Electrochemical Nitriding Research Articles

Modifying Ti-Based Gas Diffusion Layer Passivation for Polymer Electrolyte Membrane Water Electrolysis via Electrochemical Nitridation.

A gas diffusion layer represents an important element of collector and stack components used in polymer electrolyte membrane (PEM) water electrolyzers (WE). Nowadays, titanium-based gas diffusion layers (GDLs) have high stability and are frequently employed as anode GDLs, yet reliability issues emerging from passivation have limited their practical deployment. Hence, we develop an inexpensive way of producing high conductivity and corrosion resistance of Ti-based GDLs through electrochemical nitridation. The morphology and content of the nitride phase on the surface of the Ti felt GDL are efficiently regulated by adjusting reduction potential and reaction time. According to X-ray photoelectron spectroscopy studies, the modified Ti felt is coated with ammonium ions and nitrogen-incorporated oxides, namely, TiN/TiOx, on the surface. The nitride surface shows a low interfacial contact resistance (ca. 1.0 mΩ cm2 at 140 N/cm2) and excellent corrosion resistance (0.920 μA cm-2) in the simulated PEM WE environments. The electrochemical nitridation provides an economic way to introducing N layers on the surface of the Ti-based GDL with high performance, which is very promising for efficient PEM water electrolysis.

Enhanced corrosion resistance and wear resistance of duplex stainless steel processed by shot-peening combined with electrochemical nitriding

ABSTRACT To improve the wear resistance and anticorrosion property of duplex stainless steel (DSS), surface treatment combining high-energy shot-peening (HESP) and electrochemical nitriding was applied to DSS. The strong nitride peak detected through X-ray photoelectron spectroscopy indicated that HESP pretreatment accelerated the electrochemical nitriding process. The treatments improved the microhardness of DSS from 242 HV(100g) to 450 HV(100g) and the wear resistance of DSS was considerably enhanced. Electrochemical tests revealed that HESP pretreatment improved the passivation ability of the nitriding layer of DSS in the borate buffer and 3.5 wt-% NaCl solutions. The greater corrosion resistance of the nitriding layer was attributed to the passive film with lower a number of structural defects. The nitriding layer on the HESP-pretreated DSS showed good corrosion resistance in the 3.5 wt-% NaCl solution.

On the Influence of Cold Working and Electrochemical Nitridation on the Corrosion Behaviour of 316L Austenitic Stainless Steel in Acidic Environment

The present paper investigates the effect of cold working and electrochemical nitridation on corrosion resistance of 316L austenitic stainless steel (ASS). The X-ray diffraction results showed that the strain-induced martensite is formed on cold work. Also, the volumetric fraction of strain induced martensite and dislocation density increased with increase in degree of cold work. The cold working process adversely affects the corrosion resistance of 316L ASS due to the formation of the strain-induced martensite and increased dislocation density. On electrochemical nitridation, the electrochemical results show the formation of stable passive film, thus improving the corrosion resistance of 316L ASS attributed to the formation of nitrides on the surface. Moreover, the beneficial effect of electrochemical nitridation is more pronounced in cold worked samples, thus the adverse effects of cold working can be overcome by electrochemical nitridation.

The effect of electrochemical nitridation on the corrosion resistance of the passive films formed on the 2205 duplex stainless steel

Abstract The effects of electrochemical nitridation on the corrosion resistance of the 2205 duplex stainless steel were investigated. It was found that increased nitrogen content in the 2205 duplex stainless steel affected donor and acceptor concentration distribution in the passive films on the surface of the 2205 duplex stainless steel. Moreover, the total donor and acceptor concentration in passive films decreased with the increasing of nitrogen content. The electrochemically nitridation facilitated to induce compact passive film and thus improved significantly the corrosion resistance of the 2205 duplex stainless steel in borate buffer solution.

