Thermodynamics of the Al2O3–Al4C3 system: III. Equilibrium vapour pressures and activation energies for volatilisation

✍ Scribed by J.-M. Lihrmann

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 239 KB
• Volume: 28
• Category: Article
• ISSN: 0955-2219
• DOI: 10.1016/j.jeurceramsoc.2007.07.016

✦ Synopsis

The present paper addresses the vapour phase in equilibrium with the compounds of the stable Al 2 O 3 -Al 4 C 3 system, between 25 • C and 1827 • C. The volatilisation of each of them into any of five gaseous species referred to as [Al x O y ], is described in terms of an activation energy and a preexponential term; for Al 2 O 3 , also sublimation is modelled on the basis of rare vapourization data. At least up to 1300 • C, the relative importance of the various [Al x O y ] derives from the activation energies necessary to form them; above 1300 • C, both activation energy and pre-exponential terms are influential. Activation energies increase with increasing ratio y/x in [Al x O y ], from approximately 365 kJ mol -1 for [Al] to about 900 kJ mol -1 for [AlO 2 ]; the effects of temperature and mole fraction Al 2 O 3 are investigated. Up to almost 1807 • C, [Al] is the predominant species regardless of carbon monoxide pressure, and thus the most likely intermediate in processes involving vapour phase reactions. Solid-vapour equilibria are illustrated in a volatility diagram at 1787 • C.