The Thermodynamic Characterization of ZrCo–H, HfCoH, HfNiH and Zr1–xHfxNi(Co) Alloy–H Systems

• Calorimetric enthalpies determined for H absorption by ZrCo, HfCo, HfNi are determined.
• Ternary alloys, e.g., Zr1−xHfxNi, prepared and characterized by x-ray diffraction.
• Isotherms for the ternary alloys give thermodynamic parameters for H solution.

ZrCo and HfCo intermetallic compounds have the same cubic (CsCl-type) structure and their ternary (Zr1−xHfx)Co alloys are also cubic. ZrNi and HfNi intermetallic compounds have the orthorhombic structure (CrB-type) and the ternary (Zr1−xHfx)Ni alloys also have this structure. Thermodynamic data for hydride formation and decomposition in ZrCo, HfCo and HfNi intermetallic compounds have been determined from reaction calorimetry and from pressure-composition isotherms. Thermodynamic data have been determined for the three ternary alloys: (Zr0.75Hf0.25)Co, (Zr0.50Hf0.50)Co, and (Zr0.25Hf0.75)Co and the four ternary alloys: (Zr0.875Hf0.125)Ni, (Zr0.75Hf0.25)Ni, (Zr0.50Hf0.50)Ni, and (Zr0.25Hf0.75)Ni. This offers the opportunity to learn how the thermodynamic properties of the ternary alloy-H systems change with the stoichiometry of alloys with the same structure.