Desiccant means drying agent or substance which adsorbs water. They have great affinity to water with very hygroscopic properties.
When you place a properly prepared desiccant into an air stream with a humidity level higher than that of the desiccant the desiccant will remove moisture up to it’s saturation point or equilibrium capacity. Desiccant materials saturate to humidity after a period of usage and became insufficient of adsorbing any more moisture from the air. At equilibrium capacity adding more desiccant will not bring the relative humidity lower. So, the cabinets start to regeneration process in this case. The moisture adsorbed within the desiccant is excluded from the inside of the cabinet during regeneration process and the desiccant is made available for dehumidification again.
There are four types of desiccants; silica gel, montmorillonite clay, molecular sieve (zeolite), and calcium oxide. Silica gel and molecular sieves have been using in drying cabinets commonly. Zeolites became the one preferred with its advantages in many aspects especially in the applications which requires ultra-low humidity levels (1% RH).
Synthetic zeolite structure has many internal cavities that are linked by window openings of precise diameters (measured in Angstroms). Adsorbtion occurs only for molecules with smaller diameters than these cavity openings. On the other hand, molecules of greater polarity are absorbed preferably. This makes zeolites ideal for adsorbtion of water from air, as water molecules are both polar and very small.
The advantages of using zeolite to dry and to store the moisture sensitive materials are as follows:
