Application of TPO/TPR methods in oxidation investigations of CoSb3 and Mg2Si thermoelectrics with and without a protective coating of “black glass”

Abstract

One of the main problems in thermoelectric material research is degradation of thermoelectric materials caused by oxidation at elevated temperatures in air. In order to prevent these materials from oxidation, they can be covered with protective coating. A good candidate for such coating is layers made of so-called black glass, which can be successfully applied as a protective coating against oxidation. Thermal oxidation study can be demanding for measuring equipment used for in situ examination due to formation of volatile species which are corrosive for both metal and ceramic elements. This focused our attention on temperature-programmed reduction—temperature-programmed oxidation TPR/TPO methods in which the risk of damage of expensive parts of the equipment can be minimized. These methods have an important place in characterization of solid materials and can be used as the thermal analysis methods providing complementary results to TG and DTA. The aim of the study was to confirm the usefulness of TPR/TPO methods for the study of oxidation of modern thermoelectric materials and validation of “black glass” coatings as surface protection. Pure and doped (In; Ce) CoSb3 as well as pure Mg2Si were chosen for this study. XRD and SEM/EDX methods were used for material characterization, and TG/DTA measurements were carried out as reference for TPR/TPO. We succeeded to deposit “black glass” coating on Mg2Si and to show suppression of oxidation up to 495 °C. Experimental results show high usability of the TPR/TPO method in oxidation studies of thermoelectrics and protective coatings of thermoelectric materials.