Carbon is activated by breaking down the carbon structure with steam or chemicals. This creates many fine channels, known as pores, in the carbon structure. These pores are finely grained so the polluting molecules can first penetrate them and then bond with the surface.
These purifying pores are classified as:
- Micropores up to = 0,000 002 mm
- Mesopores 20 – 500 Å = 0,000 002 mm – 0,000 050 mm
- Macropores over 500 Å = 0,000 050 mm
Depending on the degree of activation, activated carbons have an active internal surface area ranging from 750 m2/g to 1,600 m2/g.
Activated carbon for air purification
The air is forced over a carbon layer for purification. There are various types of filters; the particle sizes can range from very fine to very coarse. When describing activated carbons, the particle sizes are generally listed in US mesh.
| US mesh | 4 | 6 | 8 | 12 | 16 | 20 | 30 | 40 | 50 | 60 |
| mm | 4.75 | 3.35 | 2.36 | 1.70 | 1.18 | 0.85 | 0.6 | 0.425 | 0.30 | 0.25 |
The air resistance in the filter changes depending on the particle size category, provided the carbon volume remains the same. That makes air resistance a key parameter in selecting the right particle size category.
Activated carbon in various types of filters
