Diffusion Of Metal Atoms Research Articles

Thermal oxidation characteristics of Fex(CoCrMnNi)100-x medium and high-entropy alloys

The thermal oxidation behavior of Fex(CoCrMnNi)100-x high-entropy alloys (x = 20 and 40 at.%) and medium-entropy alloy (x = 60 at.%) at temperatures ranging from 900 °C to 1100 °C under air atmosphere was investigated. The oxidation kinetics of the alloys followed the parabolic law, indicated by the increase of oxidation rate constants with increasing Fe content and temperature. The addition of Fe content lowered the configurational entropy and activation energy of the alloys, supporting the acceleration of metal atoms diffusion. Furthermore, the oxide scales formed on the surface were strongly dependent on the alloy composition. In general, a Cr2O3 inner layer, spinels (NiCr2O4 and CoMn2O4) as intermediate layers, and the outer layers of Fe3O4 and Mn3O4 were formed after oxidation at 900 °C in all alloys. On the other hand, severe internal oxidation and pores were observed in the alloy containing 60 at.% of Fe after oxidation at 1100 °C. In addition, the pores were formed due to the Kirkendall effect, acting as diffusion path and reaction place which may facilitate the oxidation process.

Large-area in plane molecular junctions by electrografting in 10 nm metallic nanotrenches

A key issue to push molecular devices toward a new range of applications is the ability to master large scale integration while preserving the device’s functionality. Furthermore, providing extra tunability of the device by external parameters, such as gating in a transistor-like configuration, is highly suited for molecular electronics. Large area molecular junctions in crossbar geometry have demonstrated high yields and compatible and compatible fabrication with Complementary Metal Oxide Semiconductor (CMOS) technology. However, such a device’s geometry favors diffusion of metallic atoms in the molecular layer and gives a very limited access to perform electrical or optical gating on molecules. In this work, we propose a new molecular junction architecture going behind these limits. We report a robust approach for the fabrication of molecular junctions based on the electrografting of a nanometer-thick molecular layer in high aspect ratio metallic nanotrenches. Nanotrenches are obtained by edge-mediated shadow deposition, resulting in laterally aligned electrodes with a 10.3 nm ± 3.3 nm average spacing along a 20 μm length. An in-solution electroreduction of diazonium salts is subsequently performed to fill the nanotrenches by a thin oligomeric layer of anthraquinone molecules. Electronic transport measurements performed at room temperature reveal the ability to produce stable molecular devices. Such a new junction’s engineering offers the key advantages of high fabrication yield, great amenability for compact assembly, and reduced leakage current. The proposed architecture opens interesting perspectives to investigate fundamental and applied questions in molecular electronics, in which coupling of the molecules with external stimuli is required.

Microstructure and properties of TiB2/Cr multilayered coatings with double periodical structures

TiB2/Cr multilayered coatings with double periodical structures were deposited by co-sputtering TiB2 and Cr targets. The influence of the periodical structure adjusted by varying the Cr sputtering power on the structure and properties of the TiB2/Cr multilayered coatings was carefully studied using scanning electron micrograph, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, residual stress tester and scratch tester. Tribological performance and oxidation behavior of the coatings were also carried out through high ball-on-disk wear and temperature static oxidation, respectively. The results indicate that the TiB2/Cr multilayered coatings exhibit the double periodical multilayered structure consisted of alternating TiB2 multilayered layers and Cr multilayered layers. The multilayered structure could refine the TiB2 grains, and significantly increase the coating hardness and toughness. Meanwhile, the coating residual stress can be effectively relaxed through the periodical multilayered structure. Accordingly, the high toughness and low residual stress make the coatings have high resistance to scratch. In addition, the multilayered structure can hinder the inward diffusion of oxygen as well as the outward diffusion of metal atoms, and thus greatly improve the oxidation resistance of the TiB2/Cr multilayered coatings compared to the pure TiB2 coating. However, increasing the thickness of the Cr layers would decrease the coating tribological performance since the soft Cr could deteriorate the mechanical properties of TiB2/Cr multilayered coatings.

