How to Recharge Silica Gel
Dave Martindale
>I want to keep the inside of my underwater video housing from developing
>condensation when it is taken into cold water. I have some silica gel
>from the local pharmacy. To be sure it will do the job I want to heat it
>to drive off the water. What temperature should I use, and for how
>long. Can I use the microwave or should I stick with the convection oven?
I have silica gel from two different manufacturers. One, packaged in small
glass containers, says "place complete unit in a hot (400-450 degree) oven
until crystals turn bright blue (about 20 min)". The other, in an aluminum
can, says "Place unit in vented 300 F oven for 3 hours (or until window turns
blue again".
So you want high temperatures for a long time - I don't think a microwave
would be useful, even for the glass-cased stuff that could be heated by
a microwave. Of course, microwaves won't penetrate the aluminum can at all.
Also, note that these silica gel packages are intended to be heated for
drying, and are made of glass and metal. I wouldn't try drying out
silica gel in a paper bag package - too much chance of fire.
>Does anyone know where to get silica gel that changes colour when it's
>used up?
The glass ones came from L.L. Bean a long time ago. The metal ones came
from Lee Valley, a Canadian mail-order tool company, but I think Edmund
Scientific carries the same ones.
Dave
j.tung
dsm...@nlnet.nf.ca (David Smith) writes:
> What temperature should I use, and for how
> long. Can I use the microwave or should I stick with the convection oven?
>
> Does anyone know where to get silica gel that changes colour when it's
> used up?
You can gleen some info from the Shutterbug ads for this stuff.
Basically, heating for an hour or so at 400 F should do it. You need
to encourage the adsorbed water to release from the silica gel. It
will not decompose with excess heating, although any impurities may
char. Silica gel is a type of sand/powdered quartz, of course. I've
never used a microwave on it, and considering the short times we're
talking here, I'd just stick with a conventional oven.
A common colored indicator is cobalt (II) chloride and goes from blue
to pink as water is adsorbed. A commercial brand is Drierite (actually
a whole series of compounds/products which adsorb different amounts of
water/weight at different rates). The problem with the indicator is
that regenerating the dry stuff involves heating in a vacuum oven,
since atmospheric pressure heating (probably the high oxygen content of
air is the problem here) results in decomposition of the indicator.
In a laboratory setting, we'd use a mixture of cheap dessicant with a
small portion of indicator. A good reference, available at most
university libraries, is a book called the Chemist's Companion. Tomes
such as the CRC Handbook of Chemistry and Physics, Lange's Chemical
Handbook, and [somebody's] Engineering Handbook will also contain
information about chosing dessicants. Personally, I'd chose one with a
larger grain size, just b/c I don't want the possibility of loose
silica gel banging around in a closed space with my camera :-).
Also, I'm not sure how much water and how fast silica gel adsorbs
compared to say calcium chloride or magnesium sulfate. The above
references cover these details, I'm not interested enough to go look
them up :-). Practically speaking, this may be a moot point, so don't
let this chemist get you sidetracked.
Sources: Edmund Scientific probably has pre-packaged sets; any chemical
supply house such as Aldrich, Fisher, Baxter, or Eastman Chemical will
probably be happy to sell you Drierite (or any constituent chemical) --
the problem will be whether or not you want as much as their smallest
package :-). These chemicals probably could be used in a dastardly
way, but my initial feeling is that they don't easily lend themselves
to various illegal uses.
jt
No opinions that my employer would acknowledge.
David Smith
condensation when it is taken into cold water. I have some silica gel
from the local pharmacy. To be sure it will do the job I want to heat it
Does anyone know where to get silica gel that changes colour when it's
used up?
David Smith
David Jacobson
A lot of Hewlett-Packard gear comes with silica gel packets in the
package. One kind is a sort of paper packet. The printed
instructions on it say to heat for 16 hours at 245 degrees F. (My
guess is that that is a rounded 120 C.)
Although it doesn't say anything about it, I chose to use an electric
toaster over as opposed to a gas oven, as the combustion of gas adds
water to the gasses.
-- David Jacobson
John Prosper
Porter's Photo sells slica gel packs which contain a color indicator
which turns from blue to pink whenever the dessicant needs
reactivation. Once it has reached a saturated pink hue, heat it in
your oven until it reverts back to blue.
You can order their catalog, Porter's Photo Catalog (Vol. A-55),
from them @ (800) 553-2001 from 8:00 - 4:30 Monday thru Saturday,
Central Time.
In case you need to order something immediately, I happen to have
my catalog handy:
Catalog # Description Price
35-0589 Blue Magic Moisture Absorber. $5.95
Absorbs moisture from relatively
compact areas (gadget bags, drawers,
chests, trunks, underwater video
housings?, etc. Supplied in
permanently sealed glass containers.
