Synthesis of highly disperse NbSi2–Si3N4 and Si3N4–NbN composite powders

Abstract

AbstractThe behavior of reaction powder mixtures of stoichiometric compositions calculated for the synthesis of higher niobium nitride and silicide in the temperature range 800–1400°С in vacuum according to the reactions 4Nb + Si3N4 and 3Nb + 2Si3N4, respectively, has been investigated. The decomposition of Si3N4 is accompanied by the formation of lower nitride and lower silicide phases of niobium. The content of the silicide phase increases with heat treatment temperature, and, at 1400°С, NbSi2 forms. The nitride phase remains practically unchanged up to 1300°С and disappears at 1400°С. On the basis of the established regularities, we have developed synthesis methods for Si3N4–NbN and Si3N4–NbSi2 powders, which include the introduction of excess Si3N4 with respect to the stoichiometric composition. The combined two‐stage technological cycle of synthesis of Si3N4–NbN involves vacuum annealing at 1000°С and subsequent nitriding at 1300°С. The synthesis method for NbSi2–Si3N4 assumes the in situ successive formation of niobium silicide phases up to 1400°С. The synthesized Si3N4–15NbN and NbSi2–14Si3N4 powders consist of multiphase agglomerates with a mean size of 5.5 and 8.8 µm, respectively, and a nanodisperse fraction with a mean particle size of 200 nm.