Activated Charcoal Cloth and Granules

Activated carbon is produced when carbonized materials of various origins (mineral coal, rubber, coconut shells...) are subjected to a controlled oxidation process. Hereby generated voids provide activated carbons with an enormous internal surface area (ap. 500 –1500 m²/g). Pure active carbons are capable of adsorbing a large variety of gaseous compounds to this internal surface, such as ozone, organic vapours and pesticides. Chlorine, NO₂ and SO₂ are adsorbed as well, although to a lesser extent. Next to pollutants, activated carbon is also adsorbing considerable quantities of water vapour, especially at higher levels of relative humidity (ap. 3% by weight at 50% RH, ap. 7% by weight at 60% RH, ap. 25% by weight at 70% RH). For the adsorption of specific compounds (like acid gases, SO₂, ...) impregnated activated carbons often are used.

Activated charcoal cloth is one of the smartest and most effective ways of addressing the problems of protecting artefacts from a variety of pollutants. ACC is 100% activated charcoal produced in a flexible textile form. It has a large internal surface area for adsorption (1050-1400 m²/g) composed entirely of micropores. ACC’s unique 20 Å width slit-shaped micropores have been proven to adsorb more effectively than the pores found in granular forms of activated charcoal.

Its large external surface guarantees optimum efficiency for the removal of pollutants from showcases, with or without ventilation. Museums giving items on loan often require to have the display cases fitted with ACC as a condition of the loan. To give an example, the uptake of 100 g charcoal cloth for acetic acid is, depending on the concentration: at 1000 ppmv: 20 g, at 10 ppmv: 7 g, at 0,1 ppmv: 1 g, at 0,01 ppmv: 0,25 g.

Activated charcoal cloth is the ideal solution for large surfaces such as back panels of showcases. If the black colour of the cloth is unwelcome it can be covered by a thin decoration fabric. ACC could have a slightly corrosive effect on some metal surfaces if they are in direct contact (battery effect). In this case a neutral fabric should be interleaved between ACC and artefacts. ACC can be provided lined with a variety of decorative fabrics. The most versatile type is ACC bonded on one side to a non-woven. Depending on your needs, you can turn up the charcoal or the non-woven side. ACC is only dusting very slightly at cut edges and can be worked like any fabric.

Granular charcoals are mainly used within filtering systems. They need some air circulation to be fully effective. For applications in stagnant air like inside showcases, charcoal cloth is generally to be preferred. You can choose between pure and impregnated carbons. Pure activated carbons are considerably faster in adsorbing than impregnated ones since the phyiscal adsorption is quicker than the chemisorption process used by the impregnated types. However, the contaminants are only loosely bonded to pure carbons. If the carbon is close to its saturation point pollutants can be liberated when humidity or temperature rises. This is being considered a disadvantage of pure activated carbons in long-term applications.