Nitriding Process Research Articles

Unraveling the role of alkali metal in the biochar for enhancing the chemical looping ammonia generation efficiency

Chemical looping ammonia generation (CLAG), efficiently converting C-based material, N2 and H2O into NH3 and CO, is considered to be one of the promising NH3 production technologies. Using biochar as the C-based material is supposed to further improve the “green” level of NH3 but there is rare report about that. This paper was desired to fill this gap. Peanut shell biochar, lotus shell biochar and corncob biochar were used to study the chemical looping ammonia generation performances of the N-support. It was found that metals contained in the biochar significantly affected the nitridation process; alkali metals were simulative while alkaline-earth metals were inhibitory, which indicated that the corncob biochar exhibit the best nitriding properties. In addition, K, with the best positive effect for nitridation, was found to be with negligible negative effect for ammoniation. Furthermore, the carbon conversion efficiency and NH3 production could be still improved by 8.46 % and 9.23 % if the corncob biochar was modified with 2 wt% K (simulating 120 cycles of nitridation/ammoniation reaction). The obtained results indicated that the biochar is a promising carbon source for CLAG.

Effect of different plasma nitriding durations on the tribological characteristics of nickel-boron-nanodiamond electroless nanocomposite coatings

The aim of this research work was to investigate the effect of plasma nitriding duration on the tribological properties of nickel‑boron/nano-diamond (NiB/ND) coatings. In this regard, NiB/ND coatings were electrodeposited on AISI 4140 steel using the electroless plating technique. Subsequently, the coated samples were plasma nitrided in a gas mixture containing 25 % nitrogen and 75 % hydrogen at 400 °C for three different durations (60, 120, and 180 min). The coatings were then characterized using X-ray diffraction, scanning electron microscopy (SEM), surface roughness profilometer, and microhardness tests to evaluate their structural and mechanical properties. To assess the tribological behavior, a pin-on-disk test was performed with a load of 10 N applied over a sliding distance of 500 m. The results indicated that plasma nitriding led to the crystallization of the coatings, which can be attributed to the formation of Ni2B, Ni3B, and h-BN phases. Furthermore, the plasma nitriding process significantly increased the coating hardness from 700 to 1523 Vickers after 1 h of treatment. The wear resistance of plasma-nitrided coatings was improved, as evidenced by a considerable reduction in the specific wear rate compared to the untreated sample. However, for the samples plasma nitrided for >60 min, a reduction in coating hardness and wear resistance was observed, which is likely due to the changes in grain size during the plasma nitriding process. The optimal plasma nitriding duration for achieving desirable properties was found to be 60 min.

Tailoring the Mo-N/Mo-O configuration in MoO2/Mo2N heterostructure for ampere-level current density hydrogen production

Mo-based electrocatalysts have garnered significant attention for their promising hydrogen evolution reaction (HER) efficiency, however, the strong adsorption of hydrogen poses a challenge to speedy gaseous hydrogen release. In this respect, regulating the coordination of Mo atoms is an efficient strategy to optimize the electronic configuration and accelerate the HER kinetics. Herein, MoO2/Mo2N heterostructures are prepared by a programmed in situ nitridation process. The precisely controlled Mo-N/Mo-O configuration in MoO2/Mo2N heterostructure weakens hydrogen adsorption on the Mo sites leading to HER with an ampere-level current density. The electrocatalyst delivers 1 A cm−2 at an overpotential of 335 mV in 0.5 M H2SO4. Furthermore, the electrocatalyst has excellent stability by maintaining a current density of 1 A cm−2 for 180 hours with a remarkable Faradaic efficiency of 99.8%. The results reveal a novel strategy to precisely modulate the electronic configurations of low-cost transition metal-based electrocatalysts boding well for industrial-scale hydrogen production.

