Raman analysis of materials corrosion: the example of SiC fibers

Abstract

Advanced materials (ceramics, fibers, composites...) exhibit unique high temperature properties but long term durability assessment is mandatory on account of high processing costs. We used Raman micro‐spectroscopy to analyze the corrosion resistance of commercially available SiC fibers versus Na+ ions, with or without fiber thermal treatment (in air or in a reducing atmosphere) prior to sodium attack. The lateral resolution of the technique approaches the submicron scale and the analysis of colored materials can be limited to a few tens of nanometers in‐depth, which makes Raman micro‐spectrometry well suited for the analysis of corrosion films. Although corrosion starts with localized defects in pristine NicalonTM fibers attacked with Na+ (in oxidizing conditions), a protective effect of a silica film is clear for oxidized fibers. The corrosion of SiC crystals seems to be related to stacking faults.

Effect of fiber microstructure studied by Raman spectroscopy upon the mechanical properties of carbon fibers

“…The detailed Raman spectrum parameters in Tables S1 and S2 were almost identical in the surface and the center, especially identical I A / I G and I D′ / I G values, which indicated that structural differences between the surface and the core of high‐performance carbon fibers were not obvious. Other high‐performance fibers also showed the same trend; for example, according to a series of study by Colomban et al, there was no structure difference on the microscale from the surface to the core of the SiC fibers after the consolidation at high temperatures …”

Characterization of the ion-amorphization process and thermal annealing effects on third generation SiC fibers and 6H-SiC

“…SiC is known to have numerous stable stoichiometric solid crystalline phases, so-called polytypes, the cubic (3C-SiC) and the hexagonal (6H-SiC) being the most common ones [12]. Raman peak parameters such as intensity, bandwidth and wavenumber provide useful information related to the phase distribution and chemical bonding of SiC and SiC fibers [13]. Table 2 gathers the characteristic Raman peak wavenumber for 3C-and 6H-SiC polytypes.…”

“…Peaks located between the 700 cm À1 and 1000 cm À1 are related to the cubic SiC polytype. Satellite peaks around 766 cm À1 are attributed to disordered SiC consisting of a combination of simple polytype domains and nearly periodically distributed stacking faults [13,14]. This explanation is consistent with the high SF density observed in Figure 2.…”

“…The high contribution of these peaks to the spectra is due to the high Raman crosssection of C2C bonds which is up to ten times higher than the Si2C bonds [15]. Regarding the C chemical fingerprint, the G peak centered around 1581 cm À1 is related to graphitic structures as a result of the sp 2 stretching modes of C bonds and the D peak centered around 1331 cm À1 , according to Colomban et al [13], should be attributed to vibrations 2/3 bonds. Finally, the shouldering appearing on the G band in both fibers, D', results from the folding of the graphite dispersion branch corresponding to G at G point.…”

How to obtain a reliable structural characterization of polished graphitized carbons by Raman microspectroscopy

“…Thus, increasing the excitation energy allows probing a smaller penetration depth of the carbon matter. [13,17] As mentioned above, an additional band was required to nicely fit the Raman spectra recorded with 2.41 eV excitation energy. For reproducible quantitative result and because of the dispersive behavior of the D band in wavenumber, a highly intrinsic degree of ordering was used in order to fit the Raman spectra with only the main features D, D and G. Indeed, the polishing process produces an inhomogeneity in the I D /I G ratio.…”