Ceramic fibers, silicon carbide-based

The Pi structure had been woven from carbon, fiberglass, ceramic fiber, silicon carbide, and even from metallic wires at Bally Ribbon Mills (BRM). This Pi structure has been patented (Schmidt et al., 2004), and it is widely used in the aerospace industry for structural joints. The base, clevis, and upright legs of the Pi structure can consist of any combination of layers based on the performance requirements. 

Other organosilicon polymer precursors for ceramics have either been prepared or improved by means of transition metal complex-catalyzed chemistry. For instance, the Nicalon silicon carbide-based ceramic fibers are fabricated from a polycarbosilane that is produced by thermal rearrangement of poly(dimethylsilylene) [18]. The CH3(H)SiCH2 group is the major constituent of this polycarbosilane. 

Besides silicon carbide based ceramic fibers, there are other promising ceramic fibers, e.g. silicon nitride, boron carbide, boron nitride, etc. 

The potential of silicon carbide pre-ceramic compounds was recognized especially after Yajima et al. had prepared silicon carbide-based ceramic fibers [1]. The development of tailor-made silicon carbide precursor molecules has to be seen in close relation to the tremendously fast growth of the field of... 

Surface flaws are common in optical fiber because of the processing technique used for the fabrication of fused-silica fibers. They are also very common in other ceramic fibers such as alumina-based or silicon carbide-based fibers. Airborne particles as well as other elements tend to attach to the surface of the fiber during process or handling. 

Another process for silicon carbide fibers, developed by Verbeek and Winter of Bayer AG [45], also is based on polymeric precursors which contain [SiCH2] units, although linear polysilmethylenes are not involved. The pyrolysis of tetramethylsilane at 700°C, with provision for recycling of unconverted (CHg Si and lower boiling products, gave a polycarbosilane resin, yellow to red-brown in color, which was soluble in aromatic and in chlorinated hydrocarbons. Such resins could be melt-spun but required a cure-step to render them infusible before they were pyrolyzed to ceramic... 

The high-temperature stability of SiC-based ceramics is well-known, and therefore its composite materials have been investigated for application to high-tem-perature structural materials [19-21]. However, well-known SiC-based fibers and matrix-materials stained with alkali salt are easily oxidized at high temperatures in air [22]. This would be a serious problem when these materials are used near the ocean or in a combustion gas containing alkali elements. In particular, a silicon carbide fiber containing boron (a well-known sintering aid for SiC) over 1 wt% was extensively oxidized under the above condition. In this... 

The last quarter of the twentieth century saw tremendous advances in the processing of continuous, fine diameter ceramic fibers. Figure 6.4 provides a summary of some of the important synthetic ceramic fibers that are available commercially. We have included in Fig. 6.4 two elemental fibers, carbon and boron, while we have excluded the amorphous, silica-based glasses. Two main categories of synthetic ceramic fibers are oxide and nonoxides. A prime example of oxide fibers is alumina while that of nonoxide fibers is silicon carbide. An important subclass of oxide fibers are silica-based glass fibers and we devote a separate chapter to them because of their commercial importance (see chapter 7). There are also some borderline ceramic fibers such as the elemental boron and carbon fibers. Boron fiber is described in this chapter while carbon fiber is described separately, because of its commercial importance, in Chapter 8. 

Based on this approach, families of silicon carbide fiber and silicon ceramic composites are now being routinely produced based on polycarbosilane precursors [22] These new materials are finding a wide range of new applications, for example, as a hot zone component in the next generation turbojets where silicon carbide composite components now routinely service at operating temperatures well in excess of 1000°C under high static thrusts (up to 50,000 psi) and high sonic pressure (up to 800 DB). No metallic components survive under these conditions. 

But CMCs will be commercially successful only when they are produced cost-effectively. Polymer-derived ceramic (PDC) technology is one of the most promising low cost fabrication methods for ceramic matrix composites, particularly for large, complex shapes. In PDC technology, a silicon-based polymer (siloxane, carbosilane, silazane, etc) with fiber or particle reinforcement is shaped and cured in the polymer condition and then pyrolyzed in a controlled atmosphere to form a stable silicon-based ceramic, such as silicon carbide, sihcon nitride, silicon oxycarbide, or silicon oxynitride. 

The physical and mechanical properties of zirconia based fibers are not sufficiently known, Inasmuch as high performance continuous fibers are not available from the market and experimental materials are scarce. The applications for ceramic oxide fibers are discussed in Chapter 12, along with related applications of carbon and silicon carbide fibers. 

Pyrolyses of siloxane materials leads to ceramic-like phases. For example, ceramic fibers based on silicon carbide have been prepared from polycar-bosilane/polymethylphenylsiloxane polymer blends. ... 

Ceramics, particularly new ceramic composites, are widely used in the cutting-tool industry. For example, alumina reinforced with silicon carbide whiskers (extremely fine fibers) is used to cut and machine cast iron and harder nickel-based alloys. Ceramic materials are also used in grinding wheels and as abrasives because of tiieir exceptional hardness (Table 12.4). Silicon carbide is the most widely used abrasive. 

Raman et al. reported the preparation of silicon carbide wiskers, SiCw, which can be employed as reinforcing fillers of ceramic-based composite materials, by pyrolyzing rayon fibers impregnated with TEOS or alkly-substituted alkoxysilanes-derived silica sol (Raman et al., 2000). 

The reference design for GFR is based around a 2400-MWth reactor core contained within a steel pressure vessel. The core consists of an assembly of hexagonal fuel elements, each consisting of ceramic-clad, mixed carbide-fueled pins contained within a ceramic hex tube. The favored material at the moment for the pin clad and hex tubes is silicon—carbide fiber-reinforced silicon carbide. 

K. Yoshida, Development of silicon carbide fiber-reinforced silicon carbide matrix composites with high performance based on interfacial and microstructure control. J. Ceram. Soc. Japan. 118... 

The TCON material is known for its impressive mechanical properties compared to its pure metallic and ceramic parts ". The TCON process allows the modifications of the ceramic precursor and molten metal to optimize the final properties of the composites for specific applications. The TCON foams studied here had a general composition based on aluminum, silicon carbide (SiC), aluminum oxide and silicon (Si). Two samples labeled TCON A and TCON B were created using pure aluminum or aluminum alloy baths. TCON A had a precursor material consisted of Si02, SIC, and hollow AI2O3 spheres. In contrast, TCON B s precursor consisted of a fiber material, which is a proprietary reinforcement developed by Fireline, Inc., and hollow AI2O3 spheres. Here, the hollow sphoical particles were added in an attempt lower the density of the foam system. 

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