Analysis of the anisotropy, stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings

E. López-Honorato; H. Zhang; R. A. Shatwell; P. Guillermier; D. Manara; P. Xiao; J. Somers

doi:10.1016/j.jnucmat.2012.08.030

Analysis of the anisotropy, stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings

E. López-Honorato, H. Zhang, R. A. Shatwell, P. Guillermier, D. Manara, P. Xiao, J. Somers

Research output: Contribution to journal › Article › peer-review

8 Scopus citations

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 (OPTAFs) 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 stacking faults as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitative analysis of the Si and carbon excess in SiC in four TRISO particles.

Original language	English
Pages (from-to)	334-340
Number of pages	7
Journal	Journal of Nuclear Materials
Volume	432
Issue number	1-3
DOIs	https://doi.org/10.1016/j.jnucmat.2012.08.030
State	Published - Jan 2013
Externally published	Yes

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title = "Analysis of the anisotropy, stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings",

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 (OPTAFs) 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 stacking faults as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitative analysis of the Si and carbon excess in SiC in four TRISO particles.",

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AU - López-Honorato, E.

AU - Zhang, H.

AU - Shatwell, R. A.

AU - Guillermier, P.

AU - Manara, D.

AU - Xiao, P.

AU - Somers, J.

PY - 2013/1

Y1 - 2013/1

N2 - 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 (OPTAFs) 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 stacking faults as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitative analysis of the Si and carbon excess in SiC in four TRISO particles.

AB - 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 (OPTAFs) 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 stacking faults as confirmed by Raman spectroscopy. Raman spectroscopy was also used to perform semiquantitative analysis of the Si and carbon excess in SiC in four TRISO particles.

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JO - Journal of Nuclear Materials

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Analysis of the anisotropy, stoichiometry and polytypes in pyrolytic carbon and silicon carbide coatings

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