Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- 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 RadiationPublication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Galindo, JosĆ©; Rodriguez, Jose; CaƱadas, Inmaculada; Fernandes, Jorge Cruz; Rosa, LuĆs GuerraABSTRACT: Using a high-flux solar furnace, loosely compacted powders of Va-group transition metal (V, Nb, and Ta) were reacted with stream of NH3 gas (uncracked NH3 gas) being heated by concentrated solar beam to a temperature (T) range between 600 and 1000 degrees C. From V, sub-nitride V2N (gamma phase) and hypo-stoichiometric mono-nitride VN possessing fcc (face-centered cubic) crystal lattice structure (delta phase) were synthesized. On the other hand, in the reaction product from Nb and Ta, hexagonal mono-nitride phase with N/M atom ratio close to 1 (epsilon phase) was detected. The reaction duration was normalized to be 60 min. In a conventional industrial or laboratory electric furnace, the synthesis of mono-nitride phase with high degree of crystallinity that yield sharp XRD peaks for Va-group metal might take a quite long duration even at T exceeding 1000 degrees C. In contrast, mono-nitride phase MN of Va-group metal was synthesized for a relatively short duration of 60 min at T lower than 1000 degrees C being co-existed with lower nitride phases.
- Heterogeneity along the Height in Disc Specimens of Graphite/Tungsten Powder Mixtures with Sub-Stoichiometric Carbon Atom Ratios Heated by Concentrated Solar Beam to 1600 CPublication . Shohoji, Nobumitsu; MagalhĆ£es, Teresa; Oliveira, Fernando Almeida Costa; Rosa, LuĆs Guerra; Fernandes, Jorge Cruz; Rodriguez, Jose; CaƱadas, Inmaculada; Martinez, DiegoCompositional heterogeneity along the thickness of compacted disc specimens of graphite/tungsten powder mixtures with substoichiometric carbon atom ratios (0.35, 0.50 and 1.00) heated by concentrated solar beam to 1600 C was characterised by X-ray diffraction. Top surface of any examined test piece was consisted purely of mono-carbide WC while the bottom surface showed different constitution depending on the net initial C/W ratio of the test piece; almost pure metallicWfor the C/W Ā¼ 0:35 specimen, dominant metallicWassociated with small proportion ofW2C for the C/W Ā¼ 0:50 and dominantW2C with trivial proportion of WC for the C/W Ā¼ 1:0. In the intermediate zone between the top and the bottom layers, the constitution held virtually constant depending on the nominal C/W ratio of the starting material: co-existing metallicWandW2C for the C/W Ā¼ 0:35, pureW2C for the C/W Ā¼ 0:50 and predominant WC with traceW2C for the C/W Ā¼ 1:00. Unlike for the top surface of the C/W Ā¼ 0:35 test piece heated in a solar furnace to 1900 C reported earlier, no evidence of formation of nano-meter scale WC whisker was detected for the top surface in any sample heated to 1600 C in the present work.
- Mechanical properties of dense cordierite discs sintered by solar radiation heatingPublication . Oliveira, Fernando Almeida Costa; Shohoji, Nobumitsu; Martinez, Diego; Fernandes, Jorge Cruz; Rodriguez, Jose; Rosa, LuĆs Guerra; CaƱadas, InmaculadaConsolidation of cordierite disc specimens was undertaken under concentrated solar beam in a solar furnace at PSA (Plataforma Solar de AlmerıƔ). Satisfactory extent of densification was achieved by the present solar-sintering experiment. The mechanical properties measured for the solar-sintered cordierite test pieces were; density Ā¼ 2:45 0:02 g/cm3, Vickers microhardness HV Ā¼ 7:31 0:29 GPa, Youngās modulus E Ā¼ 97 5 GPa, shear modulus G Ā¼ 38 2 GPa, Poisson ratio Ā¼ 0:27 0:01, fracture toughness KIC Ā¼ 1:50 0:15 MPa m1=2 and modulus of rupture evaluated by ring-on-ring test MORROR Ā¼ 57:8 13:7 MPa which were comparable to those of the counterparts sintered by conventional industrial gas furnace.
