Tensile silicon carbides

Figure 19.3. Tensile strength of CVD silicon-carbide fiber as a function of temperature.

Yajima. S., Hayashi. J., Omori, M. and Okamura, K. (1976). Development of a silicon carbide fiber with high tensile strength. Nature 261, 683-685. 

Fig. I.IB illustrates fibers typical of commercial asbestos, while Fig. l.ll shows Fiberglas and Fig. I.IJ silicon carbide whiskers. Some of the fibers in these examples are bent, occasionally through 180°, indicating considerable flexibility. Whiskers of other compounds can also bend but the tensile strength of these materials is their most remarkable feature. The measured values (Table 1.2) are at least ten times higher than those observed for the same compounds in bulk or in another morphology (Walker and Zoltai, 1979). The numerous investigations into the causes of this unique response have produced several hypotheses.

An important application of polydimethylsilane is as a source of silicon carbide (SiC) fibres, which are manufactured under the trade-name Nicalon by Nippon Carbon in Japan. Heating in an autoclave under pressure converts polydimethylsilane to spinnable polycarbosilane (-Me2Si-CH2-) with elimination of methane. The spun fibres are then subjected to temperatures of 1200-1400 °C to produce silicon carbide fibres with very high tensile strengths and elastic moduli." As a result of their conductivity, polysilanes have also been used as hole transport layers in electroluminescent devices. In addition, the photoconductivity of polymethylphenylsilane doped with Cgo has been found to be particularly impressive. ... 

Yajima, S., Hasegawa, Y., Hayashi, J., and Iimura, M. (1978). Synthesis of continuous silicon carbide fibre with high tensile strength and high Young s modulus. J. Mater. Sci. 13, 2569-76. [2, 221]... 

Nagano, T., Gu, H., Shinoda, Y., Zhan, D., Mitomo, M., and Wakai, F., Tensile ductility of liquid-phase sintered (3-silicon carbide at elevated temperatures , Mater. Sci. Forum, 1999, 304-6, 507-12. 

K. M. Prewo, Silicon Carbide Fiber-Reinforced Glass-Ceramic Composite Tensile Behavior at Elevated Temperature, J. Mat. Sci., 24,1373 (1989). 

A typical tensile creep curve for a particulate reinforced ceramic matrix composite, siliconized silicon carbide (Si/SiC),28 is shown in Fig. 4.1. In comparison to the behavior of metals and metallic alloys, tertiary creep is suppressed in this material. There is only a slight upward curvature of the creep curve prior to failure. In many other ceramic matrix composites, tertiary... 

Fig. 4.1 Tensile creep curves for siliconized silicon carbide (Carborundum KX01). Over most of the data range, these data can be represented by a constant creep rate there is a short primary creep stage, and almost no tertiary creep. The rupture strain decreases with increasing creep rate. The strain to failure, =1.5%, indicates brittle behavior even at low rates of creep detormation. Figure from Ref. 28.

Fig. 4.15 Cavity formation in siliconized silicon carbide, KX01. Cavities are always located at Si/SiC interfaces, most often between two dosely spaced SiC grains. As the cavities grew from the narrow space between the grains, they arrested on encountering a large pool of silicon. Applied tensile stress in vertical direction in the figure. From Hockey and Wiederhom.64...

L. P. Zawada, L. M. Butkus, and G. A. Hartman, Room Temperature Tensile and Fatigue Properties of Silicon Carbide Fiber-Reinforced Aluminosilicate Glass, Cer. Eng. Sci. Proc., 11[9-10], 1592-1606 (1990). 

This process is carried out in Japan by Nippon Carbon Co. to make NICALON silicon carbide fibers, with high tensile strength and excellent temperature and oxidation resistance. It can also be used to generate coatings and solid objects. Modifications of the basic process include the addition of borosiloxanes as catalysts, and the incorporation of titanium, in the form of titanium alkoxides, to produce fibers containing titanium and oxygen as well as silicon and carbon. 

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