Low-Temperature Approach to Synthesize Iron Nitride from Amorphous Iron

Zhao H., Lei M., Chen X., Tang W.

Highly efficient and facile routes are still needed to meet the increasing demand on nitrides in a variety of applications although so far some preparative routes already exist. We have extended the solid-state metathesis (SSM) method by choosing an organic compound, melamine, and oxides as precursors, which allows us to develop a relatively general and facile route to nitrides. Whereby, eight technologically important nitrides including hexagonal GaN and cubic TiN were synthesized in sealed ampoules. These reactions are dynamically facilitated by the formation of numerous interfaces between finely-divided oxide grains and gas phases with high reactivity in an intermediate stage under heating temperatures. It is found that both hydrogen and carbon reductions are involved in the reactions, thermodynamically enhancing the nitride formation process. Our results demonstrate that the reactions between an organic compound and oxides offer an attractive preparative route to nitrides in terms of the wide availability of reagents, high yield and relative generality.

Tong W.P., Tao N.R., Wang Z.B., Zhang H.W., Lu J., Lu K.

The formation kinetics of e-Fe3–2N phase in a nanocrystalline α-Fe, which was processed by surface mechanical attrition treatment, is found to be obviously increased with respect to that in the coarse-grained form. This can be attributed to the much enhanced heterogeneous nucleation rate at numerous grain boundaries in the nanocrystalline α-Fe.

Wang X., Zheng W.T., Tian H.W., Yu S.S., Xu W., Meng S.H., He X.D., Han J.C., Sun C.Q., Tay B.K.

Abstract FeN thin films were deposited on glass substrates by dc magnetron sputtering at different Ar/N 2 discharges. The composition, structure and the surface morphology of the films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Films deposited at different nitrogen pressures exhibited different structures with different nitrogen contents, and the surface roughness depended on the mechanism of the film growth. Saturation magnetization and coercivity of all films were determined using superconducting quantum interference device, which showed that if N 2 /(Ar+N 2 ) flow ratio was equal to or larger than 30% the nonmagnetic single-phase γ″-FeN appeared. If N 2 /(Ar+N 2 ) flow ratio was less than 10%, the films consisted of the mixed phases of FeN 0.056 and γ′-Fe 16 N 2 , whose saturation magnetizations were larger than that of α-Fe. If N 2 /(Ar+N 2 ) flow ratio was 10%, the phases of γ′-Fe 4 N and e-Fe 3 N appeared, whose saturation magnetizations were lower than that of α-Fe.

Loloee R., Nikolaev K.R., Pratt W.P.

Epitaxial single-crystal ferromagnetic Fe4N films (γ′ phase of iron nitride), nonmagnetic NbN films, and NbN/Fe4N bilayers were grown on MgO(100) substrates by sputter deposition in N2 gas. Electron backscatter diffraction patterns were used to characterize the structural properties including the relative crystallographic orientation of the sputter deposited Fe4N and NbN films with respect to the substrate and each other. Superconducting quantum interference device magnetometry was used to study the in-plane uniaxial anisotropy and determine the directions of the easy axes in ferromagnetic Fe4N films.

Tong W.P., Tao N.R., Wang Z.B., Lu J., Lu K.

The microstructure in the surface layer of a pure iron plate was refined at the nanometer scale by means of a surface mechanical attrition treatment that generates repetitive severe plastic deformation of the surface layer. The subsequent nitriding kinetics of the treated iron with the nanostructured surface layer were greatly enhanced, so that the nitriding temperature could be as low as 300°C, which is much lower than conventional nitriding temperatures (above 500°C). This enhanced processing method demonstrates the technological significance of nanomaterials in improving traditional processing techniques and provides a new approach for selective surface reactions in solids.

Schaaf P.

