Core–shell structure formation strategy with hydrothermal synthesis: Importance of seeds, precursor concentration, and heterogeneous reaction

While using the titanium organic complex as a starting material under widely various seed concentrations and temperature conditions, this study examined the reaction kinetics of titanium oxide formation on nickel particles. Homogeneous and heterogeneous nucleation depending on temperature were studied from the perspective of reaction engineering for core–shell type particle design. Homogeneous nucleation and the growth rate were comparable: around 250 °C with 4.8 wt% nickel loading. Heterogeneous reaction is dominant by lowering the temperature or increasing the seed amount. Moreover, acceleration of titanium oxide formation using nickel seeds and further acceleration were found after covering nickel with titanium oxide. Homogeneous amorphous shell formation was confirmed with nanoscale analysis, which is expected to be promising for applications such as multilayer ceramic capacitors.