Impact of V, Hf and Si on oxidation processes in Ti–Al–N: Insights from ab initio molecular dynamics

Increasing requirements on hard coatings in high-performance machining processes like high speed and dry cutting demands further developments even of the already well established TiAlN coatings. The aim of this work is to present a comparative study on oxidation behavior of Ti0·5Al0·5N coatings alloyed with X (X = V, Hf, Si) elements. Ab initio molecular dynamics results showed that a pronounced layered oxide appears due to the incorporation of these alloying elements thus affecting the thermal stability and antioxygenic properties. The additions of Hf and Si facilitate the formation of layered oxides with Ti-rich and Al-rich oxides, respectively, which improves the antioxidant performance at high temperatures. Contrarily, the Al-rich layer is absent during oxidation of V-containing coating. The Ti-oxides on the surface of TiAlVN and TiAlHfN coatings have different structures due to the discrepancy of O–Ti–O angle. The present findings clearly show that the V-addition results in more rutile-like TiO2 whereas the Hf-addition leads to more anatase-like2 with O–Ti–O angle of 156.3°. With further oxidation, the structures of coatings vary significantly with the alloying elements, which indicates that the alloying of Hf and Si retards the inward diffusion of O atoms, especially, the alloying of Si leads to an earlier formation of a dense sublayer rich in Al2O3, and thus promotes the oxidation resistance. The different diffusion barrier energies of Ti and Al in TiN bulk contribute to the formation of layered oxides on the surface of coating and the different oxidation behaviors. This study provides an atomistic insight to the initial as well as further stages of the oxidation process of quaternary TiAlXN, which together with the electronic structure analysis and diffusion of metal atoms gives a new basis for understanding of its oxidation behaviors.

Effect of Near Ultraviolet Irradiation on Changes in Island Metallic Films during Thermal Annealing

The effect of low-intensity near ultraviolet irradiation and subsequent thermal annealing on the surface morphology of gold and silver granular films was investigated. It was found that exposure to light does not lead to immediate changes in the extinction spectra and the microstructure of the films. However, after annealing at a temperature of about 200°C, the difference between irradiated and non-irradiated areas becomes clearly visible both visually and in the extinction spectra of the island films. For the irradiated gold film, changes in the annealing process occur much more slowly than for the non-irradiated one. For silver films, the changes after annealing vary significantly depending on whether the film is irradiated in a vacuum or in air. From the optical extinction spectra and SEM images, it can be concluded that the conditions for the annealing-induced surface diffusion of metal atoms in the irradiated area change significantly, and these changes depend on the irradiation conditions.

Wet non-thermal integration of nano binary silicon-gold system with strong plasmonic and luminescent characteristics

We report on a wet none thermal integration of the binary silicon-gold nano system. Instead of thermally based gas-solid procedures, we use charge exchange/injection-based procedures in a chemical wet environment. SEM and TEM imaging and EDX show 0-D gold-silicon coreshell structures with diameters ranging from 6 to 500 nm in addition to a variety of silicon and gold nano structures. Optical and florescence spectroscopy show that colloids exhibit strong red luminescence and plasmonic resonance in the visible. Mie theory analysis of light scattering is in agreement with the optical observation. The results and procedures are discussed in terms of the relative electron/hole affinity, Schottky potential barrier, strength of the metal-silicon bond, as well as the surface diffusion of metal atoms or clusters on the interface of the constituent materials. Integration of gold and silicon, at the nanoscale in the form core-shell architecture affords the functionalities and attributes of plasmonic light scattering imaging and fluorescence imaging that would be useful for a wide variety of applications, including optical filters, sensing, therapeutics and tracking, and cancer therapy.

Metal-atom penetration and diffusion in organic solids: difference between σ- and π- orbital molecular systems

The penetration and diffusion of metal atoms in self-assembled monolayers (SAMs) and pentacene solids were studied by first-principles calculations. It was shown in the case of SAM that metal atoms easily penetrate and diffuse in solids, reflecting the weak interaction between metal atoms and molecules. Even when diffusing metal atoms produce a cluster, such a cluster can easily diffuse in solids. In the case of pentacene, on the other hand, since the interaction between metal atoms and molecules is attractive and strong, metal atoms actively enter into solids and are tightly bonded to molecules. We found that Au atoms prefer to produce a cluster at the molecule edge and such a cluster is difficult to move, while Al atoms are scatteringly distributed and last the diffusion owing to the repulsive interaction between Al atoms. We showed that the difference in metal-atom behavior comes from the difference in electronic structure between SAM and pentacene, which are, respectively, σ- and π-orbital molecular systems.

