Electrical Conductivity of 2D-SiC_f/CVI-SiC

Electrical conductivity (EC) data for several plate forms of two-dimensional, silicon carbide composite made with chemical vapor infiltration matrix and with Hi Nicalon^TM type S fibers (2D-SiC_f/CVI-SiC) were acquired. The composite fibers were coated with pyrocarbon (PyC) of various thicknesses (50 to 310 nm) and an outer thin (~60 m) SiC “seal coat” was applied by CVD to the infiltrated plates.

The EC was highly anisotropic in the transverse and in-plane directions. In-plane EC ranged from ~150 to 1600 S/m, increased slowly with increasing temperature, and depended primarily on the total PyC thickness. High in-plane EC-values occur because it is dominated by conduction along the numerous, continuous PyC fiber coating pathways. Transverse EC ranged from ~1 to 60 S/m, and increased strongly with increasing temperature up to 800°C. The transverse EC is controlled by conduction through the interconnections of the carbon-coating network within and between fiber bundles, especially at moderate temperatures (~300 to 700°C). Below ~300°C, the electrical resistance of the pure SiC seal coat becomes increasingly more important as temperatures are further lowered.

Importantly, a “3-layer series” model predicts that transverse EC-values for a standard seal-coated 2D-SiC_f/CVI-SiC with a monolayer PyC fiber coating of ~50-nm thickness will be <20 S/m for all temperatures up to 800°C, as desired for a flow channel insert in a fusion reactor blanket component.