Iron Carbonitride Research Articles

Thermoelastic Anomaly of Iron Carbonitride Across the Spin Transition and Implications for Planetary Cores

AbstractCarbon and nitrogen are considered as candidate light elements present in planetary cores. However, there is limited understanding regarding the structure and physical properties of Fe‐C‐N alloys under extreme conditions. Here diamond anvil cell experiments were conducted, revealing the stability of hexagonal‐structured Fe7(N0.75C0.25)3 up to 120 GPa and 2100 K, without undergoing any structural transformation or dissociation. Notably, the thermal expansion coefficient and Grüneisen parameter of the alloy exhibit a collapse at 55–70 GPa. First‐principles calculations suggest that such anomaly is associated with the spin transition of iron within Fe7(N0.75C0.25)3. Our modeling indicates that the presence of ∼1.0 wt% carbon and nitrogen in liquid iron contributes to 9–12% of the density deficit of the Earth's outer core. The thermoelastic anomaly of the Fe‐C‐N alloy across the spin transition is likely to affect the density and seismic velocity profiles of (C,N)‐rich planetary cores, thereby influencing the dynamics of such cores.

Increasing Hardness and Wear Resistance of SKD61 Steel by Using Plasma Nitrocarburizing Proccess

This study observed the results of plasma nitrocarburizing processes on JIS SKD61 Steel. This research aims to use a plasma nitrocarburizing process to increase the hardness and wear resistance of JIS SKD61Steel. Before plasma nitriding was carried out, the sample had undergone a pre-treatment process. The optimum hardness value obtained after the pre-treatment process was 504 HV. The optimum hardness obtained in the plasma nitrocarburizing sample was 830 HV at temperatures 500°C for 4 hours. The optimum wear resistance or specific wear results on plasma nitrocarburizing was 0.11 x10-6mm2/kg at temperatures 400°C for 4 hours and 0.08 x10-6mm2/kg at temperature 500°C for 4 hours. XRD test results show that the phase formed in the nitrocarburizing compound layer was the iron nitride, iron carbonitride FeN, FeN0.49, ε-Fe2-3N, or ε-Fe2-3(N,C). The process of plasma nitrocarburizing has improved the mechanical properties of hardness and wear resistance of SKD61 steel.

Phase relations in the Fe-Fe3C-Fe3N system at 7.8 GPa and 1150°C: implications for C and N hosts in metal-saturated mantle

ABSTRACT The isothermal section of the Fe-Fe3C-Fe3N phase diagram at 7.8 GPa and 1150°С comprises a three-phase field of γ-Fe + Fe3C + ϵ-Fe3(С/N) in the central part and three two-phase fields (γ-Fe + Fe3C, γ-Fe + ϵ-Fe3 (С/N) and Fe3C + ϵ-Fe3(С/N)) bounded by three single-phase fields of γ-Fe, Fe3C and ϵ-Fe3(С/N) solid solutions along the triangle sides. Thus, native iron can host carbon and nitrogen in the γ-Fe + Fe3C or γ-Fe phases in the mantle depleted in volatiles (20 ppm C and 1 ppm N) at temperatures corresponding to the ∼35 mW/m2 heat flux, and in the Fe3C or ϵ-Fe3(С/N) phases if the contents of volatiles in the mantle reach 250 ppm C and 100 ppm N. Iron carbonitride has quite a large stability field even at low nitrogen concentrations in the system simulating native iron.

