XPS Characterization of Mixed Carbides Obtained from Polymer Precursors
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XPS Characterization of Mixed Carbides Obtained from Polymer Precursors GAETANO GRANOZZI§, ANTONELLA GLISENTI§ AND GIAN D. SORARU§§ §Dipartimento di Chimica Inorganica, University of Padova, Via Loredan 4, 35131 Padova (Italy) §§Dipartimento di Ingegneria dei Materiali, University of Trento, 38050 Mesiano, Trento (Italy) Abstract Polymer precursors for Si-C, Si-Ti-C-O and Si-Al-C-O systems have been obtained from polycarbosilane and the corresponding metal alkoxides. Xray Photoelectron Spectroscopy (XPS) has been used to follow the structural evolution of these preceramic compounds during the pyrolysis process. Introduction In recent years many efforts have been devoted to obtain high-tech nonoxide ceramics from polymer precursors [1]. This process is particularly attractive for its potential use in fabricating difficult to shape forms, like fibers, or coatings of highly refractory ceramics such as SiC, Si 3N4, BN, AIN, TiC and B4C. According to this route, the starting metal-organic polymer is converted into the final ceramic material by a pyrolysis process in an inert atmosphere. The first product that appears after the decomposition of the organic components is usually an amorphous solid that transforms into a microcrystalline material by further rising the firing temperature [2]. A detailed characterization of the ceramic structures at various stages of the firing process should bring important information to better understand the relationship between the precursor polymers and the final ceramic product. In this field, the most studied system is silicon carbide obtained from polycarbosilane (PC) following the process developed by Yajima [3]. It has already been shown that the same polymer can be modified by reacting with Ti, Al and Zr alkoxides to form precursors for Si-Ti-C-O [4], Si-Al-C-O [5] and Si-Zr-C-O [6] ceramics. In this paper the pyrolysis processes of PC and modified polycarbosilanes containing Ti (PTC), and Al (PAC) have been followed by X-ray Photoelectron Spectroscopy (XPS). It will be shown that, XPS analysis can bring useful and complementary information for the structural characterization of the ceramic products. Experimental section Ti-modified PC has been obtained reacting a commercially available polycarbosilane (Dow Coming X9-6348) with titanium n-butoxide in xylene following a published procedure [4]. PAC samples were prepared following the same route using Al sec-butoxide. Chemical analysis gave an atomic ratio Mat. Res. Soc. Symp. Proc. Vol. 180. ©1990 Materials Research Society
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(M/Si) of 0.15, and 0.24 for Ti, and Al, respectively. Thermogravimetric analysis (TGA) has shown that for all the systems the decomposition of organic components is almost complete around 800'C. According to these results the precursor polymers have been fired in Ar flow at 10°C/min at various temperatures from 840°C up to 1500'C. In order to minimize surface contamination, the fired samples were ground into fine powders and pressed to form thin pellets just before XPS measurements. VG ESCALAB MKII spect
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