Opportunity to achieve an efficient SiC/SiO2 interface N passivation by tuning the simultaneous oxidation modes during the SiC surface nitridation in N2 + O2 annealing

We investigated a possible guideline to design the SiC surface nitridation process for an efficient interface N passivation in high-temperature N2 + O2 annealing, based on the understandings of SiC surface nitridation kinetics. Based on the findings of the time-dependent transition of the simultaneous SiC surface oxidation mode from passive to active during the annealing with reduced O2 partial pressure condition, it was proposed that an efficient SiC surface nitridation is achievable by following these steps: triggering the passive-to-active transition of the simultaneous surface oxidation by tuning the thermodynamic conditions and SiO2 thickness, and terminating the surface reaction at the beginning of the active-oxidation-dominant period by controlling the annealing time. It is confirmed that the observed interface passivation would be attributable to the N introduction to SiC/SiO2 interface, suggesting an opportunity to achieve an efficient interface N passivation following the proposed guideline.

Effect of pulse frequency on the surface properties and corrosion resistance of a plasma-nitrided Ti-6Al-4V alloy

In this work, Ti-6Al-4V alloy, commonly used as implant material in biomedical applications, was treated by plasma nitriding. The nitriding process was carried out using an N2-H2 plasma (1000:500 sccm) at an operating pressure of about 866 Pa. The current regulation was about 1.8 A, the negative voltage was about 480–500 V, and the power was 840–940 W. The nitriding temperature was maintained at 650 ± 5 °C, and the nitriding time was 240 min. Bipolar pulse frequencies were varied at 25, 50, 100, 150, and 200 kHz. Analysis by grazing incidence x-ray diffraction spectrometer (GI-XRD) revealed the presence of δ-TiN and ε-Ti2N phases in all nitrided samples. The hardness depth profile was measured with a penetration depth of about 5 nm using the enhanced stiffness procedure (ESP). The results showed that all the nitrided samples had a surface hardness approximately three times that of the unnitrided sample. This result is consistent with that from glow discharge emission spectroscopy (GD-OES), which confirmed the diffusion distance of nitrogen atoms from the surface of about 5 μm. After plasma nitriding, the surface roughness tended to increase, resulting in an increase in the water contact angle (WCA) and a decrease in the work of adhesion. The specific wear rate (ball-on-disk) of all nitrided samples decreased and was significantly lower at a bipolar pulse frequency of 50 kHz. This result is consistent with the stability of the coefficient of friction (COF) after 6000 sliding cycles. Moreover, the nitrided sample at 50 kHz exhibited the lowest corrosion current density in artificial saliva based on the Tafel potential polarization method.

Depth profiling analysis of the nitriding layer formed by gas nitriding of Ti13Nb13Zr alloy

The gas nitriding of Ti13Nb13Zr alloy was performed in a pure nitrogen atmosphere at 1200 °C with different holding times. The variations in the phase constituents, microstructure, and mechanical properties of the nitriding layer with depth were characterized by SEM, XRD, and nanoindentation. Depending on the phase distributions in depth, the nitriding layer could be sequentially divided into an external nitride layer mainly consisting of TiN, an internal nitride layer consisting of TiN, Ti2N and TiN0.3, and an N diffusion region consisting of TiN0.3. The mechanical properties were closely associated with the phase constituents, where the nanohardness of the internal nitride layer, internal nitride layer N diffusion region and substrate were about 17.126±0.399, 12.120±0.386, 5.627±1.080, and 3.632±0.116 GPa, respectively. In the nitriding process, the N diffusion region containing needle-like TiN0.3 precipitates formed in the initial nitriding stage, and then the precipitates were gradually converted to the external and internal nitride layers, whose thickness increased with the nitriding time. Furthermore, the influence of the alloying element redistribution on the N diffusion mechanism was discussed.

Improving Corrosion-Resistant Properties of Heat-Resistant Structural Steel by a Low-Temperature Chemicothermal Treatment Based on Nitriding and Nicotriding Processes

Improving Corrosion-Resistant Properties of Heat-Resistant Structural Steel by a Low-Temperature Chemicothermal Treatment Based on Nitriding and Nicotriding Processes

A model to predict the s-phase thickness and the change in corrosion behavior toward H2SO4 of 316L austenitic stainless steel after plasma nitriding

Austenitic steels are known for their high corrosion resistance, but at the same time exhibit low hardness and wear resistance. While plasma nitriding improves tribological properties, it also affects corrosion behavior depending on the electrolyte. In this paper, a model should be present, that allows to predict the thickness of the s-Phase and the change of the corrosion behavior in plasma nitriding processes for austenitic stainless steels. For this purpose, different processes under specific variation of the temperature ranging from 360 °C to 450 °C and duration of 10 h to 24 h were performed. Other process parameters such as the voltage or gas mixture remained constant. There are two stages in the developed model: the first one allows the prediction of the s-Phase thickness by isothickness curves. The second stage implements an evaluation system of the corrosion resistance. By assigning numerical values for the observed corrosion, a quantitative comparison is allowed, which is represented by a color scaling.