Laser nitriding can be described as the irradiation of metal surfaces by short laser pulses in nitrogen containing atmospheres. This may lead to a strong take-up of nitrogen into the metal and nitride formation which can improve the metal’s surface properties, e.g. the hardness or the corrosion and wear resistance. Here, the laser nitriding of iron, carbon steel, stainless steel, and aluminum was investigated employing a combination of complementary methods. Ion beam analysis (Rutherford Backscattering Spectroscopy and Resonant Nuclear Reaction Analysis) was employed for element and isotope profiling. Mossbauer spectroscopy and X-ray diffraction were used for phase analysis. Surface profilometry, optical and electron microscopy revealed the surface topography and morphology obtained after laser nitriding. Microhardness measurements by the nanoindentation technique characterized the mechanical surface properties obtained by the treatment. By this combination of methods it became possible to resolve the influence of the treatment parameters (laser fluence, number of pulses, spot size, spatial intensity distribution, and gas pressure) in different materials treated (iron, carbon steels and stainless steel). It is shown that laser nitriding is a complex process, composed of several superimposed effects. Laser heating, melting and evaporation in combination with plasma formation and the generation of laser-supported absorption waves are the essentials of the process. Pressure- and plasma-enhanced dissolution and diffusion of nitrogen in combination with macroscopic material transport (piston effect, convection, fall-out) are further important effects determining the results. Additional marker experiments and laser treatments in isotopically enriched nitrogen atmospheres allowed to analyze these effects and to develop scenarios for the nitriding process and the material transport mechanisms. A simulation of the nitrogen depth profiles for the single spot irradiations was derived, whose results are in good agreement with the experimentally observed profiles.

Jirásková Y., Havlíček S., Schneeweiss O., Peřina V., Blawert C.

The effect of the nitrogen uptake in α-iron upon spark erosion in gaseous and liquid ammonia, plasma nitriding, and plasma immersion ion implantation is studied. The resulting phases and hyperfine parameters, measured by the Mossbauer spectroscopy, are discussed from the point of view of initial conditions of their preparation and subsequent heat and/or mechanical treatment. Spark erosion in the ammonia gas produces fine particles with the dominating ferromagnetic α-Fe phase (50%). The 20% of specimen volume form α′-Fe and α′′-Fe16N2 phases. The last 30% occupy the γ′-Fe4N, ferro- and paramagnetic e phases, and γ-Fe(N). Nitriding in the liquid ammonia allows to incorporate the higher content of nitrogen into α-iron particles which results in the formation of paramagnetic e(ζ)-Fe2N phase. This phase also dominates the surface of α-iron specimen implanted by nitrogen using plasma immersion ion implantation at 300°C/3 h, where high uptake of nitrogen (approx. 30 at%) is reached. Plasma nitriding at 510°C results in the formation of γ′-Fe4N phase.

Lu Y.F., He Z.F., Mai Z.H., Ren Z.M.

Carbon nitride thin films were deposited on iron buffer layers by pulsed laser deposition assisted with ion implantation. Two types of samples (A) and (B) were prepared with and without iron layers. Several techniques were used to study the properties of the samples. Scanning tunneling microscopy (STM) was used to observe the surface structures of the samples. The difference in their surface morphologies was studied. The STM measurements also provided the relation between tunneling current and bias voltage to study the local density of states of the sample surface by calculating (dI/dV)/(I/V). Three band edges were observed from the calculated curve. Measurements by Raman and Fourier transform infrared (FTIR) spectra were carried out to study the electronic properties of the samples. The Raman spectra showed the presence of triply bonded carbon nitride bonds (C≡N) in sample (A), while only single bonds were observed in sample (B) by FTIR spectra. The mechanical properties were studied by nanoindentation. Both hardness and bulk modulus of the thin films were measured.

Popescu M.A.

Eck B., Dronskowski R., Takahashi M., Kikkawa S.

The electronic structures of a number of binary 3d transition metal and iron nitrides, some of which still need to be synthesized, have been investigated by means of spin-polarized first principles band structure calculations (TB-LMTO-ASA). The chemical bonding in all compounds has been clarified in detail through the analysis of total and local densities-of-states (DOS) and crystal orbital Hamilton populations (COHP). The binary transition metal nitride set includes ScN, TiN, VN, CrN, MnN, FeN, CoN and NiN, both in the sodium chloride as well as in the zinc blende structure type. Antibonding metal-metal interactions for higher electron counts are significantly weaker in the zinc blende type, thus favoring this structural alternative for the later transition metal nitrides.

Roberson S.L., Finello D., Banks A.D., Davis R.F.