Investigation on the Relationship between the Surface Chemistry and the Corrosion Resistance of Electrochemically Nitrided AISI 304 Stainless Steel

The relationship between the surface chemistry and the corrosion resistance of electrochemically nitrided AISI 304 stainless steel samples has been investigated. The nitriding treatment was carried out in HNO3 0.1 M and HNO3 0.1 M + KNO3 0.5 M at room temperature. Samples were subjected to the nitriding procedure for 30 minutes under a cathodic potential of -0.7 VAg/AgCl. The chemical composition of the nitrided layers was assessed by X-ray photoelectron spectroscopy (XPS). Depth profiles of the main elements present in the nitrided layers were also obtained by XPS by etching them with argon ions. The corrosion behavior of the nitrided samples was evaluated by potentiodynamic polarization. The results showed that the nitrided layers consisted of a mixture of chromium nitrides, chromium oxides, iron oxides/oxyhydroxides, and nickel oxide. The best corrosion resistance was obtained by electrochemical nitriding in the HNO3 0.1 M + KNO3 0.5 M solution. This result could be correlated with the composition and thickness of the nitrided layer.

Synthesis of γ’-Fe4n, a New Soft Magnetic Material for Inductors and Transformers

γ’-Fe4N has many attractive properties, such as high saturation magnetization and electrical resistivity, making it an ideal candidate to replace current magnetic materials in power electronics. Doing so would allow transformers and inductors to operate in tandem with new high frequency semiconductor switches, ultimately enabling smaller devices. However, synthesis of γ’-Fe4N is challenging, especially if bulk material is desired. Furthermore, products often contain multiple phases of iron nitride or undesirable morphology and particle size. Our efforts are focused on the synthesis of nanoscale γ’-Fe4N as these materials have been shown to exhibit high permeability and therefore low loss as frequency is increased. Efforts toward the synthesis of this material, including nitridation of nanoscale iron and electrochemical nitridation of iron wire, will be presented. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

New Route of the Formation of Ordered FeNi by Electrochemical Nitriding and De-Nitriding Processes

We proposed a new synthesis route; combination of nitriding and de-nitriding method as a new process for the formation of ordered L10-FeNi. Firstly, electrochemical nitriding was investigated in LiCl-KCl-CsCl-Li3N system and a single phase of FeNiN was obtained by potentiostatic electrolysis at 1.8 V. Furthermore, de-nitriding was also investigated in LiCl-KCl-CsCl system at 573 K. From the result of XRD, obtained sample was identified as L10-FeNi and the order parameter was determined to be 0.71. We achieved the world's first the formation of FeNi which has superlattice structure by electrochemical method.

Improved corrosion resistance of 316L stainless steel by nanocrystalline and electrochemical nitridation in artificial saliva solution

The fluoride ion in artificial saliva significantly changed semiconductor characteristic of the passive film formed on the surface of 316L stainless steels. The electrochemical results showed that nanocrystalline α′-martensite improved corrosion resistance of the stainless steel in a typical artificial saliva compared with coarse grained stainless steel. Moreover, comparing with nitrided coarse grained stainless steel, corrosion resistance of the nitrided nanocrystalline stainless steel was also improved significantly, even in artificial saliva solution containing fluoride ion. The present study showed that the cryogenic cold rolling and electrochemical nitridation improved corrosion resistance of 316L stainless steel for the dental application.

Effect of grain refinement and electrochemical nitridation on corrosion resistance of the 316L stainless steel for bipolar plates in PEMFCs environment

The stain-induced nanocrystalline α'-martensite was obtained by cryogenic cold rolling at liquid-nitrogen temperature for 316L stainless steel. The electrochemical results showed nanocrystalline 316L stainless steel deteriorated its corrosion resistance in a typical proton exchange membrane fuel cell environment compared with coarse grained one. However, comparing with electrochemically nitrided coarse grained stainless steel, electrochemically nitrided nanocrystalline stainless steel improved significantly corrosion resistance in the same environment, which was supported further by Mott–Shottky analysis. X-ray photoelectron spectroscopy analysis revealed that the nanocrystalline promoted the enrichment of nitrogen and chromium and inhibited form of NH3 on the surface, which could significantly improve the corrosion resistance of the 316L stainless steel. The present study showed that the electrochemically nitrided 316L stainless steel was more suitable for the bipolar plates in proton exchange membrane fuel cell environment than the untreated one, especially for nanocrystalline stainless steel.

