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Forum Index : Other Stuff : Silica Gel Reconditioning Question
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| Georgen Guru  Joined: 13/09/2011 Location: AustraliaPosts: 462 |
From time to time I put little packet of Silica Gel into microwave oven and put it on 50% power for 5 to 10 seconds. Packets are very small, so I am worried to overdo the reconditioning. I do it few times to prevent packet getting too hot. So far so good. I am not sure what should I do next. Sometimes packet feels bit sweaty, so it is probably better to let it cool down and dry out. But here is my dilemma, while I do that my guess is that Silica Gel re-absorbs some of the moisture. Does anybody know the best/correct way to recondition exhausted silica gel? Also how many times it can be done before silica gel has to be discarded? George |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Found some information on this web page: http://www.apsnyc.com/uploads/Methods%20for%20Reconditioning %20Silica%20Gel.pdf [quote] REMOVING MOISTURE The most efficient method of removing moisture is with heat. Although silica gel has a very high melting temperature (1600º C), it will lose its chemically bound water and hygroscopic properties if heated above 300º C. In addition, there is a new class of indicator gels, incorporating organic dyes that are heat sensitive and their color indicating dye will be effected above 125-150º C (Goldberg and Weintraub 2001). Therefore, it is not recommended that indicating silica gel be heated above 120º C and regular gel be heated above 200º C. The principle impact of a lower heat of regeneration is that a longer time is required to dry the gel and there is less potential for the degradation of silica gel properties. [/quote] Quite a temperature range. On web page: http://www.proscitech.com.au/cataloguex/get_notes.asp?silica gel in section titled: “Reactivationg/drying off silica gel” It is suggested that best to keep temperature between 105C and 120C Cannot find definite information on reconditioning silica gel below 100C. It says on the net that silica gel absorbs and desorbs moisture all the time depending of relative humidity. This explains why higher temperature helps in removal of moisture from silica gel. Suppose all I can do play by ear and hope it works. Should silica gel turn to dust, will indicate too high drying temperature. Without any further comments I will just keep doing what I was doing till now. George |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Looks that Silica Gel is mostly used in cabinets as humidity regulator. I on the other hand use it only as humidity removing medium. In the end it looks that temperature under 100 deg C is very safe and silica gel can be reused and will last almost indefinitely. If it reabsorbs little bit of moisture while cooling down, no big deal. George |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
One of my jobs as a telecommunications apprentice was to dry out the silica crystals. I would pour out the crystals onto a electric fry pan set at a low heat, and stir them around the hot surface until they changed from pink to blue ( or was it the other way around? ). It took about 30 minutes to dry out a cup full. I think leaving them in a dry sunny spot will work, so long as the moisture can escape and the crystals dont get to hot. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Coming in late here - haven't checked this forum for a while. Laboratories dry silica gel at 105oC. They normally have one or more lab ovens left on at 105 all the time for just this job. (I ran labs for a lot of years). Drying is usually done on a metal or glass tray of some sort; often the same tray that the silica gel is placed on to be used in the dessicator. Typical thickness of the layer used when drying is 1-2 cms and the tray is usually left in overnight to do the job - or for weeks if you want if it's not being used - it won't hurt it at that temperature. A normal kitchen oven set somewhere between 100 and 120 should work fine. You know when it's ready if all (or most) of the crystals have reverted to blue. It can last for years when kept mostly pretty dry (as in the dessicator) but goes "off" a lot sooner if left un-dried a lot. As Glemm said; the indicator shows blue when dry and pink when needing re-heating (the colour comes from a trace of a cobalt compound added during manufacture). The distinct blue/pink colour transition tends to disappear when it needs to be replaced - it goes a bit smoky-yellow &/or just plain transparent without colouring. Greg |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
1969 I used to maintain a 978 RAN navigational radar fitted with waveguide driers. The drier unit consisted of two separate sections each being a compartment with silica gel and cobalt chloride (the pink/blue stuff). The unit had a change over lever so that hot air at around 150degF could be sucked through one half or the other. When one unit was drying, the other was in use. The temperature of the drier had to be higher than the highest ambient. Each batch used to take a couple of days to dry out. Ahh.. reminiscing - two years in the survey arm of the navy. We used an LF radio location system called Lambda. It had two accurately located (re-locatable)shore bases and a mobile ship borne one and worked on the intersection of the three circular waves - a sort of terrestrial GPS. The other system was called HIFIX and was similar. David M. |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
That's three of us who had to maintain the dessicants in the 60's David. Must have been the first training job for all tech people! Greg |
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