Microwave-Assisted Formation of Phase-Pure Rutile TiO2 from Titanium Tartrate Precursor: A Facile Route toward Dense SYNROC Ceramics

Abstract

Titanium dioxide (TiO2) is an essential ceramic component of SYNROC (synthetic rock), used for immobilizing high-level nuclear waste due to its excellent chemical stability and high density. In the present study, TiO2 was synthesized via a tartrate route using a titanium tartrate (TT) precursor. The synthesis involved oxidation of Ti3+ to Ti4+ in TiCl3 solution with ammonium nitrate, followed by complexation with tartaric acid. The resulting titanium tartrate was dried at 200 °C and subsequently calcined in both muffle and microwave furnaces at different temperatures to obtain TiO2.The thermogravimetric (TG) and differential thermal analysis (DTA) curves revealed a two-step decomposition behaviour, with initial dehydration below 250 °C and major organic decomposition around 550 °C, leading to the formation of TiO2. A broad exothermic peak near 1050 °C corresponded to the anatase-to-rutile phase transformation. X-ray diffraction (XRD) studies confirmed that the as-prepared precursor was amorphous and crystallized into the anatase phase above 500 °C, which transformed partially to rutile at 1000 °C in the muffle furnace. Under microwave heating, crystallization initiated at a lower temperature (≈300 °C) with complete transformation to rutile at 600 °C—about 400 °C lower than in the muffle furnace. FTIR spectroscopy confirmed the disappearance of organic functional groups and the formation of Ti–O bonds with increasing calcination temperature. FE-SEM micrographs revealed nearly spherical nanoparticles (25–40 nm) at lower temperatures, which agglomerated into larger grains at higher temperatures. The anatase-to-rutile transformation was found to enhance densification, leading to sintered TiO2 pellets with nearly 95% of theoretical density when sintered at 1250 °C. The results demonstrate that the tartrate route provides a facile and energy-efficient method for obtaining phase-pure rutile TiO2 suitable for advanced ceramic and SYNROC applications.