Spontaneous intercalation of Ga and In bilayers during plasma-assisted molecular beam epitaxy growth of GaN on graphene on SiC

The formation of a self-limited metallic bilayer is reported during the growth of GaN by plasma-assisted molecular beam epitaxy on graphene on (0001) SiC. Depending on growth conditions, this layer may consist of either Ga or In, which gets intercalated between graphene and the SiC surface. Diffusion of metal atoms is eased by steps at SiC surface and N plasma induced defects in the graphene layer. Energetically favorable wetting of the (0001) SiC surface by Ga or In is tentatively assigned to the breaking of covalent bonds between (0001) SiC surface and carbon buffer layer. As a consequence, graphene doping and local strain/doping fluctuations decrease. Furthermore, the presence of a metallic layer below GaN opens the way to the development of devices with a spontaneously formed metallic electrode on their back side.

Fabrication of Various Plasmonic Pt Nanostructures via Indium Assisted Solid-State Dewetting: From Small Nanoparticles to Widely Connected Networks.

In this paper, the modified solid-state dewetting (MSSD) of well-defined and various uniform Pt nanostructures is demonstrated by the auxiliary diffusion enhancement. The MSSD utilizes the introduction of metallic indium (In) layers with high diffusivity in between sapphire and platinum (Pt) layer, through which the global diffusion and dewetting of metallic atoms can be significantly enhanced. Subsequently, the In atoms can be sublimated from the NP matrix, resulting in the formation of pure Pt NPs. By the systematic control of In and Pt bi-layer thickness, various areal density, size and configuration of Pt NPs are demonstrated. The In2 nm/Pt2 nm bilayers establish very small and highly dense NPs throughout the temperature range due to the early maturation of growth. Intermediate size of NPs is demonstrated with the In45 nm/Pt15 nm bilayers with the much improved interparticle spacings by annealing between 650 and 900 °C for 450 s. Finally, the In30 nm/Pt30 nm bilayers demonstrate the widely connected network-like nanostructures. In addition, the finite difference time domain (FDTD) simulation is employed to exploit the local electric field distributions at resonance wavelengths. The dewetting characteristics of In/Pt bilayers is systematically controlled by the modifications of layer thickness and annealing temperature and is systematically described based on the diffusion of atoms, Rayleigh instability and surface energy minimization mechanism. The optical properties demonstrate dynamic and widely tunable localized surface plasmon resonance (LSPR) responses depending upon the various surface morphologies of Pt nanostructures.

Enhanced stability of plasmonic polymer solar cells using ferrocenedicarboxylic acid modification

The power conversion efficiency (PCE) of polymer solar cells (PSCs) can obviously be improved by plasmon resonance effects of noble metal nanoparticles. However, incorporating noble metal such as Ag and Au nanoparticles (NPs) can usually accelerate the deterioration of PSCs due to the diffusion of noble metal atoms, which would limit the potential application of plasmonic PSCs. PSCs with ferrocenedicarboxylic acid (FDA) modified Al-doped ZnO (AZO) layer compared to pure AZO layer can synchronously increase PCEs and ultraviolet (UV) and moisture stabilities. PSCs with Ag NPs doped Al-doped ZnO (AZO:Ag) increased to 10.20% of PCE from 9.08% PCE of the reference PSCs with pure AZO layer, but show inferior stability. Furthermore, PSCs with FDA modified AZO:Ag layer obtained 10.0% of PCEs and showed superior UV durability and moisture stability. PSCs with FDA modified AZO:Ag layer respectively maintain the original PCE values of 50% and 53% exposing UV light for 13 h and aging for 9 months at RH 10%, which are obviously higher than 36% and 34% of the original PCEs of PSCs with AZO:Ag layer. The results indicate that FDA modification is an effective strategy to solve the quick deterioration of plasmonic PSCs without evidently sacrificing PCEs.

