Ultra-dense (Bi, V, B)-oxide-added zircon ceramics fabricated by liquid-phase assisted spark plasma sintering (SPS)

Ultra-high-density zircon (ZrSiO₄) ceramics were prepared using the spark plasma sintering (SPS) technique of zircon nanopowder with the addition of three different sintering agents, i.e., Bi₂O₃, V₂O₅ and B₂O₃. The effect of each agent and the SPS parameters (temperature and pressure) on phase composition, microstructure, thermal and mechanical properties of the ceramics were evaluated. The identified crystalline phases of the sintered ceramics were zircon and monoclinic zirconia. The addition of a sintering agent affects the structure of zircon ceramics, i.e. the lattice parameter and the crystallite size. The sintered ceramics reached relative densities up to 99.9% of the theoretical one when V₂O₅ or B₂O₃ was added. SEM observations confirmed the densification of the zircon ceramics. We found the ceramics exhibited thermal conductivity ranging from 0.39 to 0.61 Wm⁻¹K⁻¹ at 373 K while the coefficient of thermal expansion was 2.3-4.0 × 10⁻⁶/°C and the Vickers hardness was obtained to be 9.52-12.66 GPa. The Young’s (E), bulk (B), and shear (G) moduli, Poisson’s ratio ν, Pugh’s ratio B/G, and the ratio of H V 3 / E * 2 of the ceramics are in a range of 240 − 288 GPa, 207 − 267 GPa, 91 − 109 Pa, 1.95 − 2.45, and 0.011 − 0.019 respectively. We found that high-density, quasi-ductile zircon ceramics can be synthesized at a low sintering temperature and short holding time.