Thermodynamics of Chemical Processes in the System of Nanocrystalline Iron–Ammonia–Hydrogen at 350 °C

Nanocrystalline iron nitriding and the reduction of nanocrystalline iron nitrides in steady states at 350 °C are described using the chemical potential programmed reaction (CPPR), thermogravimetry (TG), 57Fe Mössbauer spectroscopy (MS), and X-ray diffraction (XRD) methods. It was determined that during the process of nitriding of nanocrystalline iron, larger nanocrystallites formed the γ’ phase and the smallest nanocrystallites (about 4%) were transformed into the α” phase. Both phases were in chemical equilibrium, with the gas phase at the temperature of 350 °C. Stable iron nitride α” was also formed in the ε iron nitride reduction process. Taking the α” phase in the system of nanocrystalline Fe-NH3-H2 into account, it was found that at certain nitriding potentials in the chemical equilibrium state, three solid phases in the nitriding process and four solid phases in the reduction process may coexist. It was also found that the nanocrystallites of ε iron nitride in their reduction process were transformed according to two mechanisms, depending on their size. Larger nanocrystallites of iron nitride ε were transformed into the α-iron phase through iron nitride γ’, and smaller nanocrystallites of ε nitride went through iron nitride α”. In the passivation process of nanocrystalline iron and/or nanocrystalline iron nitrides, amorphous phases of iron oxides and/or iron oxynitrides were formed on their surface.

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Study of Phase Transitions Occurring in a Catalytic System of ncFe-NH3/H2 with Chemical Potential Programmed Reaction (CPPR) Method Coupled with In Situ XRD

Catalysts ◽

10.3390/catal11020183 ◽

2021 ◽

Vol 11 (2) ◽

pp. 183

Author(s):

Ewa A. Ekiert ◽

Bartłomiej Wilk ◽

Zofia Lendzion-Bieluń ◽

Rafał Pelka ◽

Walerian Arabczyk

Keyword(s):

Phase Transitions ◽

Chemical Potential ◽

Intermediate Step ◽

Gaseous Mixtures ◽

In Situ Xrd ◽

Α Phase ◽

Ε Phase ◽

Nanocrystalline Iron ◽

Nitriding Potential

Nitriding of nanocrystalline iron and reduction of nanocrystalline iron nitride with gaseous mixtures of hydrogen with ammonia were studied at 375 °C and atmospheric pressure using the chemical potential programmed reaction (CPPR) method coupled with in situ XRD. In this paper, a series of phase transitions occurring during the processes is shown, and a detailed analysis of the phase composition and the structure of the material is given. The influence of a variable nitriding potential on the lattice parameters of α-Fe, γ′-Fe4N, and ε-Fe3-2N phases is shown. The α phase interplanar space changes irrelevantly in the one phase area but decreases linearly with average increases in crystallite size when α→γ′ transformation occurs. The nanocrystallite size distributions (nCSDs) were determined, with nCSD of the α phase for nitriding and nCSD of the ε phase for reduction. The reduction of the ε phase can occur directly to α or indirectly with an intermediate step of γ′ formation as a result of ε→γ′→α transformations. The determining factor in the reducing process method is the volume of ε phase nanocrystallites. Those with V < 90,000 nm3 undergo direct transformation ε→αFe(N), and V > 90,000 nm3 transforms to αFe(N) indirectly. It was determined at what value of nitriding potential which fraction of the ε phase nanocrystallites starts to reduce

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Structural Properties of Iron Nitride on Cu(100): an Ab-initio Molecular Dynamics study

MRS Proceedings ◽

10.1557/opl.2011.15 ◽

2011 ◽

Vol 1290 ◽

Cited By ~ 2

Author(s):

Dodi Heryadi ◽

Udo Schwingenschlögl

Keyword(s):

Molecular Dynamics ◽

Ab Initio ◽

Structural Properties ◽

Nitride Layer ◽

Dynamics Simulation ◽

Ab Initio Molecular Dynamics ◽

Iron Nitrides ◽

Iron Nitride ◽

Magnetic Storage ◽

Reconstructed Surface

ABSTRACTDue to their potential applications in magnetic storage devices, iron nitrides have been a subject of numerous experimental and theoretical investigations. Thin films of iron nitride have been successfully grown on different substrates. To study the structural properties of a single monolayer film of FeN we have performed an ab-initio molecular dynamics simulation of its formation on a Cu(100) substrate. The iron nitride layer formed in our simulation shows a p4gm(2x2) reconstructed surface, in agreement with experimental results. In addition to its structural properties, we are also able to determine the magnetization of this thin film. Our results show that one monolayer of iron nitride on Cu(100) is ferromagnetic with a magnetic moment of 1.67μB.