Diffusion mechanisms of metal atoms in Pd[sbnd]Au bimetallic catalyst under CO atmosphere based on ab initio molecular dynamics

Reconstruction of heterogeneous catalysts during reaction, especially caused by the adsorption of reactants, is highly important for the structural evolution of nanoparticles (NPs) during activation and reaction processes. In this work, for the first time the CO-induced dynamic structure of Pd@Au core-shell NPs with different size and shape has been studied systemically using ab initio molecular dynamics. Our calculation has demonstrated that the thermostability of Pd@Au bimetallic NPs is decreased with increasing CO coverage. However, the kinetic stability can be enhanced when CO coverage is very high. With the adsorption of CO, the interaction between surface unoccupied atoms and nearby metal atoms at the second layer is strengthened, while the stress distribution in the second layer is significantly changed. The surface unoccupied metal atoms then migrate into the second layer, and metal atoms in the second layer move to surface in return. Such atomic diffusion between the top two layers leads to the atomic exchange in NPs interior layer by layer. Finally, Pd and Au atoms are redistributed in NPs, and Pd atoms accumulate at surface because of stronger CO adsorption. In a word, the segregation is dominated by the inward diffusion of surface unoccupied metal atoms. The great challenge in this work is how to establish the relationship between gas atmosphere and NP kinetic stability for determining the dynamic 3D bimetallic NPs.

Low Power Parylene‐Based Memristors with a Graphene Barrier Layer for Flexible Electronics Applications

AbstractLowering the programing power consumption is of importance to capacitate high‐efficiency flexible neuromorphic electronics. However, this remains particularly challenging for organic flexible memristor due to its high reset current. Here a robust route is reported to capitalize on graphene with native nanopores as a barrier layer for the parylene‐based flexible memristors, eventually conferring the devices to be operated with ultralow reset current (<50 µA) and programming power consumption (<150 µW). The graphene‐integrated memristor device in the architecture of Al/graphene/parylene/W (G‐memristor) lowers the reset current by ≈47 times and the programming power consumption by ≈14 times, respectively, as compared with those without the graphene barrier layer. Intriguingly, the conductive atomic force microscope characterizations reveal the metallic filamentary‐type switching mechanism of these G‐memristor devices, in which the intrinsic nanopores on graphene impart the formation of finer conductive filaments between Al electrode and parylene layer while suppressing the diffusion of mass metal atoms across the architecture. The integration of nanopores graphene as the barrier layer of organic memristors offers a promising route to low‐power flexible neuromorphic computing electronics.

Conversion of Metal-Organic Cage to Ligand-Free Ultrasmall Noble Metal Nanocluster Catalysts Confined within Mesoporous Silica Nanoparticle Supports.

Supported ultrasmall noble metal nanocluster-based (UNMN-based) catalysts are one of the most important classes of solid materials for heterogeneous catalysis. In this work, we present a novel strategy for the controlled synthesis of ligand-free UNMN nanocatalysts based on in situ reduction of a palladium-based (Pd-based) metal-organic cage (MOC) confined within monosized, thiol-modified mesoporous silica nanoparticle (MSN) supports. By taking advantage of the high mutual solubility of MOCs and MSNs in DMSO and the strong interactions between the thiol-modified MSN pore wall and MOC surface, a good dispersion of MOC molecules was achieved throughout the MSN support. The close correspondence of the MSN pore diameter (ca. 5.0 nm) with the diameter of the MOC (ca. 4.0 nm) confines MOC packing to approximately a monolayer. Based on this spatial constraint and electrostatic binding of the MOC to the thiol-modified MSN pore surface, in situ MOC reduction followed by metal atom diffusion, coalescence, and anchoring on the active sites resulted in ligand-free Pd-based UNMNs of approximately 0.9 ± 0.2 nm in diameter decorating the MSN pore surfaces. Control experiments of the reduction of a conventional palladium source or the reduction of free, unconstrained cages in solution under the same conditions only produced large metal nanocrystals (NP, >2 nm), confirming the importance of confined reduction to achieve a highly catalytically active surface. In light of this strategy, two catalytic experiments including the reaction of 4-nitrophenol to 4-aminophenol and the Suzuki C-C coupling reaction show superior catalytic activity of the engineered MSN-supported UNMN nanocatalysts compared to their free form and state of the art commercial catalysts. We believe that our new strategy will open new avenues for artificially designed UNMN-inspired nanoarchitectures for wide applications.