High‐Pressure Phase Stability and Thermoelastic Properties of Iron Carbonitrides and Nitrogen in the Deep Earth

AbstractIron‐dominant metallic phases are likely the primary hosts for nitrogen in the reduced deep Earth, hence the storage of nitrogen in the lower mantle and the core is governed by the behavior of the Fe‐N‐C system at high temperatures and pressures. In this study, phase transitions and thermoelastic properties of iron carbonitrides were investigated at high pressure‐temperature conditions by diamond anvil cell experiments and first‐principles calculations. Experimental data revealed no phase transition in ε‐type Fe4 (N0.6C0.4) or Fe7 (N0.75C0.25)3 up to 60 GPa at room temperature. At high temperature, Fe7 (N0.75C0.25)3 transforms into the Fe3C‐type phase at ∼27 GPa, and then into the Fe7C3‐type phase at ∼45 GPa, which is also corroborated by our theoretical calculations. We found that the phase stability of iron carbonitrides mainly depends on the N/C ratio, and the elastic properties of iron carbonitrides are dominantly affected by the Fe/(N+C) ratio. Iron carbonitrides with diverse structures may be the main host for nitrogen in the deep mantle. Some iron carbonitride inclusions in lower mantle diamonds could be the residue of the primordial mantle or originate from subducted nitrogen‐bearing materials, rather than iron‐enriched phases of the outer core. In addition, our experiments confirmed the existence of Fe7C3‐type Fe7C3‐Fe7N3 solid solutions above 40 GPa. Fe7C3‐type Fe7(C, N)3 has comparable density and thermoelastic properties to its isostructural endmembers and may be a promising candidate constituent of the Earth's inner core.

Static compression of Fe4N to 77 GPa and its implications for nitrogen storage in the deep Earth

AbstractCompression and decompression experiments on face-centered cubic (fcc) γ′-Fe4N to 77 GPa at room temperature were conducted in a diamond-anvil cell with in situ X-ray diffraction (XRD) to examine its stability under high pressure. In the investigated pressure range, γ′-Fe4N did not show any structural transitions. However, a peak broadening was observed in the XRD patterns above 60 GPa. The obtained pressure-volume data to 60 GPa were fitted to the third-order Birch-Murnaghan equation of state (EoS), which yielded the following elastic parameters: K0 = 169 (6) GPa, K′ = 4.1 (4), with a fixed V0 = 54.95 Å at 1 bar. A quantitative Schreinemakers' web was obtained at 15–60 GPa and 300–1600 K by combining the EoS for γ′-Fe4N with reported phase stability data at low pressures. The web indicates the existence of an invariant point at 41 GPa and 1000 K where γ′-Fe4N, hexagonal closed-packed (hcp) ε-Fe7N3, double hexagonal closed-packed β-Fe7N3, and hcp Fe phases are stable. From the invariant point, a reaction γ′-Fe4N = β-Fe7N3 + hcp Fe originates toward the high-pressure side, which determines the high-pressure stability of γ′-Fe4N at 56 GPa and 300 K. Therefore, the γ′-Fe4N phase observed in the experiments beyond this pressure must be metastable. The obtained results support the existing idea that β-Fe7N3 would be the most nitrogen-rich iron compound under core conditions. An iron carbonitride Fe7(C,N)3 found as a mantle-derived diamond inclusion implies that β-Fe7N3 and Fe7C3 may form a continuous solid solution in the mantle deeper than 1000 km depth. Diamond formation may be related to the presence of fluids in the mantle, and dehydration reactions of high-pressure hydrous phase D might have supplied free fluids in the mantle at depths greater than 1000 km. As such, the existence of Fe7(C,N)3 in diamond can be an indicator of water transportation to the deep mantle.

Synthesis, characterization and thermodynamic stability of nanostructured ε-iron carbonitride powder prepared by a solid-state mechanochemical route

Nanostructured epsilon iron carbonitride (ε-Fe3CxN1-x, x ∼ 0.05) powder with high purity (>97 wt%) was synthesized through a simple mechanochemical reaction between metallic iron and melamine. Various characterization techniques were employed to investigate the chemical and physical characteristics of the milling intermediates and the final products. The thermodynamic stability of the different phases in the Fe-C-N ternary system, including nitrogen and carbon doped structures were studied through density functional theory (DFT) calculations. A Boltzmann-distribution model was developed to qualitatively assess the stability and the proportion of the different milling products vs. milling energy. The theoretical and experimental results revealed that the milling products mainly comprise the ε-Fe3CxN1-x phase with a mean crystallite size of around 15 nm and a trace of amorphous carbon material. The thermal stability and magnetic properties of the milling products were thoroughly investigated. The synthesized ε-Fe3CxN1-x exhibited thermal stabilities up to 473 K and 673 K in air and argon atmospheres, respectively, and soft magnetic properties with a saturation magnetization of around 125 emu/g.

