S. Wannaparhun et al/Applied Surface Science 185(2002)183-196 area), respectively (Table 1). It is to be noted that most peak is mainly attributed to the aluminosilicate from of the Al(2p) signal of the composite comes from the fiber Al2O3(73.7eV(5l))only. Contrary to the as-received Nextel-720 fiber, the Al(2p) signal predominantly 3.4.2. The calculated spectra comes from the mullite phase. Following are the Once the reference spectra of the possibilities to be considered in explaining the ponents and the composite are acquired, it is important variation in the intensity of the deconvoluted peaks to compare all the XPS spectra to monitor any che- the fibers might be exposed to the environment in mical alteration. The intensity of all the XPs spectra dispersed areas, or from the nextel-720 fiber and alumina matrix can be the alumina matrix is unevenly covered with Nextel manipulated using a graphical addition method fibers at selected surface region (expanding or compressing along y-axis by fixing the x-axis). It is to be noted here that an intensity The Si/Al ratio at the surface of the composite is adjustment using a graphical method cannot be done 0.06, slightly higher than that of the matrix(0.03). The on the as-received composite's spectra. This is due to SEM image(Fig. 13b) from the surface of the as- the fact that the spectra will contain an intrinsic feature received composite substantiates our assumption that in some areas, the fibers are directly exposed to the environment. This will alter the surface Si/Al ratio of the composite slightly higher than that of the as received matrix. since XPs is a surface sensitive nstrument 3.4.1.2. XPS Si(2p). Silicon chemistry is also vital to understand the composite chemistry along with aluminum and oxygen, since these composites are primarily aluminosilicates. Fig. 1lb indicates the combination of the Si(2p)feature of the as received alumina and the fiber. Generally speaking, the Si(2p)of aluminosilicates is around 100-105 e. In the case of the as-received alumina, the intensity is quite low as compared to the background compared to that of the as-received composite. The higher Si(2p)signal in the later case is mainly due to the high aluminosilicate content in the Nextel-720 fiber Due to the uneven morphology of the composites surface, the fibers are at a depth lower than the depth 115 resolution of xps and hence cannot be detected the deconvoluted peak is obtained at 101.5 eV Table 1) The ic effect is also observed in this case as noted in the as-received Nextel-720 fiber. Similarly, this effect drives the Si(2p) peak to the lower BE of 101.5 el compared to the aluminosilicate peak (102.6 eV Fig12b. The deconvoluted peaks at 53012eV(71,93% 40 C 3.4.1.3. XPS O(Is). XPS O(Is) spectrum is shown in area) and 531. 15 ev(28.07% area) indicates Fig. 15. Graphical superimposition of the calculated and as presence of Al2O3 in the alumina matrix. The small received spectrum: (a)Al(2p);(b)Si(2p);(c)O(ls)area), respectively (Table 1). It is to be noted that most of the Al(2p) signal of the composite comes from Al2O3 (73.7 eV [51]) only. Contrary to the as-received Nextel-720 fiber, the Al(2p) signal predominantly comes from the mullite phase. Following are the possibilities to be considered in explaining the variation in the intensity of the deconvoluted peaks.  the fibers might be exposed to the environment in dispersed areas, or  the alumina matrix is unevenly covered with Nextel fibers at selected surface region. The Si/Al ratio at the surface of the composite is 0.06, slightly higher than that of the matrix (0.03). The SEM image (Fig. 13b) from the surface of the as￾received composite substantiates our assumption that in some areas, the fibers are directly exposed to the environment. This will alter the surface Si/Al ratio of the composite slightly higher than that of the as￾received matrix, since XPS is a surface sensitive instrument. 3.4.1.2. XPS Si(2p3 ). Silicon chemistry is also vital to understand the composite chemistry along with aluminum and oxygen, since these composites are primarily aluminosilicates. Fig. 11b indicates the combination of the Si(2p3 ) feature of the as￾received alumina and the fiber. Generally speaking, the Si(2p3 ) of aluminosilicates is around 100–105 eV. In the case of the as-received alumina, the intensity is quite low as compared to the background compared to that of the as-received composite. The higher Si(2p3 ) signal in the later case is mainly due to the high aluminosilicate content in the Nextel-720 fiber. Due to the uneven morphology of the composite’s surface, the fibers are at a depth lower than the depth resolution of XPS, and hence cannot be detected. The deconvoluted peak is obtained at 101.5 eV (Table 1). The IC effect is also observed in this case as noted in the as-received Nextel-720 fiber. Similarly, this effect drives the Si(2p3 ) peak to the lower BE of 101.5 eV compared to the aluminosilicate peak (102.6 eV [51]). 3.4.1.3. XPS O(1s). XPS O(1s) spectrum is shown in Fig. 12b. The deconvoluted peaks at 530.12 eV (71.93% area) and 531.15 eV (28.07% area) indicates the presence of Al2O3 in the alumina matrix. The small peak is mainly attributed to the aluminosilicate from the fiber. 3.4.2. The calculated spectra Once the reference spectra of the composite com￾ponents and the composite are acquired, it is important to compare all the XPS spectra to monitor any che￾mical alteration. The intensity of all the XPS spectra from the Nextel-720 fiber and alumina matrix can be manipulated using a graphical addition method (expanding or compressing along y-axis by fixing the x-axis). It is to be noted here that an intensity adjustment using a graphical method cannot be done on the as-received composite’s spectra. This is due to the fact that the spectra will contain an intrinsic feature Fig. 15. Graphical superimposition of the calculated and as￾received spectrum: (a) Al(2p); (b) Si(2p3 ); (c) O(1s). 194 S. Wannaparhun et al. / Applied Surface Science 185 (2002) 183–196