A quantitative, space-resolved method for optical anisotropy estimation in bulk carbons

Abstract

A B S T R A C TThis paper presents an innovative and quantitative method for characterization of bulk carbons using polarized light microscopy. It yields maps of transverse preferential orientation and quantitative transverse anisotropy. It can be utilized on any region observable with an optical microscope, at any attainable scale. It requires a set of micrographs from the same region of a carbon-based sample at different combinations of polarizer and analyzer positions. Applications of the technique to several actual carbon-based materials are presented and discussed.

Oxidation kinetics of a rough laminar pyrocarbon in O2-, H2O- and CO2-containing atmospheres

“…With a very low extinction angle, the fibers displayed a characteristic transversely isotropic texture of ex-PAN materials [53]. Coupled data from PLOM and Raman indicate that the matrix is indeed an RL PyC [44]. With a larger FWHM D value and a lower HWHM D value, the matrix graphitic planes contains a larger amount of defects than fibers ones and is less organized [6,46], suggesting a higher sensitivity to oxidation, according to the works of Ehrburger et al [54].…”

“…An optical microscope Nikon ME600L equipped with a graduated polarizer and an analyzer is used to determine the fibers and matrix anisotropy. The extinction angle A e is measured using the Polarized Light Optical Microscopy (PLOM) method established by Gillard et al [44]. A LabRAM HR (Horiba-Jobin Yvon) Raman spectrometer with a wavelength of 632.8 nm is employed to assess the Full Width at Half Maximum of the D-band (F W HM D ), the Half Width at Half Maximum of the G-band (HW HM G ) and the ratio of the Dband intensity to the G-band intensity (I D /I G ).…”

Designing porous C/C composites for oxidation resistance with an analytical model based on the kinetic and architectural features of fibers and matrix

“…Fibers displayed a characteristic isotropic texture of ex-PAN fibers [34]. Coupled data from PLOM and Raman indicates that the matrix is made of Rough Laminar (RL) PyC [29]. F W HM D data implies that matrix graphitic planes contain a larger amount of defects than fibers ones.…”

High-flux sublimation of a 3D carbon/carbon composite: Surface roughness patterns

“…It is also equipped with a graduated polariser and analyser. This set-up has been previously fully validated for the analysis of anisotropy of carbonaceous materials [31].…”

“…1). In these PLOM images, the brightness level is an indication of the level of anisotropy of carbon while the colour indicates the local anisotropy axis orientation [31]. The interfibre matrix is brighter than the fibre which indicates a more organised carbon.…”