High-temperature and melting behaviour of nanocrystalline refractory compounds: an experimental approach applied to thorium dioxide

F Cappia, D Hudry, E Courtois, A Janßen, L Luzzi, R J M Konings, D Manara
2014 Materials Research Express  
The behaviour from 1500 K up to melting of nanocrystalline (nc) thorium dioxide, the refractory binary oxide with the highest melting point (3651 K), was explored here for the first time using fast laser heating, multi-wavelength pyrometry and Raman spectroscopy for the analysis of samples quenched to room temperature. Nc-ThO 2 was melted at temperatures hundreds of K below the melting temperature assessed for bulk thorium dioxide. A particular behaviour has been observed in the formed liquid
more » ... the formed liquid and its co-existence with a partially restructured solid, possibly due to the metastable nature of the liquid itself. Raman spectroscopy was used to characterize the thermal-induced structural evolution of nc-ThO 2 . Assessment of a semi-empirical relation between the Raman active T 2g mode peak characteristics (peak width and frequency) and crystallites size provided a powerful, fast and non-destructive tool to determine local crystallites growth within the nc-ThO 2 samples before and after melting. This semi-quantitative analysis, partly based on a phonon-confinement model, constitutes an advantageous, more flexible, complementary approach to electron microscopy and powder x-ray diffraction (PXRD) for the crystallite size determination. The adopted experimental approach (laser heating coupled with
doi:10.1088/2053-1591/1/2/025034 fatcat:hi5leeni7nhf3nilrnepudbqnq