Sol-gel matrices of Bas, NAS and CAS 745 and in the resulting low diffusion rate of Ba ions from the matrix to the siC fibre related to the use of barium-free interface precursors as diffusion barriers The stability of the BAS matrix relative to protons and sodium ions is rather god heing similar to that of amorphous l As but CAs and NAS matrices exhibit a better chemical stability. This behaviour may be related to the presence of an amorphous phase in these last matrices The Sic Nicalon NLM202 fibre is more rapidly b) corroded by sodium ions than the matrices studied in this work The bas matrix seems to present a good compromise expansion coefficient, high mechanical strength and 00100 Youngs modulus), the chemical criteria (low corro sion rate by proton and sodium ions, high melting Fig. 5. Raman spectrum recorded on a monoclinic temperature)and the manufacture criteria(low celsian-matrix grain (composite 5)(a) before and(b) after sintering temperature, easy handling of the sulphuric acid attack for 15 min precursors) sodium nitrate attack are shown in Fig. 4(b). In REFERENCES cases a strong chemical attack of the SiC Nicalon NLM202 fibre is observed. whatever the matrix. The phenomenon is more drastic when using an NaCl ceramics by sodium sulphate at 1000'C. J. Mater. Sci. melt. It can be assumed that there is a diffusion of 2. Kim, H. E.& Moorhead, A. J, Effect of hydrogen alkali ions into the fibre during the hot-pressing, as ater atmospheres on corrosion and flexural strength of previously observed at high temperature with sintered a-silicon carbide J. Am. Ceram. Soc., 73 (1990 sodium-rich NASICON matrix and that this diffusion 94-699 promotes the chemical attack by sodium ions of the 3. Scanu, T.& Colomban Corrosion of ceran nitrate melt. However, the attack is more important matrix composites. J. Phys. IV, C7(1993)1927-1930. 4. Lenfant, P, Plas, D, Ruffo, M, boilot, P. in the inner region of the fibre between the periphery Colomban, Ph Ceramiqucs d'aluminc p ct de ferrite B and the core than at the fibre surface(Fig. 4(d)).A pour sonde a protons, Mater. Res. Bull., 15(1980) small attack also seems to occur in the fired interface 1817-1827 precursor near the fibre periphery. 5. Scanu,T, Guglielmi, J& Colomban, Ph, lon exchange and hot corrosion of ceramic composite matrix:A vibrational and microstructural study. Solid State Ionics 3.2.2 Anorthite(CAS) and amorphous albite(NAS) 70-71(1994)109-120 No chemical attack was found with these matrices 6. Colomban, Ph, Composites ceramique multiniveaux ou after 15 min in boiling sulphuric acid small cracks are Tinteret des methodes sol-gel. Compte-Rendus des only observed in the pyrolysed ZrSiPB precursor in 8emes Journees Nationales sur les Composites (NC-8 CAS-matrix composites, as observed for LAS-matrix ed. o. Allix, J. P. Favre P. Ladeveze. AMAC. Paris composites. Cracks are evident after 90 min in boilingColomban,Ph,Menet,M,Mouchon,E,Cour sulphuric acid for the CAS matrix, which may be temanchc C.& Parlier, M, Composites ceramique proof of a partial Ca/H ion exchange and ique multicouches elabores en utilisant un associated constriction seur d interface et un precurseur de matrice ONERA Fr2672383 EP92002355, 07/830904,199 4 CONCLUSION 8. Mouchon, E, Lagrange, J. L. &Colomban,Ph Composites SiC Nicalon/matrice Nasicon: Illustration Almost fully dense aluminosilicate-matrix composites u role des ions alcalins sur la formation d'une interface have been prepared by a sol-gel route by using lissant. Compte-Rendus des &emes Journees Nati tailored polymeric interface precursors compatible nales sur les Composites (NC-8), ed. O. Allix, J.P. Favre P Ladeveze. AMAC, Paris, 1992, pp 85-96 with SiC Nicalon fibres. Mechanical properties are 9. Mouchon, E. Colomban, Ph, Origin of the carbon ery similar to those of composites prepared by the rich sliding interface in alkali containing matrix-SiC injection of a LAs melt. The highest mechanical n nbrc composite.购,,C70(9 strength was obtained by using a monoclinic celsian matrix. The origin of this phenomenon can be found 10. Chen, M, Lee, W.E.