Quantitative Analysis of Nitrogen by Atom Probe Tomography Using Stoichiometric γ′-Fe4N Consisting of 15N Isotope

The nitrogen deficiency in steels measured by atom probe tomography (APT) is considered to arise from the obscurement of singly charged dimer nitrogen ions (N2+) by the iron-dominant peak (56Fe2+) at 28 Da. To verify this by quantifying the amount of N2+ ions, γ′-Fe4N consisting of the 15N isotope was prepared on iron substrates by plasma nitriding using a nitrogen isotopic gas (15N2). Although considerable amounts of 15N2+ were observed at 30 Da without overlap with any iron peak, the observed nitrogen concentrations of γ′-Fe4N were clearly lower than the stoichiometric composition (19–20 at%), using both pulsed voltage and pulsed laser atom probes. The origin of the missing nitrogen, excluding nitrogen obscured by other ion species, was predicted to be the occurrence of neutral nitrogen or nitrogen gas molecules in field evaporation. The generation rate of iron nitride ions (FeN2+) for 15N was significantly lower than that for 14N in γ′-Fe4N, which affected the amount of the missing nitrogen. The isotope effect suggests that the isotopic ratio cannot always be determined from only one ion species among the multiple species observed in the APT analysis. We discuss the mechanism of the isotope effect in FeN2+ formation by field evaporation.

Structure and properties of high-chromium steel irradiated with a pulsed electron beam and nitrided in a low-pressure gas discharge plasma

Ion-plasma saturation of the surface of machine parts and mechanisms with gas elements (nitrogen, oxygen, carbon) is currently one of the most effective and widely used methods of surface hardening of metal products for various purposes in the industry of developed countries. The aim of this research is to develop a complex method for modifying the surface layer of AISI 310 steel, combining irradiation with an intense pulsed electron beam and subsequent nitriding in the plasma of a low-pressure gas discharge. As a result of the studies performed, the optimal parameters of modification were revealed, which make it possible to increase the hardness of the surface layer of steel by more than 11 times, relative to the hardness of the initial material, and 8 times, relative to the hardness of steel irradiated with a pulsed electron beam. In this case, the wear resistance of the steel exceeds the wear resistance of the original and irradiated material by more than 100 times. It has been established that the high strength and tribological properties of the modified steel are due to the formation of a two-phase (iron nitride and chromium nitride) layered nanoscale structure in the surface layer.

Synthesis and behavior of bulk iron nitride soft magnets via high-pressure spark plasma sintering

In this study, dense bulk iron nitrides (FexN) were synthesized for the first time ever using spark plasma sintering (SPS) of FexN powders. The Fe4N phase of iron nitride in particular has significant potential to serve as a new soft magnetic material in both transformer and inductor cores and electrical machines. The density of SPSed FexN increased with SPS temperature and pressure. The microstructure of the consolidated bulk FexN was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. XRD revealed a primary phase of Fe4N with secondary phases of Fe3N and metallic iron. Finite element analysis (FEA) was also applied to investigate and explain localized heating and temperature distribution during SPS. The effects of processing on interface bonding formation and phase evolution were investigated and discussed in detail to provide insight into fundamental phenomena and microstructural evolution in SPSed FexN. Graphic abstract

Metal telluride-nitride electrocatalysts for sustainably overall seawater electrolysis

High-efficiency alkaline seawater electrolysis is a promising strategy to promote the sustainability of wide-ranging hydrogen (H2) production, and the global goal of carbon neutrality. Searching for an ideal candidate with low cost and high electrocatalytic performance for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is a major objective. Herein, we report delicate, heterostuctured NiTe-NiCoN and NiTe-NiFeN electrocatalysts constructed of nickel cobalt nitride and nickel iron nitride nanosheets uniformly anchored on NiTe nanorod arrays, respectively, which ensure outstanding HER and OER activity along with ultra-long-term stability. Impressively, the NiTe-NiCoN || NiTe-NiFeN couples in alkaline seawater solution delivered 500 mA cm−2 at a record low voltage of 1.84 V, and realized an industry-level performance via a solar-powered system and a wind-power system. Further comprehensive analysis has revealed that interface engineering strategy not only ensures that the surficial nitride exposes abundant active sites, but also induces electron modulation that optimizes the binding strength of absorption/desorption for the reaction intermediates to enhanced the the intrinsic activity, as well as facilitate faster electron-mass transfer. Notably, a high electric field intensity generated by the unique nanosheet-nanorod structure induces a local “hydroxide enrichment” environment that effectively promotes the OER kinetics, while inhibits the side effects of chlorine. This work shed lights on these novel heterostructured electrocatalysts with strong synergy, while demonstrating the key role of the unique nanostructures in high-efficiency seawater electrolysis.

A Facile Route for the Preparation of Monodisperse Iron nitride at Silica Core/shell Nanostructures

Uniform-sized iron oxide nanoparticles obtained from the solution phase thermal decomposition of the iron-oleate complex were encapsulated inside the silica shell by the reverse microemulsion technique, and then thermal treatment under NH3 to transfer the iron oxide to iron nitride. The transmission electron microscopy images distinctly demonstrated that the as-prepared iron nitride at silica core/shell nanostructures were highly uniform in particle-size distribution. By using iron oxide nanoparticles of 6.1, 10.3, 16.2, and 21.8 nm as starting materials, iron nitride nanoparticles with average diameters of 5.6, 9.3, 11.6, and 16.7 nm were produced, respectively. The acid-resistant properties of the iron nitride at silica core/shell nanostructures were found to be much higher than the starting iron oxide at silica. A superconducting quantum interference device was used for the magnetic characterization of the nanostructure. Besides, magnetic resonance imaging (MRI) studies using iron nitride at silica nanocomposites as contrast agents demonstrated T2 enhanced effects that were dependent on the concentration. These core/shell nanostructures have enormous potential in magnetic nanodevice and biomedical applications. The current process is expected to be easy for large-scale and transfer other metal oxide nanoparticles.

In situ N K-edge XANES study of iron, cobalt and nickel nitride thin films

A prototype in situ X-ray absorption near-edge structure (XANES) system was developed to explore its sensitivity for ultra-thin films of iron-nitride (Fe-N), cobalt-nitride (Co-N) and nickel-nitride (Ni-N). They were grown using DC-magnetron sputtering in the presence of an N2 plasma atmosphere at the experimental station of the soft XAS beamline BL01 (Indus-2, RRCAT, India). XANES measurements were performed at the N K-edge in all three cases. It was found that the N K-edge spectral shape and intensity are greatly affected by increasing thickness and appear to be highly sensitive, especially in low-thickness regions. From a certain thickness of ∼1000 Å, however, samples exhibit a bulk-like behavior. On the basis of the obtained results, different growth stages were identified. Furthermore, the presence of a molecular N2 component in the ultra-thin regime (<100 Å) was also obtained in all three cases studied in this work. In essence, this prototype in situ system reveals that N K-edge XANES is a powerful technique for studying ultra-thin films, and the development of a dedicated in situ system can be effective in probing several phenomena that remain hitherto unexplored in such types of transition metal nitride thin films.