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Oscillatory Kinetics in the Process of Reduction of Nanocrystalline Iron Nitride γ′-Fe4N

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.7b04418 ◽

2017 ◽

Vol 121 (27) ◽

pp. 14712-14716 ◽

Cited By ~ 3

Author(s):

Katarzyna Skulmowska ◽

Rafał Pelka ◽

Walerian Arabczyk

Keyword(s):

Iron Nitride ◽

Nanocrystalline Iron

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Transmission Electron Microscopy Investigation on the Electron-stimulated Oxidation of Iron Nitrides by 2-MeV Electron Irradiation

Journal of Materials Research ◽

10.1557/jmr.2005.0240 ◽

2005 ◽

Vol 20 (7) ◽

pp. 1918-1926 ◽

Cited By ~ 1

Author(s):

Z.Q. Liu ◽

H. Hashimoto ◽

T. Sakata ◽

H. Mori ◽

M. Song ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Iron Oxide ◽

Electron Irradiation ◽

High Resolution Electron Microscopy ◽

Ex Situ ◽

Iron Nitrides ◽

Iron Nitride ◽

Transmission Electron ◽

Nitride Sample

An iron nitride sample was irradiated by 2-MeV electrons intermittently for 2100 s with a dose rate of 6.3 × 1024 e.m.−2 s−1 inside a 3-MV high-voltage transmission electron microscope. The electron-stimulated oxidation of Fe4N and Fe2–3N was investigated in situ and ex situ using conventional transmission electron microscopy and high-resolution electron microscopy. It was found that both Fe4N and Fe2–3N nitrides were oxidized by the residual gas in the vacuum chamber to form Fe3O4 oxides. The orientation relationship between Fe4N (γ′) and Fe3O4 (o) was (110)γ′//(220)o, [001]γ′//[001]o, and that between Fe2–3N (ϵ) and Fe3O4 (o) was (110)ϵ//(−220)o, [1–11]ϵ//[001]o. Crystal lattice deformation from iron nitride to iron oxide took place during the dynamic oxidation process. Structural models were proposed to understand the oxide formation, and the models were confirmed by experimental observations. The irradiation effects of Fe4N and Fe2–3N crystals were compared. The results show that Fe4N is more sensitive than Fe2–3N to electron irradiation. These results are important not only for the fabrication of insulating iron oxide film, but also in the field of the surface modification of iron nitride to improve its mechanical properties.

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Soil and Plant Water

Solute Movement in the Rhizosphere ◽

10.1093/oso/9780195124927.003.0006 ◽

2000 ◽

Author(s):

Peter B. Tinker ◽

Peter Nye

Keyword(s):

Gravitational Field ◽

Kinetic Energy ◽

Chemical Potential ◽

Energy State ◽

Plant Water ◽

Chemical Potentials ◽

Solid Phases ◽

The Difference ◽

Electrically Charged ◽

Liquid And Solid Phases

Water is of central importance in the transport of solutes, whether by diffusion or mass flow, and whether in soils or plants (Lösch 1995). It is also extremely important for the biota that live in the soil (Parr et al. 1981). Water is an unusual component of the environment, because its structure suggests it should be a gas at normal temperatures rather than a liquid, and it is the only common compound in the biosphere that occurs to a significant extent in the vapour, liquid and solid phases. We begin this chapter with a very brief statement of the thermodynamic approach to the study of water, which defines the water potential. Without an understanding of chemical potentials, it is difficult to deal with the relationships of ions and water in the soil and the plant. Therefore, in this chapter we give an introduction to this subject with special reference to water, which we then take further in chapters 4 and 5. A clear exposition of this is given in Nobel (1991). The concept of chemical potential is fundamental. It is a measure of the energy state of a particular compound in a particular system, and hence of the ability of a unit amount of the compound to perform work and thereby cause change. In particular, the difference in potential at different points in a system gives a measure of the tendency of the component to move from the region with the high potential to the region with the low potential. A component of a system can have various forms of potential energy in this sense, all of which contribute to the total chemical potential. Here, we exclude chemical reaction energy and kinetic energy. The main forms of energy that contribute to the chemical potential of a specified compound or material are due to its concentration (which may release energy on dilution), to its compression (which may perform work on expansion), to its position in an electrical field (which may release energy if the component is electrically charged and moves within the field), and to its position in the gravitational field (which may release energy as the component moves downwards).

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The Coupling of Chemical and Transport Processes in Near-Field Modelling

MRS Proceedings ◽

10.1557/proc-84-683 ◽

1986 ◽

Vol 84 ◽

Cited By ~ 1

Author(s):

S.M. Sharland ◽

P.W. Tasker ◽

C.J. Tweed

Keyword(s):