& James, P. F, Synthesis of monoclinic celsian glass-ceramic from alkoxides n the rather dense structure of monoclinic celsian Non-Crysi. Solids,147-148(1992)532-536Sol-gel matrices of BAS. NAS and CAS 745 800 700 600 500 400 300 200 100 Wavenumbers (cm-l) Fig. 5. Raman spectrum recorded on a monoclinic celsian-matrix grain (composite 5) (a) before and (b) after sulphuric acid attack for 15 min. sodium nitrate attack are shown in Fig. 4(b). In all cases a strong chemical attack of the Sic Nicalon NLM202 fibre is observed, whatever the matrix. The phenomenon is more drastic when using an NaCl melt. It can be assumed that there is a diffusion of alkali ions into the fibre during the hot-pressing, as previously observed at high temperature with sodium-rich NASICON matrix’ and that this diffusion promotes the chemical attack by sodium ions of the nitrate melt.16 However, the attack is more important in the inner region of the fibre between the periphery and the core than at the fibre surface (Fig. 4(d)). A small attack also seems to occur in the fired interface precursor near the fibre periphery. 3.2.2 Anorthite (CAS) and amorphous albite (NAS) No chemical attack was found with these matrices after 15 min in boiling sulphuric acid: small cracks are only observed in the pyrolysed ZrSiPB precursor in CAS-matrix composites, as observed for LAS-matrix composites.5 Cracks are evident after 90 min in boiling sulphuric acid for the CAS matrix, which may be proof of a partial Ca’+/H+ ion exchange and associated constriction. 4 CONCLUSION Almost fully dense aluminosilicate-matrix composites have been prepared by a sol-gel route by using tailored polymeric interface precursors compatible with Sic Nicalon fibres. Mechanical properties are very similar to those of composites prepared by the injection of a LAS melt. The highest mechanical strength was obtained by using a monoclinic celsian matrix. The origin of this phenomenon can be found in the rather dense structure of monoclinic celsian, and in the resulting low diffusion rate of Ba2+ ions from the matrix to the Sic fibre related to the use of barium-free interface precursors as diffusion barriers. The stability of the BAS matrix relative to protons and sodium ions is rather good, the corrosion rate being similar to that of amorphous LAS’ but CAS and NAS matrices exhibit a better chemical stability. This behaviour may be related to the presence of an amorphous phase in these last matrices. The Sic Nicalon NLM202 fibre is more rapidly corroded by sodium ions than the matrices studied in this work. The BAS matrix seems to present a good compromise between the mechanical criteria (low expansion coefficient, high mechanical strength and Young’s modulus), the chemical criteria (low corro￾sion rate by proton and sodium ions, high melting temperature) and the manufacture criteria (low sintering temperature, easy handling of the precursors). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Bianco, R. & Jacobson, N., Corrosion of cordierite ceramics by sodium sulphate at 1000°C. J. Muter. Sk., 24 (1989) 2903-2910. Kim, H. E. & Moorhead, A. J., Effect of hydrogen￾water atmospheres on corrosion and flexural strength of sintered a-silicon carbide. J. Am. Ceram. Sot., 73 (1990) 694-699. Scanu, T. & Colomban, Ph., Corrosion of ceramic matrix composites. J. Phys. IV, C7 (1993) 1927-1930. Lenfant, P., Plas, D., Ruffo, M., Boilot, J. P. & Colomban, Ph., Ceramiques d’alumine 0 et de ferrite p pour sonde a protons. Mater. Rex Bull., 15 (1980) 1817-1827. Scanu, T., Guglielmi, J. & Colomban, Ph., Ion exchange and hot corrosion of ceramic composite matrix: A vibrational and microstructural study. Solid State Zonics, 70-71(1994) 109-120. Colomban, Ph., Composites ceramiques multiniveaux ou l’intCr&t des methodes sol-gel. Compte-Rendus des 8smes JournCes Nationales sur les Composites (JNC-8), ed. 0. Allix, J. P. Favre & P. Ladeveze. AMAC, Paris, 1992, pp. 73-84. Colomban, Ph., Menet, M., Mouchon, E., Cour￾temanche C. & Parlier, M., Composites ceramique￾ceramique multicouches Clabores en utilisant un precurseur d’interface et un precurseur de matrice. Brevets ONERA Fr2672383, EP9200235.5, USO7/830904,1991. Mouchon, E., Lagrange, J. L. & Colomban, Ph., Composites Sic Nicalon/matrice Nasicon: Illustration du role des ions alcalins sur la formation d’une interface glissante. Compte-Rendus des 8smes Journe’es Nati￾onales sur les Composites (JNC-8), ed. 0. Allix, J. P. Favre & P. Ladeveze. AMAC, Paris, 1992, pp. 85-96. Mouchon, E. & Colomban, Ph., Origin of the carbon rich sliding interface in alkali containing matrix-sic Nicalon fibre composites. J. Phys. N, C7 (1993) 1941-1944. Chen, M., Lee, W. E. & James, P. F., Synthesis of monoclinic celsian glass-ceramic from alkoxides. J. Non-Cryst. Solids, 147-148 (1992) 532-536