N and C Interstitial Diffusion and Thermodynamic Interactions in $$\varepsilon $$-Iron Carbonitride

The simultaneous diffusion of N and C over the interstitial sites of the Fe-sublattice of $$\varepsilon $$ -iron carbonitride was studied. To this end, gas nitrocarburizing experiments of pure Fe and Fe-C alloys were performed at 853 K (580 °C), leading to two different types of microstructures containing $$\varepsilon $$ (sub)layers. These microstructures were investigated by light microscopy, electron probe microanalysis, and X-ray diffraction in order to evaluate the components of the (N and C) diffusivity matrix. The off-diagonal components of the diffusivity matrix were shown to have significant, non-negligible values. These results provided insight into the thermodynamics of the Fe-N-C system.

A Mössbauer spectroscopy study of Ti–Fe interfaces produced by the PVD process

The deposition of hard coatings of the type TiC/N on steels enhances the surface properties of the coated substrate. Steel substrates have been pre-heated by the Arc Bond Sputtering process (ABS™), which uses a combined steered arc and unbalanced magnetron arrangement. A critical stage of the ABS process is the titanium ion etch which improves the adhesion of the TiN coating to the substrate. This work uses conversion electron Mössbauer spectroscopy (CEMS) to study the phase formations in the near surface region of mild steel substrates after various Ti ion etch pre-treatments using the steered arc discharge within the ABS process. The work has also investigated a second method using a Balzers BAI 640R coating unit. Appropriate enrichment using the Mössbauer isotope 57Fe has been used, enhancing the interfacial sensitivity of the CEMS technique to detect and identify phases formed by various ion etch processes. The results for the ABS pre-treatments indicate that oxides and carbonitrides that may be formed during the initial stages of the Ti ion etch, are removed after a longer etch. For a conventional 10-min Ti ion pre-treatment a significant formation of both a crystalline FeTi and a Te-rich amorphous phase occurs. The existence of the crystalline phase has also been confirmed by X-ray diffraction. For comparison, samples that had been pre-treated and coated in the Balzers process show some evidence of the FeTi amorphous phase and the development of an iron carbonitride, often identified as ϵ−Fe 2–3(CN).

Oxidation behavior and magnetic properties of metallic ultrafine particles

Iron (including bcc and fcc structures), iron nitride, iron carbide, and iron carbonitride ultrafine particles (< 100 nm in size) have been prepared by laser-induced pyrolysis of iron carbonyl, ammonia and ethylene mixtures. Transmission electron microscopy, X-ray diffraction, oxygen, nitrogen and carbon determiners, and a vibrating sample magnetometer were employed to characterize the metallic particles and measure their magnetic properties. It is found that the presence of carbon in the metallic particles not only significantly affects the oxygen content, but also affects the state of the oxygen at the particle surface, and thereby affects the magnetic properties of the ultrafine particles. In addition, taking advantage of the paramagnetism of face-centered-cubic structured iron (γ-Fe) ultrafine particles, the morphologies and magnetic properties of the iron oxide layers formed on the particle surfaces were determined. Convincing evidence was obtained indicating that the iron oxide layers formed on the metallic particles are composed of very fine crystallites and provide no contribution to the saturation magnetization of the particles. The structure of the iron oxide layers on the iron particle surfaces is also discussed and we conclude that the oxide layer formed at room temperature is a single Fe3O4 layer, rather than a mixture of Fe3O4 and γ-Fe2O3.

