Cold sintering of SiC ceramics with the assistance of amorphous SiO2 surface layer

Abstract

The cold sintering process (CSP) densifies ceramics powder at lower temperatures (<300 °C) than conventional sintering by applying a small amount of solvent such as water and a uniaxial pressure of several hundred megapascals. However, this method can only be applied to materials with high solubility in solvents, and direct hardening of low solubility materials such as SiC is difficult. In this study, hardened SiC/SiO 2 bodies were fabricated by CSP from SiC particles whose surface was oxidized by preheating, using NaOH solution as a solvent. The compressive strength and relative density of the hardened SiC/SiO 2 bodies fabricated from a mixture of SiC particles with 15.3 mass% SiO 2 and 5 mol/L NaOH solution were 520 MPa and 80%, respectively. These values were considerably higher than those of hardened SiC/SiO 2 bodies fabricated by CSP from a mixed powder consisting of untreated SiC particles and amorphous SiO 2 particles. When the surface-oxidized SiC particles were used as a starting material, the mismatch in chemical bonding between SiC and SiO 2 and uneven distribution of the binder were reduced, resulting in high mechanical strength for the hardened SiC/SiO 2 bodies.