Stress corrosion cracking characteristics of CF8A austenitic stainless steels and interactions between multiple cracks in a simulated PWR environment

The stress corrosion cracking behaviors of CF8A austenitic stainless steels in a simulated pressurized water reactor environment are systematically investigated by slow-strain-rate tensile tests. Numerous transgranular stress corrosion cracking (TGSCC) cracks are identified upon the fracture of CF8A austenitic stainless steel surfaces. The specimens tested at lower strain rates showed higher fractions of TGSCC, a larger number of cracks, and smaller crack opening displacement. These phenomena are caused by anodic dissolution and crack interactions. The anodic dissolution is dominant at lower strain rates, and thus the crack-tip morphologies are changed by the diffusion of metal atoms and micro-pores. The crack interactions increase rapidly with increasing number of cracks and decrease of the crack-tip radius and crack spacing ratio. In addition, the inhomogeneity of the growth of interaction cracks results in the small cracks being shielded by the preferred growth cracks. On the contrary, the main cracks are accelerated by the stagnation of small cracks, eventually becoming critical cracks that lead to specimen fracture.

Brazing of metallized SiC ceramic to GH99 superalloy using graphene nanoplatelets reinforced AgCuTi composite filler

A two-step process involving, first, the pre-metallization of the SiC ceramic, followed by the vacuum brazing using graphene nanoplatelets (GNPs) reinforced AgCuTi composite filler was developed to join SiC ceramic and GH99 superalloy. The metallization characteristics, joint microstructure and fracture behavior were investigated. Through pre-metallization, a smooth metallic coating formed on the SiC ceramic surface; the carbide layer adjacent to SiC ceramic had a semi-coherent interface with it. Brazing process showed that in situ synthesized TiC particles with fine-grains were evenly dispersed in the filler matrix due to GNPs acting as nucleation sites, promoting the refinement of microstructure of the joint. Moreover, the effect of GNPs in retarding the diffusion of metal atoms limited the reaction of Ti with Cu and Ni, thereby reducing the negative impact induced by the brittle compounds. The maximum shear strength of 26.4 MPa was obtained at AgCuTi-1%GNPs, which was ∼151.4% higher than the joint brazed using AgCuTi filler.

Complex oscillatory decrease with size in diffusivity of {100}-epitaxially supported 3D fcc metal nanoclusters.

Diffusion and coalescence of supported 3D metal nanoclusters (NCs) leads to Smoluchowski Ripening (SR), a key pathway for catalyst degradation. Variation of the NC diffusion coefficient, DN, with size N (in atoms) controls SR kinetics. Traditionally, a form DN∼N-β was assumed consistent with mean-field analysis. However, KMC simulation of a stochastic model for diffusion of {100}-epitaxially supported fcc NCs mediated by surface diffusion reveals instead a complex oscillatory decrease of DN with N. Barriers for surface diffusion of metal atoms across and between facets, along step edges, etc., in this model are selected to accurately capture behavior for fcc metals. (This contrasts standard bond-breaking prescriptions which fail dramatically.) For strong adhesion, equilibrated NCs are truncated pyramids (TP). Local minima of DN sometimes but not always correspond to sizes, NTP, where these have a closed-shell structure. Local maxima generally correspond to N≈NTP + 3 for N = O(102). For weak adhesion, equilibrated NCs are truncated octahedra (TO), and local minima of DN occur for sizes close or equal to those of just a subset of closed-shell structures. Analytic characterization of energetics along the NC diffusion pathway (which involves dissolving and reforming outer layers of facets) provides fundamental insight into the behavior of DN, including the strong variation with N of the effective NC diffusion barrier.

Atomistic study of an ideal metal/thermoelectric contact: The full-Heusler/half-Heusler interface

Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are important thermoelectric materials for converting waste heat into electricity. Reduced electrical resistivity at the hot interface between the half-Heusler material and a metal contact is critical for device performance; however, this is yet to be achieved in practice. Recent experimental work suggests that a coherent interface between half-Heusler and full-Heusler compounds can form due to diffusion of transition metal atoms into the vacant sublattice of the half-Heusler lattice. We study theoretically the structural and electronic properties of such an interface using a first-principles based approach that combines ab initio calculations with macroscopic modeling. We find that the prototypical interface HfNi2Sn/HfNiSn provides very low contact resistivity and almost ohmic behavior over a wide range of temperatures and doping levels. Given the potential of these interfaces to remain stable over a wide range of temperatures, our study suggests that full-Heuslers might provide nearly ideal electrical contacts to half-Heuslers that can be harnessed for efficient thermoelectric generator devices.

