Phase equilibria in aluminum-carbon system at high temperatures

The partial excess Gibbs energies of carbon and aluminum in liquid Al-C were used with the equilibrium vapor pressures of pure Al and pure C to obtain the phase diagrams (1) at 1 bar of total pressure, and (2) at pressures sufficient to suppress the gas phase. The first diagram contains [gas+graphite → liquid] tectoid-type reaction at 2900±20K with the tectoid composition of 0.681 mol fraction of aluminum. The [gas/graphite] boundary is subject to large errors due to the large errors in the vapor pressure of pure graphite, but its general form is acceptable. The second diagram consists entirely of the condensed phases with peritectic reaction [liquid+graphite → Al₄C₃] at 2429 K. The [liquid/graphite] phase boundary was obtained from the graphite solubility in liquid solutions at 2429-2800 K, yielding the partial excess Gibbs energy of carbon in solution.

The resulting phase boundary is as reliable as the melting point of graphite, taken to be 4130 K.