Silica gel - Page 1
Forum section: electronics / general

author: ipman
author_rank: Regular Contributor
timestamp: July 04, 2011, 04:40:37 pm
content: Does anybody use silica gel along with unused and stored tools?I use those crystals in some refrigerator bags to store unused accesories or even meters. For example, my Fluke i410 clamp is stored in such a bag, along with silica gel crystals to absorb humidity inside. The bag is hermetically sealed, so they will absorb much of the humidity inside, making that bag a dry atmosphere.I even put some crystals in the DMM itself, near the fuses. Even with Fluke 189 which is not waterproof, but quite sealed, I was suprised to see them wet.Recomandation: use the color changing ones, the best are orange/green ones, which are not toxic at all. The blue/red are toxic unfortunatelly, but if you are not going to eat them, they will do no harm.

author: Richard W.
author_rank: Regular Contributor
timestamp: July 04, 2011, 05:37:55 pm
content: Quotethe colour pigment in the blue-red silica gel is carcinogenic because of the cobalt. even the dust is dangerous.QuoteThe silicagel in the meter will draw water, from everywhere! even through the small gaps in the housing. Now you have more humidity in the meter than before. If the meter gets warm, the silica releases the water now you have even more water inside.The solution with the fridge-bags is much better!If i don't use my testgear, i put it in a big aluminum box with a can of silica.Everything below 50% rh should be fine.Important for accuracy is a constant climate. Fast changes of humidity and temperature should be avoided.

author: ipman
author_rank: Regular Contributor
timestamp: July 05, 2011, 04:37:41 am
content: Silica gel will not release the water by just sligthly heating them. They need at least 100 degrees celsius, 120 recomended by the manufacturer, for two full hours to release the water they accumulated.And, on the other side, the multimeter is not waterproof, but quite sealed. So the air from outside has no means to get sucked inside, and if it does, the humidity will go to the silica gel which is near fuses.Correct me if I am wrong about it.

author: Richard W.
author_rank: Regular Contributor
timestamp: July 06, 2011, 07:59:12 pm
content: Quote from: ipman on July 05, 2011, 04:37:41 amDrying works as long as the gel isn't fully saturated.If it is saturated, the gel stabilizes the humidity.This stable humidity is maybe higher than the current humidity in the air.

author: ipman
author_rank: Regular Contributor
timestamp: July 06, 2011, 08:03:27 pm
content: Part correct. The gel has the indicator, so you know when it's saturated. And when it does, it's surface is full of water, but will not atract anymore or release it, because the bonding is very strong.Given the fact that the crystals are away from PCB in the fuses compartment, I say this may work somehow. The air inside the meter is hardly moving at all.

author: Richard W.
author_rank: Regular Contributor
timestamp: July 07, 2011, 01:24:39 pm
content: Silica gel releases the water at high temperatures and/or low humidity.It is also used to keep the humidity of food at a constant level. Thats what a manufacturer said.But of course, i can not proof this.QuoteMaybe, its not harmful to the meter, but when the gel is saturated then it is useless.So you have to change/dry the gel very often.I wouldn't like to open and close my meter all the time, but thats a personal decision.The idea with the fridge-bag is much better

author: XynxNet
author_rank: Regular Contributor
timestamp: July 07, 2011, 03:36:22 pm
content: In my opinion there is no reason to use silica gel in normal conditions (european climate).Sure humidity changes, but it seldom reaches problematic levels and as long as there is air exchange, any moisture evaporates fairly quick.The one exeption is storing wet gear in some sort of airtight container or sealing airtight containers in humid conditions.I suspekt manufacturers use silica gel because many products are boxed in countries with high temperature and high humidity, which produces problems with condensation while shipping those products in colder climate (container ship) or to countries with lower average temperatures.

author: ipman
author_rank: Regular Contributor
timestamp: July 07, 2011, 06:07:10 pm
content: Wikipedia says that it will release the humidity only above 100 degrees celsius and slowly. The waters molecules are "glued" at the surface of the silica gel, which will not realease them easily.That material is used also in wave guides to prevent arching.

author: rf-loop
author_rank: Super Contributor
timestamp: July 07, 2011, 06:26:39 pm
content: Wikipedia.. really reliable source for knowledge...keep smiling..Demystifying Silica gelAnd if it is not enough, there is also list of references for reading (if find).So this can also use as buffering RH (as stabilisation), not only for "drying" or "keep dry".This is not any question if need in europe or not. Many cases it need.Also in europe we go many times over dew point and if some surface have lower temp as dew point then water gas condensate to surface. So example inside closed package air may need "dry" so that dew point go lower as expected temperature in transport or store time. Specially things what are nearly hermetically sealed OR if temp change is fast.You can test it. Put your camera to +3. Wait rainy day. Take it out... why? What if you have packaged it with air +25 and relative humidity (RH) example 70%. What is dew point? Put it with this air to sealed plastic. Go under dew point. Do you like wet camera. Do you like if inside objective between lenses are water... how if this water stay there 3 months in some stock. How about electronic... maybe there are real time battery inside...We need it in europe, in america, in china, in alaska, in south africa all over this Tellus.But it need littlebit understand basic fundamental physics.