Diffusion Nitride Coatings for Heat-Resistant Steels.

The effect of ion nitriding and nitriding in a melamine-based powder mixture on the structure and properties of AISI A290C1M steel was studied in the paper. Using ion nitriding made it possible to shorten the technological cycle's duration by 5-6 times compared to two-stage nitriding, optimize the diffusion layer's composition, provide a technologically simple process automation scheme, and improve the quality of nitride coatings. After the proposed mode of ion nitriding, a saturated layer depth of 0.25-0.32 mm, hardness up to 1000 HV, and an increase in wear resistance by 2.17 times were obtained. Using 95% melamine + 5% sodium fluoride during nitriding in a powder mixture significantly simplified the technological process. It did not require additional expensive equipment, which in turn significantly simplified the nitriding process with energy savings. The proposed technology and the composition of the mixture contributed to a significant acceleration of the nitriding process of AISI A290C1M steel, compared to traditional gas nitriding, and to obtain a hardness of the nitride layer of 970 HV and an increase in wear resistance by 2.6 times. A nitriding speed is explained by a significantly higher amount of atomic nitrogen when using melamine instead of ammonia and by the almost simultaneous disintegration of nanodispersed particles when the nitriding temperature was reached. After nitriding in a powder mixture, steel was subject to the slightest wear.

The Impact of Heating Rate on the Kinetics of the Nitriding Process for 52100 Steel.

The aim of this study was to determine the impact of the heating rate of steel balls made of AISI 52100 alloy steel on the kinetics and efficiency of the gas nitriding process when carried out using a chemical reactor with precise thermo-gravimetric measurements, which allowed for changes in sample mass during heating and nitriding to be monitored with an accuracy of 50 µg. In the chemical reactor, the examined alloy steel was subjected to a heating process at the selected nitriding temperature of 590 °C. Two heating variants were used: the first variant relied on heating to the nitriding temperature with different rates-1 °C per minute, 2 °C per minute, 5 °C per minute and 10 °C per minute, respectively-whereas the second variant relied on the fast-25 °C per minute-heating of treated specimens to a temperature of 475 °C, at which, the nitrogenous potential of the atmosphere promotes faster nitrogen diffusion deep into the nitrided substrate, followed by reheating up to the nitriding temperature at different rates: 1 °C per minute, 2 °C per minute, 5 °C per minute, and 10 °C per minute, respectively. To evaluate the impact of heating rate kinetics and effectiveness during nitriding on the obtained surface layer quality, we investigated the phase composition, microhardness distribution, and thickness of the obtained diffusion layers. It was found that heating to a temperature of 475 °C in the nitriding process does not significantly affect the average mass gain of a sample. Above this temperature, within the range of nitriding temperatures, the extension of time increases the sample's mass gain. Simultaneously, it was found that the use of a constant heating rate allows for thicker nitrided layers and a greater sample hardness to be obtained. Dual-stage heating, in turn, is more effective in the context of sample mass gain per time unit.

A detailed analysis of the structural, morphological characteristics and micro-abrasive wear behavior of nitrided layer produced in α (CP–Ti), α+β (Ti–6Al–4V), and β (TNZ33) type Ti alloys

