PNNL

Abstract

Electrical conductivity (EC) data for several plate forms of two-dimensional, silicon carbide composite made with chemical vapor infiltration matrix and with Hi Nicalon™ type S fibers (2D-SiCf/CVI-SiC) were acquired. The composite fibers were coated with pyrocarbon (PyC) of various thicknesses (50 to 310 nm) and an outer thin (~60 µm) 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 carboncoating 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 2DSiCf/ CVI-SiC with a monolayer PyC fiber coating of ~50- nm thickness will be