Sacrificial carbon fiber–nickel hydroxide core–shell particles for nickel oxide diffusion from pore surfaces to grain interfaces in zirconia

Abstract

The sacrificial use of core–shell particles offers a versatile strategy for generating porous structures while increasing oxide–oxide interfaces within porous materials through diffusion of oxide species from pore surfaces to grain interfaces. In this study, carbon fiber (CF)–nickel hydroxide core–shell particles were combined with zirconia and calcined to produce porous zirconia sintered bodies containing nickel oxide at zirconia grain boundaries. Core–shell particles bearing vertically aligned platy nickel hydroxide on CF surfaces are prepared by a hydrothermal reaction. Upon calcination with zirconia at 1300 °C for 12 h, the CF cores were removed by combustion, and the nickel hydroxide shells were converted into tubular nickel oxide hollow particles, whose interiors acted as pores within the zirconia matrix. Complementary analyses—including X-ray diffraction, electron microscopy, elemental analyses, and synchrotron radiation multiscale X-ray computed tomography—revealed that nickel oxide is present in minute quantity, forming thin layers at zirconia grain boundaries and on portions of the pore surfaces. Compared with zirconia sintered without the core–shell particles, the zirconia–core–shell particle system suggests that interfacial diffusion of nickel oxide suppresses zirconia grain growth. These results demonstrate that both the CF core and the nickel hydroxide shell act sacrificially to create interconnected pores while designing additional oxide–oxide interfaces at pore surfaces, thereby generating an increased three-phase oxide–oxide–pore interfacial environment within the sintered bodies.