Doni D. Jayaseelan

Microstructural evolution of HfB2 based ceramics during oxidation at 1600–2000°C

Abstract HfB2–2 wt-%-La2O3, HfB2–20 vol.-%SiC and HfB2–20 vol.-%SiC–2 wt-%La2O3 were sintered by spark plasma sintering for 5 min between 1900 and 2000°C. Oxidation studies were carried out in static air on sintered ultra high temperature ceramics at 1600, 1800 and 2000°C, and the weight change and microstructure changes after oxidation were examined. LaBO3 formed on the surface after oxidation for 1 h above 1600°C in all La2O3 containing materials, and the cross-section microstructure shows growth of LaBO3 fibres from pores due to vapour phase reaction. Addition of La2O3 altered the oxidation kinetics of HfB2, significantly increasing the oxidation layer thickness above 1600°C. However, above 1800°C reaction has occurred between the sample and the zirconia crucible.

Densification behaviour and physico-mechanical properties of porcelains prepared using spark plasma sintering

ABSTRACT Porcelain powder was consolidated using spark plasma sintering (SPS) at a constant heating rate of 100°C min−1 to peak temperatures ranging from 1000 to 1200°C and was observed to sinter at relatively low temperature ∼920°C under the SPS conditions while conventional sintering requires ∼1050°C. SPS produced densification rates about 10 times greater than conventional sintering. The dwelling step at the optimal peak temperature was negligible due to rapid flow of the molten glass assisted by applied pressure. SPSed samples exhibited denser microstructures, resulting in improved physico-mechanical properties compared with conventionally sintered samples such as apparent bulk density improved from 2.38 to 2.48 g cm−3, Vickers hardness improved from 3–5 to 6–7 GPa, and fracture toughness improved from 2–3 to 4–6 MPa m1/2.