The oxidation behavior and magnetic properties of iron carbonitride ultrafine particles

Iron nitride and iron carbonitride (ICN) ultrafine particles (20–80 nm in size) have been synthesized by laser-induced pyrolysis of the Fe(CO)5–NH3–C2H4 system. The oxidation behavior, surface morphologies, and structural characteristics as well as magnetic properties of these particles are reported and discussed. It is found that the presence of very thin carbon coating (1–2 nm) on the ICN particles plays an important role in preventing the oxidation of the particles. Accordingly, the ICN ultrafine particles exhibit higher saturation magnetization (142 emu/g) than the iron nitride ones (124 emu/g).

Synthesis and characterization of iron carbonitride ultrafine particles

Iron carbonitride (ICN) ultrafine particles (20–80 nm in size) have been synthesized by laser-induced pyrolysis of Fe(CO)5–NH3–C2H4 mixture. The surface morphology, structural characteristics, oxidation behavior, and the magnetic properties of the ICN particles were reported. The role the thin carbon layer formed on the particle surface played in the oxidation behavior and in the enhancement of the magnetic properties has been studied. A carbon layer (1–2 nm) seems to protect the particles effectively from reaction of the iron carbonitride with oxygen, and the ICN particles thereby exhibit a high saturation magnetization of 142 emu/g. Additionally, the unilateral lattice expansion of the ICN compound was interpreted in terms of the structural and chemical bonding features of the ICN compound.

Migration of nitrogen implanted into iron induced by the presence of a buried carbon-rich layer

A redistribution of nitrogen atoms towards a buried carbon-rich layer is observed for thin iron films implanted at 250 °C. The effect is attributed to the formation of ε-Fe3−x(C,N) iron carbonitride. Above 300 °C the ε-carbonitride phase becomes unstable and consequently the redistribution effect vanishes leading to well-separated profiles of nitrogen and carbon atoms.

Corrosion studies of ion implanted iron and carbon steel

Aqueous corrosion by gravimetric means was carried out with high purity iron and carbon steel (0.96%) materials by the use of 70 keV He+, C+, N+ and O+ ions. Surface composition and depth profiles of the implanted material were done by AES sputter etching techniques. Eventual formation of chemical compounds or amorphous structures was studied by X-ray diffraction techniques. The results indicate that nitrogen implantation gives rise to far the most pronounced corrosion improvement. Although the mechanism for this beneficial effect is not clear, the formation of iron carbo-nitride which was found by the X-ray studies, is thought to play an important role.

Mössbauer study of f factors in iron carbonitrides

f-Factors of iron atoms, whith one and two interstitial nearest neghbours, in an iron carbonitride has been studied. Debye temperatures of 360 K and 620 K respectively, has been found.

Some observations on the production of low porosity ε phase iron carbonitride surface layers on ferrous materials

Etude de la production de couches composees a faible porosite par nitrocarburation en phase gazeuse d'un acier a faible carbone utilisant un gaz de traitement contenant de tres faibles niveaux de gaz de nitruration

Formation of iron carbonitride and iron carbide phases during nitrogen ion implantation

AbstractPolycrystalline iron is implanted with nitrogen ions with high doses at room temperature. During nitrogen ion implantation iron is doped with carbon by recoil implantation. The formation and the transformation of iron carbonitrides and iron carbides are investigated by high‐voltage electron microscopy. The implantation‐induced phase formation of iron carbonitride phases are discussed.

Catalytic and magnetic properties of iron ?-nitride and carbonitride in reactions of dehydrogenation and amination of alcohols

1. The catalytic properties of iron nitride (Fe2N) and carbonitride (Fe2C0.29N0.71) in the reactions of amination and dehydrogenation of alcohols were compared. 2. In the course of the amination and dehydrogenation reactions on a nitride catalyst, there is an “elution” of part of the introduced nitrogen from the surface with the formation of the structure of the lower nitride. 3. For related structures of the nitride and carbonitride, a correlation was detected between the catalytic activity and the average magnetic moment of the iron atom in the alloy.