The Experts below are selected from a list of 151332 Experts worldwide ranked by ideXlab platform
Masahiro Katsura - One of the best experts on this subject based on the ideXlab platform.
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thermodynamics of nitride and hydride formation by the reaction of metals with flowing nh3
Journal of Alloys and Compounds, 1992Co-Authors: Masahiro KatsuraAbstract:Abstract The state where the equilibrium dissociation of ammonia, NH 3 = − 1 2 N 2 + 3 2 H 2 , is not reached can be produced by flowing NH 3 . In this case NH 3 must be considered to be in an unstable state. Nitrogen-rich metal nitrides, which cannot be obtained by action of N 2 under normal pressures, can be prepared by use of a stream of NH 3 . This suggests that high nitrogen Activity may arise from the high instability exhibited by a stream of NH 3 . It may be highly probable that a stream of NH 3 also acts as a hydriding agent with high Hydrogen Activity. A thermodynamic analysis was performed with the object of gaining insights into these aspects from the equilibrium point of view.
Michael Rohwerder - One of the best experts on this subject based on the ideXlab platform.
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on the robustness of the kelvin probe based potentiometric Hydrogen electrode method and its application in characterizing effective Hydrogen Activity in metal 5 wt ni cold rolled ferritic steel as an example
Science and Technology of Advanced Materials, 2019Co-Authors: Waldemar Krieger, Michael RohwerderAbstract:ABSTRACTQuantitative detection of Hydrogen in metal is important in providing a better basis for fundamental investigations of Hydrogen embrittlement and Hydrogen-related corrosion phenomena. Therm...
Nobumitsu Shohoji - One of the best experts on this subject based on the ideXlab platform.
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roles of unstable chemical species and non equilibrium reaction routes on properties of reaction product a review
Journal of Surfaces and Interfaces of Materials, 2014Co-Authors: Nobumitsu ShohojiAbstract:Chemical species might be held in a state being away from equilibrium state, at least temporarily, as represented by non-graphitic carbon and gaseous ammonia NH3 with suppressed extent of dissociation by flowing. Such chemical species X in unstable state would possess chemical Activity a X considerably higher than that of the same element in equilibrium (reference) state. In case of carbon, a C of amorphous carbon is higher than that of graphite (equilibrium state of C; a C = 1). Thus, when metal M is reacted with excess C, carbon content x ′ in carbide MCx′ in equilibrium with amorphous carbon becomes higher than x in MCx in equilibrium with graphite. In case of uranium carbo-nitride UCxN1−x in equilibrium with excess free C under given conditions of temperature T and N2 gas partial pressure p(N2 , x ′ in UCx′N1−x′ in equilibrium with amorphous carbon was experimentally demonstrated to be higher than x in UCxN1−x in equilibrium with graphite. Gaseous ammonia NH3 with suppressed extent of dissociation by flowing would yield very high nitrogen Activity a N and modestly high Hydrogen Activity a H while NH3 dissociated to N2 and H2 to reach equilibrium state in closed reaction chamber would yield a N and a H to be represented by respective partial pressures, p(N2 1/2 and p(H2 1/2, in the gas phase. Synthesis of mono-nitride MoN of Mo in N2 gas was reported to be impossible even at high pressure up to 300 atm in autoclave but MoN co-existing with sub-nitride Mo2N might be synthesized in flowing NH3 gas at normal pressure. As such, unstable chemical species might allow us to synthesize novel reaction product that cannot be prepared by using stable chemical species alone in the reactant. However, special care must be taken in usage of unstable chemical species. For example, in case of non-graphitic carbon, graphitization might proceed with considerably fast rate when the reaction temperature is set to be well above 2000 K and thence no effect of high a(C) might be gained at reaction temperature exceeding 2000 K. On the other hand, in case of flowing NH3 gas, extent of dissociation of NH3 gas would depend on the position along the flow path of NH3 gas stream (i.e., tends to rise inevitably on going from the up-stream side to the down-stream side) as well as on the NH3 gas flow rate (i.e., at specific position in the flow path tends to rise with diminishing NH3 gas flow rate). On the other hand, rapid solidification processing with cooling rate reaching to 106 K/s has been employed for refinement of microstructure of alloys and for extension of solubility limit as well as for formation of amorphous phases. Rapid solidification is considered as ultra-fast quenching process of high temperature micro structure, or more precisely, retention of atomistic configuration in molten state of multi-component system through extraction of heat with very high rate to inhibit atom diffusion processes to reach inherent equilibrium state defined