Abstract
Nitriding experiments for powder specimens of Mo and Fe were carried out using a solar furnace SF40 at PSA (Plataforma Solar de Almeria) in Tabernas (Spain) in uncracked ammonia NH3 gas (NH3 gas with suppressed extent of dissociation by flowing) aiming at determining the range of linear velocity v of NH3 gas flow to yield higher nitride phases, δ-MoN for Mo and e-Fe2N 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-Mo2N and metallic Mo for Mo powder specimen heated to 900 oC in NH3 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 NH3 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 NH3 gas tended to decrease along the NH3 gas flow path on going from the up-stream side to the down-stream side.
Highlights
On account of unique properties of nitrides of transition metals, intensive research efforts have been invested for nitride synthesis
Synthesis of "higher" nitride such as δ-MoN of Mo cannot be realized in N2 gas environment even at very high N2 gas partial pressure p(N2) of order of several hundreds of atm for prolonged reaction duration of several tens of hours [1, 4,5,6,7,8,9,10,11,12,13,14,15,16]
X-ray diffraction (XRD) peak positions obtained for Mo specimens in uncracked NH3 gas at different linear flow velocity v through the reaction tube at T = 800 and 900 oC for duration t = 60 min are listed in Table 2 being compared with standard peak positions for δ-MoN, two types of Mo2N (β and γ) and metallic Mo
Summary
On account of unique properties of nitrides of transition metals, intensive research efforts have been invested for nitride synthesis. Inumaru et al [1] investigated aspects of high-pressure synthesis of δ-MoN in view of δ-MoN being a superconducting material. Synthesis of nitride MN through reaction of metal M in N2 gas atmosphere requires high temperature due to high chemical stability of N2 gas molecules. Synthesis of "higher" nitride such as δ-MoN of Mo cannot be realized in N2 gas environment even at very high N2 gas partial pressure p(N2) of order of several hundreds of atm for prolonged reaction duration of several tens of hours [1, 4,5,6,7,8,9,10,11,12,13,14,15,16]
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