Tailoring neutron-shielding boron-metakaolin geopolymers with B4C filler: Surfactant-driven interfacial and microstructural control

Abstract

The incorporation of boron (B) as a neutron absorber into metakaolin-based geopolymers for the remediation of radioactive debris following nuclear accidents has attracted considerable attention. In this study, boron carbide (B₄C) was employed as a functional filler, while cetyltrimethylammonium bromide (CTAB) acted as both a dispersant and a stabiliser to enhance the neutron shielding properties of metakaolin-based geopolymers. Although the addition of B₄C improved processability via a “roller-ball” effect and had no discernible impact on the geopolymerisation process, its weakly polar, negatively charged surface led to the formation of a loose, weak-shell interfacial transition zone (ITZ) between the filler and the matrix, thereby reducing mechanical strength and chemical stability. In contrast, CTAB self-assembled into an interdigitated monolayer on the B₄C surface, reversing its surface charge to positive and promoting its uniform dispersion within the matrix. While CTAB slightly inhibited the dissolution of metakaolin, it preferentially interacted with B₄C, thereby mitigating the adverse effects on the geopolymerisation process. Moreover, CTAB promoted gelation within the ITZ surrounding B₄C, facilitating the development of a dense, potassium-deficient, yet electrostatically stabilised microstructure. This synergistic interaction enhanced interfacial bonding between the filler and the matrix, enabled efficient stress transfer, and significantly improved mechanical performance and chemical stability. Furthermore, the B₄C–CTAB-modified geopolymers demonstrated enhanced neutron shielding performance. Overall, this work offers a promising approach for engineering high-performance, multifunctional geopolymer composites for nuclear and environmental applications.