FIGURE 3.17 (A) Silicon carbide fibers reinforcing an alumina matrix, (B) silicon carbide fibers reinforcing a silicon carbide matrix, (C) unidentified fibers reinforcing a silicon nitride bonded silicon nitride matrix, and (D) other fibers reinforcing a proprietary matrix. Materials available from Honeywell, Inc.

specimens measuring 3 x 4 x 50 mm and tensile bars 12 cm long with a gage area of 8 x 40 mm were exposed for 100 h at 1260°C (2300°F) in an argon-steam atmosphere at a total pressure of 3.4 atm (50 psia) and various concentrations of steam, conditions that exceed those experienced in steam cracking. Argon was used instead of hydrocarbons since earlier studies showed no corrosion by hydrocarbons. Strength tests were conducted at room temperature.

Figure 3.17 shows the excellent retention of CFCC physical strength after this severe exposure to steam at high-temperature and pressure. Additional experiments are required because some specimen were too narrow to accommodate the fiber weave, resulting in lower strength due to configuration rather than the harsh environment.

The pump housing application described earlier required examining the corrosion resistance of CFCCs to commonly pumped chemicals. Figure 3.18 presents this data. Flexural bars measuring 0.25 x 3 x 0.1 in. were immersed in each chemical for 500 h. Temperatures were chosen to match those expected in the pump. After exposure, the bars were dried and flexure strength measured. This relatively simple test and the obvious corrosion resistance of CFCCs encouraged more specific and complicated testing.

Since an initial focus of the CFCC development was for gas turbine combustor liners, a lab-scale high-temperature and pressure apparatus was designed to simulate that application. Exposure conditions included a pressure of 150 psia,

Exposure of CFCC to Various Organic and Inorganic Species

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