Should be usable in microwave ovens.
35-0022 Silica Gel Air Dryer $15.95
For larger jobs. One air dryer will
reputedly maintain a safe moisture
level over 2500 cubic inches of sealed
space. One set includes two metal
cartridges. DON'T USE IN MICRO
WAVE OVENS.
--
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| John A. Prosper | Internet: pro...@cs.fsu.edu |
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Joseph A. Cali
wrote:
> dsm...@nlnet.nf.ca (David Smith) writes:
> >I want to keep the inside of my underwater video housing from developing
> >condensation when it is taken into cold water. I have some silica gel
> >from the local pharmacy. To be sure it will do the job I want to heat it
> >to drive off the water. What temperature should I use, and for how
> >long. Can I use the microwave or should I stick with the convection oven?
>
> I have silica gel from two different manufacturers. One, packaged in small
> glass containers, says "place complete unit in a hot (400-450 degree) oven
> until crystals turn bright blue (about 20 min)". The other, in an aluminum
> can, says "Place unit in vented 300 F oven for 3 hours (or until window turns
> blue again".
>
> So you want high temperatures for a long time - I don't think a microwave
> would be useful, even for the glass-cased stuff that could be heated by
> a microwave. Of course, microwaves won't penetrate the aluminum can at all.
> >Does anyone know where to get silica gel that changes colour when it's
> >used up?
> Dave
The blue indicator is cobalt chloride so be careful about contaminating
your oven if you want to prepare food in it as well. Silica gel will
dehydrate quite well at much lower temperatures just above the boiling
point of water. You don't need to nuke it. A gentle heat is fine. In view
of the contamination problems in the oven, I'd recommend heating it in an
old discarded aluminium saucepan or a cheap one bought for the purpose, on
the lowest possible heat on the stove. Don't cook in the saucepan
afterwards.
From "Dangerous Properties of Industrial Materials"
The lethal dose for a child is 1.5 g/kg of body weight
The toxic dose for a child is 48mg/kg of body weight
Exposure being chronic or acute.
As hazardous materials go this is not too bad but I wouldn't go using it in
my oven or microwave unless i could give it a bloody thorough clean
afterwards.
--
Joseph A. Cali ph 61-6-2493246
Research School of Earth Science email joe....@anu.edu.au
Australian National University
Canberra 0200 Australia
mdu...@commerce.otago.ac.nz
>From: jaco...@cello.hpl.hp.com (David Jacobson)
>Subject: Re: How to Recharge Silica Gel
>Date: 19 May 1995 16:03:16 -0700
>In article <3p8qbj$4...@coranto.ucs.mun.ca>,
>David Smith <dsm...@nlnet.nf.ca> wrote:
>>I want to keep the inside of my underwater video housing from developing
>>condensation when it is taken into cold water. I have some silica gel
>>from the local pharmacy. To be sure it will do the job I want to heat it
>>to drive off the water. What temperature should I use, and for how
>>long. Can I use the microwave or should I stick with the convection oven?
>>
>>Does anyone know where to get silica gel that changes colour when it's
>>used up?
>>
>>David Smith
>A lot of Hewlett-Packard gear comes with silica gel packets in the
>package. One kind is a sort of paper packet. The printed
>instructions on it say to heat for 16 hours at 245 degrees F. (My
>guess is that that is a rounded 120 C.)
>Although it doesn't say anything about it, I chose to use an electric
>toaster over as opposed to a gas oven, as the combustion of gas adds
>water to the gasses.
> -- David Jacobson
Sorry Dave, a basic physics test would disagree with this. Regardless, I hate
gas ovens because they're dabnerous things, especially when unmonitored for
long periods.
Anyhow, the best way to dessicate silica gel is under sustained, moderate
temperatures. For example, on a sunny window sill for a good long day, or if
you live in a crummy climate, in an oven, at say 150 deg F for 3-4 hours. I
would recommend against very high temperatures as it tends to shorten the life
of silica gel (including the number of times it can be re-used.
cheers
Mike Duffy
David Smith
may have gone astray. If you have read this before, please forgive me.
I am wondering how to recharge silica gel. I use it to keep the inside
of my underwater housing from getting wet through condensation. I think
it can go in the oven, but for how long, and at what temperature?
By the way, a good source for silica gel is the local pharmacy. They get
it with their drug shipments and throw it out.
In addition to keeping the insides of video housings dry, it's good for
protecting your camera equipment in humid environments. I wish I had had
it when I was in Nigeria for a couple of years. My lenses developed mold
on the coatings. If I had kept the lenses in a ziplock bag or Tupperware
container with some silica gel, I would have saved my lenses.
David Smith