Textured h-BN Ceramics Prepared by Slip Casting

This paper reports the texturing behavior of hexagonal boron nitride (h-BN) ceramics prepared by slip casting, followed by spark plasma sintering, using either irregularly shaped or plate-like h-BN as the starting materials. In this study, well-dispersed h-BN ethanol-based suspensions with 30 vol% solid loading were prepared by adding 2.5 wt% polyetherimide dispersant. It was found that both kinds of h-BN exhibited a substantially strong orientation during slip casting, which was featured by the alignment of the c-planes of the BN crystals perpendicular to the casting direction. Analysis and experimental results revealed that the texture development resulted from ethanol flow during slip casting and intrinsical surface properties of h-BN. Consequently, the orientation degree was very sensitive to the thickness of green bodies, which decreased when the thickness exceeded a certain value, and finally disappeared. Densities of ∼92.0% and 88.9% of the theoretical for the irregularly shaped and plate-like h-BN, respectively, were achieved after sintering at 1800°C/50 MPa. The thermal conductivity of the as-prepared BN ceramics showed a strong dependence on the grain orientation, being substantially higher along the BN layers than across them. © 2011 The American Ceramic Society.