BORON CARBIDE CONTINUOUS FILAMENTS. PART II.

The purpose of this program was to develop and evaluate a process for producing continuous lengths of boron carbide filament having tensile strengths approaching 500,000 psi and elastic moduli close to that of bulk boron carbide 60-70 million psi are being developed. Filaments were produced by depositing the reaction product of born trichloride, hydrogen and methane on a heated tungsten filamentary substrate which had a boron primer coat. Excess hydrogen was used as a carrier gas. Initial evaluation of the boron carbide filaments as a reinforcement for epoxy resins indicated that no wetting problem between the filamentresin existed, that the transfer of stresses to the filaments was efficient, and that the wet strength problem, which is characteristic of boronepoxy composites, may not be as severe when boron carbide filaments are used. Characterization studies were performed on typical filament specimens, and the results indicated an amorphous structure with two prevailing surface morphologies, 1 granular or 2 nodular, depending on the mode of nucleation. The final apparatus evolved for the production of B4C filaments utilized a high mass flow gas system in a seven stage reactor which had a deposition zone twenty-one inches long.