Ceramic fibers Tyranno

High temperature stability of these nonoxide fibers in air is another critical problem. Thermal stability of ceramic fibers derived from polymeric precursors is of special concern mainly because, as mentioned above, they frequently have undesirable phases present in them. Polycarbosilane-derived SiC fibers, such as Nicalon or Tyranno, involve a thermal oxidation curing process as described above and can contain as much as 10 wt % oxygen (Okamura and Seguchi, 1992). Such fibers decompose at temperatures above 1200 C in a nitrogen or argon atmosphere with SiO and CO gas evolution ... 

SiC fibers were produced using polycarbosilanes by Yajima et al. in 1975 [1,2]. Besides SiC fibers, Si-Ti-C-O fibers prepared from a polytitanocarbosi-lane have been obtained by adding a titanium tetrabutoxide to polycarbosilane or polysilane [3]. SiC fibers (Nicalon) and Si-Ti-C-O fibers (Tyranno) are manufactured on an industrial scale. Colorless silicon oxynitride fibers and silicon nitride fibers [4] have been obtained by the nitridation of polycarbosilanes in the author s laboratory. Polymers used for ceramic precursor and the resulting ceramic fibers are listed in Table 1. 

Titanium can be introduced in PCS precursors as titanium tetrabutoxide, Ti(OC4H9)4, to yield Si-C-O(Ti) ceramic fibers such as Tyranno (Equation 6) (48). Fibers produced from such PCS(Ti) precursors have a slightly higher pyrolysis temperature (Tp) than that previously mentioned for their pure PCS counterparts [49]. As a result, they also retain their amorphous state and hence their tensile strength to a slightly higher temperature. 

Nicalon and Tyranno ceramic fibers, two well-known preceramic derived commercial products, are marketed for structural applications. Nicalon is a SiC based ceramic fiber processed using chemistry and techniques first developed by Yajima and coworkers [6-14]. Tyranno fibers are SiC/TiC based fibers produced via novel modifications to the original Yajima work [15-17]. Elastic moduli and tensile strengths for both fibers are of the order of 250-300 GPa and 2-3 GPa respectively. Textron s CVD SiC fibers (not preceramic) offer tensile strengths of up to 4 GPa [18]. The elastic modulus of sintered, hot pressed SiC is in the range of 400-450 GPa [19]. These compare with tensile strengths of =< 8 GPa and an elastic modulus of= 580 GPa for single crystal, SiC whiskers [18]. 

These disparities in physical properties arise because ceramic fibers produced from preceramic polymers are (1) not fully dense (2) amorphous, and (3) rarely pure. Both the Nicalon and Tyranno fibers exhibit densities of 2.7 g/cc versus 3.2 g/cc for fully dense SiC. The HPZ fibers exhibit densities of 2.3 g/cc vs 3.2 g/cc for fully dense Si3N4- A typical chemical composition for Nicalon is SiCj 4qH q O Q4. Similarly, the empirical formula for Tyranno fibers is > SiCj jTi q40[) g. 

The multifilament fiber (10-20 xm diameter) as commercially produced consists of a mixture of /3-SiC, free carbon and SiOj. The properties of this fiber are summarized in Table 6.5. The properties of Nicalon start to degrade at temperatures above about 600°C because of the thermodynamic instability of composition and microstructure. A ceramic grade of Nicalon, called Hi Nicalon, having low oxygen content is also available Yet another version of a multifilament silicon carbide fiber is Tyranno, produced by Ube Industries, Japan. This is made by pyrolysis of poly (titano carbosilanes) and contains between 1.5 and 4wt% titanium. 

The fabrication of glass or glass ceramic matrices by hot pressing is outlined at moderate temperatures and pressures, but they are sufficiently high to cause formation of interphases between SiC-fibers - namely NICALON and TYRANNO - their coatings and the matrix. Formation of very complex... 

The maximum temperature of use for NICALON- or TYRANNO-fiber reinforced glasses and glass-ceramic is limited by the transformation temperature of the glass phases, i.e., about 500 °C for SiCAiorosilicate-glasses,... 

The three major constituents of any continuous fiber ceramic matrix composite are the reinforcing fibers, the matrix and a fiber-matrix interphase, usually included as a coating on the fibers. HiPerCompTM composites can be processed with various monofilament and multifilament fibers, such as the SCS family of monofilament SiC from Specialty Materials, Inc. CG-Nicalon and Hi-Nicalon Type S from Nippon Carbon Company Tyranno ZE , Tyranno ZMl and Tyranno S A from Ube Industries and Sylramic fiber from COl Ceramics. However, the composites described in this paper all utilize Hi-Nicalon SiC fiber from Nippon Carbon Company. A companion paper, in this book, by Jim DiCarlo [11] from NASA gives the properties of slurry cast composites reinforced with Sylramic and Sylramic-iBN fibers. 

Chen, L., Behlau, G., Gogotsi, Y., and McNallan, M.J. Carbide derived carbon (CDC) coatings for tyranno ZMI SiC fibers, in 27th International Cocoa Beach Conference on Advanced Ceramics and Composites A, Cocoa Beach, Florida, vol. 24 (eds. W.M. Kiiven and H.T. Lin), 57-62, 2003. 

Y. Gogotsi and M. Yoshimura, Low temperature oxidation, hydrothermal corrosion and their effects on properties of SiC (Tyranno) fibers. J. Am. Ceram. Soc., 78, 1439-1450, 1995. 

Kumagawa, K., Yamaoka, H., Shibuya, M., Yamamura, T. (1997). Thermal stability and chemical corrosion resistance of newly developed continuous Si-Zr-C-0 Tyranno fiber. Ceramic Engineering and Science Proceedings, 18, 113-118. doi 10.1002/9780470294437.chl2. 

---