Direct determination of standard Gibbs energies of the formation of 4CaO·P2O5 and 3CaO·P2O 5 by transpiration method

Abstract

The standard Gibbs energy changes of the following reactions have been measured by using transpiration method; 4CaO·P2O(s)+5C(s) 4CaO(s)+P2(g)5CO(g)δG°/kj=1623.6-0.953T(±2.7), (1373 < 1573), (3CaO×P2O5)(s)5C(s)= 3(4CaO·P2O5)(s)5C(s)+P2(g)+5CO(g) The standard Gibbs energies of the formation of 4CaO·P2O 5 (δG°f,(4CaO·P2O5)) and 3CaO·P2O5 (°G°f,(3CaO·P 2O5)) have been derived as follows; δGf(4CaO· P2O5)/kJmol-1 > T/K > 1573) δGf(4CaO·P2O5)/kJmol-1= -4 200.1+0.912T, (1448 > T/K > 1523) The reasons for discrepancies from reported values were discussed from the view point of whether the activity of phosphorus is measured directly or not. © 2013 ISIJ.