TEMPERATURE-DEPENDENCE OF THE MIXING ENTHALPY AND EXCESS HEAT-CAPACITY IN THE LIQUID-SYSTEM IRON-ZIRCONIUM

The mixing enthalpy Delta H-m of the liquid system Fe-Zr was measured in the Zr-rich range at 2180 K up to chi(Fe) = 0.57 and at 2280 K up to chi(Fe) = 0.58. Under the assumption of the associate Fe2Zr the temperature dependence determined can be described with the regular associate model. Based on the experimental data the following parameters are calculated: C-1 = -76 kJ/mol, C-2 = -24 kJ/mol, C-3 = 3.72 kJ/mol, Delta H-Fe2Zr(F) = -126.84 kJ/mol and Delta S-Fe2Zr(F) = -61.5 J/(mol . K). Therefore, a description of the excess heat capacity Delta Cp(AB)(chi S) is available. The variation of Delta Cp(AB)(chi S) With composition is given for 1923 K, 2180 K and 2280 K. The calculated model provides a corresponding description for literature values of Delta H-m in the Fe-rich range at 1923 K up to chi(Zr) = 0.26. The concentration and temperature dependence of Delta H-m is related to drop calorimetric enthalpy measurements of liquid Fe(2)Zi- in the range 1923-2208 K. The resulting standard enthalpy of formation H-Fe2Zr(298) = 37930 J/mol is in accordance with the available literature data and it confirms the mixing enthalpy measurements.