Cerium oxide inclusion nucleation mechanism based on classical nucleation theory and two-step nucleation

It is challenging to assess the mechanism responsible for the nucleation of inclusions in metals at high temperatures. The present work therefore systematically investigates the nucleation of cerium oxide inclusions according to classical nucleation theory and a two-step nucleation mechanism. The nucleation rates and nucleation radii of these inclusions are obtained, and the results demonstrate a considerable difference between theoretical and experimental values. On the basis of a two-step nucleation mechanism, (CeO2)n and (Ce2O3)n (n = 1–6) clusters were constructed and the thermodynamic properties of both these clusters and of cerium oxide nanoparticles were analyzed. In addition, the entropies and heat capacity changes of cerium oxides were determined using first principles calculations and are found to be consistent with literature data. The present data indicate that the cerium oxide inclusion nucleation pathway can be summarized as [Ce] + [O] → (CeO2)n/(Ce2O3)n → (Ce2O3)n → (Ce2O3)2 → core(Ce2O3 crystal)–shell((Ce2O3)2 cluster) nanoparticles → (Ce2O3)bulk.