Polycrystalline Fe3N films have been grown via chemical vapor deposition (CVD) on 50-μm thick polycrystalline Ti substrates using iron acetylacetonate (IAA) and anhydrous ammonia (NH3) in a cold-wall vertical pancake-style reactor. X-ray diffraction data indicated that single phase Fe3N was present in films deposited at and above 600°C; below this temperature no deposition occurred. The composition of the Fe3N films did not vary with changes in the deposition temperature, the NH3 flow rate or the deposition rate at a constant deposition pressure of 100 Torr. The surface macrostructure of the as-deposited films was independent of the deposition temperature and was very similar to that of the uncoated Ti substrate. The microstructure of the films was porous with a thickness variation of ≈1 μm across the surface of the films. Larger grains were produced at 600 and 800°C, while smaller and more uniform grains were produced at 700°C. Energy dispersive X-ray data indicated that films deposited at and above 600°C contained low levels of both carbon and oxygen.

Koltypin Y., Cao X., Prozorov R., Balogh J., Kaptas D., Gedanken A.

A method for the preparation of nanoparticles of iron nitride powders is reported. Iron nitride particles have been synthesised by two methods. In the first, Fe(CO)5 was sonicated in a decane solution under a gaseous mixture of NH3 and H2 (3.5:1 molar ratio) at ca. 0 °C. The second method was based on nitriding the sonochemically prepared amorphous iron at ca. 400 °C for 4 h under a mixed stream of NH3–H2(3.5:1 molar ratio). Different products were obtained in the two cases. The product of the sonication of Fe(CO)5 was amorphous Fe2–3N and a small quantity of iron oxide. The X-ray diffraction patterns in the second case showed Fe4N as a main product. The magnetic properties of both products were measured. The coercive force HC of the Fe4N is 190 Oe, and the saturation magnetization sigma;s is 170 emu g–1 .

Landmarks in Organo-Transition Metal ChemistryEssentials of Inorganic ChemistryTransition Metal CompoundsMolecular Orbitals of Transition Metal ComplexesTransition Metal ChemistryAspects of the Chemistry of Transition Metal ComplexesThe Chemistry of Coordination Complexes and Transition MetalsTransition Metals in Coordination EnvironmentsQuantum Chemistry: The Challenge of Transition Metals and Coordination ChemistryConcepts in Transition Metal ChemistryThe Chemistry of Transition Metal Compounds Containing Sulfur-donor LigandsTransition Metal Reagents and CatalystsTheoretical Aspects of Transition Metal CatalysisMetal-Ligand Multiple BondsChemistry Of Transition ElementsChirality in Transition Metal ChemistryElectron Transfer and Radical Processes in Transition-metal ChemistryTransition Metals in the Synthesis of Complex Organic MoleculesOrganic Synthesis Using Transition MetalsTransition-Metal Organometallic ChemistryMagnetism and Transition Metal ComplexesTransition Metals and Sulfur – A Strong Relationship for LifeMagnetic Properties of Transition Metal CompoundsInorganic Chemistry of the Transition ElementsElectronic Structure and Properties of Transition Metal CompoundsOrganometallic Chemistry of the Transition ElementsThe Organometallic Chemistry of the Transition MetalsTransition Metal Organometallic ChemistryAspects of the Chemistry of Transition Metal Complexes CarryingTransition Metal-Catalyzed Couplings in Process ChemistryOrganotransition Metal Chemistry A Mechanistic ApproachOrganometallic ChemistryCluster ChemistryAn Introduction to Transition-metal Chemistry: Ligand-field TheoryThe Chemistry of Transition Metal Carbides and NitridesChemistry of the First Row Transition MetalsMössbauer Spectroscopy and Transition Metal ChemistryOrganotransition Metal ChemistryAlkene Polymerization Reactions with Transition Metal CatalystsTransition Metal Oxides

Chen Y., Halstead T., Williams J.S.

