Recently, ultrafast high-temperature sintering (UHS)¹ and blacklight sintering² have been identified as promising rapid densification methods with comparable process rates of up to 200 °C s^-1 and great experimental simplicity. While heat transfer in UHS is based on IR radiation during Joule heating of graphite with electric current, blacklight sintering is based on the absorption of short wavelength radiation. Absorption is maximized when the photon energy of the light is higher than the corresponding band gap of the ceramic. However, in both processes, the temperature of the green body is mainly controlled by the equilibrium of absorption and emission of light.
The physics behind both densification techniques is intriguing and will be explored in this study. Alumina (Al₂O₃), a well-known structural ceramic with a band gap of 8.8 eV, is compared to one of the most established functional materials, barium titanate (BaTiO₃), with a band gap of 3.2 eV. Both ceramics are thermally treated by both UHS and blacklight. During densification, the thermal profile is monitored, and then micrograph  are acquired to provide information on the sintering degree. In addition, the Archimedean density is determined to construct sintering trajectories.
By varying the dwell time from 10 s to 60 s and the active time of the pulsed Xe-flash lamp (Heraeus Noblelight, Cambridge, UK) from 6 to 10.8 %, BaTiO₃ is densified up to 90 % of the theoretical density under blacklight. Similar parameters are chosen for UHS, resulting in BaTiO₃ with comparable density but a substantial reduction of the material. Al₂O₃ is fully densified by UHS.
In summary, the sintering comparison of alumina and barium titanate confirms a strong influence of the band gap on blacklight sintering.
1. Wang, C. W., et al. (2020). "A general method to synthesize and sinter bulk ceramics in seconds." Science 368(6490): 521.
2. Porz, L., et al. (2022). "Blacklight sintering of ceramics." Materials Horizons 9(6): 1717-1726.