Fabrication and properties of Ni-modified graphene nanosheets reinforced Sn-Ag-Cu composite solder

Ni-modified graphene nanosheets (GNSs) are prepared by uniformly mixing and heating reduced graphene oxide nanosheets (r-GONSs) and nickel acetate. Ni-modified graphene nanosheets (Ni-GNSs) reinforced Sn-2.5Ag-0.7Cu composite solder is made using mechanical alloying. The change laws of the Ni nanoparticle distribution, phase composition, and crystallinity during the reinforcement preparation are discussed. The morphology and thickness of intermetallic compound (IMC) layers with different Ni-GNSs contents during the liquid-solid reactions of the wetting interface were studied. The results show that the nanocrystalline Ni nanoparticles obtained by the thermal decomposition method have a uniform distribution, pure single phase and higher crystallinity. The morphology of the IMC was scallop-shaped. The IMC layer thickness of the composite solders decreased with the increasing amount of Ni-GNSs. Microstructural studies also revealed that Ni-GNSs were adsorbed onto the surface of the IMC layers, effectively blocking the diffusion of metal atoms. The role of Ni-GNSs in retarding the growth of IMC during the soldering process is presented. When the GNSs content is greater than 0.05 wt%, the reinforcement showed obvious agglomeration, which led to the growth of the IMC layers. The addition of 0.03–0.05 wt% GNSs will be helpful to decrease the surface tension of the liquid composite solder between the flux and copper substrate and increase the effective stress transfer between the edge of the graphene and solder matrix, causing an excellent wetting effect and high ultimate tensile stress.

Inter-diffusion of plasmonic metals and phase change materials

This work investigates the problematic diffusion of metal atoms into phase change chalcogenides, which can destroy resonances in photonic devices. Interfaces between Ge2Sb2Te5 and metal layers were studied using X-ray reflectivity (XRR) and reflectometry of metal-Ge2Sb2Te5 layered stacks. The diffusion of metal atoms influences the crystallisation temperature and optical properties of phase change materials. When Au, Ag, Al, W structures are directly deposited on Ge2Sb2Te5 inter-diffusion occurs. Indeed, Au forms AuTe2 layers at the interface. Diffusion barrier layers, such as Si3N4 or stable diffusionless plasmonic materials, such as TiN, can prevent the interfacial damage. This work shows that the interfacial diffusion must be considered when designing phase change material tuned photonic devices, and that TiN is the most suitable plasmonic material to interface directly with Ge2Sb2Te5.

Catalytic Etching of Platinoid Gauzes During the Oxidation of Ammonia by Air. Reconstruction of the Surface of a Platinoid Gauze Backside in the Course of Ammonia Oxidation at 1133 K

Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study microstructure, morphology and chemical composition of the surface and near-surface layers of polycrystalline wire of commercial platinoid gauzes containing Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) after ammonia oxidation (10 vol % NH3) by air at 1133 K for 50 h in the presence of these gauzes. Upon the completion of the catalytic reaction of ammonia oxidation, reconstruction (catalytic etching) of the surface layer on the backside of gauze wire (in the direction of the gas flow) was observed, in which the regions with different degrees of etching were identified. The analysis of these regions showed that the catalytic etching of the platinoid wire is initiated by etching the surface layer in the region of grain boundaries and dislocations in the course of highly exothermic catalytic reaction of ammonia oxidation by oxygen penetrated in the regions of defects. The regions with minimal etching contain smooth grains with crystalline terraces, 50 nm high, and with etching pits with size of ~72 nm in a concentration of 4.2 × 108 cm–2. The region with medium etching includes rough grains with etching pits with size of ~85 nm in a concentration of 2.5 × 108 cm–2. The regions with maximal etching consist of recrystallized grains with large pores with sizes of 350–400 nm in concentration of 8.9 × 106 cm–2. These grains are separated by voids with a width of 1–5 μm and a depth of 10 μm, which increases the specific surface area in the surface layer of wire. The growth of the specific surface area of the platinoid wire is accompanied by an increase in the volume rate of ammonia oxidation and, as a result, local overheating due to the high exothermicity of the reaction. With increasing temperature, the rate of diffusion of metal atoms increases, which, in turn, accelerates etching in this region. These processes lead to increasing the region of etching along the wire, which points to the autocatalytic regime of etching of platinoid gauzes in ammonia oxidation by oxygen.