Fe 3 N, γ′-Fe 4 N and a supersaturated solid solution of N in Fe have been formed by ball milling of pure iron powder in a nitriding atmosphere. The structural development was monitored by X-ray diffractometry and the chemical composition of the end milling product was determined using Rutherford backscattering spectroscopy. The influence of milling temperature and atmosphere on nitriding reactions was investigated by milling Fe powder at three different temperatures (room temperature, 200 °C and liquid-nitrogen temperature) and in two nitriding atmospheres (nitrogen and ammonia). A high nitrogen concentration and a large quantity of nitride (Fe 3 N) were obtained at low milling temperatures (room temperature and below), Ammonia gas is a more efficient nitriding gas for the formation of iron nitride, presumably as a result of the catalytic effect of hydrogen.

Jacobs H., Rechenbach D., Zachwieja U.

Single crystals of γ′-Fe 4 N were prepared by high pressure ammonolysis. Our earlier published results (H. Jacobs and J. Bock, J. Less- Common Met., 134 (1987) 215) differ from those which are now reported. γ′-Fe 4 N crystallizes in the CaTiO 3 (perovskite) structure type: X-ray single-crystal diffractometer data, space group Pm 3 m, Z=1 and a=3.7900(6) A ̊ , R R w (w = 1) = 0.017 0.023 , N(F o 2 ) ⩾ 3σ(F o 2 ) = 59 and N (var) = 6. Powder samples of ϵ-Fe 3 N were prepared in a technical furnace. The crystal structure was studied by neutron powder diffraction at 9 K, room temperature and 609 K. ϵ-Fe 3 N crystallizes in a hexagonal structure type: space group P6 3 22, Z = 2, a = 4.6982(3) A ̊ and c = 4.3789(3) A ̊ , N(F o ) = 34 and 5 structural parameters refined, R Profile = 4.43%, R Bragg = 4.14% for the measurement at room temperature.

Appiah-Ntiamoah R., Kim H.

AbstractThe prevailing practice advocates pre–oxidation of electrospun Fe–salt/polymer nanofibers (Fe–salt/polymer Nf) before pyrolysis as advantageous in the production of high–performance FeOx@carbon nanofibers supercapacitors (FeOx@C). However, our study systematically challenges this notion by demonstrating that pre–oxidation facilitates the formation of polydispersed and large FeOx nanoparticles (FeOx@CI−DA) through “external” Fe3+ Kirkendall diffusion from carbon, resulting in subpar electrochemical properties. To address this, direct pyrolysis of Fe–salt/polymer Nf is proposed, promoting “internal” Fe3+ Kirkendall diffusion within carbon and providing substantial physical confinement, leading to the formation of monodispersed and small FeOx nanoparticles (FeOx@CDA). In 1 M H2SO4, FeOx@CDA demonstrates ~2.60× and 1.26× faster SO42− diffusivity, and electron transfer kinetics, respectively, compared to FeOx@CI−DA, with a correspondingly ~1.50× greater effective surface area. Consequently, FeOx@CDA exhibits a specific capacity of 161.92 mAhg−1, ~2× higher than FeOx@CI−DA, with a rate capability ~19 % greater. Moreover, FeOx@CDA retains 94 % of its capacitance after 5000 GCD cycles, delivering an energy density of 26.68 Whkg−1 in a FeOx@CDA//FeOx@CDA device, rivaling state–of–the–art FeOx/carbon electrodes in less Fe–corrosive electrolytes. However, it is worth noting that the effectiveness of direct pyrolysis is contingent upon hydrated Fe–salt. These findings reveal a straightforward approach to enhancing the supercapacitance of FeOx@C materials.

Gui Q., Zhang C., Zhan T., Peng X., Li J., Tao S., Wu Q., Xu J., Hong B., Wang X., Ge H.

The magnetic properties of SMCs are typically challenging to further enhance, after compaction into a specific shape. However, in this study, a gas-nitriding process is employed to diffuse nitrogen atoms into iron-based magnetic toroidal after being prepared, resulting in an improvement in effective permeability and reduction in core losses. The results indicate that the saturation magnetization decreases with increasing nitriding time, reaching its minimum value at a nitriding time of 24 h, where Ms measure at 199.8 emu/g. The sample nitrided for 12 h exhibits superior effective permeability, high-frequency stability, DC-bias property, and total core loss, indicating its suitability for high-frequency applications. The gas-phase nitride process can further enhance the performance of the prepared soft magnetic composites, which is of significant value in scientific applications.

Li L., Cartigny P., Li K.

