Corrosion of the Filled Skutterudite Sm_0.1(Fe_0.45Ni_0.55)₄Sb₁₂ by NaCl Solutions: An Electrochemical Study

Filled skutterudites form a wide class of intermetallic compounds thoroughly studied for their promising thermoelectric performance. An electrochemical study was performed on a set of two samples of filled skutterudite with composition Sm_0.1(Fe_0.45Ni_0.55)₄Sb₁₂ differing for the content of additional phases. The aim of the study is to test their resistance to corrosion by a 0.1 M NaCl solution, with particular reference to the effect of the presence of possible extra phases forming during synthesis. Measurements were carried out by electrochemical impedance spectroscopy and potentiodynamic polarization after reaching equilibrium; corrosion products grown on the sample surface after polarization tests were analyzed by scanning electron microscopy. The polarization resistance resulted in increase with the skutterudite amount within the sample, thus pointing at the role of the extra phases (Fe,Ni)Sb₂ and Sb in promoting a localized attack and in accelerating the corrosion rate. This evidence sets a clear indication toward the need for monophasic skutterudites in order to minimize the action of corroding agents in the perspective of optimizing the device durability.