Dielectric and mechanical properties of porous Si₃N₄-Kovar composites prepared by low-temperature oxidation sintering

The aim of this study is to investigate the impact of the Kovar glass content on the mechanical and electrical properties of Si3N4-Kovar composites sintering at air atmosphere. To achieve this, Si3N4-Kovar composites were prepared using molding technology with the Kovar glass powder ranging from 20 to 70 wt%. The phase composition, morphology, bulk density, apparent porosity, flexural strength at room temperature, dielectric constant, and dielectric loss of the composites were all examined in relation to changing the Kovar glass content. During the sintering process, the alpha-quartz on the surface of Si3N4 particles acted as the crystal nucleus, inducing the crystallization of the glass at the wetting position that the Kovar glass and the surface of the Si3N4 particles. A small amount of the beta-quartz phase was crystallized at 750-850 degrees C, followed by a large amount of the beta-quartz phase crystallizing above 900 degrees C. Additionally, some beta-quartz phase transformed into the metastable beta-cristobalite phase that could exist below 1470 degrees C. During the cooling process, the beta-cristobalite phase transformed into a low-temperature alpha-cristobalite phase, while the beta-quartz phase transformed into a low-temperature alpha-quartz phase. The results indicate that the Si3N4-Kovar glass composite with 60 wt% the Kovar glass content sintered at 900 degrees C exhibits higher density (1.88 g/cm(3)), lower porosity (25.4%), higher flexural strength (55.34 MPa), lower dielectric constant (3.46), and lower dielectric loss (4.26 x 10(-3)).