The present work aimed to create a hard surface on a titanium surface via plasma nitriding to improve microhardness and wear properties of the as-cast (α-CP-Ti (CP–Ti), α+β-Ti6Al4V (Ti–Al–4V), and β-Ti-33Nb–33Zr (TNZ-33) samples. For the nitriding process, two temperature conditions (650 °C and 700 °C) were used. The presence of nitrides was evaluated by XRD. The microstructure and chemical composition were studied by electron microscopy and EDS. The roughness was evaluated by confocal microscopy. The microhardness and wear properties were analyzed using the Vickers microhardness and micro-abrasive wear test. Plasma nitriding led to the formation of TiN on CP-Ti, TiN, and Ti2N on Ti–6Al–4V, and TiN and ZrN on TNZ-33 samples. At 700 °C, the TiN increased on CP-Ti, while the Ti2N increased for Ti–6Al–4V and the ZrN increased for TNZ-33. The length of the nitride layer decreased when the temperature increased for CP-Ti and Ti–6Al–4V samples. However, for the TNZ33 alloy, the layer increased from 6.3 to 7.6 μm. The chemical analyses confirmed the presence of nitrogen on the substrate surfaces. After the nitriding process, all materials significantly increased the hardness. The hardness after plasma nitriding can be followed by: CP-Ti > TNZ-33> Ti–6Al–4V (at 650 °C); CP-Ti > Ti–6Al–4V > TNZ-33 (at 700 °C). The wear properties of all samples were improved after plasma nitriding treatment.

Evaluation of adhesive damage in a nitrided stainless steel under cyclic contact loading

In this study, adhesive damage in a nitrided AISI 316L stainless steel is evaluated by cyclic contact loading. The AISI 316L steel was hardened by the salt bath nitriding process at a constant temperature (580 °C) and three different exposure times (1 h, 3 h and 5 h). Mechanical properties such as Young's modulus (E) and hardness (H) were obtained by nanoindentation testing, where the H3/E2 ratio was used as an indicator of the fracture resistance of the nitride layers. Cyclic contact loads were applied to the nitrided steels using a spherical indenter of 3 mm in diameter. The layer/substrate systems were evaluated under 50,000 load cycles and a constant frequency of 5 Hz. Adhesive damage was observed at the interface between the compound-layer and the diffusion zone, where the samples with a thicker nitride layer showed more severe damage. In addition, the finite element method was used to obtain the stress field in the nitrided AISI 316L steel caused by cyclic contact loading, where both the maximum principal stress and the maximum shear stress were related to the adhesive damage observed in the experimental test.

Tuning Binding Strength of Multiple Intermediates towards Efficient pH‐universal Electrocatalytic Hydrogen Evolution by Mo8O26‐NbNxOy Heterocatalysts

AbstractDeveloping efficient and robust hydrogen evolution reaction (HER) catalysts for scalable and sustainable hydrogen production through electrochemical water splitting is strategic and challenging. Herein, heterogeneous Mo8O26‐NbNxOy supported on N‐doped graphene (defined as Mo8O26‐NbNxOy/NG) is synthesized by controllable hydrothermal reaction and nitridation process. The O‐exposed Mo8O26 clusters covalently confined on NbNxOy nanodomains provide a distinctive interface configuration and appropriate electronic structure, where fully exposed multiple active sites give excellent HER performance beyond commercial Pt/C catalyst in pH‐universal electrolytes. Theoretical studies reveal that the Mo8O26‐NbNxOy interface with electronic reconstruction affords near‐optimal hydrogen adsorption energy and enhanced initial H2O adsorption. Furthermore, the terminal O atoms in Mo8O26 clusters cooperate with Nb atoms to promote the initial H2O adsorption, and subsequently reduce the H2O dissociation energy, accelerating the entire HER kinetics.

Tuning Binding Strength of Multiple Intermediates towards Efficient pH-universal Electrocatalytic Hydrogen Evolution by Mo8 O26 -NbNx Oy Heterocatalysts.

Developing efficient and robust hydrogen evolution reaction (HER) catalysts for scalable and sustainable hydrogen production through electrochemical water splitting is strategic and challenging. Herein, heterogeneous Mo8 O26 -NbNx Oy supported on N-doped graphene (defined as Mo8 O26 -NbNx Oy /NG) is synthesized by controllable hydrothermal reaction and nitridation process. The O-exposed Mo8 O26 clusters covalently confined on NbNx Oy nanodomains provide a distinctive interface configuration and appropriate electronic structure, where fully exposed multiple active sites give excellent HER performance beyond commercial Pt/C catalyst in pH-universal electrolytes. Theoretical studies reveal that the Mo8 O26 -NbNx Oy interface with electronic reconstruction affords near-optimal hydrogen adsorption energy and enhanced initial H2 O adsorption. Furthermore, the terminal O atoms in Mo8 O26 clusters cooperate with Nb atoms to promote the initial H2 O adsorption, and subsequently reduce the H2 O dissociation energy, accelerating the entire HER kinetics.

