A Carbon Phase Diagram provides a graphical representation of possible states of all crystalline substances at different temperatures, pressures and compositions. Utilizing the principles of thermodynamics, these diagrams or curves are an easy way to determine what form a particular compound may exist in under the given parameters.
The carbon phase diagram is composed of five distinct regions, each region representing a unique state of the element carbon. Carbon can exist in three states at a range of temperatures and pressures, solid, liquid and gaseous, with additional forms occurring at extreme conditions. The three main states of carbon are graphite, diamond, and amorphous.
Graphite is a form of carbon made up of a flaky structure, similar to that of clay. At normal temperatures and pressures, the graphite is composed of tightly packed sheets and the intense bonds between the atoms result in this particular form of carbon having a black color. Graphite is practically insoluble but it can exist in a solid, liquid, or gaseous state at certain temperatures and pressures.
Diamond is an allotrope of carbon that is extremely hard and transparent. Large amounts of energy are necessary to form diamond. It is the hardest known natural material and a diamond is composed of the same atoms as graphite, but the arrangement of the atoms results in its unique characteristics. Diamond forms from graphite under very high temperatures and pressures and can exist as a solid even in extreme conditions.
Amorphous carbon is a form of carbon that does not follow the crystalline structure of the other three forms. It is composed of a structured allocation of carbon atoms that does not form into crystalline shapes like the other forms of carbon. Amorphous carbon is a much softer form of carbon than diamond or graphite. It can exist in either a solid state or a liquid form.
The fourth region of the carbon phase diagram is the supercritical fluid region. In this region, the carbon is no longer considered a solid or a liquid but is in a supercritical state. This state occurs when the temperature and pressure are beyond the critical point (the intersection of the vapor pressure and temperature curves) and the properties of a gas and a liquid are both present. Carbon in this state can exist in a wide variety of forms, depending on the conditions.
The fifth region of the carbon phase diagram is the metastable zone, which occurs under extreme conditions. In this zone, thermodynamic stability is not guaranteed and the carbon can exist as double (or dual) phases, three-phase mixtures, or even alloys.
By utilizing the information of the carbon phase diagram, scientists and engineers can accurately predict the physical state of carbon under a given set of temperatures and pressure, providing valuable information for a range of applications. From materials and structural engineering to chemical reactions, the carbon phase diagram is a powerful tool for understanding the behavior of the element carbon in a physical environment.
