Sorbents for Gaseous Pollutants in Showcases

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ACTIVATED CARBONS – VARIOUS STYLES

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.

nach obenActivated Charcoal Cloth 

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 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.

CCI-activatetd carbon cloth FM10 L100 (formerly FM4/250SL, woven, bonded on one side to a white non-woven: 120 g active carbon/m²,  internal surface area typically 900 - 1100 m²/g, width: 108 cm, thickness: 0,5 mm.

1 lin.m 51,- €
5 lin.m 250,- €
10 lin.m 490,- €
50 lin.m 2400,- €
 

Also available unlined, price: € 3,-/lin.m less than FM10 lined on one side
The internal surface of unlined fabric is a bit higher, typically 1000 - 1200 m²/g, but it is fraying quite easily.

CCI-activated carbon cloth type FM10/T150, with alkaline impregnation, tenfold higher adsorption capacity for H2S, NOx and other acid gases. Bonded on one side to a white non-woven. Thickness ca. 0,5 mm, width 100 cm. Internal surface area typically 1000 - 1200 m²/g.
This product is very alkaline, please avoid contact with skin, eyes, art objects, metals (aluminum, zinc, ...) and delicate surfaces!

1 lin.m 61,- €
5 lin.m 295,- €
10 lin.m 570,- €
50 lin.m 2.650,- €
 

nach obenGranular activated charcoal:

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 carbon from coconut shells.

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.

Activated charcoal from coconut shells is used for many applications due to its extra fine pores. Therefore coconut shells belong to the best raw materials for production of activated carbon. The chips are 2,4 - 4,8 mm large, apparent density 450 ± 25 g/l, internal surface area: ap. 1100 m²/g, iodine number: >1050 mg/g, moisture (as packed) max. 10 w/w %, ash content: 5 % max,

Activated charcoal from coconut shells, type K48, unimpregnated

1 kg
8,00 €
5 kg
32,50 €
25 kg
150,00 €
100 kg 550,00 €

 

nach obenImpregnated activated carbons: Impregnated granular peat-carbon

The most common pollutants in showcases are acidic gases like acetic or formic acid, liberated by organic materials like wood. These compounds - as well as SO2 common in urban areas - are best controlled by activated carbons with alcaline impregnation. Impregnated styles adsorb by chemisorption. Generally this process is a little bit slower than the purely physical adsorption by pure activated carbons, but the pollutants are more firmly bound to the carbon. Thus, in long-term applications there will be less chance that the pollutants might be liberated again.

 

Activated carbon KC10, impregnated with NaOH, extruded cylinders, base material: mineral coal, diameter ap. 4 mm. It is used to remove small amounts of acidic vapours from air. Apparent density: 500 ±5% g/l ; moisture (as packed) max. 10 w/w %; pH: alcaline, iodine number: 900 mg/g/min, CTC value for adsorption of CCl4: 60% min.
This product is very alkaline. Please avoid contact with skin, eyes, art objects, metals (aluminum, zinc, ...) and delicate surfaces!

Activated carbon KC10

2 kg
10,00 €
5 kg
42,50 €
25 kg
187,50 €
100 kg
715,00 €

 

 



nach obenII) SPECIAL SORBENTS FOR THE PROTECTION OF SILVER AGAINST TARNISHING

Tarnishing of silver is mainly caused by hydrogen sulfide and - to a minor degree - other pollutants like sulphur oxides, nitrogen oxides and chlorine. Relative humidity is an important factor in these reaction processes.

Many current methods of protecting silver from tarnishing (lacquering, coatings or vapour phase inhibitors) have shown serious negative side-effects. Removing the gaseous contaminants is therefore a convincing and safe way of protecting precious silver objects (including photographic materials, other metals and metallic based paints) leaving the objects untouched and unchanged.

