2011 Volume 52 Issue 4 Pages 719-727
Reactions of d-group transition metals including Ti, V, Nb and Ta with N2 gas were investigated at target temperature of 2000°C under heating with concentrated solar beam at PROMES-CNRS in Odeillo (France). In the typical experimental setup using graphite crucible as the sample holder, synthesis of pure nitride with fcc (face centred cubic) structure was proved to be difficult on account of inevitable C2 radical plume with high carbon activity a(C) from the graphite components and the majority of reaction products were carbo-nitride. By insertion of Sky blue filter in the solar beam path before entering into the parabolic concentrator, C2 radical formation appeared to be efficiently suppressed and phases with high N content were synthesized. However, under conditions in which C2 radical plume yield was considerable, nitrogen content in the reaction products became suppressed and tetragonal Nb4N3 yielded in place of fcc NbN from Nb or N-deficit sub-nitride Ta2N in place of mono-nitride TaN formed.