Thermal Oxidation of Sputter‐Coated Reaction‐Bonded Silicon Nitride

Ceramic coatings prepared by sputtering and reactive sputtering were applied to reaction‐bonded silicon nitride surfaces to prevent extensive oxidation of the underlying material. The high‐density nitride‐based coatings retard the oxidation of the substrate by forming an oxygen diffusion barrier which seals the open porosity while maintaining dimensional and thermal stability. The oxidation kinetics of the coated and uncoated reaction‐bonded silicon nitride substrates were compared at T = 1000 ° to 1200°C. Oxidation of the underlying material in this temperature range was substantially reduced when suitable coatings were used and the crystalline oxidation product (cristobalite) was essentially eliminated.