[en] The reaction products of gaseous NbCl₅ with ammonia were NbCl₅.5NH₃ at 200 ⁰C, NbCl₅.5NH₃, Nb₄N₅, and NH₄Cl at 250-500 ⁰C, Nb₄N₅ and NH₄Cl at 550-950⁰C, delta-NbN and NH₄Cl at 1000⁰C, delta-NbN, Nb₂N, NH₄Cl, and HCl at 1100⁰C, and delta-NbN, Nb₂N, Nb₄N₃, delta'-NbN, epsilon-NbN, NH₄Cl, and HCl at 1200-1300⁰C. 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. 235⁰C, the NbCl₅.5NH₃ reacts with ammonia to form Nb₄N₅. Above ca. 1000⁰C, the Nb₄N₅ decomposes to delta-NbN. Above about 1100⁰C, 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 1100⁰C and Nb₂N, Nb₄N₃, delta'-NbN, and epsilon-NbN at 1200-1300⁰C. When the Nb₄N₅, formed by the vapor-phase reaction, is heated in an argon atmosphere, it changes to delta-NbN at ca. 1000⁰C, to delta-NbN and epsilon-NbN at 1100-1200⁰C, and then to Nb₄N₃ and delta-NbN at 1300⁰C. The niobium nitrides formed above 1200⁰C are uniform, ultrafine powders with particle diameters of the order of 1/100 μm. (author)