3. Carbon Triple Point (Graphite/Liquid/Vapor)

Determination of parameters (P, T) for the triple point of carbon (solid–liquid–gaseous) began in 1939 (Basset), and continued in 1959 (Noda). But the impressive result was obtained only in 1976 (Gokcen) for the pressure at the triple point of carbon (∼120 bar). Study of Shoessov at pressures up to 1000 bar, however, had no progress in temperature measurement. The study only by Haaland (1976) [18] gave a truthful value for the melting temperature (close to 5000 K). In addition, Haaland gave a brief analysis of the main results on different high-temperature carbon investigations, noting that the vapor (more precisely, carbon sublimate) affect the quality of the temperature measurements. Later researchers have taken a number of measures to avoid that of the steam jet (sublimate) has appeared in the optical path under temperature measurements. The determination of specific input energy under beginning of melting, enabled investigators to interpret the accuracy of the temperature measurements near the melting point of graphite. Millisecond heating current (M. Sheindlin) allowed us to obtain reliable dependence of enthalpy (input energy) against temperature of the graphite in the solid state up to 4500 K. This experiment is discussed in this chapter. Experiments of different duration (from seconds to nanoseconds) showed no dependence of the melting temperature on the heating rate (Table 3.3). The results of the various experiments performed as under heating by current or by laser heating give the matching results on the melting temperature of graphite (4800–4900 K), provided that the pressure is maintained above 110 bar.