Desiccant for Insulating Glass

The desiccant of choice for insulating glass units is typically the 3A Molecular Sieve (Angstrom, 1Å = 0.1 nm). Synthesized from raw materials including bauxite, NaOH, Na2SiO3, KOH, and Ca(OH)2, it is manufactured through processes like pelletizing, high-temperature calcination, and screening. This desiccant adsorbs moisture at ambient temperatures and releases it at elevated temperatures, making it ideal for drying both gases and liquids.

Within insulating glass, it effectively removes both water vapor and trace residual organic compounds. This ensures the glass remains clean and transparent even at extremely low temperatures. Furthermore, it significantly reduces the substantial internal and external pressure differentials caused by major seasonal and daily temperature fluctuations. This effectively prevents the distortion or breakage of the glass due to expansion and contraction, thereby substantially extending the service life of the insulating glass unit.

Key Advantages Over Traditional Silica Gel and Mineral Desiccants

Molecular sieves offer distinct benefits compared to conventional options:

• Consistent Performance in Low Temperatures: They maintain their adsorption capacity at 0°C or below, unlike silica gel and mineral desiccants, whose capacity drops significantly in cold or hot conditions, adversely affecting the insulating glass’ dew point.
• Effective in Low Humidity: Adsorption capacity remains high even in environments with relative humidity below 20%, whereas silica gel and mineral desiccants see a marked decrease in performance under dry conditions.
• Selective Adsorption: Molecular sieves can adsorb any substance with a molecular size smaller than their own pore diameter, allowing for targeted moisture removal.
• Adsorbs Both Vapor and Liquid Water: They are effective against water in both its gaseous and liquid states.
• High Durability and Stability: They are hard, stable, and will not crack, produce dust, swell, deform, or volatilize upon contact with water.

Types of Molecular Sieves

Molecular sieves are categorized based on their chemical composition and pore size:

• 3A Molecular Sieve: Pore size ~3Å (0.3 nm). Primarily adsorbs water molecules, excluding larger molecules like nitrogen and oxygen from the air.
• 4A Molecular Sieve: Pore size ~4Å (0.4 nm). Adsorbs water, methanol, ethanol, and other small molecules.
• 5A Molecular Sieve: Pore size ~5Å (0.5 nm). Suitable for adsorbing slightly larger molecules, such as n-hexane.
• 13X Molecular Sieve: Pore size ~10Å (1.0 nm). Ideal for adsorbing larger gas molecules like carbon dioxide and hydrogen sulfide.

Why is the 3A Molecular Sieve Uniquely Qualified for Insulating Glass?

Selective Adsorption for Stable Pressure: The 3A Molecular Sieve’s key feature is its selective adsorption of only water vapor. The primary function of the desiccant in an insulating glass unit is to absorb moisture. A water molecule has a kinetic diameter of about 2.6Å, while nitrogen and oxygen molecules in the air are larger at 3.6Å and 3.4Å, respectively. The 3Å pore size allows water in but blocks these atmospheric gases. Other desiccants (like 4A Molecular Sieve) adsorb not just water but also oxygen, nitrogen, and carbon dioxide. As outside temperatures fluctuate, these desiccants can release or re-adsorb these gases, causing an imbalance between the internal pressure of the glass unit and the external atmospheric pressure. This imbalance can distort the glass and shorten its lifespan. The 3A sieve prevents this issue entirely.

Non-Corrosive and Safe: The 3A Molecular Sieve is mildly alkaline (pH ~10.5), a property that is non-damaging to the aluminum spacers used in insulating glass units. In contrast, some desiccants like calcium chloride are corrosive. As they absorb moisture, they can degrade the spacer and sealant, increasing the risk of unit failure. The 3A Molecular Sieve poses no such risk, ensuring the integrity and safety of the glass unit.

Superior Adsorption Performance: The 3A Molecular Sieve boasts an excellent water adsorption rate of up to 0.04g/s and a high adsorption capacity of at least 20% of its own weight. This high efficiency ensures the insulating glass maintains a very low internal relative humidity for a long period, guaranteeing long-term durability. Ordinary desiccants have a slower adsorption rate and, at ambient or high temperatures (≥40°C), can undergo desorption (releasing moisture back into the cavity), which can compromise the transparency of the glass.

Stable Physical Adsorption: At ambient temperatures, the 3A Molecular Sieve does not react with water hydrolytically. The adsorption of water is primarily a physical process driven by van der Waals forces – intermolecular attractions. On a microscopic level, the pore structure of the molecular sieve creates an electrostatic equilibrium. When a polar water molecule enters the pore, it can dissociate into H⁺ and OH⁻ ions. During adsorption, these ions interact with the internal electrostatic field of the sieve, restoring balance and releasing energy (observed as a temperature increase). Critically, this process is a physical reaction, not a chemical one. Therefore, under normal conditions, the adsorption of water by the 3A Molecular Sieve is stable and will not lead to hydrolysis.