Si3N4 and Si3N4/SiC composite rings for dynamic sealing of circulating fluids

Silicon nitride (Si3N4) and silicon nitride/silicon carbide (Si3N4/30 wt.% SiC) seal rings were tested as self-mated pairs and dissimilar sealing systems against grey cast iron. The tribological experiments were conducted in a ring-on-ring tribometer at V≈4 m s−1 of linear speed, in the range of 0.3–1 kN of applied load, under a pressure of 2×105 Pa of a mixture of 20 vol.% of hydrogen peroxide in deionised water, which gives an effective pressure (P) between 0.2 and 1.3 MPa. The homologous tribosystems are ineffective to seal due to catastrophic abrasive wear. The system with better performance is the dissimilar pair Si3N4/grey cast iron, that presented wear coefficient values of K=4.2×10−8 mm3 N−1 m−1 for the ceramic ring and K=1.3×10−7 mm3 N−1 m−1 for the metallic ring, in tests driven for about 60 h and 890 km, with full sealing. An amorphous passivating film of silica protects the ceramic surface. This system still presents an excellent combination K×PV≈0.1 μm h−1, this product being a measure of the surface loss of a machine component for a given time of service.