Enhanced Densification of Cerium (IV) Oxide during Spark Plasma Sintering under a Carbon Dioxide Atmosphere

Abstract Cerium dioxide (CeO2) finds extensive utility in electro ceramics applications, including solid oxide fuel cells, oxygen sensors, and catalysts. However, Spark Plasma Sintering (SPS) of CeO2 presents challenges due to the heightened mobility of O2− ions in the presence of an electric field, as well as its reactivity with graphite tooling. Traditionally, CeO2 is sintered in an oxidative environment to prevent it from reducing to CeO2−δ or Ce2O3. Nevertheless, oxidative atmospheres are detrimental to the graphite and steel tooling used in SPS processing. In this study, we investigated CeO2 SPS in a CO2 atmosphere and observed substantial enhancement in the relative density (RD) of the as-sintered samples in comparison to those sintered in an Ar atmosphere. The improved densification is attributed to reduced formation of oxygen vacancies in the CO2 atmosphere. Furthermore, the reaction between CeO2 and graphite generates COx gases, and that reaction can be reversed in a CO2 atmosphere. In summary, CeO2 SPS in a CO2 environment demonstrates superior densification, effectively mitigating the challenges associated with ionic mobility and graphite reactivity.