High temperature mass spectrometric studies over Zr-Al binary system: Thermodynamic properties over <ZrAl3(cr) + ZrAl2(cr) > and <ZrAl2(cr) + Zr2Al3(cr) > biphasic regions

Vaporisation thermodynamic studies were performed over <ZrAl3(cr)+ZrAl2(cr)> and <ZrAl2(cr)+Zr2Al3(cr) > and <ZrAl2(cr)+Zr2Al(3)(cr) biphasic region of Al-Zr system by employing Knudsen Effusion Mass Spectrometry (KEMS) in the temperature range between 1,233 to 1,535 and 1,208 to 1,458 K, respectively. It was observed that these samples undergo incongruent vaporisation with Al(g) alone in the vapour phase. Following are the recommended p-T relations deduced in the present study: log (p(Al)/Pa) = (-18,663 +/- 132)/T + (12.23 +/- 0.10) (1,233-1,535 K) < ZrAl3(cr) + ZrAl2(cr)>. log (p(Al)/Pa) = (-18,982 +/- 112)/T + (11.92 +/- 0.08) (1,208-1,458 K) < ZrAl2(cr) + Zr2Al(3)(cr)>. From the p-T and K-T relations, based on the second and third law methods of thermodynamics, the enthalpy changes of the following reactions were evaluated: ZrAl3(cr) = ZrAl2(cr) + Al(g) and 2ZrAl(2)(cr) = Zr2Al(3)(cr) + Al(g). Subsequently, the enthalpies of the formation of ZrAl2(cr) and Zr2Al(3)(cr) were deduced.