Phase Diagram and Diamond Synthesis in the Aluminum—Carbon System at a Pressure of 8 GPa

Abstract

Diamond crystallization in the Al-C system under high static pressure and temperatures has been investigated and diamond synthesis regularities have been established. Phase equilibria in the binary Al-C system at a pressure of 8 GPa have been studied using metallographic and X-ray diffraction analyses as well X-ray spectrum microanalysis. The samples were prepared by quenching. The experimental results have been used to define the unknown parameters in phenomenological models of the phases that compete at high pressures. The phase diagram of the Al-C system has been thermodynamically calculated and constructed at 8 GPa. It has been found that at a pressure of 8 GPa the incongruent mode of the melting of the Al 4 C 3 carbide is retained and between 2470 and 2800 K the L + D two-phase region appears in the phase diagram.

Thermodynamic calculation of the Al-B system at pressures to 8 GPa

“…The pressure dependence of the molar volume of phases is described in the Murnaghan approx imation [6]. Molar volumes, coefficients of thermal expansion, bulk moduli and their pressure derivatives for aluminum, boron, aluminum borides, and liquid phase are taken from [7][8][9][10]. The values for AlB 2 and AlB 12 , which are absent in the literature are taken equal to corresponding values for β B 106 .…”

Thermodynamic calculation of the phase diagram for the Al–B–C system at pressure 7.7 GPa

“…The results of the investigations into the phase formation in the Al-B-C system at pressures to 6 GPa are described in [3,4]. The phase diagrams of the Al-B, Al-C, and B-C binary systems at 8 GPa were calculated in [5][6][7]. The phase diagram of the Al-B-C ternary system at high pressures has not been constructed.…”

“…The models of phases and the parameters of stability and interaction between the system phases at the ambient pressure were taken from [2]. For the calculations of the phase equilibria in Al-B, Al-C, and B-C binary systems at high pressure the results reported in [5][6][7] are used. The liquid phase is described in the approximation of subregular solutions, the mixing volume of the ternary system is taken equal to zero.…”