PNNL

Abstract

The degradation of the internal structure of plutonium (IV) oxalate during calcination was investigated with Transmission Electron Microscopy (TEM), electron diffraction, Electron Energy-Loss Spectroscopy (EELS), and 4D Scanning TEM (STEM). TEM lift-outs from cuboid particles of precipitated Pu(IV) oxalate were prepared that had been calcined at 300°C, 450°C, 650°C and 950°C. The resulting phase at each calcination temperature was identified as PuO2 with electron diffraction. The grain size distribution was obtained with high-resolution TEM and 4D-STEM. In the case of 4D STEM, the images were further analyzed to provide distributions. In the 300°C calcined sample, the grains were