Magnetism induced by electrochemical nitriding on an austenitic stainless steel

The surface of a Fe-Ni-Cr Alloy (SUS316L) plate was electrochemically nitrided in molten LiF-KF salt including Li3N at 873K. The crystal structure changed from fcc structure to bct structure with nitrogen introduction. The Nitrogen diffusion layers were predominately formed at nitrogen concentration of 23 at%. The nitriding process drastically also changed its magnetic property from non-magnetic to ferromagnetic. The magnetic field of 20 kOe saturated the magnetic moment with its magnetization of 81 emu/g at 10K. The anisotropic magnetization is ascertained. Based on CrN formation and Cr extraction from the original Fe-Ni-Cr system, the induced ferromagnetism was discussed.

Formation of a protective nitride layer by electrochemical nitridation on 316L SS bipolar plates for a proton exchange membrane fuel cell (PEMFC)

In the present study, an attempt has been made to increase the corrosion resistance of 316L stainless steel (SS) bipolar plates (Bp) through electrochemical nitridation using a nitrate bearing electrolyte solution of 0.1 M HNO3 and 0.5 M KNO3.

Modifying a Stainless Steel for PEMFC Bipolar Plates via Electrochemical Nitridation

AbstractAISI446 stainless steel was electrochemically nitrided at room temperature. X‐ray photoelectron spectroscopy (XPS) analysis indicated that the nitrided steel was covered with surface ammonia and a layer of nitrides (mainly of mixed chromium nitrides). The nitride layer for 4 h nitrided steel at –0.9 V was about 2.5 nm thick. Dominating oxides appear on the steel's surface, so nitrogen incorporated oxides is a suitable term to describe the nitrided surface. The nitrided surface showed very low interfacial contact resistance (ICR) and excellent corrosion resistance in simulated polymer electrolyte membrane fuel cell (PEMFC) environments. The excellent stability of the nitride steel was confirmed by XPS depth profiling before and after testing in the PEMFC environments. Electrochemical nitridation provides an economic way for modifying the steel's surface to approach the U.S. Department of Energy 2015 goal for bipolar plates.

Nitriding of 316 stainless steel in molten fluoride salt by an electrochemical technique

Electrochemical nitriding of type 316 stainless steel (316 SS) in molten fluoride salt (LiF–KF, FLiK) containing Li 3N was investigated. Formation of chromium nitride CrN and iron nitride α-Fe x( x>8) N was confirmed. Cyclic voltammogram measurements and electrolysis treatment were carried out using an Al–Li alloy reference electrode at 873 K. After potentiostatic treatment at 1.0 V vs. Li/Li + for 100 min, the specimen was characterized by SEM, XPS, EPMA, and XRD. SEM observation revealed that the initially smooth surface changed into a rugged structure covered by a wrinkle structure about 1–2 μm in width after electrolysis. XPS analysis revealed that chromium nitride (CrN) was selectively formed at the surface layer. According to the EPMA analysis, the treatment promoted nitrogen diffusion from the surface to a depth of 35 μm. CrN was formed from the surface to a depth of 2 μm. It was determined that iron nitride α-Fe x( x>8) N was formed from there to a depth of 35 μm as an inside diffusion layer, but neither Fe 2N nor Fe 4N was detected. Formation of CrN and α-Fe x( x>8) N was also confirmed by XRD measurement and XPS analysis. The formation of chromium nitride and iron nitride was discussed in terms of thermodynamics.