Roaldite (Fe 4 N) is one of the few nitride minerals found in meteorites. Their nitrogen (N) isotopic signatures carry important information for understanding the early N cycle in the proto-solar nebula. However, the lack of knowledge on the N isotopic effects from nitride formation to its survival from frictional heating during landing impedes the interpretation and application of N isotope compositions of nitride minerals in meteorites. Here, we carried out laboratory experiments under a recently proposed roaldite forming condition, i.e., NH 3 (as starting N source) reacting with metallic Fe at medium temperatures. We observed Fe 4 N formation over a large range of temperatures from 300 °C to 700 °C. The formation of Fe 4 N was associated with equilibrium N isotope fractionations with α Fe4N-NH3 values of 0.9907 (±0.0004) at 300 °C and 0.9936 (±0.0004) at 500 °C, respectively. In the experimental pressure conditions (initial P NH3 = 3.9–6.4 bar, P Total < 8.3 bar), the formed Fe 4 N remained stable at 300 °C, but was unstable and quickly decomposed to Fe and N 2 at 500 °C and 700 °C. The decomposition of Fe 4 N was associated with large kinetic isotope fractionations with α N2-Fe4N values of 0.9811 (±0.0009) at 500 °C and 0.9839 (±0.0011) at 700 °C, respectively. Our experimental results suggest that roaldite formed from NH 3 can carry an isotopic signature very close to that of its source, but partial decomposition (if there is any) can easily shift its N isotope composition for several tens of per mil, and in extreme cases, to >300‰. Thus, great caution is needed when using N isotope composition of roaldite (and probably other nitride minerals as well) to trace source information.

Zhidkov I.S., Kukharenko A.I., Makarov A.V., Savrai R.A., Gavrilov N.V., Cholakh S.O., Kurmaev E.Z.

The results of the influence of low-temperature plasma nitriding at 350 °C on the Cr N and Fe N bonds formation of Fe-Cr-Ni austenitic steel before and after nanostructure frictional treatment are presented. The measurements of high-energy resolved X-ray photoelectron Fe 2p, Cr 2p, Ni 2p and N 1s spectra and valence bands (VB) showed that chromium and iron form Cr N and Fe N bonds whereas the nickel is in metallic state. It is concluded that the expanded austenite formed directly on the surface of the steel after low temperature plasma nitriding can be classified as a nanocomposite medium consisting of Cr N and Fe N clusters dispersed in a Fe-Cr-Ni-N matrix.

Perez H., Jorda V., Bonville P., Vigneron J., Frégnaux M., Etcheberry A., Quinsac A., Habert A., Leconte Y.

This paper reports original results on the synthesis of Carbon/Nitrogen/Iron-based Oxygen Reduction Reaction (ORR) electrocatalysts by CO2 laser pyrolysis. Precursors consisted of two different liquid mixtures containing FeOOH nanoparticles or iron III acetylacetonate as iron precursors, being fed to the reactor as an aerosol of liquid droplets. Carbon and nitrogen were brought by pyridine or a mixture of pyridine and ethanol depending on the iron precursor involved. The use of ammonia as laser energy transfer agent also provided a potential nitrogen source. For each liquid precursor mixture, several syntheses were conducted through the step-by-step modification of NH3 flow volume fraction, so-called R parameter. We found that various feature such as the synthesis production yield or the nanomaterial iron and carbon content, showed identical trends as a function of R for each liquid precursor mixture. The obtained nanomaterials consisted in composite nanostructures in which iron based nanoparticles are, to varying degrees, encapsulated by a presumably nitrogen doped carbon shell. Combining X-ray diffraction and Mossbauer spectroscopy with acid leaching treatment and extensive XPS surface analysis allowed the difficult question of the nature of the formed iron phases to be addressed. Besides metal and carbide iron phases, data suggest the formation of iron nitride phase at high R values. Interestingly, electrochemical measurements reveal that the higher R the higher the onset potential for the ORR, what suggests the need of iron-nitride phase existence for the formation of active sites towards the ORR.

Gao T., Jin Z., Zhang Y., Tan G., Yuan H., Xiao D.

