In-situ investigation of the anatase-to-rutile phase transition in titanium dioxide nanoparticles by non-ambient high-resolution X-ray diffraction

This work investigates the anatase-to-rutile phase transformation of 6 to 10 nm titanium dioxide nanoparticles under non-ambient conditions using high-resolution X-ray diffraction in an Anton Paar DHS 1100 stage. While the reaction was significantly delayed or even inhibited under vacuum, sintering effects remained evident. Scherrer analysis and Scanning Electron Microscopy (SEM) imaging with up to 200kX magnification were employed to reveal particle sizes and morphological changes during different stages of the calcination. In air, the phase transition was observed in-situ between 500 °C and 800 °C. Exponential decay modeling of the anatase reflection intensity yielded an activation energy of E a 1 = (217 ± 4) kJ/mol. Johnson–Mehl–Avrami–Kolmogorov (JMAK) modeling of the emerging rutile phase revealed two distinct growth regimes: (i) diffusion-limited growth with instantaneous nucleation (Avrami exponent n ≈ 0.5–1, E a 1 ′ = (213 ± 6) kJ/mol) and (ii) nucleation-limited growth with continuous nucleation (Avrami exponent n ≈ 1–2, E a 2 = (438 ± 4) kJ/mol). These findings are consistent with aforementioned Scherrer analysis and SEM imaging as well as previous literature and provide deeper understanding of the transformation mechanism during calcination. Furthermore, the successful application of the JMAK model under these specific conditions demonstrates its utility in describing complex nanoscale phase transformations. • Microscopy and Scherrer analysis reveal TiO 2 nanoparticles coarsening from 6 nm to μ m. • In-situ X-ray diffraction tracks the anatase to rutile phase transformation. • Exponential decay modeling gives an activation energy of 217 kJ per mol. • Johnson–Mehl–Avrami–Kolmogorov modeling reveals two kinetic regimes. • Diffusion-controlled growth shows 213 kJ mol −1 , nucleation 438 kJ mol −1 activation energy.