General pollutant scavengers like Purafil or activated carbon considerably slow down tarnishing of silver objects. Comparative tests however showed that special zinc-oxide based sorbents or Pacific Silvercloth provide by far superior protection.

nach oben1) Pacific Silvercloth

is a 100% cotton fabric embedded with thousands of fine silver particles. It is produced by precipitation of pure, colloidal silver on a cotton fabric. The fabric absorbs tarnish producing gases before they reach the silver items. It is 96,5 cm wide, napped and comes in only one colour which is brown (colour of the colloidal silver on the fibres). Pacific Silvercloth is twice as effective as fabrics embedded with zinc or other metals. It can be effective for several decades depending on the environment. It can be placed directly on silver or glued to drawers or cabinet walls. Pacific Silvercloth does not emit any chemicals (unlike fabrics contanining vapour phase inhibitors) and has successfully been used in many museums and silverware shops (consult Petersen or ConsDist archives for references). It can be used for silver on display and in storage cabinets. For silverware in frequent use (like in churches) protective bags can be custom made using Pacific Silvercloth. If drawers are to be lined with Pacific Silvercloth, an extra lap should cover the drawer in order to completely surround the objects contained. Absorption of pollutants changes the colour of the fabric from brown to black, so the colour gives a certain indication if the fabric is still effective.Wear a dust mask when working with the cloth.

The important factor is not the quantity of Silvercloth (inside showcases, the quantity of H2S to absorb will be relatively small) but where you place it. You should place it close to the leaks of the showcase where the polluted air is supposed to enter the case. Protection will be perfect if you can make sure that the pollutants have to pass through or along Pacific Silvercloth before reaching your silver object. For showcases with doors we recommend to cover the vertical joints with clear tape 3M Type 850.

If for optical reasons you cannot place Pacific Silvercloth close to the doors then you should try to offer a maximum surface of Silvercloth to the pollutants so there will be a high probability that the pollutants will react with the Silvercloth rather than react with the object.

Pacific Silvercloth, width 96,5 cm, lin.m (regardless the quantity)
20,- €

Bags of Silvercloth can be custom made to the sizes you need, for example as protection for chalices. 

Flat bags open on one side with a double cotton-cord (+ price of the cloth)
10,- €
Bags with round bottom and double cotton cord (+ price of the cloth)
13,- €
Order

nach oben2) Zinc Oxide Catalyst G 72-D

 

 

 

 

 

 

4,5 mm thick extrusions (5-7 mm long) composed of 90% ZnO, 6,4% Al2O3, 0,6% Na2O, internal surface area ca. 50 m²/g, apparent density ap. 1,1 kg/l. The catalyst shows a high affinity for hydrogen sulfide. In tests it offered a better protection to silver than activated carbon or Purafil.

Zinc oxide G 72-D is designed for air filtration units. For application as a static adsorbent the pellets may be crushed to smaller granules. For passive use in showcases we rather recommend Pacific Silvercloth (see above).

According to the producer the product can be used up to an adsorption of 5% sulphur (by weight). For museum applications we probably should exchange the product at a lower level, e.g. at 1 - 2 % by weight. We can offer a sulphur analysis for 120,- € to 100,- € depending on number of samples. By checking sulphur content after 1 - 2 years of exposure you can determine remaining life time and exchange rhythm in a given showcase.

Zinc oxide G 72-D
1 kg
51,- €
5 kg
240,- €
10 kg
470,- €
50 kg
2300,- €
Order

Please note: this product is water endangering and has to be disposed of properly (disposal key number (EAK) : 16 08 - Spent catalysts).



Terms of sales and delivery

Products on stock are usually sent out within one week. Nevertheless, please order as early as possible. Transport is normally by FedEx Economy (±2-3 days within Europe), carriage is charged according to weight, dimensions and number of parcels.
All prices are exclusive VAT. Payments can be made within 30 days by bank transfer, within 14 days with 3% discount. All prices are subject to change without prior notice according to our terms and conditions. Check our website for actual information.

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