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

Pioneering a so far unexplored research field, 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-ThO2 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 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-ThO2. Assessment of a semi-empirical relation between the Raman active T2g 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-ThO2 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 for the crystallite size determination. The adopted experimental approach (laser heating coupled with Raman spectroscopy) is therefore proven to be a promising methodology for the high temperature investigation of nanostructured refractory oxides.

CAPPIA Fabiola;  HUDRY Damien;  COURTOIS Eglantine;  JANSSEN Arne;  LUZZI L.;  KONINGS Rudy;  MANARA Dario; 

2014-08-18

IOP Science

JRC88555

2053-1591,   

http://iopscience.iop.org/2053-1591/1/2/025034/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC88555,   

10.1088/2053-1591/1/2/025034,