184 S. Wannaparhun et al /Applied Surface Science 185(2002)183-196 reaction can lead to alteration in the physiochemical deposited on a preform of a woven Nextel-720 fiber properties of the composite [21-30]. Therefore, it is fabric during composite fabrication process developed important to establish the correlation between chemi University of California at Santa Barbara. The woven cal and mechanical properties(physiochemical prop- fabric was cut and laid up in layers according to the erties)of the as-manufactured composite for future desired thickness and volume fraction reinforcement. mass-production of all oxide CMCs. Both quantitative The as-received composite has the following properties and qualitative measurements of physiochemical as reported by the manufacturer: density, 2.60 g/cm; properties are important for monitoring the process volume fraction, 43. 6% fiber and porosity, w28.2 X-ray photoelectron spectroscopy (XPS)is selected Further information regarding processing of the com- as a surface analytical tool to provide key chemical state posite was reported elsewhere [15, 16 information of the CMCs. This is because XPs is pable of providing chemical information of a 2. 2. X-ray photoelectron spectroscopy large-thinregion. This particular advantage will accom- modate us to extract the information from the interface A PHI 5400 ESCA was used in the present study as a formed between the fiber and the matrix phase in CMCs major surface analytical tool. Mg Ko of energy a few detailed investigations have been documented 1253.6 eV was used as the X-ray source. After acquir 31-33 for the use of XPS valence band to investigate ing the XPS spectra, the binding energy (BE)values any chemical interaction between carbon fiber and were shifted due to the differences in the polarizability phenolic matrix. Besides, XPS has been successfully and chemical potential of the compounds. Any char a key component of the Nextel-720 fiber[34-38. 53). at 284.6ev 14448). Using a peakfit software In this study, XPS was used in detail in conjunction with TEM to monitor any chemical alteration in the using Gaussian/Lorentzian peak shape, which include CMCduring fabrication XPS analyses of the individual X-radiation satellites in the fitting routine composite components(e. g, Nextel-720 fiberandalum- ina matrix)are compared to the as-manufactured CMCs 23. Process monitoring concept The present study was intended to investigate the via bility of XPS as a tool for quality control of oxide CMC Fig. I shows an analytical route for monitoring any chemical interaction between the fiber and the matrix 2. Experimental and o(ls) spectra of the as-received Nextel-720 fiber 2.. A Nextel-720/alumina CMC (Al(2p)Fiber, Si(2p)Fiber, and o(ls)Fiber), the alumina matrix(Al(2p)Matrix, Si(2p)Matrix, and O(ls)Matrix) A Nextel-720M/alumina CMC was manufactured and the composite(Al(2p)As-received, Si(2p )As-received, by Composites Optics Ceramics Company(COI-C) and O(Is)As-received) were acquired. The calculated underan Air Force SBIR contract using sol-gelprocess. Spectra(Al(2p)cal, Si(2p)cal, and O(s)ca)were nens were supplied by Sie obtained by adding the XPS spectrum of the as- of Nextel-720 fibers infiltrated in the alumina matrix. BE scale. The calculated XPS spectra were obtained The Nextel-720 fiber was manufactured by 3M Corporation and supplied as eight-harness satin fabric. Al(2p)cal= Al(2p)Fiber+ Al(2p)Matix in the fabric roximately 400 Si(2p)cal= Si(2pE filaments, 10-12 um in diameter, and 0/90 orienta tions. The chemical composition of the fiber is approx o(ls)Cal=o(ls)Fiber +o(1s)Mat mately 85%A1 0, and 15% SiO, by weight. In terms of Ideally, there would be no chemical interaction at the phase composition, the CMC consists of 60% mullite fiber/matrix interface, if and only if the following and 40% a-A1 0, by weight [39-42) according to a conditions are satisfied binary Al2O3-SiO2 phase diagram [43]. Alumina was Al(2p)Cal= Al(2p)As-received (4)reaction can lead to alteration in the physiochemical properties of the composite [21–30]. Therefore, it is important to establish the correlation between chemi￾cal and mechanical properties (physiochemical prop￾erties) of