In-Situ High Temperature X-Ray Diffraction Study of UO2 Nanoparticles

Nanocrystallites of UO2 with a size of 3-5 nm were studied in situ with high-temperature x-ray diffraction (HT-XRD), thermogravimetry (TGA) and differential thermal (DTA) analysis. The evolution of the crystallite size, the lattice parameter and the strain were determined from ambient temperature up to 1200 C. Below 700 C, a weak effect on the crystallite size occurs and it remains below 10 nm, while a strong expansion of the lattice parameter is measured. The strain decreases with temperature and is completely released at 700 C. Above this temperature, begins the sintering of the nanocrystallites reaching a size of about 80 nm at 1200 C. The weight loss curve observed in TGA is assigned to water molecules desorption and is correlated with the strain evolution observed by HT-XRD. The linear thermal expansion and the thermal expansion coefficient at 800 C are 1.3% and 16.9 x 10-6 C-1, respectively.JRC.E.6-Actinides researc