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Why do we use 3A molecular sieve as IG desiccant?

    Source:未知 Author:admin Release time:2016-01-09

The following form lists 4 types of common desiccants often used in IG and their aperture values. This form also shows which kinds of molecules are likely to be absorbed by these desiccants.

Desiccant Type Pore Size (angstrom) Absorb Substances Repel substances
3A 3 H2O All others
4A 4 H2O, nitrogen Ar, Kr, large molecule gases
13X 8.5 H2O, most gases, small molecule liquids Large molecule liquids
Silica gel 200-300 All Non

Though most molecular sieves have been affinity to water, such as other molecular sieve 4A, 5A, 13X, and type Y and so on. They all also adsorb other molecules from air. The pore of 3A molecular sieve is 3 angstrom, which can only adsorbs molecule smaller than this size, water molecule is just meet this size, so molecular sieve 3A can only adsorb water other than Nitrogen and Oxygen in air.
If use other molecular sieve as desiccant, these molecular sieves can also adsorb nitrogen or oxygen in air at lower temperature, and could release air at higher temperature, the inflated and shrinking air could cause window to be distorted with the temperature changing at day-night or seasons changing. Up to now, molecular sieve 3A is the unique proper desiccant which is suitable for insulating glass unit.