Calcium Chloride
Calcium chloride, CaCl2, is a common salt and the compound of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. It has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in concrete. The anhydrous salt is also widely used as a desiccant, where it will adsorb so much water that it will eventually dissolve in its own crystal lattice water. It can be produced directly from limestone, but large amounts are also produced as a by-product of the Solvay process. Because of its hygroscopic nature, the anhydrous form must be kept in tightly-sealed containers. It is used to turn kelp into a solid. more information regarding Calcium Chloride can be found here at Wikipedia
Examples: Absorpoles, Absorbag, Absortop
Calcium Chloride aggressively absorbs moisture from the air, first causing a swelling of the crystals. If the air is humid enough and the temperature is high enough, the crystals melt and liquid saline solution brine) is formed.
If the brine is exposed to the air it continues to absorb moisture until equilibrium is reached. The equilibrium point varies very strongly with the humidity of the air. Under humid conditions it is possible for the salt to absorb more than ten times its own weight of moisture.
In practical desiccant terms absorption of more than 1-2 times the weight of the salt must be considered over-saturation, as increased liquid pressure will cause even a Tyvec pouch to leak. Unless the brine is sequestered as in the Absorpole, any drop in the humidity of the surrounding air will lead to often very dramatic re-evaporation.
Calcium Chloride desiccants work well over a temperature range from freezing up to 100C or more. At low temperature the salt does not absorb moisture under dry conditions. In practical terms calcium chloride desiccants are effective at Relative Humidity above 20-30%, but are relatively more effective under moist conditions.
In the Absorpole product where the brine is sequestered away from contact with the air, the absorbency decreases at elevated temperature as the crystals melt more easily. This is the reason that in voyages under hot conditions you will sometimes find Absorpoles with all the salt used up and only ½ liter of moisture collected.
CaCl2 desiccants packed in pouches do not suffer from this reduction in absorbency, but are on the other hand at risk of over-saturation and destructive re-evaporation.
