We continue to review some of the most important materials in heat treatment and metallurgy.
Carbon (chemical symbol: C)
Carbon is one of the most important elements to humankind. one of the building blocks of life and critical to the field of metallurgy. It is the fourth-most-common element in the universe by mass after hydrogen, helium and oxygen. Carbon is the second-most-prevalent element in the human body after oxygen, and it makes up about 18.5% of us by mass. Carbon is sometimes referred to as the “king of the elements” due to its huge number of compounds in existence – almost 10 million to date, more than any other element.
There are several forms, or allotropes, of carbon, with the most common being graphite, diamond and amorphous carbon. Each has vastly different physical properties. Graphite, for example, is dull black, electrically conductive and soft enough to leave a mark on paper or other surfaces it touches. In fact, the word graphite is Greek for “to write.”
Diamond, on the other hand, is semi-transparent, reflective, electrically non-conductive and the hardest naturally occurring material known. Amorphous carbon is a different form of carbon that has no long-range crystalline order. Examples include charcoal, soot, coke, activated charcoal, carbon films used in semiconductors and nanocomposites, among many others. Due to their unique properties, various forms of amorphous carbon are used in the textile, plastic and health-care industries as well as for gas and water filtering, electrical equipment and food packaging.
Carbon’s most important contribution to metallurgy is steel, which is an alloy of iron and up to 2.14% carbon by weight. Carbon is added to the molten iron. When cooled, the carbon atoms fill interstitial gaps in the atomic structure, adding significant strength. Steelmaking has been around since the early second millennium B.C., with evidence of it found in Turkey. Modern steelmaking began with the Bessemer process, a technique for removing impurities from the molten steel by blowing air through it. Using a Bessemer convertor (Fig. 2), 3 to 5 tons of steel could be processed in 10-20 minutes, a vast improvement over previous methods. Steel is one of the most prevalent man-made materials in the world, with over 1.6 billion tons produced annually.
Here are a few important facts about carbon.
- Atomic number: 6
- Atomic weight: 12.0107
- Melting point: 3823 K (3550°C or 6422°F)
- Boiling point: 4098 K (3825°C or 6917°F)
- Density: 2.2670 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Non-metal
- Period number: 2
- Group number: 14
- Group name: none