The enthalpy of formation and the heat capacity of liquid and undercooled liquid Al‐Cu‐La alloys

Abstract

The integral enthalpy of mixing δH of liquid lanthanum‐rich and aluminium‐rich Al‐Cu‐La alloys was determined by solution calorimetry at 1078 K. An adiabatic calorimeter was used to measure the heat capacity Cp of liquid Al25Cu20La55 and Cu67La33 alloys. The association model was applied to calculate the thermodynamic functions of liquid Al‐Cu‐La alloys using the model parameter of the three limiting binary alloys. The results show systematic positive deviations from the experimental data. An additional ternary association reaction was assumed with a stoichiometry near to the composition of maximum deviation between calculated and experimental ΔH values. The new description reveals a good agreement with the experimental ΔH(x, 1078) and the Cp(x, T) data. The calculated Cp(T) curve of the undercooled liquid Al25La55Cu20 alloy exhibits a maximum.

Temperature–composition dependence of thermodynamic mixing functions of liquid alloys of copper with rare-earth metals

“…For most systems, whose models were constructed relying on several isotherms of thermodynamic properties, this tendency of the temperature dependence of the excess heat capacity is expressed very clearly, and ex P C Δ becomes almost zero in the range of supercooled melts in these systems. Note that this result is in agreement with the results reported in [20,41], which focus on the temperature dependence of heat capacity of easily supercooled compositions. In the framework of the IAS model, this behavior of the excess heat capacity in case of significant supercooling may be associated with almost complete absence of nonassociated atoms in supercooled liquid.…”

“…The minimum values of integral Gibbs energy calculated in these papers also fall into the range of copper-rich alloys at x REM = 0.40. According to studies of the heat capacity for melts of copper with yttrium, lanthanum, and cerium-subgroup metals [9,[19][20][21], the maxima of excess heat capacities of mixing are also shifted toward the range of compositions with x REM = 0.30-0. 35.…”

“…The mixing enthalpies ΔH of the following liquid alloys have been studied in greatest detail: Cu-Sc [1-4], Cu-Y [1, 2, 5-7], Cu-La [1, 2,8], Cu-Ce [8][9][10], Cu-Pr and Cu-Nd [10,11], Cu-Sm [12], Cu-Eu [13], Cu-Gd [14][15][16], Cu-Dy [13], Cu-Ho [15], Cu-Er [17,18], Cu-Tm [15], Cu-Yb [13], and Cu-Lu [1, 15,16]. The excess heat capacity ex P C Δ was studied in a few papers: Cu-Y [19], Cu-La [19,20], Cu-Ce [19,21], and Cu-Pr, Cu-Nd [19]. The isotherms of thermodynamic activity of copper a Cu were studied for Cu-Y [22], CuLa [23,24], Cu-Gd [25], and Cu-Lu [26] melts.…”

“…At present, the number of publications that represent original experimental information on the thermodynamic properties of Cu-REM melts is close to 30. The studied properties include the partial and integral mixing enthalpies of components [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], high-temperature content of the enthalpy [19] and heat capacity [20,21] of liquid alloys, and activity [22][23][24][25][26] of components. The thermodynamic properties of liquid alloys in sixteen systems, excepting the systems of copper with promethium and terbium, have been experimentally studied to varying extents.…”

Phase equilibria and thermodynamics of binary copper systems with 3d-metals. VII. Concentration-temperature dependences of the thermodynamic functions of mixing for liquid alloys of copper and transition metals

“…This function displays a complex temperature-concentration dependence. The isotherms of [59][60][61]. The IAS model suggests that such a behavior of the excess heat capacity at high levels of supercooling is due to the absence of nonassociate atoms in a supercooled fluid.…”