Spark plasma sintering of cerium (IV) oxide 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 increased 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 CeO_2−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 slight increase 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 CO_x 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.