Nitriding layer characteristics of modified AISI422 martensitic stainless steel in tempered state

In this study, the nitriding layer of the modified AISI422 martensitic stainless steel was characterized by several method, including optical microscopy (OM), micro-hardness tester, X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM), to study the phase transformation at the whole nitriding layer during the plasma nitriding. In order to investigate the evolution of the nitriding process the TEM samples of the nitriding layer has been prepared from the white layer to the un-nitriding zone by the focus ion beam method. With nearly 20 h nitriding process, the white layer, vein-like structure and the diffusion zone was clearly observed though the OM. Together, the TEM results show that the γ′-Fe4N and the micro holes existed in the white layer and the thick vein-like structure. And the morphology of the continuous precipitation of CrN was highly related with the depth of the nitriding layer. Excepted the normal coarsening mechanism, the EDS results indicate that the discontinuous precipitation of CrN may also originate from the transformation of the M23C6(M=Cr) during the nitriding process. Meanwhile, the residual stress value is not directly proportionate to the nitriding depth or the N contents. Furthermore, it could be affected by the N contents and the degree of the CrN spinodal decomposition, and these two factors lead the maximum value of the compress stress appears at the depth of 120μm.

Phase controlled Fe2N@Fe3O4 core-shell nanoparticles hybridized with nitrogen-doped reduced graphene oxide for boosted charge transfer in asymmetric supercapacitor

Due to environmental concerns and requirements for sustainable development, there are increasing demands for electrode materials with high energy density in supercapacitors, utilizing earth-abundant materials. In that response, we designed a novel composite material by hybridizing core–shell nanoparticles (NPs), which were composed of iron oxide (Fe3O4) and its derivative iron nitride (Fe2N) as plentiful elements in the earth crust or air, with nitrogen-doped reduced graphene oxide (NrGO). The electrode prepared with the Fe2N@Fe3O4 NPs/NrGO demonstrated outstanding specific capacitance of 341.3 F g−1 at 0.5 A g−1, along with an improved rate capability approximately 4 times higher than that of pristine Fe3O4 NPs/GO. Also, the Fe2N@Fe3O4 NPs/NrGO exhibited stable performance within a wide potential range of −1.05 to 0.15 V and excellent cycle stability of 91.2 % at 5 A g−1 after 10,000 cycles. These exceptional characteristics might be attributed to the enhanced electrical conductivity and increased surface area of the material, achieved through the simultaneous formation of the NrGO from the GO and the phase-transformed Fe2N from the pristine Fe3O4 in a monolithic nitridation process. In addition, the core–shell hybrid was used for an asymmetric supercapacitor (ASC) anode, and it exhibited a wide potential range of 1.65 V and a maximum energy density of 28.6 Wh kg−1 at a power density of 825.0 W kg−1. Moreover, a green LED was successfully powered by the serial connection of two ASCs. These results and demonstrations prove that our strategies for designing materials composition, hybrid heterostructure, and core–shell configuration are highly effective in improving energy density, making them promising and economical next-generation energy device materials utilizing earth-abundant elements (e.g. Fe, O, N).

Differences in Oxidation Behavior of Conventionally Cast and Additively Manufactured Co-Base Alloy MAR-M-509

AbstractHigh-temperature oxidation behavior of conventionally cast and additively manufactured (AM) Co-base alloy MAR-M-509 was compared in the present study. The specimens were exposed in air at 1000 °C and characterized by means of scanning electron microscopy equipped with energy/wavelength dispersive x-ray spectroscopy (EDX/WDX) and electron backscatter diffraction as well as transmission electron microscopy. Substantial differences in the oxidation processes of two alloy versions were observed. Faster oxidation of the cast alloy was mainly induced by (1) oxidation of coarse primary carbides, (2) internal oxidation and nitridation processes and (3) incorporation of other alloy constituents (e.g., Co, Ni, W) into the Cr-oxide scale. AM specimens, in contrast, formed a more homogeneous, thinner and better adherent external oxide scale. The results are discussed in terms of differences in the chemical composition and alloy microstructure, including the grain size distribution in the material and the morphology of the strengthening precipitate phases.

