CORROSION OF CERAMIC-MATRIX COMPOSITES

Air stable ceramic matrix composites are promising for thermostructural applications such as aircraft engine parts. Turbine parts are subject. to both sulphuric acid and sodium molten salts corrosion due to sulphate traces in engine fuel and to the NaCl air content. The chemical stability is a very important criterion but this point has not received much attention to date. We report here a study of acidic and sodium corrosion of various aluminosilicate matrices LAS matrices (Li2OAl2O32-6SiO2,nP2O5) in the amorphous, beta eucryptite and beta spodumene forms, BAS matrix (BaOAl2O32SiO2) in the form of monoclinic and hexagonal celsian, NASICON matrix (Na3Zr2Si2PO12) and mullite matrix. Microstructure damages and ion exchange have been analysed by X-ray diffraction, IR absorption, scanning electron microscopy and Raman microprobe. Drastic corrosion is observed for beta spodumene containing composites with the formation of strong hydrogen bond or with the cell expansion due to Li/Na+ exchange. Medium acidic attack occurs for glassy LAS, beta eucryptite, BAS and NASICON matrix composites. On the other hand, beta eucryptite, NASICON and monoclinic celsian resist to alkaline melts. Mullite matrix composites are never corroded.