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

Abstract

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.

Synthesis of Non-Cubic Nitride Phases of Va-Group Metals (V, Nb, and Ta) from Metal Powders in Stream of NH3 Gas under Concentrated Solar Radiation

“…Metal powders of V, Nb, and Ta were subjected to nitridation reactions in the solar furnace SF40, with the nominal power of 40 kW, at PSA [12] in flowing NH 3 gas (Figure 1). Details of the experimental procedures are identical to those described in the paper [11] published in 2019; the only difference are the tap-densified powders (instead of Mo and Fe powders [11], powders of V, Nb, and Ta were subjected to nitridation reactions). At the focal spot of the concentrated solar beam, the radiative flux reaches 7000 Suns (1 Sun = 1 kW•m −2 ).…”

“…However, in such a configuration with a spherical reactor chamber, the effect of increasing extent of dissociation (α) of flowing NH 3 gas along the flow path from the upstream side to the downstream side was not evaluated. To overcome this problem, we developed a linear flow tube reactor and the first results acquired using this novel reactor setup were published in 2019 [11]. The experiment reported in [11] was done aiming at synthesizing higher nitrides, δ-MoN and ε-Fe 2 N, respectively, of Mo and Fe in a stream of NH 3 gas with linear flow speed (v) between 1.14 and 11.4 mm•s −1 under heating with concentrated solar beam using the solar furnace SF40 [12] at Plataforma Solar de Almería (PSA), Spain, at the processing temperatures T = 800 and 900 • C for tap-densified (loosely compacted) powders of Mo specimen and T = 500 and 600 • C for tap-densified powders of Fe.…”

“…To overcome this problem, we developed a linear flow tube reactor and the first results acquired using this novel reactor setup were published in 2019 [11]. The experiment reported in [11] was done aiming at synthesizing higher nitrides, δ-MoN and ε-Fe 2 N, respectively, of Mo and Fe in a stream of NH 3 gas with linear flow speed (v) between 1.14 and 11.4 mm•s −1 under heating with concentrated solar beam using the solar furnace SF40 [12] at Plataforma Solar de Almería (PSA), Spain, at the processing temperatures T = 800 and 900 • C for tap-densified (loosely compacted) powders of Mo specimen and T = 500 and 600 • C for tap-densified powders of Fe. Specimen powders were placed in four drilled holes of 8 mm in diameter and a depth of 5 mm for rectangular specimen holder block made of refractory steel (ferritic steel with dimensions: length 67 mm, height 20 mm and width 30 mm).…”

“…The four holes were held at equal distance being designated with P1, P2, P3, and P4 on going from upstream side to downstream side. The distance between the center of P1 and P4 was set to be 45 mm (see Figure 2 in [11]). The volume fraction of higher nitride was greater at P1 than at P4 in respective reaction condition corresponding to increasing extent α of NH3 gas dissociation along the NH 3 flow direction, i.e., decreasing a(N) of uncracked NH 3 gas along the NH 3 flow direction.…”

Solar Heat for Materials Processing: A Review on Recent Achievements and a Prospect on Future Trends

“…Carrying out the solar experiments also in a stream of gas, which in this case was uncracked ammonia NH 3 gas (NH 3 gas with suppressed extent of dissociation by flowing), other researches [55] have shown that higher nitrides of Mo (δ-MoN) and Fe (ε-Fe 2 N) can be successfully synthesized. For that they have developed an experimental setup consisting of a linear reaction tube made of silica glass and sample holder made of refractory steel in order to carry out nitriding experiments for powder specimens of Mo and Fe in uncracked NH 3 gas at specified linear flow rate under irradiation of concentrated solar beam.…”