3D printing and in situ transformation of SiCnw/SiC structures

Successful preparation of photopolymerizable ceramic slurries using non-oxide ceramics and their 3D printing is highly challenging as the ceramic powders often possess high UV-light absorbance. Even though pre-oxidation of the powders could improve the slurry printability, the residual oxygen element in the material would eventually deteriorate the material purity and performance. In this study, a separated redox route (pre-oxidation, 3D printing and carbothermal reduction) was proposed to overcome these challenges. SiC ceramic powder was pre-oxidized into SiC@SiO2 core-shell form to lower the UV-light absorbance. It was found that the ultraviolet (UV) light absorbance value of SiC powder at 405 nm decreased 20% from 0.357 to 0.284 after pre-oxidation process. The UV-light penetration depth of SiC@SiO2 ceramic slurries at 40 ~ 55 vol% solid loading ranging from 14.81 to 12.82 µm, which surpassed two times that for 40 vol% raw SiC ceramic slurry. Different-shaped structures of SiC@SiO2/resin green ceramic bodies were successfully fabricated by vat photopolymerization 3D printing. The oxygen element resided was then eliminated by carbothermal reduction to avoid detriment of SiO2 to the mechanical performance of the SiC ceramics. Phenolic epoxy acrylate resin with 14 wt% pyrolytic carbon (PyC) yield was chosen as the carbon source and thus the SiC@SiO2/resin green body pyrolyzed into SiC@SiO2/PyC ceramics after 1200 °C. It was found that after the heating temperature was further raised to 1600 °C, most of the pre-introduced SiO2 shells on the surface of SiC particles were in situ transformed into SiC nanowires through carbothermal reduction reaction between SiO2 and PyC, and the content of oxygen element in the ceramic matrix sharply dropped from 20.21% to 2.08%. The results demonstrated that through the proposed redox route, the photopolymerization-related issues including high UV-light absorbance and pre-oxidation-induced impurity for 3D printing of SiC ceramic slurries can be tackled. Finally, high purity porous SiCnw/SiC ceramic components with different structures were produced. This study provides a promising route for the preparation and 3D printing of photopolymerization ceramic slurries using non-oxide ceramics possessing high UV-light absorbance.