Vaporization thermodynamics of MgB2 and MgB4

Abstract

The vaporization behavior of MgB2 and MgB4 under thermodynamic conditions has been studied by the Knudsen effusion-mass spectrometry technique. In the temperature range explored (883–1154 K), magnesium borides are observed to decompose by loss of gaseous Mg only. The equilibrium pressures of Mg(g) have been measured during high-temperature decompositions involving MgB2/MgB4 and MgB4/MgB7 two-phase mixtures and the corresponding standard reaction enthalpies were determined. The decomposition temperatures for MgB2 and MgB4 were also inferred by the relevant Van’t Hoff plot

MgCl and Mg2Cl2: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with MgMg Bonds

“…[24][25][26][27] In principle, the following reactions to produce MgCl 2 The subtraction of Equation (2) from Equation (1) yields the relevant components for the equilibrium presented in Equation (3). Finally, supported by several experiments on the thermal stability of MgB 2 [24][25][26]30] as well as by quantum-chemical calculations on MgCl and Mg 2 Cl 2 , the temperature-dependent partial pressure curves of MgCl 2 , MgCl, and Mg 2 Cl 2 are obtained ( Figure 1). Figure 1 also contains the decomposition pressure curve for MgB 2 ; that is, for all hypothetical model reactions discussed herein, the applied HCl pressure must be higher than the partial pressure of magnesium.…”

“…We chose MgB 2 , a well-known compound with unexpected superconducting capabilities, [21][22][23] as its Mg partial pressure had been examined in detail and amounts to not more than 10 À3 mbar at 800 8C. [24][25][26][27] In principle, the following reactions to produce MgCl 2 The subtraction of Equation (2) from Equation (1) yields the relevant components for the equilibrium presented in Equation (3). Finally, supported by several experiments on the thermal stability of MgB 2 [24][25][26]30] as well as by quantum-chemical calculations on MgCl and Mg 2 Cl 2 , the temperature-dependent partial pressure curves of MgCl 2 , MgCl, and Mg 2 Cl 2 are obtained ( Figure 1).…”

Thermodynamic and kinetic aspects of decomposition of MgB2 in vacuum: Implications for optimization of synthesis conditions

“…[12]. In Knudsen experiments, MgB 2 powders were used while, in Langmuir runs, cold sintered pellets of magnesium diboride were directly exposed to vacuum at high temperatures.…”

“…Both these problems are qualitatively predicted considering the high thermodynamic stability of MgO and also the aforementioned high volatility of Mg, even in these binary compounds. Indeed, it has been shown by Brutti et al [12] that magnesium diboride decomposes at high temperature, above 883 K (measured onset temperature) [12], under thermodynamic conditions, by the reaction 2MgB 2 (s) ¼ MgB 4 (s)+Mg(g). Empirical approach to overcome these problems generally underestimates the complexity and effects of the thermodynamics and kinetics of gas-solid reactions.…”

MgCl und Mg2Cl2: von theoretischen und thermodynamischen Überlegungen zur Spektroskopie und Chemie von Mg‐Mg‐Spezies

“…800 8C nur etwa 10 À3 mbar beträgt. [24][25][26][27] Prinzipiell [37][38][39][40][41][42] bestätigt, bei denen ein Zugang zu metallreichen Verbindungen, z. B. zu metalloiden Ga n R m -Clusterverbindungen (n > m), bisher nicht beobachtet wurde.…”