Thermal decomposition of magnesium sesquicarbide

Abstract

The structure of Mg2C3 and the course of its decomposition were studied. The powder X-ray diffraction patterns were analyzed to obtain the lattice parameters for hexagonal Mg2C3, a = 743.4 ± 0.5 pm, c = 1 056.4 ± 1.6 pm. Thermal decomposition data were obtained for temperatures 670-740 °C and pressure 130 Pa; they could be fitted satisfactorily by kinetic equations for various processes, including the 1 st order decomposition reaction, and so the controlling phenomenon of the reaction cannot be deduced based on the kinetic data. The 1 st order rate constants and reaction halflives were evaluated for various temperatures and approximated by the Arrhenius equation to calculate the parameters AA = 1.97 . 1014 s-1, EA = 333 kJ mol-1. The conditions of synthesis of Mg2C3 are discussed from the point of view of the choice of a suitable hydrocarbon for the reaction with magnesium. The thermal stability of the sesquicarbide increases with increasing pressure; it could be formed from dicarbide and sustained even at a temperature of 1 450 °C by applying a pressure as high as 6 GPa.

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

“…Mg 2 C 3 forms from metastable MgC 2 and remains stable up to 1720 K at 6 GPa, well in agreement with Figures and a (i.e., present as a solid at 6 GPa at the isotherm diagram section of 1500 K and not at 2000 K).…”

“…In our experiments, the β-Mg 2 C 3 formation was observed only at 5 GPa and heating above 1500 K 9 i.e., at high enough temperature for the formation of the liquid phase in the system (Figure 4a). • Mg 2 C 3 forms from metastable MgC 2 and remains stable up to 1720 K at 6 GPa, 11 well in agreement with Figures 2 and 4a (i.e., present as a solid at 6 GPa at the isotherm diagram section of 1500 K and not at 2000 K).…”

“…The C–Mg eutectic remains degenerated. The calculated T 1 ( p ) of ∼1600 K is in agreement with a quite high experimental value of the Mg 2 C 3 decomposition temperature of ∼1700 K at 6 GPa …”

Synthesis of β-Mg2C3: A Monoclinic High-Pressure Polymorph of Magnesium Sesquicarbide

“…Both carbides are thermodynamically metastable with respect to their formation elements: Δ H f ° = +79.5 kJ/mol and +87.86 kJ/mol for Mg 2 C 3 and MgC 2 , respectively . The structural units within these carbides were originally deduced from hydrolysis measurements, which either yielded acetylene or propadiene (or propyne) depending on the carbon anions present. − Only later were definitive structural solutions possible confirming the nature of the carbon within, ,, likely a result of the intrinsic metastability and reactivity of these compounds. Fjellvåg and Karen reported the structural characterization of Mg 2 C 3 in 1992, as obtained from neutron diffraction measurements on relatively pure samples .…”

Carbon‐fibre reinforced magnesium alloys: nanostructure and chemistry of interlayers and their effect on mechanical properties

“…In the chemical literature ( Irmann, 1948; Schneider & Cordes, 1955; Hájek et al ., 1983a , 1983b), the system C/Mg is treated as a chemically non‐reactive one. This is because the two binary magnesium carbides MgC 2 and Mg 2 C 3 are endothermic compounds which start to decompose at about 500 °C and 650 °C, respectively.…”