Enhanced thermal conductivity of Si3N4 ceramics through pyrolytic carbon prepared by gel casting using DMAA

To reduce the lattice oxygen content of Si 3 N 4 green bodies, samples were prepared using an N,N-dimethylacrylamide (DMAA) system. The endothermic and exothermic peaks are related to the decomposition of organic matter and the reaction between pyrolytic carbon and impurity oxides in the sintering process. Multi-step heat preservation during the thermal degreasing process reduced the carbon content and defects. The α→β phase transformation and aspect ratio of grains changed from 89.2% to 4.84:1 at 1640 °C to 96.3% and 7.80:1 at 1700 °C, respectively. The relative density, hardness, fracture toughness, and thermal conductivity of the Si 3 N 4 samples reached 98.5%, 1353 HV, 8.51 MPa·m 1/2 , and 97.1 W·m −1 ·K −1 , respectively. Pyrolytic carbon can react with SiO 2 , which reduces the content of the glass phase in the green body and affects the dissolution and precipitation process and lattice oxygen content. In the structure of the Si 3 N 4 sample, carbon particles with sizes of 100–500 nm and near-spherical shapes were observed. Intergranular-phase YMgSi 2 O 5 N was formed during the sintering process, which was conducive to improving the thermal conductivity. This article uses lower temperature and no pressure conditions to prepare Si 3 N 4 ceramics, which can provide reference for batch and low-cost production.