The Graphite-Diamond Transformation

The stability of graphite and diamond and the diamond-graphite transformation were reviewed in Ch. 11, Sec. 4.2. This transformation is mostly of academic interest since few people would want to obtain graphite from diamond. However the opposite transformation, graphite to diamond, is of considerable importance. 

Graphite transforms into diamond upon the application of pressure P (in atm) and temperature T (K). This relationship is expressed by the following equation  

The equation was determined from extensive thermodynamic data which include the heat of formation of graphite-diamond, the heat capacity of graphite as a function of temperature, and the atomic volume and coefficient of thermal expansion of diamond. Some of these data are still uncertain and the generally-accepted values are listed in Table 12.2. 

The PT relationship of Eq. 1 is shown graphically In Fig. 12.2. It has been generally confirmed by many experiments. 

Hgure 12.2. Pressure-temperature diagram of diaieorKl-graphite with melting lines of nickel and nickel-graphite eutectic.  

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