Zn-air battery, as an ideal energy conversion and storage device, is always limited by the expensive and less-than-ideal air electrode materials. The coupling of outstanding oxygen evolution reaction (OER) active sites (oxides derived from Co-Fe nitrides) and superior oxygen reduction reaction (ORR) active centers (metal-N-C and graphitic N) to acquire high-performance and low-cost catalysts is an ideal solution. Herein, we have successfully combined cobalt-iron bimetallic nitrides with N-doped multi-walled carbon nanotubes (Co-Fe-N@MWCNT) as a robust bifunctional material. Benefiting from the synergistic effect between Co, Fe and MWCNTs, Co-Fe-N@MWCNT not only possesses large electrochemically active surface area and effective transport path, but also realizes the integration of superior OER and ORR active sites. Only a low overpotential (290 mV) is needed to achieve a current density of 10 mA cm -2 for OER and the ORR catalytic activity is close to that of the commercial Pt/C. Additionally, Co-Fe-N@MWCNT as an ideal air electrode material can also be applied in Zn-air battery, which exhibits low voltage drop and favorable stability. The voltage gap has a slight change (about 0.03 V) even after 100 cycles of galvanostatic charge-discharge. More importantly, the synthetic strategy in our work may facilitate the design of more high-efficient bifunctional catalysts in various domains.

Zhou C., Fasel C., Ishikawa R., Gallei M., Ikuhara Y., Lauterbach S., Kleebe H., Riedel R., Ionescu E.

In the present study, a C/SiFeN(O)-based ceramic paper with in situ generated hierarchical micro/nano-morphology was prepared upon thermal treatment of a cellulose-base paper surface-modified with a polymeric single-source precursor prepared from perhydropolysilazane (PHPS) and iron(II) acetylacetonate (Fe(acac)2). The ammonolysis at 1000 °C of the paper/precursor hybrid materials leads to a C/SiFeN(O)-based ceramic paper which exhibits the same morphology as that of the cellulose paper. Subsequent annealing of the ceramic paper in nitrogen atmosphere at temperatures from 1200 to 1400 °C results in the in-situ generation of ultra-long silicon nitride nanowires with aspect ratios in the range of 103 on the surface and in the macropores of the ceramic paper. The nanowires exhibit round Fe3Si tips at the end, indicating that the growth occurred via iron-catalyzed VLS (vapor-liquid-solid) mechanism. The combination of single-source precursor, porous template and in situ VLS growth of 1D nanostructures provides a convenient one-pot synthesis approach to produce ceramic nanocomposites with hierarchical morphologies.

Ren M., Ren J., Hao P., Yang J., Wang D., Pei Y., Lin J., Li Z.

Liu S., Huo Q., Chen R., Chen P., Li Y., Han Y.

An iron nitride with high surface area was synthesized from an iron-based metal organic framework (Fe-MOF) in this work. During the synthesis process, the Fe-MOF of MIL-53 served as a hard template, a template to impart a certain degree of morphology for iron oxide products and to form porosities for iron nitride products. Moreover, it played the roles of iron sources for the synthesis of the final iron oxides and the iron nitrides. The physicochemical properties of the materials were characterized by a series of technologies including XRD, SEM, and N2-adsorption/desorption. The results showed that the iron nitride synthesized from MIL-53 wasα-Fe2-3N. And, theα-Fe2-3N showed the morphology with loosely aggregated particles which favored the formation of rich interparticle porosities. As a result, the surface area of theα-Fe2-3N was larger than those of samples usingα-Fe2O3as precursors and its value was 41 m2/g. In addition, the results agreed that both raw material properties (such as crystallinity and surface areas) and nitriding approaches had significant effects on the surface areas of iron nitrides. Also the results were proved by the iron oxide synthesized with different methods. This new synthetic strategy could be a general approach for the preparation of late transition metal nitrides with peculiar properties.

Wang H., Wang K., Song H., Li H., Ji S., Wang Z., Li S., Wang R.

N-doped porous carbon material derived of fish bones showed excellent catalytic activity towards oxygen reduction reaction in alkaline medium, as well as long-term stability.

Imai Y., Sohma M., Suemasu T.

