Silica Gel vs. Alternatives

Are there really better alternatives on the market to silica gel packets? What

might any of you use? I heard one can go make their own packets by scooping in

a "required amount" in whatever sized packet. I need something for a BIG storage

trunk inside a small apartment that contains even smaller boxes of slides/camera

gear.

You can buy CaSO4 under the brand name of Drierite. The indicating type turns pink when it is exhausted, but you can heat it in an oven at 400 C to dry it out an reuse it. It will be blue when it is ready to go again. I don't know how practical it would be for you, but in a lab environment it works well.

 

Perhaps you would be better off sealing the individual smaller boxes in zip-lock bags.

I hear that Kitty Litter is mostly silica gel. You might even be able to buy generic silica gel from pet stores.

No, "kitty litter" is mostly <b><i>clay</i></b>, although some types contain small amounts of silica gel. Google it. Not a good substitute for real silica gel.<p>

 

Sal B.

Sealing in zip-lock bags without a drying agent is no good as you will just end up sealing the moisture in - fungus will get by just fine in these conditions as the spores get everywhere and are already present. Sealing with a drying agent should work fine for years at a time if needed - there are still spores present but they will remain dormant in dry conditions (of course, if humidity later goes up somehow, through a broken seal perhaps, then you will have a fungus problem at that time).

 

If you are lucky enough to live in a low-humidity area (like me) then you can get by without drying agents, but then I wouldn't seal the items up either.

You can get plastic tubs of silica gel with a plastic grille at the top for bigger areas in different sizes. The gel is arranged in layers with some type of special material so the moisture gets trapped even more. We used one of the biggest ones to help dry out our bathroom after there was a problem with the roof and it became damp. You can buy them at the supermarket, they're not expensive at all. Perhaps you could put sachets in each small box, and then a tub in the storage crate?

<i>Sealing in zip-lock bags without a drying agent is no good as you will just end up sealing the moisture in </i><P>Sorry, I left out the part about sealing them with the drying agent. I would be worried that if the boxes are just placed in a trunk, you would probably exhaust the desiccant quickly.<P>I should have typed: "Perhaps you would be better off sealing the individual smaller boxes in zip-lock bags <I>with desiccant packets</i>"

I use a product called Zorb-it for my camera bag and for the lens trunk for my 500mm lens. Seems to work okay. It (the dessicant pack) swells up in high humidity to soak up moisture and shrinks when the air is dry. I used to have a big bag (4x6) of silica gel in my camera bag but I remember reading somewhere that eventually it loses its ability to absorb moisture over time. Not that I had any real problems with silica gel. So, I think it should be fine for your application taking into account the size of your storage trunk to determine the amount you need.

Yes Jam, I've just learned about Zorb-It. Is it really all that BETTER than silica-gel?

I don't have a scientific/definitive yes or no answer or a way to quantify its(Zorb-it) abilities compared to silica gel. All I could say is it seems to be working for me. I noticed that in dry climate, like during winter with the forced air heater on(low humidity) the dessicant packs have shrunk. Now with summer and more humid weather arriving the packs are expanding. I assume they are absorbing moisture.

Yes, there is silicate kitty litter complete with the blue moisture indicator. Cheap and available at your local supermarket.

<p>See here for a technical analysis of various desiccants:<br>

http://www.sorbentsystems.com/desiccants_charts.html</p>

<p>I would ignore the table "Properties of Absorbents" as they seem to be biased towards the conditions which favor molecular sieves.</p>

<p>Conclusions: Silica gel, clay and molecular sieve can all absorb the same amount of water within the first 2 hours at 75% RH. For more extended time periods, silica gel is the clear winner. <br>

Condensation occurs at 100% RH, this is what can damage electronics so this is what should be avoided. From figure 2 we see that most forms of dessicants become saturated and their performance asymptotes as RH is increased...except for silica gel, the one exception that continues to absorb more and more the closer you get to the dew point.<br>

By the time condensation occurs, silica gel will have absorbed 35% water by its mass, whereas CaSO4 ( Drierite) will have only absorbed 10% by mass. In other words, you need a ton of Drierite to absorb the same amount as Silica gel. Not only that, but from fig 1 it is more than twice as slow as silica gel to absorb that water.<br>

Below 40% RH, silica gel does not do so well...better choices for this lower humidity point are CaO and molecular sieve (synthetic zeolite). However, from fig 1 we see that CaO is extremely slow to absorb.</p>

<p>From fig 3 we see the real advantage of Molecular sieves are that they continue to hold their moisture as the temperature heats up, meaning that they trap/hold onto what water they absorb more reliably. Silica gel doesn't do very well above 100 degrees F. However, if your intention is to use the gel to prevent condensation when moving from cold outdoor temperatures to warm indoor temperatures, this does not matter at all.<br>

In fact, it is a good thing...it means that you can heat it up in the oven and reuse it, whereas the molecular sieve has trapped the water permanently. <br>

Now silica gel is by far the most convenient, you probably have some free samples that you received with your electronics...its cheap to buy, reusable, and you don't require much of it. In contrast, the other alternatives are slow to absorb, quickly reach saturation, aren't reusable, and can be extremely expensive (eg, molecular sieve). </p>

<p>I guess there's a reason why electronics manufacturers all use silica gel..</p>