Through the research of graphite crucible technicians, it is found that the coincident coating with reasonable structure and excellent functional gradient characteristics can be prepared by using silicon metal powder as the primary impregnating material and using the embedding method in the closed sagger, that is, the SiC transition layer SiC fine layer Si-SiO2 complex phase coating. With the extension of the high-temperature holding time, the coating thickness and the SiO2 content of the outer layer dominated by SiC are added. The bond between the coating and the substrate is primarily chemical, which has both mechanical bonding and high bonding strength. The oxidation resistance of the coated graphite crucible was tested. The test results show that the anti-oxidation coating prepared by the embedding method has excellent anti-oxidation performance at 1100°C-1300°C. The single coatings composed of dip coating are mainly SiC and Si3N4.
The anti-oxidation test results show that a single coating has excellent anti-oxidation effect, but due to the difference in the expansion coefficient between the coating and the substrate, the thermal shock resistance of the coating is poor, and it simply drops. In the preparation of composite coatings, the inner coating is mainly SiC, and the outer coating is MoSi2 and Al2O3, respectively.
The antioxidant effect is not obvious in the range of 1000°C-1300°C. According to the performance test effect of graphite coating, the anti-oxidation coating of graphite crucible prepared by embedding method can significantly improve the oxidation resistance of graphite crucible, reduce the porosity of graphite crucible matrix, and improve the flexural strength of graphite crucible.