hence what I am doing is freezing a substance under vacuum. I'll keep at it for a few more days and update on the progress.
  4. Oct 19, 2015 #3


    User Avatar
    Science Advisor
    Gold Member

    What are you actually trying to do ?
  5. Oct 19, 2015 #4
    Well, the idea is to dry this carbon which is soaking in Phosphoric acid to obtain carbon-phosphoric acid powder to be later activated at high temperature under inert environment. This creates surface groups on the carbon as well as increases porosity.
  6. Oct 26, 2015 #5
    AN Update:
    Contrary to my expectations, it worked! the gooey phosphoric acid soaked material turned into powder 4 days later. If anyone is interested in the vacuum chamber schematics, let me know.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Freeze drying Phosphoric acid