Formation energies and magnetic moments of tri-, tetra-, and octa- ferromagnetic element nitrides have been calculated using spin-polarized Perdew–Wang generalized gradient approximations of the density functional theory. From the energetic point of view, Fe 4 N are more stable compared to Fe and N 2 gas. Ni 4 N may be a metastable phase since mixture of Ni 3 N and Ni would be more energetically stable. Fe 4 N may be also a metastable from energetic point of view but effect of configurational entropy caused by N-vacancy and of disregarded random occupation of interstitial sites by N observed in Fe 3 N must be evaluated so as to make precise evaluation, which is beyond the scope of the present work. Co 4 N are not stable compared to Co metal with the hcp structure and N 2 gas, but more stable in case Co metal with the fcc structure is used as a reference state. Only Fe 8 N with the α″-Fe 16 N 2 type structure would be stable among octa-metal nitrides with the assumed structure of the α″-Fe 16 N 2 type and the Ni 32 N 4 type structure. All of Fe 3 N, Co 3 N, and Ni 3 N are stable, but Ni 3 N would be non-magnetic in contrast to ferromagnetism of other tri-metal nitrides.

Wang H., Wu Z., Kong J., Wang Z., Zhang M.

Metastable transition metal oxides were used as precursors to synthesize transition metal nitrides at low temperature. Amorphous MoO 2 was prepared by reduction of (NH 4 ) 6 Mo 7 O 24 solution with hydrazine. As-synthesized amorphous MoO 2 was transformed into fcc γ-Mo 2 N at 400 °C and then into hexagonal δ-MoN by further increasing the temperature to 600 °C under a NH 3 flow. The nitridation temperature employed here is much lower than that employed in nitridation of crystalline materials, and the amorphous materials underwent a unique nitridation process. Besides this, the bimetallic nitride Ni 2 Mo 3 N was also synthesized by nitridating amorphous bimetallic precursor. These results suggested that the nitridation of amorphous precursor possessed potential to be a general method for synthesizing many interstitial metallic compounds, such as nitrides and carbides at low temperature.

Guan J., Yan G., Wang W., Liu J.

This work describes an easy and flexible approach for the synthesis of 2D nanostructures by external composite field-induced self-assembly. Amorphous iron nanoplatelets with a large aspect ratio were prepared by reducing a concentrated FeSO4 solution with NaBH4 without any templates or surfactants under a magnetic field and a shear field, and characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Based on the morphological dependence of the resultant iron nanostructures on the kinetic parameters such as reactant concentration, reaction temperature, external fields as well as reaction time, etc., a novel conceivable formation mechanism of the iron nanoplatelets was substantiated to be a self-assembly of concentrated iron nuclei induced by the synergistic effect of both a magnetic field and a shear field. Due to the amorphous nature and shape anisotropy, the as-synthesized iron nanoplatelets exhibit quite different magnetic properties with an enhanced coercivity of >220 Oe from isotropic iron nanoparticles. In the oxidation of cyclohexane with hydrogen peroxide as a “green” oxidant, the as-obtained amorphous iron nanoplatelets show a conversion more than 84% and a complete selectivity for cyclohexanol and cyclohexanone due to the unique structure. Moreover, their catalytic performances are strongly influenced by their morphology, and the iron atoms located on the faces tend to catalyze the formation of cyclohexanol while those on the sides tend to catalyze the formation of cyclohexanone. The external composite field-induced solution synthesis reported here can be readily explored for fabricating other 2D magnetic nanoplatelets, and the resulting iron nanoplatelets are promising for a number of applications such as high efficient selective catalysis, energy, environment fields and so forth.

Kurian S., Gajbhiye N.S.

The Mossbauer spectra of e-Fe 3 N at 5 K show several sextets which indicate a disordered arrangement of nitrogen atoms. Even though the 5 K spectra hints out a distribution for the Fe atoms coordinated with two nitrogen atoms (Fe(II)), the in-field spectrum showed that the Fe(II) atoms are magnetically different. It is found that the arrangements of magnetic spins with the direction of easy magnetic axis are different for the two Fe(II) sites. In addition to this, the presence of an antiferromagnetic phase is revealed in an in-field Mossbauer spectrum at 5 K.

Zheng J., Yang R., Chen W., Xie L., Li X., Chen C.