Difference between revisions of "Charcoal"

Revision as of 17:05, 17 August 2015

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.

Properties

Chemical

Charcoal ignites in open air to release carbon dioxide, leaving ash behind. Sugar charcoal, made by dehydrating sugar with concentrated sulfuric acid, contains no ash, and it's actually amorphous carbon. Oxidizing agents, such as concentrated nitric acid can oxidize charcoal.

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 free ash 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.

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, is preferred, as it pyrolyzes better, it's easier to mill and has less ash content.

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%).

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

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. 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.

References

Relevant Sciencemadness threads

• Production of small quantities of crude Wood Charcoal Carbon powder