Availableonlineatwww.sciencedirect.com SCIENCE E噩≈S Journal of the European Ceramic Society 23(2003)1207-1213 www.elsevier.com/locate/jeurceramsoc Sol-gel preparation and thermo-mechanical properties of porous xAlO3-ySiO coatings on SiC Hi-Nicalon fibres Martine Verdenelli, Stephane Parola Fernand Chassagneux, Jean-Marie Letoffe, Henri vincent. Jean-Pierre Scharff. Jean bouix Laboratoire des Multimateriaux ef Interfaces UMR CNRS 5615, Universite Claude bernard Lyon 1, 69622 Villeurbanne cedex, france Received 15 June 2002: received in revised form 30 August 2002: accepted 7 September 2002 mixed aluminium silica oxides were elaborated by the sol-gel process from aluminium tri-sec-butoxide and tetraethylorthosilicate on Hi-Nicalon fibres. The porosity was generated by addition of a surfactant, namely cetyl- trimethylammonium bromide(CTAB). SiC Hi-Nicalon fibres were coated by the dip-coating technique. After annealing in air(500- 1200C)crack-free coatings were observed, with a thickness in the range 100-1000 nm. The fibres were tensile tested and results were analysed by the Weibull statistic. They showed good mechanical properties compared to the commercial fibres. The systems were characterized by thermal gravimetry, differential scanning calorimetry, X-ray diffraction, BET and scanning electron micro- scopy. The powders obtained in the same conditions as the coatings were highly porous with surface areas in the range 540-150 m-/ g depending on the annealing temperature(400-1000oC) C 2002 Elsevier Science Ltd. All rights reserved Keywords: AlO3; Composites; Porosity; SiC fibres; Sol-gel processes; Sio 1. ntroduction of controling the porosity by adding various templates were of a great interest for our purpose. Several templates Fibre-reinforced ceramic matrix composites (CMCs) can be used to create the porosity in the oxide, the chelat are of great interest for applications under high thermal ing ligand acetylacetonate(acac-)and the ionic surfactant conditions or mechanical constraints(e. g. vehicles, aero- cetyltrimethylammonium bromide C16H33N(CH3)3Br space). The concept of porous and/or oxide interphase for (CTAB) for respectively micro-and meso-porosity are the deflection of matrix cracks has been known for several reported here. Silica doped alumina systems were selec- years(Fig. 1).-However, it has never been demonstrated ted for their high temperature of crystallization and whether a such interphase could work or not. More melting, in order to maintain the porosity even at high recently it was reported that oxide coatings can act as a temperature. Two binary mixtures are reported here, 3 diffusion barrier and provide, for example, suitable pro- Al2O 2 SiO(1)and a 10%(in weight) SiO2 doped tection against oxidation or corrosion reactions. -I In this alumina(2), which, according to the equilibrium phase work, the elaboration and characterization of oxide inter- diagram should give respectively the mullite phase phase with controlled porosity on Hi-Nicalon SiC fibres Al6Si2O13, and a solid solution xAl2O3-ySiO2 which re reported together with their mechanical behavior leads to a mixture of two phases a-Al2O3(corundum Several methods can be used to elaborate thin films and the mullite on fibres, including chemical vapour deposition(CVD puttering and the sol-gel process. Among the numerous advantages of the sol-gel process compared to conven- 2. Experimental procedure tional methods, the low temperature and the possibility 2. 1. Sol preparation Corresponding author. Tel. + 33-472-448-167: fax: 33-472 431-568 All experiments were performed under an inert atmo E-mail address: stephane. parola(@ univ-lyonl fr(S. Parola) sphere using standard Schlenk techniques. 2-Propanol 0955-2219/03/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(02)00296-0Sol-gel preparation and thermo-mechanical properties of porous xAl2O3–ySiO2 coatings on SiC Hi-Nicalon fibres Martine Verdenelli,Stephane Parola*,Fernand Chassagneux,Jean-Marie Le´toffe´, Henri Vincent,Jean-Pierre Scharff,Jean Bouix Laboratoire des Multimate´riaux et Interfaces UMR CNRS 5615, Universite´ Claude Bernard Lyon 1, 69622 Villeurbanne cedex, France Received 15 June 2002; received in revised form 30 August 2002; accepted 7 September 2002 Abstract Porous thin films of mixed aluminium silica oxides were elaborated by the sol-gel process from aluminium tri-sec-butoxide and tetraethylorthosilicate on Hi-Nicalon fibres. The porosity was generated by addition of a surfactant,namely cetyl￾trimethylammonium bromide (CTAB). SiC Hi-Nicalon fibres were coated by the dip-coating technique. After annealing in air (500– 1200
C) crack-free coatings were observed,with a thickness in the range 100–1000 nm. The fibres were tensile tested and results were analysed by the Weibull statistic. They showed good mechanical properties compared to the commercial fibres. The systems were characterized by thermal gravimetry,differential scanning calorimetry,X-ray diffraction,BET and scanning electron micro￾scopy. The powders obtained in the same conditions as the coatings were highly porous with surface areas in the range 540–150 m2 / g depending on the annealing temperature (400–1000
C). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Al2O3; Composites; Porosity; SiC fibres; Sol-gel processes; SiO2 1. Introduction Fibre-reinforced ceramic matrix composites (CMCs) are of great interest for applications under high thermal conditions or mechanical constraints (e.g. vehicles,aero￾space). The concept of porous and/or oxide interphase for the deflection of matrix cracks has been known for several years (Fig. 1).15 However,it has never been demonstrated whether a such interphase could work or not. More recently it was reported that oxide coatings can act as a diffusion barrier and provide,for example,suitable pro￾tection against oxidation or corrosion reactions.611 In this work,the elaboration and characterization of oxide inter￾phase with controlled porosity on Hi-Nicalon SiC fibres are reported together with their mechanical behavior. Several methods can be used to elaborate thin films on fibres,including chemical vapour deposition (CVD), sputtering and the sol-gel process. Among the numerous advantages of the sol-gel process compared to conven￾tional methods,12 the low temperature and the possibility of controling the porosity by adding various templates were of a great interest for our purpose. Several templates can be used to create the porosity in the oxide,the chelat￾ing ligand acetylacetonate (acac) and the ionic surfactant cetyltrimethylammonium bromide C16H33N(CH3)3Br (CTAB) for respectively micro- and meso-porosity are reported here. Silica doped alumina systems were selec￾ted for their high temperature of crystallization and melting,in order to maintain the porosity even at high temperature. Two binary mixtures are reported here,3 Al2O3–2 SiO2 (1) and a 10% (in weight) SiO2 doped alumina (2),which,according to the equilibrium phase diagram should give respectively the mullite phase Al6Si2O13,and a solid solution xAl2O3–ySiO2 which leads to a mixture of two phases a-Al2O3 (corundum) and the mullite. 2. Experimental procedure 2.1. Sol preparation All experiments were performed under an inert atmo￾sphere using standard Schlenk techniques. 2-Propanol 0955-2219/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(02)00296-0 Journal of the European Ceramic Society 23 (2003) 1207–1213 www.elsevier.com/locate/jeurceramsoc * Corresponding author. Tel.: +33-472-448-167; fax: +33-472- 431-568. E-mail address: stephane.parola@univ-lyon1.fr (S. Parola).