When it comes to molecular sieves for insulating glass, why do we choose 3A instead of 4A?
The effective pore size of 3A molecular sieve is about 3 Å. The effective pore size of 4A molecular sieve is about 4 Å. According to Table 1, the radius of water molecules is smaller than the pore size of 3A molecular sieve, which can be adsorbed by 3A molecular sieve. While the molecular radius of oxygen and nitrogen is larger than the pore diameter of 3A molecular sieve and cannot be adsorbed by 3A molecular sieve. However, 4A molecular sieve can adsorb water, oxygen, nitrogen, and even more favorably adsorb nitrogen with larger polarity.
It should be noted that the nitrogen adsorbed by 4A molecular sieve is very sensitive to temperature changes:
For example, 250ml of 4A molecular sieve can release more than 700ml of gas when it rises from room temperature to 70℃. And the gas release of 3A molecular sieve will be lower than 50ml.
If used as insulating glass desiccant, when the outside temperature rises, 4A molecular sieve will release adsorbed nitrogen and oxygen, resulting in insulating glass internal pressure is greater than the outside air pressure, insulating glass will be convex. When the outside air temperature decreases, 4A molecular sieve and re-adsorption of nitrogen and oxygen, so that the outside pressure is greater than the internal pressure of the insulating glass, insulating glass concave or recovery.
This inhalation and exhalation "breathing phenomenon" will greatly reduce the service life of the insulating glass, experience shows that the use of 4A molecular sieve insulating glass, its service life is only 3A molecular sieve of a quarter.
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