Processing and characterization of boron nitride composites and films

Abstract

While carbon/carbon composites (C/C) have found broad use in commercial aircraft brakes, their further application is limited by high fabrication costs, susceptibility to oxidation, and high electrical conductivity. Boron nitride (BN) provides a suitable alternative to carbon because of its oxidation resistance and its low dielectric constant. This thesis describes a novel approach to the synthesis of BN composites and films based on borazine, the boron-nitrogen analog of benzene. Characteristics of the oligomer are described and a more optimum processing route to the BN structures is proposed. Specifically, it is shown that the treatment of the oligomer in the melt phase can enhance the crystallinity of the final BN. The stability, electrical properties, wear, and mechanical behavior of BN matrix composites are then presented. The substitution of a BN matrix in place of a carbon matrix is shown to enhance the oxidation stability, improve the wear resistance, and offer the potential for a low dielectric, thermally stable composite. Finally, the feasibility of either dip or spin coating thin BN films is demonstrated and parameters controlling the thickness and dielectric constant in the films are described.