The Mg–C phase equilibria and their thermodynamic basis

Abstract

AbstractThe Mg–C binary phase equilibria and thermodynamic data are critically evaluated in this work. The necessity is demonstrated to meticulously evaluate the original experimental literature instead of relying on erroneous statements in a previous review that had led to a completely different phase diagram. The two Mg carbides, Mg2C3and MgC2, are both shown to be metastable based on the examination of the thermodynamic data and the original experimental work on their formation and decomposition. Using the Calphad method, a thermodynamic description of the Mg–C system is developed. The stable phase diagram at 1 bar was calculated without assuming any binary interaction parameters. The solubilities of C in liquid Mg, having recently been measured to be tens of ppm between 800°C and 900°C, verify the calculated phase diagram. The metastable Mg2C3and MgC2phases were also modeled and their descriptions were directly derived from the thermodynamic data. The complete Mg–C description allows the calculation of metastable phase equilibria involving these carbides by suspending graphite and diamond.