Dielectric properties SiOC-Nextel

Ceramic matrix composites are under active consideration for low-observable military applications, where dielectric properties are a key performance factor. The frequency range of interest is the 8-12 GHz microwave range. The composite system must have low electrical conductivity. The SiOC-Nextel 312 system meets that requirement (as compared to ceramic composites made with conductive silicon carbide fibers). 

Two screening studies have been done on the dielectric properties of an SiOC-Nextel 312 BN composites. In the first study in 1992 by Lockheed Missiles, a frequency range of 8 to 12 GHz was used and the properties were measured by either a Horn-Lens dielectrometer or a Fabry-Perot resonator system. All measurements were taken at room temperature. The composites were prepared from eight plies of AF-14 plain weave fabric. Four infiltration cycles were used for densification. The total porosity of the composites was about 11 %. The data generated for the Nextel 312 system are shown in Figure 20. Note that as an additional processing variable, two test specimens were heated in air (at 450°C and at 750°C) to remove any residual carbon. 

In 1994, the Wright Laboratory of the USAF collaborated with AlliedSignal (now Honeywell) to measure the dielectric properties of a SiOC Nextel 312 BN woven 3-D... 

FIGURE 20. Dielectric Properties of SiOC Nextel 312 BN 2-D Composites... 

FIGURE 21. Dielectric Properties versus Temperature of SiOC Nextel 312 BN 3-D Coinxwites... 

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