uniquely as functions of temperature T and alloy composition. On the other hand, under certain mode of operation of solar furnace using concentrated solar beam as the reaction heat source, rapid heating to reach reaction temperature around 2000 K from ambient temperature within order of a second or even less is realized. During carbide synthesis from tungsten (W ) under such operation mode of solar furnace, the authors detected evidence of formation of WmCn phases that did not correspond to the phase anticipated by referring to available equilibrium binary W–C phase diagram at the processing temperature. This experimental evidence is tentatively appreciated in terms of small energetic differences among WmCn phases with varying m/n ratios. That is, once certain WmCn phase is formed during rapid heating of W/C powder mixture, the formed phase would remain stable at the processing temperature T even if it is not the genuine equilibrium phase at T without being transformed to the genuine equilibrium phase at the specified T due to smallness of driving force for the phase transformation
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role of unstable chemical species non graphitic carbon and flowing nh3 gas on the equilibrium point of the reaction product carbide carbo nitride or nitride
Materials Science Forum, 2004Co-Authors: Nobumitsu ShohojiAbstract:Elementary carbon in solid state might exist in variety of allotropic forms including graphite, diamond and amorphous carbon. Among them, graphite is in the stable form with chemical carbon Activity a(C) = 1 whereas diamond is in meta-stable state and amorphous carbon is in un-stable state with a(C) higher than 1. Experimental evidences showed that carbide and carbo-nitride being in equilibrium with carbon possessing a(C) higher than 1 was with higher C content than the corresponding ones in equilibrium with graphite. In case of gaseous ammonia NH 3, higher nitrogen Activity a(N)and higher Hydrogen Activity a(H) than the ones corresponding to the equilibrium partial pressure levels, p(N 2) and p(H 2), might be gained by suppressing its dissociation to a level away from the equilibrium state for the given temperature T by flowing. Thus, under flowing NH 3 gas, nitride or carbo-nitride with N content higher than that in equilibrium with N 2 gas at p(N 2) anticipated from the dissociation equilibrium at the given T might be obtained. Chronological development of this line of work started by Prof. Masahiro Katsura in early seventies at Osaka University is reviewed in this paper as I was one of collaborators involved in this very exciting research work from the early stage of its development.
Sheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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steering charge kinetics in metal free g c3n4 melem hybrid photocatalysts for highly efficient visible light driven Hydrogen evolution
Applied Surface Science, 2020Co-Authors: Dong Yang, Gao Xiao, Sheng ZhangAbstract:Abstract The low efficiency of photogenerated charge separation is a critical factor to restrict the efficiency of photocatalytic reaction. Extensive research efforts have been devoted to charging kinetics to improve the efficiency of photogenerated charge separation and transfer to catalytic sites. In this research, the heterostructure and interfacial electron polarization are formed between melem and graphitic carbon nitride (g-C3N4) through first-principles calculation, which can greatly suppress the electron-hole recombination. The synergistic advantage of g-C3N4/melem hybrid reveals great enhancement in photocatalytic Hydrogen Activity. Subsequently, we prepared the composite material of g-C3N4/melem by molecular engineering strategy, and found that the photocatalytic efficiency of g-C3N4/melem was twice of pristine g-C3N4. This study provides an insightful idea to improve the efficiency of photogenerated charge separation.
J Chene - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen embrittlement susceptibility of tempered 9 cr 1 mo steel
International Journal of Hydrogen Energy, 2011Co-Authors: Loic Marchetti, E Herms, Pierre Laghoutaris, J CheneAbstract:Abstract The influence of the subsurface Hydrogen Activity on the Hydrogen embrittlement (HE) susceptibility of a tempered 9%Cr–1%Mo ferritic-martensitic steel (T91) has been studied by constant extension rate tests (CERT) performed under cathodic charging during straining at 20 °C. Changes in the Hydrogen Activity on the surface were obtained by varying the cathodic current density imposed during a tensile test completed to fracture. The broken samples were observed by scanning electron microscopy (SEM). The results show a strong dependence of the extent of the brittle zone with the subsurface Hydrogen Activity. This effect could be attributed to an enhancement of the apparent diffusion coefficient of Hydrogen when increasing H Activity. Increasing H Activity could enhance both the trapping rate on pre-existing and strain-induced traps and H dragging by moving traps such as dislocations.
