Formation process of niobium nitride by the reaction of niobium pentachloride with ammonia in the vapor phase and properties of the niobium nitride formed

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)