Synthesis of size-controlled and dispersible Sm2Fe17N3 magnetic particles by reduction diffusion process using molten salt

The synthesis of size-controlled Sm2Fe17 magnetic particles is a prerequisite for the fabrication of high-performance Sm2Fe17N3 permanent magnetic materials. Here, Sm2Fe17 was synthesized using a cost-effective reduction-diffusion method. The calcium chloride molten salt was introduced to control the particle size and achieve a single phase of Sm2Fe17. The effects of reduction-diffusion reaction temperature and the amount of added calcium chloride on the phase constitution and microstructure of the final product of reduction-diffusion were systematically investigated. Adding an appropriate amount of calcium chloride can effectively inhibit the overgrowth and sintering of the reduced particles. By employing the strategy of adding 20 wt% of calcium chlorides into the green compacts, we were able to successfully synthesize uniform Sm2Fe17 particles that are well-dispersed, with an average size of 2.2 μm. Furthermore, by combining the optimal reduction-diffusion conditions and the nitriding process, the hard magnetic Sm2Fe17N3 material was successfully obtained. This study could be useful for the development of high-performance Sm2Fe17N3 magnetic materials utilizing reduction-diffusion technology.

Innovative process to obtain thin films and micro-nanostructured ZrN films from a photo-structurable ZrO2 sol-gel using rapid thermal nitridation

Zirconium nitride (ZrN) is widely used in many industrial sectors for its outstanding performances including its mechanical properties, high chemical and thermal stability. Associated with its plasmonic behavior, these properties make ZrN a suitable candidate for optical applications at high temperature or in extreme environments. The authors present an innovative, easy-to-use and rapid process for producing ZrN thin films from a photo-structurable ZrO2 sol-gel using a rapid thermal nitridation (RTN) process. In this process, a ZrO2 sol-gel layer is converted into a ZrN thin film in a few minutes by rapid thermal annealing (RTA) under ammonia gas. Compared to physical or chemical vapor deposition, usually used to produce ZrN thin films, the advantages of the sol-gel method include suitability for non-planar and large substrates and the possibility of nanotexturing of crystallized ZrN surfaces in considerably less time, at a larger scale and at a lower cost. The ZrO2 and ZrN thin films were characterized by Raman spectroscopy, X-ray diffraction and Transmission Electron Microscopy, to confirm complete nitridation. The optical, electrical and tribological properties were also investigated. Finally, the nitridation method was also used on structured ZrO2 layers and showed the versatility of the process e.g. enabling the production of micro-nanostructured ZrN films without using any etching techniques.

High-Efficient Gas Nitridation of AISI 316L Austenitic Stainless Steel by a Novel Critical Temperature Nitriding Process

To improve the surface properties of austenitic stainless steels, a thick S-phase layer was prepared by using a novel critical temperature nitriding (CTN) process. The properties of the thick S-phase layer were optimized by controlling the process parameters. The microstructures and phase compositions of CTN-treated layers were characterized by the optical microscope, scanning electron microscope and X-ray diffraction, respectively. The surface properties, including corrosion and wear resistance, were systematically investigated by the electrochemical workstation, micro-hardness tester and ball-on-disk tribometer, respectively. The results showed that a thick S-phase layer with a thickness of 18 to 25 μm can be fabricated in a short time by critical temperature nitriding, which represented higher efficiency than conventional low-temperature nitriding. Although the most top surfaces of CTN-treated layers contain massive iron nitrides, there are no precipitates in the inner nitrided layer. The electronic work function calculated by first-principles method has confirmed that those iron nitrides had a slight influence on the corrosion resistance of nitrided layers. The optimized CTN-treated layer exhibited a comparable corrosion resistance and wear resistance as the low-temperature nitrided layer. The CTN process is considered a potentially highly efficient surface modification method for austenitic stainless steels.