Two-step sintering assisted consolidation of bulk titania nano-ceramics by spark plasma sintering

This work investigates the feasibility to the fabrication of high density of nano-grained titanium dioxide ceramics by two-step sintering process under spark plasma conditions. First step is carried out by fast-heating-rate sintering in order to obtain an initial high density and a second step is held at a lower temperature by isothermal sintering aiming to increase the density without obvious grain growth. Experiments are conducted to determine the appropriate temperatures for each step. The temperature range between 840 and 850 °C is effective for the first step sintering (T1) due to its highest densification rate. The isothermal sintering is then carried out at 810–830 °C (T2) for various hours in order to avoid the abnormal grain growth and improve the density at the same time. TiO2 bulk ceramics with nano-sized grain were fabricated successfully by combination of spark plasma sintering (SPS) with the two step sintering method (TSS). Titanium dioxide nano-ceramics with >95% theoretical density could be obtained with T1 and T2 taken as 850 °C and 830 °C, respectively. The relative grain growth quotient D/Do for the used starting powder was almost ∼1. Further XRD investigations indicated no obvious anatase–rutile transition was found in the prepared nano-crystalline ceramics.