are all silica gel packets reuseable? and, if they aren’t specifically labelled ‘color indicating’, how can you tell when they’re saturated? Also, do you leave them in their packets for recharging in an oven or microwave, or do you take the beads out of the packets? In advance, many thanks.
In: Chemistry
You do not take them out of the packets. If the packets have any metal, you only do this is a regular oven, not a microwave.
Silica gel works by absorbing (or is it adsorbing? I can’t remember) water. To drive that water off and “regenerate” them, simply heat them up over 120˚C.
Silica gel can absorb up to 37% of its own mass in moisture in very humid environments. In areas with lower humidity or higher temperatures, it will be less, as there’s sort of a dynamic equilibrium where some water leaves the silica while new water sticks to it.
So, you can generally tell when non-indicating silica gel is saturated (for a given relative humidity and temp) based on mass. It’s not perfect since the absorption process is dependent on humidity and temperature, but it should be close enough for most uses.
A basic test would be to freshly regenerate some gel, record its weight on a cheap digital kitchen scale, and then leave it sitting out for a week. Measure the weight again and that will be your saturated mass. Then you know when your gel has gained that % mass, it needs to be regenerated.
I just leave the gel in the packets unless I have good reason to remove it. As long as the packets don’t have any metal, it should be fine to microwave them. Otherwise, an oven also works as long as the temp doesn’t go so high that it melts the packets (again, 120˚C should be enough).
Just put it in the oven in with color changing silica gel beads you have, that’s what I do. When the all the color changing ones have changed color, all of the gel will be good, or at least good enough. Just be aware that some silica gel packets have a sandy material in them that is hard to move around
It really depends what are you using them for and how much the performance matters to you. I am maintaining a set of astronomical cameras that are cooled to -40 degrees and located around the world – yes, my silicagel is color-indicating, but I still refresh it at any time I am able to physically visit the sites, because the color changes are not very reliable in indicating the progress of the saturation. But this is spending dollars to prevent spending thousands – in a less sensitive application, you can just play it more by ear – or get at least some color-changing pearls and drop them in with the rest for rough indication.
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