Upscaling Ultrafast High-Temperature Sintering (UHS) to consolidate large-sized and complex-shaped ceramics

Despite the well-recognized advantages of Ultrafast High-temperature Sintering (UHS) based on the application of a graphite felt/paper heater, the technology, however, remains mostly suitable to consolidate thin-shaped samples. This work proposes a novel UHS configuration based on the graphite powder medium (P-UHS) to obtain much larger and complex-shaped products. As a proof-of-concept, nearly full dense and homogeneous macro-/microstructures bulk alumina ceramics with size of 10×10×25 mm3 were densified under a heating rate of 770 °C/min. In comparison with the conventional firing (5 °C/min) approach, the combination of ultrafast heating rate and high temperature (≥1772 °C) induced a very high densification rate mostly driven by lattice diffusion. The very rapid sintering cycle also prevented any detectable carbon contamination. Indeed, the proposed P-UHS approach combines together fine tuning of the microstructures and ultralow energy requirements.