Thermal study of the solid-state reactions on Pt-15%Rh/Hg system

• We coated Pt-15%Rh foil electrochemically with Hg.
• The TG curve of Pt-15%Rh/Hg foil shows four distinct mass loss steps.
• At the end of the first mass loss step only bulk Hg is removed.
• In the second mass loss step only PtHg4, characterized by XRD, is decomposed.
• In the third and in the fourth mass loss step the PtHg2 and RhHg2 are decomposed and Hg is removed from a solid solution of Pt-15%Rh(Hg).

Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) were used for the study of solid-state reaction on Pt-15%Rh with electrodeposited mercury. The results suggest when heated the mercury film react with the Pt-15%Rh alloy to form intermetallics having different thermal stabilities indicated by three mass loss steps. The first mass loss step occurs between room temperature and 184 °C only the bulk Hg is removed and PtHg4, PtHg2 and RhHg2 were characterized by XRD. The second step, between 184 and 271 °C, was attributed to PtHg4 decomposition with formation of PtHg2 stabilized by RhHg2. The third step, between 271 and 340 °C, was attributed to decomposition of a solid-solution of PtHg2/RhHg2. The fourth step, between 340 and 600 °C, was ascribed to: (1) a thermal decomposition of PtHg2, formed by a PtHg eutectoid reaction (∼340 °C) on the surface and (2) Hg removal from a solid solution of Pt-15%Rh(Hg).