Formation Process of Niobium Nitride by the Reaction of Niobium Pentachloride with Ammonia in the Vapor Phase and Properties of the Niobium Nitride Formed

Abstract

Abstract The reaction products of gaseous NbCl5 with ammonia were NbCl5·5NH3 at 200 °C, NbCl5·5NH3, Nb4N5, and NH4Cl at 250–500 °C, Nb4N5 and NH4Cl at 550–950 °C, δ-NbN and NH4Cl at 1000 °C, δ-NbN, Nb2N, NH4Cl, and HCl at 1100 °C, and δ-NbN, Nb2N, Nb4N3, δ′-NbN, ε-NbN, NH4Cl, and HCl at 1200–1300 °C. In the vapor-phase reaction of gaseous NbCl5 with ammonia, the reaction of gaseous NbCl5 with ammonia to form NbCl5·5NH3 occurs first. Above ca. 235 °C, the NbCl5·5NH3 reacts with ammonia to form Nb4N5. Above ca. 1000 °C, the Nb4N5 decomposes to δ-NbN. Above about 1100 °C, in addition to these reactions, the nitriding of niobium, formed by the reduction of gaseous NbCl5 with the hydrogen resulting from the thermal dissociation of ammonia, also occurs to form Nb2N at 1100 °C and Nb2N, Nb4N3, δ′-NbN, and ε-NbN at 1200–1300 °C. When the Nb4N5, formed by the vapor-phase reaction, is heated in an argon atmosphere, it changes to δ-NbN at ca. 1000 °C, to δ-NbN and ε-NbN at 1100–1200 °C, and then to Nb4N3 and δ-NbN at 1300 °C. The niobium nitrides formed above 1200 °C are uniform, ultrafine powders with particle diameters of the order of 1/100 μm.