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).