Title: Analysis of the anisotropy, stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings
Citation: JOURNAL OF NUCLEAR MATERIALS vol. 432 no. 1-3 p. 334-340
Publication Year: 2013
JRC N°: JRC67403
ISSN: 0022-3115
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC67403
DOI: http://dx.doi.org/10.1016/j.jnucmat.2012.08.030
Type: Articles in periodicals and books
Abstract: Silicon carbide (SiC) and pyrolytic carbon (PyC) coatings in tristructural isotropic (TRISO) coated fuel particles were characterised by a combination of 2-modulator generalised ellipsometry microscopy (2-MGEM), Raman spectroscopy and transmission electron microscopy. We compared the values of anisotropy obtained from 2-MGEM and Raman spectroscopy to investigate the effect of sampling area and microstructure. No linear correlation in anisotropy was found between these two techniques despite both sampling areas of 2-5 µm. The largest deviations were observed for highly anisotropic samples with optical anisotropy factors (OPTAF) above 1.1. For medium and low anisotropy samples (OPTAF < 1.1) the relationship is close to linear. The limited use of only the average value of diattenuation does not give an accurate representation of the characteristics of the coatings as significant areas can exist with considerably higher diattenuations that could increase the probability of failure under neutron irradiation. We also observe a change in the diattenuation of SiC due to the presence of α-SiC as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitaive analysis of the Si and carbon excess in SiC in four TRISO particles.
JRC Directorate:Nuclear Safety and Security

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