Microwave-assisted two-step sintering of Gd2Ti2O7–TiO2 composites for enhanced thermal and mechanical stability

Burnable absorber (BA) pellet candidates for boron-free small modular reactors require high density, microstructural stability, and efficient heat dissipation, yet suitable oxide-based candidates remain limited. A two-phase oxide composite (20 mol% Gd 2 O 3 –80 mol% TiO 2 ) was sintered at 1300–1400 °C, yielding Gd 2 Ti 2 O 7 and rutile TiO 2 as equilibrium phases. Kinetic analysis yielded a densification activation energy of 95.3 kJ·mol −1 and grain-growth activation energies of 184.1 and 592.9 kJ·mol −1 for Gd 2 Ti 2 O 7 and TiO 2 , respectively. Two-step sintering (TSS) suppressed abnormal grain growth, yet densification remained insufficient. Microwave-assisted two-step sintering (MTSS) was subsequently introduced, achieving a relative density of 97.41%, a grain size of 1.49 µm, and a Vickers hardness of 9.2 GPa through accelerated densification and improved microstructural uniformity. Thermal conductivity was improved by 19.54% at 100 °C, primarily owing to reduced pore-induced thermal resistance. These findings demonstrate that MTSS offers a promising sintering route for oxide-based BA pellet candidates, with favorable microstructural stability and thermal performance.