- Influence of linear flow velocity of uncracked ammonia (NH3) gas on formation of higher nitrides, š -MoN and š-Fe2N, under concentrated solar irradiation in the SF40 solar furnace at PSAPublication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Galindo, JosĆ©; Fernandes, Jorge Cruz; RodrĆguez, JosĆ©; CaƱadas, Inmaculada; Rosa, LuĆs GuerraABSTRACT: Nitriding experiments for powder specimens of Mo and Fe were carried out using a solar furnace SF40 at PSA (Plataforma Solar de AlmerĆa) 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, Ī“-MoN for Mo and Īµ-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 mmĀ·s-1 and 11.4 mmĀ·s-1. By X-ray diffraction (XRD) analysis, presence of Ī“-MoN was detected besides Ī³-Mo2N and metallic Mo for Mo powder specimen heated to 900 ĀŗC in NH3 gas flow at v = 1.14 mmĀ·s-1 but XRD peaks identifiable as Ī“-MoN became indiscernible when v was increased to 11.4 mmĀ·s-1. On the other hand, for Fe powder specimen exposed to NH3 gas flow at v = 1.14 mmĀ·s-1 at T = 500 ĀŗC, remnant metallic Ī±-Fe was detectable by XRD at the down-stream side of the specimen holder but no metallic Ī±-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.
- Thermal decomposition of Ī“-MoN and Īµ-Fe2N synthesized under concentrated solar radiation in NH3 gas streamPublication . CaƱadas, Inmaculada; Oliveira, Fernando Almeida Costa; Rodriguez, Jose; Shohoji, NobumitsuABSTRACT: Decomposition temperatures of Ī“-MoN and Īµ-Fe2N synthesized with flowing NH3 gas under concentrated solar radiation heating were evaluated by Differential Scanning Calorimetry (DSC) in Argon (Ar) gas environment. The measured decomposition temperature of Ī“-MoN and Īµ-Fe2N were dependent on the solar synthesis conditions, particularly either NH3 or N2 gas flow rate at temperature. Sample containing Ī“-MoN showed two exothermic peaks around 680 and 900 ā¦C, attributed to the reactions of Ī“-phase into Ī³-single-phase and (Ī³+Ī²)-two-phase Mo2N, respectively, attributed to the dissociation reaction of Ī“-phase into Ī³-single phase and the dissociation reaction of Ī³-phase into metallic M saturated with N, respectively. Decomposition of Īµ-Fe2N took place into Ī³ā-Fe4N in two steps occurring at 606 and 660 ā¦C, respectively. When N2 instead of ammonia (NH3) gas was used, complete dissociation of Ī³ā-Fe4N into Fe took place at around 610 ā¦C. Full decomposition of Ī³ā-Fe4N into metallic Ī±-Fe(N) was corroborated by X-ray diffraction (XRD) analysis.
- Low-temperature nitriding of VA-group metal powders (V,Nb,Ta) in flowing NH3 gas under heating with concentrated solar beam at PSAPublication . Fernandes, Jorge Cruz; Oliveira, Fernando Almeida Costa; Rosa, LuĆs Guerra; RodrĆguez, JosĆ©; CaƱadas, Inmaculada; MagalhĆ£es, Teresa; Shohoji, NobumitsuOver the last two decades, we have been using concentrated solar beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or gas. In recent works [1,2] nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH3 gas with suppressed extent of dissociation (uncracked NH3) was attempted under heating with concentrated solar beam. It was demonstrated that mono-nitride -MoN of Mo and sub-nitride -Fe2N of Fe that are known to be impossible to synthesize in N2 gas environment even at elevated pressure p(N2) were successfully synthesized by the reactions of these metals in stream of NH3 gas under heating with concentrated solar beam up to 800ĀŗC. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH3 gas under irradiation of concentrated solar beam. By up to 90 min heating in uncracked NH3 under concentrated solar beam up to 800ĀŗC, reaction products were identified by X-ray diffraction (XRD) analysis to be consisted of mono-nitride MN co-existent with sub-nitride M2N.
- Low-temperature nitriding of VA-group metal powders (V,Nb,Ta) in flowing NH3 gas under heating with concentrated solar beam at PSAPublication . Fernandes, Jorge Cruz; Oliveira, Fernando Almeida Costa; Rosa, LuĆs Guerra; RodrĆguez, JosĆ©; CaƱadas, Inmaculada; MagalhĆ£es, Teresa; Shohoji, NobumitsuOver the last two decades, we have been using concentrated solar beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or gas. In recent works [1,2] nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH3 gas with suppressed extent of dissociation (uncracked NH3) was attempted under heating with concentrated solar beam. It was demonstrated that mono-nitride -MoN of Mo and sub-nitride -Fe2N of Fe that are known to be impossible to synthesize in N2 gas environment even at elevated pressure p(N2) were successfully synthesized by the reactions of these metals in stream of NH3 gas under heating with concentrated solar beam up to 800ĀŗC. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH3 gas under irradiation of concentrated solar beam. By up to 90 min heating in uncracked NH3 under concentrated solar beam up to 800ĀŗC, reaction products were identified by X-ray diffraction (XRD) analysis to be consisted of mono-nitride MN co-existent with sub-nitride M2N.