the as-manufactured composite for future mass-production of all oxide CMCs. Both quantitative and qualitative measurements of physiochemical properties are important for monitoring the process. X-ray photoelectron spectroscopy (XPS) is selected as a surface analytical tool to provide keychemical state information of the CMCs. This is because XPS is capable of providing chemical information of a large-thinregion.Thisparticularadvantagewillaccom￾modate us to extract the information from the interface formed between thefiberandthematrixphaseinCMCs. A few detailed investigations have been documented [31–33] for the use of XPS valence band to investigate any chemical interaction between carbon fiber and phenolic matrix. Besides, XPS has been successfully utilized in studying various aluminosilicates chemistry, a key component of the Nextel-720 fiber [34–38,53]. In this study, XPS was used in detail in conjunction with TEM to monitor any chemical alteration in the CMC during fabrication. XPS analyses of the individual compositecomponents(e.g.,Nextel-720fiberandalum￾inamatrix)arecomparedtotheas-manufacturedCMCs. The present study was intended to investigate the via￾bility of XPS as a tool for quality control of oxide CMC. 2. Experimental 2.1. A Nextel-720/alumina CMC A Nextel-720TM/alumina CMC was manufactured by Composites Optics Ceramics Company (COI-C) underanAirForce SBIRcontract usingsol–gelprocess. Composite specimens were supplied by Siemens Westinghouse Corporation. The composite consisted of Nextel-720 fibers infiltrated in the alumina matrix. The Nextel-720 fiber was manufactured by 3M Corporation and supplied as eight-harness satin fabric. The tows in the fabric contain approximately 400 filaments, 10–12 mm in diameter, and 0/908 orienta￾tions. The chemical composition of the fiber is approxi￾mately 85% Al2O3 and 15% SiO2 by weight. In terms of phase composition, the CMC consists of 60% mullite and 40% a-Al2O3 by weight [39–42] according to a binary Al2O3–SiO2 phase diagram [43]. Alumina was deposited on a preform of a woven Nextel-720 fiber fabric during composite fabrication process developed byUniversityofCaliforniaatSantaBarbara.Thewoven fabric was cut and laid up in layers according to the desired thickness and volume fraction reinforcement. The as-received composite has the following properties as reported by the manufacturer: density, 2.60 g/cm3 ; volume fraction, 43.6% fiber and porosity, 28.2%. Further information regarding processing of the com￾posite was reported elsewhere [15,16]. 2.2. X-ray photoelectron spectroscopy A PHI 5400 ESCAwas used in the present study as a major surface analytical tool. Mg Ka of energy 1253.6 eV was used as the X-ray source. After acquir￾ing the XPS spectra, the binding energy (BE) values were shifted due to the differences in the polarizability and chemical potential of the compounds. Any char￾ging shifts were removed by fixing the C(1s) BE at 284.6 eV [44–48]. Using a peakfit softwareTM, non-linear least square curve fitting was performed using Gaussian/Lorentzian peak shape, which include X-radiation satellites in the fitting routine. 2.3. Process monitoring concept Fig. 1 shows an analytical route for monitoring any chemical interaction between the fiber and the matrix during composite fabrication. XPS Al(2p), Si(2p3 ), and O(1s) spectra of the as-received Nextel-720 fiber (Al(2p)Fiber, Si(2p3 )Fiber, and O(1s)Fiber), the alumina matrix (Al(2p)Matrix, Si(2p3 )Matrix, and O(1s)Matrix), and the composite (Al(2p)As-received, Si(2p3 )As-received, and O(1s)As-received) were acquired. The calculated spectra (Al(2p)Cal, Si(2p3 )Cal, and O(1s)Cal) were obtained by adding the XPS spectrum of the as￾received fiber and matrix with respect to a constant BE scale. The calculated XPS spectra were obtained using the following equations: Alð2pÞCal ¼ Alð2pÞFiber þ Alð2pÞMatrix (1) Sið2p3 ÞCal ¼ Sið2p3 ÞFiber þ Sið2p3 ÞMatrix (2) Oð1sÞCal ¼ Oð1sÞFiber þ Oð1sÞMatrix (3) Ideally, there would be no chemical interaction at the fiber/matrix interface, if and only if the following conditions are satisfied: Alð2pÞCal ¼ Alð2pÞAs-received (4) 184 S. Wannaparhun et al. / Applied Surface Science 185 (2002) 183–196