author: ipman
author_rank: Regular Contributor
timestamp: July 07, 2011, 08:04:31 pm
content: Forgot to mention something: water molecules adheres to silica gel surface only when they are near, it will not attract humidity like a vacuum cleanerThe insides of the multimeter are not air-tight, but air is not able to move freely because of PCB-s, the components themselves, etc.

author: pirulo123
author_rank: Contributor
timestamp: July 08, 2011, 01:17:19 am
content: What a coincidence!, I was thinking about using them everywhere I stock my unused parts,I read about the popcorn cracks in IC's a few days ago and I got really worried because humidity here is very high.Since baking the components it's quite hard and difficult and expensive ! I'm going to buy silica bags to protect everything in the lab ! ;-)Everywhere in the lab I've stuff that can cause cancer... It seems everything can cause cancer this days... I don't care... I wont wear a thin foil hat to protect my brain from cosmic rays....

author: ipman
author_rank: Regular Contributor
timestamp: July 08, 2011, 06:51:20 am
content: Buy orange-green silica gel, it's not toxic.Blue/red one contains cobalt, which is toxic/carcingogenic.

author: flolic
author_rank: Frequent Contributor
timestamp: July 08, 2011, 07:40:59 am
content: Quote from: ipman on July 07, 2011, 08:04:31 pmYou would be surprised how moisture pass through seemingly airtight housing. Believe me, I know what I'm talking.I have cooled astronomical camera which must be without any humidity, otherwise moisture condenses and freezes on the imaging sensor. I do my best to make it airtight, but at the end I must renew silica gel every few months because moist (air) still creep in through microscopic imperfections on seals...Every change of temperature makes the air change its volume. During winter, if you take your instrument from heated house out, as it cools it will suck in cold moist air. Do the math

author: ipman
author_rank: Regular Contributor
timestamp: July 08, 2011, 03:55:34 pm
content: You are right, but a couple of months is long enough, given my meter has some 70 hours battery life (official).That meter does not leave my house. Allmost never, I have another one for field use.

author: ipman
author_rank: Regular Contributor
timestamp: January 03, 2012, 09:42:31 am
content: Time to bring back this topic back to life.Afther more than 6 months, the silica gel crystals were saturated and I regenerated them by reheating. This seems to be a good life, not much humidity going in through the sealed plastic bag.Also, the few crystals inside the meter beside the fuses were also saturated, so I replaced them also.In the mean time, I found some paper bags filled with silica gel from shoe boxes. The content is generally transparent balls, but some of them are yellow or even orange. Cannot figure out what should be inside, anyone have silica gel expertise to help?

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 03, 2012, 12:29:38 pm
content: i heard last time humidity can go through wall/concrete and its possible where the air/heat going in one direction but humidity going the other/opposite way. the only way (i know) to release humidity/water from silica is by heating it (above water boiling point i guess). i dont quite see the point to protect electrical (excluding high precision thousands of dollars) equipment from humidity, they should be able to withstand it? but if you are really serious about humidity protection, get a drybox. i've been reheating silica for so many times until i got feed up.

author: ipman
author_rank: Regular Contributor
timestamp: January 03, 2012, 02:00:47 pm
content: Silica gel will never dry the air completely, there are other chemicals to do that.Yes, they are supposed to withstand humidity, but it will not hurt to bring RH to around 40% or lower, because at this limit any humidity-related corrosion is inhibited. And 40%RH is obtainable with an ordinary fridge sealed bag for aliments.Silica gel can be regenerated countless times if you don't go above specified temperature, usually 120 celsius for indicator type.But what confuses me about the paper bags is that some of them contain mostly transparent balls, but there are also some yellow or orange ones among them. I don't know why, maybe the colored ones are indicator type?

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 03, 2012, 02:39:54 pm
content: maybe the colored one is more toxic or more expensive? thats why its only a few.

author: ipman
author_rank: Regular Contributor
timestamp: January 04, 2012, 08:21:18 am
content: Only the blue one contains cobalt, which is toxic.The orange-yellow ones do not contain cobalt, so they are safe (non-toxic to humans). Tough, it's not recommended to eat them, because if you eat a considerable amount, they will dry body fluids considerably low.