Carbon in its pure elemental solid form assumes two lattice structures based on temperature and pressure conditions; these two structures are more commonly known as graphite and diamond. Although seemingly unrelated if placed side by side, graphite and diamond can be expressed in a simple chemical reaction, shown below. Entropy values for graphite and diamond at standard conditions are shown in Table 1.
Although it was known for many years that graphite and diamond were related by pressure and temperature, the phase diagram for carbon was not created until 1997. Laser-based experiments showed the interconversion between graphite, diamond, and liquid/gaseous carbon. Unlike a typical phase diagram with three curves meeting at a triple point, this diagram includes additional curves as the solid state is divided into its two constituents.
Figure 1.Phase Diagram
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