Effect of BN addition on mechanical and electrical properties of oxidative sintered porous Si3N4-BN composites

In order to explore the effects of BN addition on the mechanical and electrical properties of oxidative sintered Si3N4-BN composites, Si3N4-BN composites with BN powder dosage of 0-40 wt% are prepared by molding technology, and the effects of different BN contents on the phase, morphology, bulk density, porosity, flexural strength at room temperature, dielectric constant and dielectr loss of the composite system are studied. With the increase of BN content, at different temperatures, the oxidation product B2O3 of BN and the oxidation product SiO2 of Si3N4 firstly react on the surface to form B2O3–SiO2 glass phase, which densify the surface and affects the oxidation degree of internal grains. At the same time, a small amount of B2O3 escaping from the surface, so that the open pores of the composites decrease firstly and then increase slightly, and the dielectric constant increases firstly and then decreases. The results show that when the amount of BN micronized powder is 10 wt%, the oxidation sintered Si3N4-BN composite material at 1500 °C have pores that retain the sheet structure of boron nitride, and the amorphous material flows to fill the pores, so it have high volume density (1.85 g/cm3), low porosity (apparent porosity 6.37%), and high mechanical properties (flexural strength 127.86Mpa), higher dielectric constant (3.94) and lower dielectr loss (4.0 × 10−4).