Sciencemadness Discussion Board - Silica Gel

Silica Gel

FGP - 20-11-2003 at 07:06

Has anyone on this forum ever tried regenerating silica gel in a micro wave oven?
Comments & advice please.

Mumbles - 20-11-2003 at 14:30

I don't see why it wouldn't work. I've done Magnesium Sulfate in the microwave before. It should theoretically work. I'm not the highest authority on these things though. I would recomend doing this in a microwave not used for food purposes though. Judging from the warnings from the ones in my shoe, they're not to pleasant to the human body.

Marvin - 20-11-2003 at 18:13

Silica gel loses its ability to dehydrate if its overheated. If theres one thing microwave ovens do very well, its make hotspots.

I have yet to be convinced that microwave ovens can be considered to have any use in a lab, even a home one.

FGP - 21-11-2003 at 02:26

Thanks Marvin. I'm inclined to take your advice although the supplier of the silica gel thought it okay to use the microwave.
Like you, I have doubts. You don't have a reference confirming the degradation of silica gel by overheating do you?
Fred. (FGP)

vulture - 21-11-2003 at 14:15

Annealing, heating a material above a certain temperature for a certain time is widely used to make materials inert.

Fused MgO won't dissolve in acid, but fresh will.

The same thing happens with SiO2 when it's overheated, it forms larger crystals and the molecules come together.

Mumbles - 21-11-2003 at 15:48

Perhaps you should just try a small amount, to see if theres any degradation of the absorbtion. Silica gel, is fairly common and not very expensive, so if lets say 10 grams is annealed and no longer absorbs water, its not a great loss.

Just curious, but what brought about this question?

KABOOOM(pyrojustforfun) - 21-11-2003 at 20:38

I make my own silica gel from sand (preferably fine. and rich in SiO<sub>2</sub>

wash the sand with hot water then pour the washed sand in a jar and slowly add Hcl (starts to bubble) till it covers the sand. stir occasionally, if it doesn't fizz when you stir you can decant the acid wash several times with water . put the sand in a cheap/useless glass jar and pour NaOH sol. after a week filter the remained sand and neutralize the filtrate with HCl within a few minutes a gel/film with a very artistic scene becomes visible...
it was how I did but now I think purification of sand (neutraliing the insoluble carbonate/hydroxide with acid) is not necessary.<a href="http://www.angelfire.com/rnb/pjff/wetsio2.jpg">the gel just after filtering</a><br><a href="http://www.angelfire.com/rnb/pjff/drysio2.jpg">the same after a week or so</a>

unionised - 22-11-2003 at 05:03

Marvin,
I'm puzzled why you don't think microwave ovens have a lab use. These people
http://www.usedlabequip.com/microwave.html
seem to disagree.
I'm also fairly sure that silica is pretty innert in the body and the only problem that would arise from eating it, is that it would get hot as it picked up water from the gut.
http://216.171.162.32/articleDetail.aspx?id=21

[Edited on 22-11-2003 by unionised]

kryss - 23-11-2003 at 14:44

Silica - the dry dust - is actually very dangerous if you breathe it in - causes silicosis.

unionised - 23-11-2003 at 14:52

Crystaline silica (Quartz to be exact) is; silica gel isn't (or, at least it is a great deal less so).

Silica Gell going to dust?

FGP - 24-11-2003 at 03:00

Quote:

Originally posted by kryss
Silica - the dry dust - is actually very dangerous if you breathe it in - causes silicosis.

KRYSS. I'm only talking about sachets containing 100g. I don't think that say one minute in a microwave would reduce the granules to powder. Mind you - I still haven't tried it. However after 40 seconds in the microwave the colour indicator is partially restored. FGP

unionised - 24-11-2003 at 14:29

Even if it is converted into dust and you breathe it in, it still doesn't cause silicosis. (I'm sure I already said that).

Hermes_Trismegistus - 28-11-2003 at 01:41

Silica gel turns brown, scorches, and produces copius and noxious smoke when placed in a microwave to dry. And doesn't even really dry quickly.

Experience trying to dehydrate gel for drying large quantaties of green flowers as a kid. We were.....inebriated...(very)....and didn't notice at first....his old lady was tres pizzed off!

tres tres pissed off.

Hermes_Trismegistus - 28-11-2003 at 01:42

P.S.

Microwaves do have many uses in labs, very specialised, very sophisticated chem labs and average bio labs and.....

Hermes_Trismegistus - 28-11-2003 at 02:03

P.S.S.

Don't eat silica gel, it bonds to intestinal wall by h2o absorbtion.

very bad

ask any silly fourteen year old girl who tried to commit suicide by eating hundreds of generally harmless pills, the same problem can arise

goo stuck to flesh wall

UGGGhhh!

vulture - 28-11-2003 at 02:39

Please use the edit function!!!

decomposition temperature

Hermes_Trismegistus - 12-10-2004 at 15:23

The silica gel I am using turned a yellowish tinge (although still transparent) when I dried it in my oven at ~ 140 degC for a few hours.

It also became sticky and a little gooey, however the msds I have for it notes it's melting temp as 3100 degC.

I am confused. Does someone have a decomposition temperature for it?