The State of Carbon

On January 27, 2021, a paper in the journal Nature a new paper announced that the structure of diamond holds even at pressures of 2 trillion pascals. These are pressures that are more than five times the pressure in the Earth’s core. This makes looking at the material structure of carbon, whether it is a carbon fiber, or graphite, or diamond important.

As part of a general science class or by watching a program on television, each of us has learned that materials, either elements or compounds, exists generally in one of three physical states: solid, liquid or gas.  Of course the physicists of the world will argue that there are other states of matter: plasma, glasses, or Bose-Einstein condensates.  But, did you know a pure compound can exist in a number of different forms in its solid state?

The term used to describe this phenomena is called an allotrope.  The word was coined in about 1885 and is derived from the prefix allo-, meaning other and the suffix –trope, meaning form.  While a number of elements and compounds have different allotropes, carbon and sulfur seem to have the widest variety of solid structures.  For the moment let’s focus on carbon, which is part of the economic foundation of oil and gas industry and thus Woodward, OK.

Petroleum and natural gas are comprised of hydrocarbons.  A hydrocarbon is an organic molecule that contains hydrogen and carbon atoms.  These atoms combine to form a variety of materials such as alkanes, alkenes, cyclic compounds and aromatic compounds.  These compounds can have anywhere from one carbon atom to more than 60 carbon atoms for materials made from petroleum fractions.  As refiners processed the petroleum, they observed that they could produce relatively pure carbon materials such as coke or carbon black.  Coke is essentially a manmade version of coal used in the production of electricity and in foundry processes.  In nature, there are three types of coal: subbituminous, bituminous and anthracite.  Yet, these solid products don’t form a regular structure like a salt or sugar crystal, because of the number of impurities and the physical processes by which they are formed.  Carbon black, although a solid and a particle, also does not form a regular crystal structure.

Carbon does form a number of regular structures which are present in our everyday environment.  Diamond is probably the most recognizable crystal structure of carbon. Diamond is the hardest structure known.  In this structure, the carbon atoms bond together in tetrahedral arrangements.  A tetrahedron is a solid shape that looks like a three sided pyramid.  Natural diamonds are produced as a result of high pressure and temperatures that occur in the Earth’s mantle.  Geologists believe (geology.com) the conditions that produce diamonds occur at depths of approximately 90 miles, where temperatures are at least 2000 degrees Fahrenheit and pressures are greater than 725,000 pounds per square inch.  According to the Gemological Institute of America, the first synthetic diamonds were produced by General Electric in 1954. (Although, there were a number of prior claims by individuals and companies dating back to 1772.)  

Graphite is another solid carbon material.  Instead of forming a three dimensional crystal like that seen in a diamond, the carbon in graphite forms layers of a two dimensional one.  The individual layers are a lattice.  The carbon atoms join together to make a hexagonal shape and these shapes are combined to look like chicken wire.  While graphite does occur naturally, graphite can be manufactured via a graphitization process where an amorphous source of carbon is baked to temperatures around 5400 degrees Fahrenheit. Graphite properties are very different than that of diamond.  While diamond is the hardest of materials graphite is very soft.  Diamond is an insulator while graphite is a conductor.  Carbon fibers have a structure similar to that of graphite.

If you change some of the six-membered rings in the lattice structure of graphite with a five-membered one, materials now known as fullerenes are formed.  These materials were prepared in 1985 by scientists at Rice University.  The production of fullerenes has led to the production of other structures such as carbon tubes, called nanotubes due to their physical dimensions. 

The work with fullerenes, carbon nanotubes, and other small particles has led to a variety of new science.  These materials are now being looked at for medical and process applications.  But, the size of the materials also represents a new hazard as these materials can enter into the human body through the lungs and skin.  Industrial hygienists and other safety personnel have been working closely with companies and other research scientists that produce these materials to learn about the hazards and how to control them.

Carbon has a variety of physical forms.  It is important to our local economy.  It has found a variety of uses, energy to building materials, and potential medical therapies.  While it may be a common material, the possibilities at least for now seem endless.

This material was originally published in the Ponca City News Midweek in 2015 and was updated for the Woodward News in 2019. Now it has been updated for All About Science.

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