Influence of Linear Flow Velocity of Uncracked Ammonia (NH₃) Gas on Formation of Higher Nitrides, ??-MoN and ??-Fe₂N, under Concentrated Solar Irradiation in the SF40 Solar Furnace at PSA

摘要

Nitriding experiments for powder specimens of Mo and Fe were carried out using a solar furnace SF40 at PSA (Plataforma Solar de Almería) in Tabernas (Spain) in uncracked ammonia NH_(3) gas (NH_(3) gas with suppressed extent of dissociation by flowing) aiming at determining the range of linear velocity v of NH_(3) gas flow to yield higher nitride phases, δ-MoN for Mo and ε-Fe_(2)N for Fe. Standard solar exposure duration at a specified reaction temperature T was set to be 60 min over range of v between 1.14 mm·s~(-1) and 11.4 mm·s~(-1). By X-ray diffraction (XRD) analysis, presence of δ-MoN was detected besides γ-Mo_(2)N and metallic Mo for Mo powder specimen heated to 900 oC in NH_(3) gas flow at v = 1.14 mm·s~(-1) but XRD peaks identifiable as δ-MoN became indiscernible when v was increased to 11.4 mm·s~(-1). On the other hand, for Fe powder specimen exposed to NH_(3) gas flow at v = 1.14 mm·s~(-1) at T = 500 oC, remnant metallic α-Fe was detectable by XRD at the down-stream side of the specimen holder but no metallic α-Fe was detected at the up-stream side of the specimen holder suggesting that chemical activity a(N) of N atom in uncracked NH_(3) gas tended to decrease along the NH_(3) gas flow path on going from the up-stream side to the down-stream side.