Thermodynamics of the formation of magnesium–zinc intermetallic compounds in the temperature range from absolute zero to high temperature

The standard Gibbs energies of formation (ΔfGT∘) of Mg–Zn binary compounds in the temperature range from near absolute zero to high temperature were determined by calorimetry for the first time. Their heat capacities (Cp) from near absolute zero (2 K) to high temperature were measured by the relaxation method and differential scanning calorimetry. Their ΔfGT∘ values were determined by combining the Cp data with the standard enthalpies of formation at 298 K (ΔfH298∘) which were previously determined by solution calorimetry in hydrochloric acid solution. From near absolute zero to 300 K, the ΔfGT∘ values increase monotonically, and then above 300 K they can be evaluated as a linear function of temperature as follows (in kJ mol−1): ΔfGT∘(Mg48Zn52)=-12.15×102+0.135T(±300)(300–530K);ΔfGT∘(α-Mg2Zn3)=-69.95+1.15×10-2T(±20)(300–557.14K);ΔfGT∘(β-Mg2Zn3)=-68.00+8.00×10−3T(±20)(557.14–640K);ΔfGT∘(MgZn2)=-41.61+6.66×10−3T(±9)(300–680K);ΔfGT∘(Mg2Zn11)=-118.17+2.67×10−2T(±39)(300–530K). The results obtained are expected to be useful as basic thermodynamic data for Mg-based alloys.