Silica gel Orange – Colorless
Silica gel (also called silica, silica gel or drying beads, etc.) is the most commonly used drying agent in aeration drying. It consists of 99% silicon dioxide (SiO2). Narrow pore silica gel has a large internal surface area of up to 850 m²/g due to its high porosity. The pore structure is not uniform. The funnel-shaped openings have a diameter of about 2 to 12.5 nm. This allows loading with water molecules in several layers (capillary condensation), which explains the very high uptake capacity of this adsorbent. Due to its extreme hydrophilicity (attraction of polar substances, such as water) and easy regeneration by raising the temperature to about 120°C, it is preferably used as a desiccant.
Especially at a relative humidity of approx. 70 %rH, silica gel shows its excellent absorption capacity. The maximum water absorption capacity is approx. 37 % of the dry weight of the fill.
Silica gel orange colorless has a weaker color change than e.g. silica gel orange-green. In addition, the color change takes place only at a higher water loading of approx. 20-25%.
Other silica gels
Chemical properties
Chemical name: Amorphous silicon dioxide
Composition: SiO2
CAS number: SiO2 63231-67-4
| Narrow-pore | |
|---|---|
| Appearance and shape | Round, solid balls |
| Grain size | 3 – 5 mm |
| Bulk density | 0,75 – 0,85 kg/l |
| Pore volume | 0,35 – 0,45 ml/g |
| Breaking strength | > 200 N |
| Specific surface | 600 – 800 m²/g |
| Silicon dioxide (SiO2) | 99% |
| Trace elements | 1% |
| Water adsorption capacity | > 370 ml/kg |
Equilibrium loading
The combination of narrow-pore silica gel and water corresponds to a convex isotherm type. The isotherm exhibits a steep slope. The monomolecular occupancy of the silica gel is completed at about 30%, after which multilayer occupancy of the adsorbent surface and capillary condensation take place. At an adsorption capacity of about 35% it takes a plateau and increases only slightly.
Adsorption isotherms of narrow-pore and wide-pore silica gels
Isotherms of narrow-pore silica gel at 20°C, 40°C, 60°C
Color indicators
Silica gel is dyed with an indicator to visually indicate the loading of water vapor. The metal salt iron sulfate is used. When water is adsorbed on the surface of the silica gel, the granules changes the color.
Color change of silica gel Orange-Colorless
0%
5%
10%
15%
20%
40%
Regeneration
In practice, the most common regeneration method is temperature increase. When desorbing water vapor from silica gel, the temperature must be above 100°C. For silica gels without a color indicator, a regeneration temperature between 150°C and 175°C is recommended. However, color indicators would be damaged at these temperatures. For silica gels with color indicator, a regeneration temperature of 121°C to a maximum of 140°C is therefore recommended.