Types Of Molecular Sieves
There are various types of desiccants for insulating glass units (IGUs) currently on the market, including 3A, 4A, and 5A molecular sieves, as well as calcium oxide, calcium chloride, and clay-based desiccants. Among these, 3A and 4A molecular sieves and calcium chloride desiccants are the most common.
What is 3A?
3A, 4A, and 5A molecular sieves are all made from materials known as "alkali metal aluminosilicates." Their primary difference lies in pore size: a 3A molecular sieve has an effective pore size of approximately 0.3 nm (nanometers), a 4A sieve has one of about 0.4 nm, and so on.
Why 3A?
The effective pore size of "Type A molecular sieves" is crucial, as it determines the maximum molecular size that can be adsorbed. Water molecules in the air have a diameter of approximately 0.28 nm, while oxygen and nitrogen molecules have diameters of about 0.34 nm and 0.36 nm, respectively. Consequently, only 3A molecular sieves selectively adsorb water vapor from the air, whereas other Type A sieves also adsorb gases such as oxygen and nitrogen.
If a molecular sieve adsorbs gases, a potential issue arises: it will take in and release gas in response to temperature fluctuations caused by the time of day or the season. The greater the temperature change, the more significant this gas exchange becomes.
This gas exchange causes the insulating glass unit to contract and expand (bulge), which accelerates the aging of the sealant and, in extreme cases, can lead to glass breakage.
In addition to "Type A molecular sieves," calcium oxide, calcium chloride, and clay-based desiccants are also commonly found on the market. "Calcium-based" desiccants tend to corrode aluminum spacers and damage the butyl sealant, thereby shortening the lifespan of both the sealant and the insulating glass unit itself.
"Clay-based" desiccants, on the other hand, have a very low water adsorption rate, causing the insulating glass unit to reach the end of its effective service life within a very short period.
In summary, selecting 3A molecular sieves as the desiccant is a fundamental prerequisite for ensuring the reliable quality of insulating glass units. Moreover, the market price for the insulating glass used in residential doors and windows is at least 100–200 RMB per square meter-a price point that easily covers the cost of the molecular sieve (amounting to tens or hundreds of grams per unit); skimping on this component results in a product fit only for the low-end market.
