Heat press molding of open-celled porous Si-SiC ceramics consisting of skeletal strut via gelcasting with flexible and thermosetting polyurethane resin

Abstract

A novel powder processing method for the fabrication of thin open-celled porous siliconized silicon carbide (Si-SiC) ceramic substrates is reported. Green SiC–carbon (C) substrate is first formed via a newly developed gelcasting method, using an organic-solvent-based slurry comprised of submicron SiC and nanometer C powders, along with a flexible and thermosetting polyurethane resin, based on the replica method with polyurethane foam as a template. Subsequently, the flexible semi-wet green substrate is uniaxially compressed under heating for molding to a set thickness; this is possible because of its thermosetting property (heat press molding). Although the slurry viscosity is highly sensitive to fine fluctuations in the powder volume concentration (PVC; 0.45–0.48), the PVC criterion for homogeneous powder solidification and improvement in the green SiC–C strut quality is determined to be 0.46. At 0.48 PVC, it is confirmed that the formed green SiC–C struts reproduce the template morphologically with a high correlation coefficient of 0.96 for the average strut thickness. As regards the open-celled sintered Si-SiC substrate (thickness: 6mm), the Si-SiC strut appears to be skeletal with a triangular vertical cross-section, which can be successfully warped or twisted without cracking; furthermore, the mechanical strength is evidently improved via the heat press molding.