Radioactive Waste ◽

Chemical Equilibrium ◽

Near Field ◽

Transport Processes ◽

Primary Interest ◽

Field Modelling ◽

Long Time ◽

Waste Repository ◽

Solid Phases ◽

Chemical Conditions

AbstractNear-field modelling is concerned with the description of the migration, chemical and degradation processes that may occur within an engineered radioactive waste repository and its immediate environs. The object is to gain understanding of such processes in order to predict the long-time evolution of the repository and to assess the degree of containment provided by the proposed engineered construction. The conditions of primary interest to our programme concern the waste contained within a steel canister and buried in a concrete environment within a clay geology. The chemistry of the near-field is controlled in that it is the consequence of the choice of near-field components, but it may be extremely complex. Intrusion of external groundwater and degradation of the chosen materials will lead to variations in the chemistry in both space and time. It is vitally important to understand these changing chemical conditions since they determine the solubility and sorption of any released radionuclides. In this paper, we describe the computer program CHEQMATE (CHemical EQuilibrium with Migration And Transport Equations), which has many applications in modelling various changes in chemistry in the near-field. The program combines an ionic migration code with the geochemical program PHREEQE [1]. The program maintains local chemical equilibrium in the system as the transport processes evolve. The program includes automatic mineral accounting; solid phases are added or removed from the equilibrium as precipitation or dissolution occurs. We illustrate the use of the CHEQMATE program with an example of a coupled chemical and transport problem, particularly relevant to the near-field of a waste repository.

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Phase Transformations and Interstitial Atom Diffusion in Iron-Nitride, Iron-Carbonitride and Iron-Carbide Layers

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.46.32 ◽

2006 ◽

Vol 46 ◽

pp. 32-41 ◽

Cited By ~ 5

Author(s):

Andreas Leineweber ◽

Tatiana Liapina ◽

Thomas Gressmann ◽

Marc Nikolussi ◽

Eric J. Mittemeijer

Keyword(s):

Solid State ◽

Phase Transformations ◽

Interstitial Atom ◽

Iron Carbide ◽

Layer Growth ◽

Iron Nitrides ◽

Iron Nitride ◽

Study Phase ◽

Atom Diffusion ◽

Kinetics Of

α-Iron foils were exposed to various gas atmospheres containing all or a number of the components NH3, CO, H2 and N2 for different periods of time at 550°C. In this way surficial compound layers were generated which contain different iron nitrides (ε, γ’), iron carbonitride (ε) and/or iron carbide (cementite, Fe3C). These compound layers were used to study phase transformations associated with N- and/or Cdiffusion processes in the corresponding phases. These studies involved (a) the layer-growth kinetics of cementite and (b) various solid-state phase transformations occurring in compound layers upon annealing in vacuum.

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On galvanic cells produced by the action of light. Preliminary communication.

Proceedings of the Royal Society of London ◽

10.1098/rspl.1904.0128 ◽

1905 ◽

Vol 74 (497-506) ◽

pp. 369-378 ◽

Cited By ~ 1

Author(s):

Meyer Wilderman ◽

Ludwig Mond

Keyword(s):

Chemical Reaction ◽

Chemical Equilibrium ◽

Chemical Potential ◽

The Other ◽

Gibbs Equation ◽

Galvanic Cells ◽

Chemical Potentials ◽

Fundamental Conception ◽

Statics And Dynamics ◽

Preliminary Communication

In my paper “On Chemical Statics and Dynamics” (‘Phil. Trans.,' A, vol. 199, 1902, p. 337), and especially ‘Zeit. Physik. Chemie,' voL 42, 1902, pp. 316—335, I deduced, from thermodynamics, the laws experimentally found by me for velocity of chemical reaction, and for chemical equilibrium under the action of light, from the fundamental conception that the chemical potential of substance in light and in the dark is different, becoming greater in light. The foundation for this conception was that two metallic plates immersed in a liquid and connected to a circuit form a “galvanic” combination, when one plate is exposed to light while the other is kept in the dark; and, according to Gibbs’ equation, v " — v ' = α a ( μ ' a — μ " a ), no galvanic cell could be formed, unless the chemical potentials at the two electrodes were different in light and in the dark.

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Magnetoresistance of Post-Annealed Iron Nitride Related Thin Films

Advances in Science and Technology ◽

10.4028/www.scientific.net/ast.52.70 ◽

2006 ◽

Vol 52 ◽

pp. 70-74 ◽

Cited By ~ 3

Author(s):

Shinichi Kikkawa ◽

K. Sakon ◽

Y. Kawaai ◽

T. Takeda

Keyword(s):

Thin Films ◽

Iron Nitrides ◽

Iron Nitride ◽

Low Oxygen ◽

Nitrogen Gas ◽

Zinc Blende ◽

System 2 ◽

Sputter Deposited ◽

Mr Effect ◽

Deposited Film

Iron nitrides thermally decompose to α-Fe releasing their nitrogen above 300°C. MR effect was found out in the thin films obtained by post-annealing of the following two kinds of sputter deposited iron nitride related films. (1) α-Fe particles dispersed in AlN granular film was obtained by an annealing of Al0.31Fe0.69N sputter deposited film in hydrogen. The MR=0.82% was found out in this nitride system. (2) Fe3O4 thin films were prepared by thermal decomposition of sputter deposited iron nitride films in low oxygen partial pressure. The iron nitrides were defect rock salt type γ΄˝-FeNx (0.5≤x≤0.7) and zinc blende type γ˝-FeNy (0.8≤y≤0.9) at the sputter nitrogen gas pressure of 1Pa and 6Pa. MR ratios of the oxide films were about 2%.

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