<unk>  charcoal bread for sale in a farmer's market. A gram of<unk>  can have a surface area in excess of , with being readily achievable. Carbon aerogels, while more expensive, have even higher surface areas, and are used in special applications. Under an electron microscope, the high surface-area structures of<unk>  are revealed. Individual particles are intensely convoluted and display various kinds of porosity; there may be many areas where flat surfaces of graphite-like material run parallel to each other, separated by only a few nanometers or so. These micropores provide superb conditions for adsorption to occur, since adsorbing material can interact with many surfaces simultaneously. Tests of adsorption behaviour are usually done with nitrogen gas at 77 K under high vacuum, but in everyday terms<unk>  is perfectly capable of producing the equivalent, by adsorption from its environment, liquid water from steam at and a pressure of 1/10,000 of an atmosphere. James Dewar, the scientist after whom the Dewar (vacuum flask) is named, spent much time studying<unk>  and published a paper regarding its adsorption capacity with regard to gases. In this paper, he discovered that cooling the carbon to liquid nitrogen temperatures allowed it to adsorb significant quantities of numerous air gases, among others, that could then be recollected by simply allowing the carbon to warm again and that coconut based carbon was superior for the effect. He uses oxygen as an example, wherein the<unk>  would typically adsorb the atmospheric concentration (21%) under standard conditions, but release over 80% oxygen if the carbon was first cooled to low temperatures. Physically,<unk>  binds materials by van der Waals force or London dispersion force.<unk>  does not bind well to certain chemicals, including alcohols, diols, strong acids and bases, metals and most inorganics, such as lithium, sodium, iron, lead, arsenic, fluorine, and boric acid.<unk>  adsorbs iodine very well. The iodine capacity, mg/g, (ASTM D28 Standard Method test) may be used as an indication of total surface area. Carbon monoxide is not well adsorbed by<unk> . This should be of particular concern to those using the material in filters for respirators, fume hoods or other gas control systems as the gas is undetectable to the human senses, toxic to metabolism and neurotoxic. Substantial lists of the common industrial and agricultural gases adsorbed by<unk>  can be found online.<unk>  can be used as a substrate for the application of various chemicals to improve the adsorptive capacity for some inorganic (and problematic organic) compounds such as hydrogen sulfide (H2S), ammonia (NH3), formaldehyde (HCOH), mercury (Hg) and radioactive iodine-131(131I). This property is known as chemisorption. Iodine number Many carbons preferentially adsorb small molecules. Iodine number is the most fundamental parameter used to characterize<unk>  performance. It is a measure of activity level (higher number indicates higher degree of activation) often reported in mg/g (typical range 500–1200 mg/g). It is a measure of the micropore content of the<unk>  (0 to 20 Å, or up to 2 nm) by adsorption of iodine from solution. It is equivalent to surface area of carbon between 900 and 1100 m2/g. It is the standard measure for liquid-phase applications. Iodine number is defined as the milligrams of iodine adsorbed by one gram of carbon when the iodine concentration in the residual filtrate is at a concentration of 0.02 normal (i.e. 0.02N). Basically, iodine number is a measure of the iodine adsorbed in the pores and, as such, is an indication of the pore volume available in the<unk>  of interest. Typically, water-treatment carbons have iodine numbers ranging from 600 to 1100. Frequently, this parameter is used to determine the degree of exhaustion of a carbon in use. However, this practice should be viewed with caution, as chemical interactions with the adsorbate may affect the iodine uptake, giving false results. Thus, the use of iodine number as a measure of the degree of exhaustion of a carbon bed can only be recommended if it has been shown to be free of chemical interactions with adsorbates and if an experimental correlation between iodine number and the degree of exhaustion has been determined for the particular application. Molasses Some carbons are more adept at adsorbing large molecules. Molasses number or molasses efficiency is a measure of the mesopore content of the<unk>  (greater than 20 Å, or larger than 2 nm) by adsorption of molasses from solution. A high molasses number indicates a high adsorption of big molecules (range 95–600). Caramel dp (decolorizing performance) is similar to molasses number. Molasses efficiency is reported as a percentage (range 40%–185%) and parallels molasses number (600 = 185%, 425 = 85%). The European molasses number (range 525–110) is inversely related to the North American molasses number. Molasses Number is a measure of the degree of decolorization of a standard molasses solution that has been diluted and standardized against standardized<unk> . Due to the size of color bodies, the molasses number represents the potential pore volume available for larger adsorbing species. As all of the pore volume may not be available for adsorption in a particular waste water application, and as some of the adsorbate may enter smaller pores, it is not a good measure of the worth of a particular<unk>  for a specific application. Frequently, this parameter is useful in evaluating a series of active carbons for their rates of adsorption. Given two active carbons with similar pore volumes for adsorption, the one having the higher molasses number will usually have larger feeder pores resulting in more efficient transfer of adsorbate into the adsorption space. Tannin Tannins are a mixture of large and medium size molecules. Carbons with a combination of macropores and mesopores adsorb tannins. The ability of a carbon to adsorb tannins is reported in parts per million concentration (range 200 ppm–362 ppm). Methylene blue Some carbons have a mesopore (20 Å to 50 Å, or 2 to 5 nm) structure which adsorbs medium size molecules, such as the dye methylene blue. Methylene blue adsorption is reported in g/100g (range 11–28 g/100g). Dechlorination Some carbons are evaluated based on the dechlorination half-life length, which measures the chlorine-removal efficiency of<unk> . The dechlorination half-value length is the depth of carbon required to reduce the chlorine concentration by 50%. A lower half-value length indicates superior performance. Apparent density The solid or skeletal density of<unk> s will typically range between 2000 and 2100 kg/m3 (125–130 lbs./cubic foot). However, a large part of an<unk>  sample will consist of air space between particles, and the actual or apparent density will therefore be lower, typically 400 to 500 kg/m3 (25–31 lbs./cubic foot). Higher density provides greater volume activity and normally indicates better-quality<unk> . ASTM D 2854 -09 (2014) is used to determine the apparent density of<unk> . Hardness/abrasion number It is a measure of the<unk> 's resistance to attrition. It is an important indicator of<unk>  to maintain its physical integrity and withstand frictional forces. There are large differences in the hardness of<unk> s, depending on the raw material and activity levels. Ash content Ash reduces the overall activity of<unk>  and reduces the efficiency of reactivation: the amount is exclusively dependent on the base raw material used to produce the<unk>  (e.g. coconut, wood, coal, etc.). The metal oxides (Fe2O3) can leach out of<unk>  resulting in discoloration. Acid/water-soluble ash content is more significant than total ash content. Soluble ash content can be very important for aquarists, as ferric oxide can promote algal growths. A carbon with a low soluble ash content should be used for marine, freshwater fish and reef tanks to avoid heavy metal poisoning and excess plant/algal growth. ASTM (D2866 Standard Method test) is used to determine the ash content of<unk> . Carbon tetrachloride activity Measurement of the porosity of an<unk>  by the adsorption of saturated carbon tetrachloride vapour. Particle size distribution The finer the particle size of an<unk> , the better the access to the surface area and the faster the rate of adsorption kinetics. In vapour phase systems this needs to be considered against pressure drop, which will affect energy cost. Careful consideration of particle size distribution can provide significant operating benefits. However, in the case of using<unk>  for adsorption of minerals such as gold, the particle size should be in the range of .<unk>  with particle size less than 1 mm would not be suitable for elution (the stripping of mineral from an<unk> .
Activated carbon
Caphosol
Dissolvable tobacco
Chlorofluorocarbon
Mustard gas
Bioactive glass
Podophyllum resin
Carbonated water