Improved Flexural Strength in Digital-Light-Processing-Printed Si3N4 Ceramics by Removing Carbon Residue

The debinding step is vitally important to obtain defect-free ceramics in the fabrication of ceramics by means of DLP-3D printing. However, the residual carbon from the decomposition of the organic matter during the debinding process severely affects the quality and mechanical properties of the sintered ceramics. In this work, it has been proven that the carbon residue can participate in a carbothermal reduction reaction at 1300 degrees C and lead to the formation of macroscopic defects such as delamination and cracks that occurred in the surface of the sintered silicon nitride ceramics. Based on this, we propose an approach to eliminate the carbon retained in silicon nitride compacts fabricated with the stereolithography technique. The amount of carbon residue that remained in the debinded silicon nitride bodies is 0.58 % based on thermogravimetric analysis in air atmosphere. When the oxidation temperature and holding time in the air were 450 degrees C and 5 h, respectively, the residual carbon in the samples could be sufficiently removed. The flexural strength of sintered ceramics without the removal of carbon residue is only 184.88 +/- 8.16 MPa; sintered silicon nitride ceramics after removal of residual carbon can reach 469.78 +/- 11.86 MPa. The research results in this study provide great reference value for the preparation of defect-free ceramics.