Thermoelastic equation of state and melting of Mg metal at high pressure and high temperature

Abstract

The p-V-T equation of state of magnesium metal has been measured up to 20 GPa and 1500 K using both multianvil and opposite anvil techniques combined with synchrotron X-ray diffraction. To fit the experimental data, the model of Anderson-Grüneisen has been used with fixed parameter δ T . The 300-K bulk modulus of B 0 = 32.5(1) GPa and its first pressure derivative, B 0 ' = 3.73(2), have been obtained by fitting available data up to 20 GPa to Murnaghan equation of state. Thermal expansion at ambient pressure has been described using second order polynomial with coefficients a = 25(2)×10 -6 K -1 and b = 9.4(4)×10 -9 K -2 . The parameter describing simultaneous pressure and temperature impact on thermal expansion coefficient (and, therefore, volume) is δ T = 1.5(5). The good agreement between fitted and experimental isobars has been achieved to relative volumes of 0.75. The Mg melting observed by X-ray diffraction and in situ electrical resistivity measurements confirms previous results and additionally confirms the p-T estimations in the vicinity of melting.

Phase Relationship of Mg2Si at High Pressures and High Temperatures and Thermoelectric Properties of Mg9Si5

“…The thermal expansion data of Mg 2 Si at 0 GPa were obtained from a previous study. 21 The atomic volume of Mg at a given pressure and temperature was calculated using the equations of states of Mg. 37 The data at 11 GPa are not connected by the dashed line because the crystal structure of the HPRT phase is unknown.…”

Mg–C System up to 20 GPa: Its Phase Diagram and Stable Magnesium Carbides

“…Pressure dependencies of molar volumes were represented using the Murnaghan approximation . Bulk moduli, their pressure derivatives, and thermal expansion coefficients for simple substances and compounds were taken from previous experimental measurements: Mg, Mg 2 C, β-Mg 2 C 3 , diamond, graphite, and liquid carbon . The data for liquid Mg were found on the basis of the p , T melting curve of magnesium. , Previous ab initio results have shown that β-Mg 2 C 3 has formation enthalpy (at 0 K) close to that of the α-Mg 2 C 3 phase; so, for the β phase, we used available thermodynamic data for the α phase at ambient pressure.…”

“…Bulk moduli, their pressure derivatives, and thermal expansion coefficients for simple substances and compounds were taken from previous experimental measurements: Mg, Mg 2 C, β-Mg 2 C 3 , diamond, graphite, and liquid carbon . The data for liquid Mg were found on the basis of the p , T melting curve of magnesium. , Previous ab initio results have shown that β-Mg 2 C 3 has formation enthalpy (at 0 K) close to that of the α-Mg 2 C 3 phase; so, for the β phase, we used available thermodynamic data for the α phase at ambient pressure. The expression G Cliquid = G graphite + 100,000 – 24.21· T was adopted from ref instead of the expression G Cliquid = G graphite + 117,369 – 24.63· T because of more reasonable agreement with the experimental melting p , T curve of graphite, which results in the liquid–graphite–diamond triple-point parameters11.2 GPa and 4140 K (instead of 12.4 GPa and 4700 K).…”

“…The heating time was similar to PE experiments. Pressure and temperature estimations were made either using calibrations obtained ex situ and in situ by Si and Mg melting, phase transitions in silicates, 24 or by direct thermocouple measurements, and using equations of states of Mg, 18 MgO, 21 and Si. 22 X-ray diffraction phase analysis was performed using a Rigaku Rapid diffractometer employing Mo Kα radiation and a curved area detector (at EPL-CIW), as well as using a diffractometer PANALYTICAL X'Pert Pro MTD with a Cu anode source.…”

“…27 Pressure dependencies of molar volumes were represented using the Murnaghan approximation. 28 Bulk moduli, their pressure derivatives, and thermal expansion coefficients for simple substances and compounds were taken from previous experimental measurements: Mg, 18 Mg 2 C, 17 β-Mg 2 C 3 , 9 diamond, graphite, and liquid carbon. 29 The data for liquid Mg were found on the basis of the p,T melting curve of magnesium.…”