Charcoal

Charcoal is a black lightweight residue, consisting of carbon, partially pyrolyzed organic matter and ash, obtained by removing water and other volatile constituents from vegetal and sometimes animal products. Although charcoal contains plenty of free carbon, charcoal is NOT an allotrope of carbon, neither could it be considered elemental carbon of any proper chemical grade at all (particularly "clean" charcoal, or one that was ground and leached with water, may count as technical grade amorphous carbon).

Properties

Chemical

Charcoal will burn in open air if ignited to release carbon dioxide and small traces of water, leaving ash behind. Sugar charcoal, made by dehydrating sugar with concentrated sulfuric acid, contains no ash, and chemically it's practically amorphous carbon, so it should leave almost no ash after it burned completely. Oxidizing agents, such as concentrated nitric acid can oxidize charcoal, while oxidizing mixtures, like aqua regia, nitrating mixture and piranha solution will slowly oxidize it to carbon dioxide. Charcoal ignites on contact with fluorine at room temperature.

Physical

Charcoal is a black lightweight solid, with a gray luster. Partially pyrolyzed charcoal has a distinct wood-like smell, while the higher purity type is odorless. It is not soluble in any solvents. It has a very high specific surface, which allows it to adsorb various gasses and liquids.

There are various types of charcoal:

• Plant charcoal: made via dry distillation of wood. Comes in two types: hardwood charcoal and softwood charcoal. The most common type of charcoal.
• Animal charcoal: also knows as bone black, is produced from the dry distillation of bones. Contains only around 10% carbon, the rest being magnesium and calcium phosphates.
• Activated charcoal: made by the activation of low or ash-free charcoal. It has a very high specific surface (5000 m²/g) and it's commonly used in gas filters.
• Sugar charcoal: obtained by dehydrating sugar with sulfuric acid, has almost no ash. It's actually amorphous carbon.
• Artists' charcoal: comes in various forms, such as compressed charcoal, which are sticks of powdered charcoal of various types, mixed with a binder, or vine charcoal.

Availability

Charcoal is available at most stores, supermarkets, hypermarkets, gas stations in paper bags. Generally it's made of hardwood, making it difficult to mill. Biochar, a type of charcoal used in agriculture can be purchased from agricultural stores.

Gas mask filters contain pellets of activated charcoal. Activated charcoal can also be purchased from pharmacies.

Compressed and vine charcoal can be purchased from art stores. Purification may be required to remove the binder.

For various pyrotechnic mixtures, it's important to know which type of charcoal is suitable for your needs.

Charcoal can sometimes be found in nature as the rare mineral fusain, which is just fossilised charcoal, and it may be collected by hobbyists.

Preparation

Charcoal can be made by the dry distillation of wood. In a metal container, which can be anything from a used tin can to a steel pipe, add wood pellets or scrap wood pieces. Partially cover the top with a plate (this is optional). Heat the container and wait until the wood no longer gives off any fumes, but make sure the charcoal doesn't catch fire. Let it cool and collect the resulting charcoal. If you're using hardwood like oak, it's possible that the charcoal core might not of pyrolyzed properly. Softwood, like willow, grapevine or balsa, is preferred, as it pyrolyzes better, it's easier to mill and has less ash content. Do not use fibrous plant material, like cotton or corn silk, as it does not pyrolyze well, the outer fibrous mass acting as an insulator for the central mass. When pyrolyzed, the external part of the fibrous mass will turn to ash, and as you go deeper inside, the material will become a mixture of partially charred organic mass and slightly burned fibrous material.

The mound method is the best and simplest method for making bulk charcoal. It involves igniting pieces of dry wood in a makeshift mud kiln and then sealing it to suppress the burning and initiate the charring process. The method is super simple and does not require any materials except for those you can find in a forest (or garden).

If a continuous production of charcoal is required, a charcoal kiln is a better idea, as it can be reused many times.

High purity charcoal can be made by dehydrating sugar with concentrated sulfuric acid. The H₂SO₄ is neutralized and the solution is either filtered or repeatedly decanted. The resulting charcoal is washed with distilled water to remove any ions and dried.

Animal charcoal can be obtained via the dry distillation of bones. Unlike the wood-derived charcoal, it contains only about 10% carbon, the remainder being calcium and magnesium phosphates (>80%). You must do this outside, in a remote location, as the pyrolysis product of animal bones consists mostly of Dippel's oil, a foul smelling liquid.

Projects

• Make black powder
• Make carbon disulfide
• Make elemental phosphorus (animal charcoal)
• Reduce iron oxides to elemental iron
• Make an air filter
• Absorb toxic spills
• Drinking water filtration
• Charcoal crystal garden
• Ink (bone black)

Handling

Safety

Charcoal posses little toxicity to life, and it's even used in medicine. Charcoal dust however is irritant to lungs and may contribute to various illnesses. Poorly pyrolyzed charcoal from potentially harmful or toxic wood, like walnut, elderberry, oleander may still contain traces of their respective toxins, and it's best to not breath the dust. Avoid making charcoal from these types of wood and instead use more common plants.

Charcoal tends to stain almost everything and is difficult to clean. A good detergent and a brush will remove most stains.

Storage

Charcoal does not require any special storage, though it's best to keep it away from moisture and volatile compounds. Activated charcoal should be kept in closed containers, to prevent it from adsorbing volatile compounds.

Disposal

Charcoal can be safely burned. Activated charcoal that adsorbed various gasses should be treated before reuse or disposal.

Charcoal, best grounded, is an excellent soil amendment, and thus can simply be dumped in the ground.

References

Relevant Sciencemadness threads

• Production of small quantities of crude Wood Charcoal Carbon powder