Standard Free Energy of Formation of Alumina

The standard free energy of formation of alumina, Delta G degrees(f) (Al(2)O(3)) has been determined in the temperature range 1350 degrees-1550 degrees C, by studying the reaction 2Al((1)) + 3/2 O(2)(g) = Al(2)O(3(alpha)) using electrochemical cells of the type Pt((s)) - Al(2)O(3(s)), Al((1))vertical bar Al(2)O(3) in liquid slag vertical bar O(2(g)), Pt((s)) and C((s)), Al((1))vertical bar Al(2)O(3(s)) vertical bar ionic oxide slag vertical bar Al(2)O(3(s))vertical bar Fe-C((1)), CO((g)), C((s)) Evaluation of the experimental data gives Delta G degrees(f) (Al(2)O(3)) = -394,680 + 77.8T cal/mole (1640 degrees-1830 degrees K) = -1652.45 + 0.3257T kJ/mole (1640 degrees-1830 degrees K) and a value of the standard enthalpy of formation of alumina, Delta H degrees(298) (Al(2)O(3)), of -392.60 kcal/mole (-1643.7 kJ/mole) which is about 8 kcal/mole more positive than the generally accepted thermochemical value of -400.40 kcal/mole (-1676.4 kJ/mole). A value for Delta H degrees(298) (Al(2)O(3)) of about -393 kcal/mole is consistent with data in the literature from low temperature formation cell measurements at similar to 1000 degrees C and from mineralogical studies.