Oxygen sensors are commonly used in various industrial sectors, in particular to control the oxygen activity in molten steel [1]. The typical electrolyte used in these sensors is partially stabilized zirconia with magnesia (Mg-PSZ), due to an excellent combination of properties, largely related to the content of three crystalline phases (monoclinic, tetragonal and cubic). In Mg-PSZ the percentage and distribution of each phase in microstructural terms depend on the chemical composition and maximum sintering temperature, but also on cooling conditions. The study of the relationships between composition, processing and thermal properties of Mg-PSZ was the central objective of this work.
Several materials were prepared with compositions ranging from 2.5 to 10% (molar percentage) of MgO, sintered at 1700 °C, but involving different cooling profiles. These materials were primarily characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dilatometric thermal analysis (DIL). The results confirmed a strong compositional effect, but also a clear relevance of the cooling profile on phase content, thermal behavior and microstructure.
Since the tetragonal to monoclinic phase transformation is triggered by milling, powder XRD is unable to provide a proper phase quantification. However, taking advantage of the significant volume changes observed with this transformation, an original methodology of phase quantification is hereby presented, based on DIL, circumventing the limitations of surface (only) analyses involving sintered bodies. This solution can be further used in detailed kinetic studies on phase transformations in similar systems.
Acknowledgments: Work performed with funding from CICECO‐Aveiro Institute of Materials (FCT UID/CTM/50011/ 2013), based on Portuguese funds from FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.
References
[1] A.I.B. Rondão, E.N.S. Muccillo, R. Muccillo, F.M.B. Marques, J. Appl. Electrochem. 47 (2017) 1091–1113.
Sensors , Advanced characterisation , Electrochemical behavior
