Percorrer por autor "Ramos, Carlos"
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- Synthesising carbo-nitrides of some d-group transition metals using a solar furnace at PSAPublication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Rosa, Luís Guerra; Fernandes, Jorge Cruz; Magalhães, Teresa; Coelho, Manuel Caldeira; Rodriguez, Jose; Cañadas, Inmaculada; Ramos, Carlos; Martinez, DiegoCarbo-nitride synthesis was undertaken using a solar furnace at PSA in flowing N2/Ar gas mixture under total pressure 1 atm and processing temperature T = 1600ºC for some d-group transition elements (Ti; Zr, V, Nb, Mo, W) starting from 1.5G/M (graphite/metal powder mixture with mole ratio 1.5:1) compact to ensure co-presence of free carbon with the reaction product. Clear X-ray diffraction (XRD) evidence of formation of carbo-nitride was detected for Ti (IVa group metal) showing higher N content in the carbo-nitride synthesised in N2 gas environment at partial pressure p(N2) = 1 atm than that at p(N2) = 0.5 atm. For M = V and Nb (Va group metals), formation of mono-carbide MC single-phase was detected in the N2 environment showing no evidence of formation of carbo-nitride in spite of presence of N2 in the environment. For M = Mo and W (VIa group metals), formation of higher carbide, among several options of carbide phases, appeared to be promoted in the N2 gas environment although, like in cases with the Va group metals, no evidence of dissolution of N into the reaction product was detected. As such, at T = 1600ºC in N2 gas environment up to p(N2) = 1 atm under concentrated solar beam, carbo-nitride formed from the 1.5G/M mixture only for IVa group metal (Ti) but not for Va and VIa group metals. Anyway, it seemed certain that N2 gas affected somehow the reaction path between G and M to yield the carbide phase for M = V, Nb, Mo and W.
- Synthesizing higher nitride of molybdenum (Mo) and iron (Fe) in ammonia (NH3) gas stream under irradiation of concentrated solar beam in a solar furnacePublication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Fernandes, Jorge Cruz; Rosa, Luís Guerra; Rodriguez, Jose; Cañadas, Inmaculada; Ramos, Carlos; Magalhães, Teresa; Cestari, F.Flowing gaseous ammonia NH3 with suppressed extent of dissociation (un-cracked NH3) is acknowledged to function as a powerful nitriding medium to realize formation of metal nitride MNx with considerably high N/M ratio x that cannot be achieved through reaction of M with N2 gas. For example, mono-nitride d-MoN of Mo and e-FeNx phase of Fe with x = 0.33 ˜ 0.50 (i. e. hypo-stoichiometric sub-nitride e-Fe2N) were reported to be difficult to prepare in N2 gas environment even at elevated pressure but might be synthesized in flowing NH3 gas at normal pressure when reaction temperature and NH3 gas flow rate were set adequately. In the present work, nitriding experiments for Mo and Fe were carried out in flowing NH3 gas under irradiation with concentrated solar beam. The acquired experimental evidences demonstrated that temperature range for formation of d-MoN was somewhat extended in flowing NH3 gas under heating with concentrated solar beam compared with that under heating in conventional laboratory or industrial electric furnace. On the other hand, no such merit of extending temperature range for formation of e-Fe2N in flowing NH3 gas was detected in the present work under heating with concentrated solar beam.