OT: Silica gel additives

Thoughts about what exactly? Yes, there are many, many dangerous chemicals. There are even more when you consider augmentation, two moderately safe substances have much greater risk when in combination.

What toxic materials are you referring to in humidity indicators?

--

  Rick C. 

  - Get 1,000 miles of free Supercharging 
  - Tesla referral code - https://ts.la/richard11209

Cobalt chloride and methyl violet.

"Thoughts" here means opinions about the risk vs benefits. Would you use them in your wardrobe, kitchen cupboard, toolbox, camera case and numerous other places where they can serve a useful purpose?

I remember reading a Reader's Digest article a long time ago that spoofed publications that go overboard with warnings against the possible side effects of new products and inventions. The article announced water as a useful but potentially deadly new product.

I don't remember all the details but the article described how a bucket of water is enough to drown a dozen people, a storage tank could wipe out a city, how it's made up of two dangerous elements and so on. I enjoyed the article and would like to read it again but I can't find it.

Good molecular sieve (5A grade) will adsorb about its own weight of water before saturating. Silica gel isn't as good as that, iirc, but works OK unless it's hotter than the vapour source.

According to wiki, the indicator stuff is either cobalt chloride or methyl violet, neither of which is good for you if it gets into your blood. But how's it going to do that? It's not as though silica gel is particularly appetizing stuff.

For some of our sensor protos, we use a mixture of ~95% 5A molecular sieve and 5% indicator silica gel, packed in bags intended for use in steam autoclaves for surgical instruments. You do have to calculate how much water is likely to get into the volume you're trying to keep dry.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

I doubt they will be effective against monsoon humidity levels left in the open. The only way you might do it is in a hermetically sealed room. Your best best is a chiller based air dehumidifier or aircon but they use a lot of electricity and still don't really hack it.

Don't eat it.

Snag is cobalt chloride salts were declared a suspected carcinogen (with a highish probability of being right about a decade ago). The silica gel with indicator in was banned fairly quickly after that in Europe.

When I was growing up cobalt chloride was the geek childrens' invisible ink of choice - way better than lemon juice (which is still allowed). I wonder how many chemicals are allowed in a modern childs chemistry set?

It is probably a bit of an over reaction but a suspected inhalation carcinogen (proven in animals) is not ideal in a dusty matrix.

--
Regards, 
Martin Brown

Unless small children were going to be handling it, I'd have no hesitation whatever about using indicator silica gel in one of those nice autoclave bags, but you have to calculate how much water is going to get in there. For instance, you might have 20C temperature swings on a daily basis, so that the air density in the confined space changes by

7% or so every day, even if it isn't out in the sun. Similarly, barometric pressure changes by about +-5% on time scales of a few days.

Based on historical temperature/humidity data, it isn't hard to estimate how much water is going to get into the box. If you don't use it often, putting the item into a loosely-fitting plastic bag will help a great deal in reducing water vapour ingress.

Look up 'dihydrogen monoxide' on wikipedia.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

There's been a few like that:

--
  Jasen.

It only works in totally unventillated, ie sealed storage.

Any ventillation at all will rapidly overcome silica's absorption capacity.

RL

+1 on air dehumidifier. I have two in my basement that keep the humidity at about 42%.

Dan

I've been thinking along the same lines, but not with molecular sieve. That is, plain silica gel with much smaller amounts of the coloured type in a separate sachet close by.

I can find only one source of molecular sieve here. It's 4A grade

- at 20 times the price of plain silica gel.

A good source of cheap silica gel here is cat litter. It does not have indicator. It comes from China.

John

cals. There are even more when you consider augmentation, two moderately s afe substances have much greater risk when in combination.

Cobalt chloride seems to be safer than methyl violet. I would use that if I had the need. But why would I use it in any of the places you mention? We have sufficient humidity around here that silica gel would need to be re activated or replaced every week in the summer. Much better to run the air conditioner and just get rid of the problem.

--

  Rick C. 

  + Get 1,000 miles of free Supercharging 
  + Tesla referral code - https://ts.la/richard11209

e l

nd

ated.

tain

n

ost

is

e

dry.

Really? They import cat litter from China? I'm surprised it is affordable . Cat litter is dug from the earth. Other than fancy marble and such, wha t rocks are dug from the earth and shipped around the world without having been refined in some manner to increase its value? I don't recall the pric e of litter, but I know it's not much per pound!

--

  Rick C. 

  -- Get 1,000 miles of free Supercharging 
  -- Tesla referral code - https://ts.la/richard11209

Silica gel cat litter? Surely it's made of clay.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Not strictly true, but as I pointed out upthread, you do have to estimate how much moisture is going to be exchanged and size the desiccant pouch appropriately. We do this in fire-detection sensors used on cotton harvesters--they undergo a lot of temperature swings, and the case has to have a small filtered air vent to prevent liquid water getting sucked in past the O-ring seals.

Turns out that 50 grams or so of Linde 5A is good for about 20 years. There's a T/H sensor on the board to make doubly sure that we aren't getting condensation on the board or the window.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Also look for dihydrohen monoxide.

Joe Gwinn

Just want to say... You do realize that not all of the desiccant has to be of the color-indicating type. You can just use plain white desiccant and sprinkle in only enough color-indicating beads that allow a visual indication of the dryness level.

1% or 2% color-indicating (by volume) should be plenty good enough for a visual. And so that's roughly a 98% reduction in toxic materials.

I still go with the high-octane stuff myself. And I prefer the blue-pink variety over the others as the color / condition is easier to judge. (IMO). The green/yellow (or green/orange) ones are only green & yellow at the extreme edges of dry/wet conditions. The blue-pink seems to give more range.

But desiccant comes in all kinds of crazy colors.

As I said in reply to someone else above, that's what I've been thinking. But I think it will be easier to 'read' the colour if the two types are kept separate.

I didn't know that. Thanks for the info.

icating type. You can just use plain white desiccant and sprinkle in only enough color-indicating beads that allow a visual indication of the dryness level.

a visual.

tion is easier to judge. (IMO). The green/yellow (or green/orange) ones a re only green & yellow at the extreme edges of dry/wet conditions. The blu e-pink seems to give more range.

It's been done already. I've seen canisters where only the top lid had color-indicating, but the re st of the container contained plain desiccant.

Here are two quick examples on Amazon:

el+Canister

ster