surface science ELSEVIER Applied Surface Science 185(2002)183-196 www.elsevier.com/locate/apsusc Surface chemistry of Nextel-720 alumina and Nextel-720/ alumina ceramic matrix composite(CMC) using XPS-A tool for nano-spectroscopy S. Wannaparhun', S Seal, V. desai Advanced Materials Processing and Analysis Center(AMPAC) and Mechanical, Materials and Aerospace Engineering(MMAE). University of Central Florida, Eng. 381, 4000 University Blvd., Orlando, FL 32816, USA Received 5 July 2001: accepted 11 September 2001 Abstract Oxide-based ceramic matrix composites( CMCs)are prime candidates for high temperature turbine applications. Increasing demand of CMCs necessitates the development of quality monitoring procedures. Sol-gel derived Nextel-720 fiber/alumina matrix CMC is one of the potential candidate material for land-based gas turbine applications. X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy (TEM) were utilized to investigate any surface/interface chemical alteration of the Nextel-720 fiber reinforcement and the alumina matrix during fabrication. The calculated XPS spectra of the composite were obtained by simply adding the spectra of the as-received Nextel-720 fiber and the alumina matrix. The calculated XPS spectra and the acquired XPS Al(2p), Si(2p), and o(ls)spectra from the as-received materials were compared using a superimposition method to investigate any chemical alteration during composite fabrication for quality control measures. This paper is aimed to serve as a reference for future XPS studies of CMCs exposed to aggressive turbine environments. C 2002 Elsevier Science B V. All rights reserved PACS: 87. 64 Lg Keywords: Ceramic matrix composites; Nextel-720 fiber; XPS or ESCA; TEM; Aluminosilicate; Gas turbines 1. Introduction candidate for high temperature land-based gas turbine component because it can reduce NOx and CO emis Ceramic matrix composites(CMC) are widely used sion for no cooling medium systems [8-10 as high temperature materials for power generation An interfacial property of a CMC plays an and aerospace applications for structural advantages tant role on their ductile-brittle transition, which ver their metallic counterparts [1-7. Nextel-720/ depends on various crack-propagating modes [11 alumina CMC, an oxide-based CMC, is a potential 18]. Crack deflection within the bulk region of the composite is aimed to obtain high ductility as well as Corresponding author. Tel :+1-407-823-5277: high strength from the fiber reinforcement. Sol-gel is E-mail address: seal mail ncf. edu(S. Seal). the primary process for manufacturing a continuous Currently: Ph. D. student, Materials Science and Engineering fiber-reinforced ceramic composite(CFCC)[19, 20] University of Florida, Gainsville. During fabrication, a surface and interfacial chemical 0-4332/02/- see front matter C 2002 Elsevier Science B V. All rights reserved. S0169-4332(01)00594-3Surface chemistry of Nextel-720, alumina and Nextel-720/ alumina ceramic matrix composite (CMC) using XPS–A tool for nano-spectroscopy S. Wannaparhun1 , S. Seal* , V. Desai Advanced Materials Processing and Analysis Center (AMPAC) and Mechanical, Materials and Aerospace Engineering (MMAE), University of Central Florida, Eng. 381, 4000 University Blvd., Orlando, FL 32816, USA Received 5 July 2001; accepted 11 September 2001 Abstract Oxide-based ceramic matrix composites (CMCs) are prime candidates for high temperature turbine applications. Increasing demand of CMCs necessitates the development of quality monitoring procedures. Sol–gel derived Nextel-720 fiber/alumina matrix CMC is one of the potential candidate material for land-based gas turbine applications. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were utilized to investigate any surface/interface chemical alteration of the Nextel-720 fiber reinforcement and the alumina matrix during fabrication. The calculated XPS spectra of the composite were obtained by simply adding the spectra of the as-received Nextel-720 fiber and the alumina matrix. The calculated XPS spectra and the acquired XPS Al(2p), Si(2p3 ), and O(1s) spectra from the as-received materials were compared using a superimposition method to investigate any chemical alteration during composite fabrication for quality control measures. This paper is aimed to serve as a reference for future XPS studies of CMCs exposed to aggressive turbine environments. # 2002 Elsevier Science B.V. All rights reserved. PACS: 87.64 Lg Keywords: Ceramic matrix composites; Nextel-720 fiber; XPS or ESCA; TEM; Aluminosilicate; Gas turbines 1. Introduction Ceramic matrix composites (CMC) are widely used as high temperature materials for power generation and aerospace applications for structural advantages over their metallic counterparts [1–7]. Nextel-720/ alumina CMC, an oxide-based CMC, is a potential candidate for high temperature land-based gas turbine component because it can reduce NOx and CO emis￾sion for no cooling medium systems [8–10]. An interfacial property of a CMC plays an impor￾tant role on their ductile–brittle transition, which depends on various crack-propagating modes [11– 18]. Crack deflection within the bulk region of the composite is aimed to obtain high ductility as well as high strength from the fiber reinforcement. Sol–gel is the primary process for manufacturing a continuous fiber-reinforced ceramic composite (CFCC) [19,20]. During fabrication, a surface and interfacial chemical Applied Surface Science 185 (2002) 183–196 *Corresponding author. Tel.: þ1-407-823-5277; fax: þ1-407-823-0208. E-mail address: sseal@mail.ncf.edu (S. Seal). 1Currently: Ph.D. student, Materials Science and Engineering, University of Florida, Gainsville. 0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0169-4332(01)00594-3