12 Nano/microstructure - institut de chimie et des materiaux paris-est

DK4027_book.fm Page 331 Monday, May 16, 2005 2:01 PMNano/microstructure and Multiphase Materials 331properties to be achieved in the different parts of the materials. This work wasmade for CeO 2 , an electrolyte for high-temperature fuel cells and its electricalproperties (e.g., the concentration of defects). Raman prediction was in agreementwith electrochemical and thermodynamic measurements. 9,100,101 Prediction of themechanical properties of SiC fibers from Raman spectra is also possible.A model has been used to calculate carbon grain size distribution in the asreceivedSA3 cross section (Figure 12.16c). A ring of larger carbon speciesappears on the fiber’s periphery, indicating a higher short-range order, which isconsistent with the decrease in Raman peak widths. This size increase near thesurface can be linked to the elaboration process, revealing a higher temperaturein this area. Heat-treated fibers show a large increase in this ring. The observedsize distribution indicates that crystal growth of the carbon moieties is obtainedeven deep in the fiber (a small area of low short-range order remains at the core).The relationship between Raman parameters and mechanical properties allowsconversion of the Raman image in a predictive “mechanical” image. As anexample, we present in Figure 12.16c the expected ultimate strength to beachieved for the different fiber regions. In this example, the highest values areexpected from the fiber core. Other types of fibers exhibit homogeneous behavioror an inverse configuration. Note that if a map gives a didactic view, a line scanoffers a better compromise between rapidity and quality of information. Anexample is shown in Figure 12.17 with a line scan (~18 µm) between two adjacentNLM SiC fibers in a mullite matrix composite (a ZrO 2 -based coating has beenapplied onto the fibers).200 400 600 800 1000 1200 1400 1600 1800Wavenumber / cm −1FIGURE 12.17 Spectral in-line scan (2 µm step) of a composite cross section. Spectrawere recorded from one NLM202 fiber to another, through the {aluminosilicate + (ZrO 2 ;GeO 2 )} tailored interface and the mullite matrix. (Reprinted from Colomban, P., Ramanmicrospectrometry and imaging of ceramic fibers in CMCs and MMCs, 103, 517, 2000.With permission from The American Ceramic Society.)