Silica Gel Drying

So it’s time for the whole pile of silica gel to go into the oven. The various packages suggested something around 12 hours at about 250 °F, so I set the oven timer for 11:59 and let it cook overnight:

Assorted Silica Gels

Assorted Silica Gels

The granules in the trays go into sealed glass jars, where they will remain dry until needed. The assorted beads & kibble in the plates get bagged up and go in the fireproof safe along with the big bag in the front, where they ought to be good for maybe half a year. It’s a new safe, so we’ll see how that works out; I tucked a note with the weights inside the safe.

I found a “sealed” plastic bucket of assorted packages that I’d dried and weighed a decade ago and then lost in the back of the shelf. It had gained 2 ounces, but the packages have rotted out and the beads weren’t in good shape; they were the consumer-grade bags that aren’t intended to be dried and reused.


  1. #1 by Erik on 2011-09-15 - 10:03

    Hmmmm… so I’m wondering where this leads? Some years ago I had the misfortune of putting steel stuff in a “fireproof” safe. I came back a few months later and it was all rusted. Turns out that many (including my) “fireproof” safes use a double wall, and the inside layer is packed with silica gel saturated with water. The idea being that if there’s a fire, the fire has to boil all that water before the inside gets over 100C. Side effect of that is that the inside of my safe ran about 100% humidity. So, are you going to use silica gel to dry the air made humid by saturated silica gel? Anyway, my safe is now a printer stand.

    • #2 by Ed on 2011-09-15 - 11:35

      the fire has to boil all that water before the inside gets over 100C

      That’s true for the “media safe” out in the garage, but this one seems to have a solid plastic liner with a seal around the lined door. At least to a first approximation, the concrete / gel / gunk in the double-wall outer shell should be isolated from the interior.

      Now that you mention it, though, I should toss a data logger in there and record the humidity for a while. Dry silica gel should hold it at about 40%, which is enough below the basement’s (expensively maintained) 55% to make the gel’s end-of-life obvious.

      Thanks for the reminder!

  2. #3 by Raj on 2011-09-16 - 03:17

    I usually put the silica paper bags directly on my lab hotplate and set it to 60C (arbirary value IMHO, probably low heat setting) and cover the bags with a 2L beaker. You can see the water condensing inside the beaker. I wipe it off every few hours till I see no more condensation. Now they are ready for re use.

    • #4 by Ed on 2011-09-16 - 08:37

      I like the direct feedback: heat until the water stops coming out.

      Next time, that ancient aluminum griddle / hotplate / warmer I use to warm PCB etchant should do the trick …


      • #5 by Raj on 2011-09-17 - 03:44

        Ed, there was some manufacturers who made colored silica gel. The color changed from blue to white. Heating would restore the color and that was a good indicator. At the farm during the rainy season we need it badly to prevent cameras and such from getting ruined from high humidity.

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