Tyranno fiber

In addition to not offering properties expected for phase pure SiC, the original Yajima process suffers from other drawbacks that include a multistep precursor synthesis and the inability to self-cure. Finally, the presence of oxygen limits the upper use temperature for both Nicalon and Tyranno fibers to ca 1200 °C because above this temperature CO and SiO gases evolve, generating defects (large crystallites, pores and voids) that contribute to substantial decreases in mechanical properties. 

As an aside, Jacobson and DeJonghe have reported that simply heating Nicalon or Tyranno fibers at temperatures of ca 1600°C with sources of boron (e.g. boron metal, TiB2 etc.) leads to sufficient incorporation of boron into the fibers such that they densify and stable, nearly phase pure, SiC fibers are obtained. No data are provided about fiber composition118. 

Yajima s innovation directly contributed to Si-C-0 fiber (Nicalon NCK, Toyama, Japan) and Si-Ti-C-0 fiber (Tyranno Ube Industries, Tokyo, Japan) production in the early years. The Tyranno fiber production process showed the possibility of introducing various alkoxides in the starting PCS to modify the resulting SiC grain boundaries. 

It is to be expected that such phases may also control the later crystallization of SiC by heterogeneous nucleation. Such effects have been described in [150, 165, 166] concerning the crystallization of Si-C-(O) precursors containing metals like Ti, Zr, Al, i.e., precursor systems from which different types of Tyranno fibers are formed [167]. In the case of the Al-containing system it was observed that - under the given unusual conditions - SiC polytype 2H is stabilized by AI2OC which is isostructural to SiC 2H. 

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,... 

Hydrothermal formation of carbon on SiC was first observed in the course of corrosion studies of amorphous Si-Ti-C-O (Tyranno) fibers performed at 300-800°C at about 100 MPa [47,48,53]. Increasing downshift of the carbon D band in the Raman spectra with increasing reaction temperature from 1355-1360cm in microcrystalline graphite to 1350cm , 1336 cm , and 1330 3cm after hydro-thermal treatments at 300°C, 500°C, and 600-800°C respectively indicated the possible formation of sp -bonded carbon [50]. 

UBE Chemicals synthesized amorphous Si-Ti-C-O fibers from the PCS-titanium alkoxide compound polymer. These so called Tyranno fibers show excellent properties and can be spun thinner than the Nicalon fibers (see Table 4). However heating above 1000°C results in a crystallization of the fiber. In the mid 1990s the German company Bayer AG synthesized an amorphous Si-B-N-C fiber, by pyrolysis of a polyborosilazane polymer [56]. This SiBN3C fiber (see Fig. 11) has a tensile strength of 3 GPa and maintains its amorphous character up to 1800°C. The advantage of the production route from liquid to solid to produce SiC has also attracted attention for... 

Yajima et al. have reported the synthesis of continuous silicon carbide fibers from an organic polymer [30]. SiC fibers have been commercially produced by Nippon Carbon Co. under the trade name Nicalon , and similar SiC fibers containing Ti are produced by UBE Industries under the trade name Tyranno fiber [31]. 

FIGURE 13.1.3 A photograph of Tyranno fiber fabrics (courtesy of Ube Industry). 

Tyranno fiber, shown in Figure 15.1.3, is produced from pyrolysis of poly-titanocarbosilanes containing 1.5-4.0 mass% titanium, and has a diameter of 8.5-15 xm, a tensile strength of 3.3 GPa and an elastic modulus of 195 GPa. The fiber is durable up to a temperature of 1500°C. 

Properties. As shown in Table 14.9, the properties of CVD-SiC fibers are slightly superior to those of Nicalon or Tyranno fibers. The CVD-SiC fibers retain much of their mechanical properties when exposed to high temperature in air up to 800"C for as long as one hour as shown in Figure 14.8.15 ... 

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. 

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. 

---