Electrochemical nitridation of a stainless steel for PEMFC bipolar plates

AISI446 steel has been electrochemically nitrided in 0.1 M HNO 3 + 0.5 M KNO 3 solution at room temperature. XPS analysis revealed surface NH 3 and a deeper nitride layer. The surface layer of the stainless steel modified by electrochemical nitridation was thus composed of a nitrogen-incorporated oxide film. The nitrided steel showed very low interfacial contact resistance ( ca. 18 mΩ cm 2 at 140 N/cm 2) and excellent corrosion resistance in simulated PEMFC environments. Electrochemical nitridation provides an economic way to modify the stainless steel’s surface, and is very promising for application to fuel cell bipolar plates.

Modifying a stainless steel via electrochemical nitridation

Nitridation is widely used to modify the materials surface. An electrochemical nitridation procedure, simple to handle at room temperature, is introduced for the surface modification of alloys. A nitrogen-incorporated oxide film was formed on the stainless steel's surface in a nitrate-bearing solution using the electrochemical method.

Electrochemical nitriding of Sn in LiCl–KCl–Li 3N systems

Electrochemical nitriding of a liquid phase tin metal has experimentally been confirmed by using the oxidation of nitride ions in molten LiCl–KCl–Li 3N melts according to the following reactions: N 3 − = N ads + 3 e − N ads + Sn = SnN x From the XPS analysis, N 1s signal and Sn 3d signals are observed, which corresponds to the formation of SnN x , after conducting argon ion sputtering for 1000 s. This showed that a thick and stable nitride film was formed by electrochemical nitriding.

Electrochemical Nitriding of Cobalt by Molten Salt Electrochemical Process

Electrochemical nitriding of Co was achieved by potentiostatic electrolysis at 0.80 and 1.20 V (vs. in LiCl-KCl eutectic melt containing at 723 K. From X-ray photoelectron spectroscopy and X-ray diffraction analyses, it was confirmed that the obtained nitrided layer consisted of the free energies of formation of this nitride is positive and the equilibrium nitrogen partial pressure of those are of the order of atm at 723 K. This result suggests an equivalent nitrogen pressure of at least the order of atm was imposed by the adsorbed nitrogen atoms formed by anodic oxidation of nitride ion at Co electrode surface. © 2004 The Electrochemical Society. All rights reserved.

Electrochemical surface nitriding of zirconium in LiCl–KCl–Li3N systems

Abstract Electrochemical surface nitriding of zirconium has been investigated in LiCl–KCl–Li 3 N systems. From the XPS results, ZrN was formed on the outermost part of the Zr electrode surface when potentiostatic electrolysis was conducted at 1.0 V (versus Li + /Li), the reaction scheme of which was expressed as: N 3− = N ads +3 e − , N ads + Zr = ZrN . It was also found, from the results of XPS analysis, that the thickness and nitrogen concentration of the nitride layer increased as the applied potentials were made more positive. By comparing the cyclic voltammograms of the nitrided zirconiums prepared by the electrochemical nitriding process and the plasma nitriding process, the two anodic dissolution potentials in the LiCl–KCl melt at 723 K were almost the same at 2.2 V. This indicated that the corrosion resistance property of the nitrided layer formed by electrochemical nitriding was identical to that formed by plasma processing.

Hydrogen Impermeability of TiN Films and Its Dependence on Nitrogen Concentration at High Temperatures

The hydrogen impermeability of titanium nitride films and its dependence on nitrogen concentration have been estimated by molten salt electrochemical techniques at 723 K. Surface nitriding of titanium substrates was conducted by two methods, i.e., gas nitriding and molten salt electrochemical nitriding. Hydrogen concentration in the titanium nitride films was directly measured by elastic recoil detection (ERD) analysis. It was confirmed that the titanium nitride film worked as a hydrogen permeation barrier at high temperatures. When titanium coexisted with titanium nitrides, the hydrogen impermeability decreased with the increase of the volume concentration of titanium, which worked as the hydrogen-diffusing medium. © 2000 The Electrochemical Society. All rights reserved.