Properties Of Metals Research Articles

Theoretical study of HfS2 as anode material of zinc ion battery in sports wearable equipment

In this study, the density functional theory (DFT) based on first-principles calculations was used to conduct a comprehensive theoretical calculation of the Zn adsorption HfS2 system (Zn-HfS2) to develop the potential of HfS2 as an anode material for zinc ion batteries (ZIBs). The calculation results show that the adsorption energy decreases gradually (−1.368 eV) with the increase of shear deformation. There is a significant charge transfer from Zn to HfS2 monolayer, and the electrons of Zn atoms flow to S atoms. The intrinsic HfS2 shows a band gap value of 2.055 eV, and Zn-HfS2 shows a metal property with a zero band gap. The adsorption of Zn leads to an increase in energy near the Fermi level, indicating that the adsorption of Zn enhances the electronic conductivity of HfS2. The deformation reduces the barrier of Zn in the diffusion path to 0.16 eV. The maximum specific capacity of HfS2 to Zn is 447.445 mAh/g. The calculation results will help promote the application of zinc ion batteries in wearable devices.

Optimising structural health monitoring systems: A 2D numerical investigation on impedance matching for FML with integrated sensors

AbstractFibre metal laminates (FML) represent an innovative class of advanced composite materials that integrate the mechanical properties of both metals and fibre‐reinforced composites (FRP). Combining the strength and ductility of metals with the lightweight and high stiffness of FRP and FMLs have emerged as new material compositions for applications in chemical, nuclear, automobile, and aerospace engineering disciplines. Structural health monitoring (SHM) using guided ultrasonic waves (GUW) is the state‐of‐the‐art for non‐destructive testing of thin‐walled structures. When applied to FML, SHM plays a crucial role in monitoring the integrity over time and detecting potential damage such as delamination, fibre breakage, or other structural anomalies. In SHM with GUW, a wave‐field is emitted by actuators. This wave‐field can be affected by damage in the structure, thereby changing its propagation characteristics. Sensors monitor the interaction between damage and GUW, which can be utilized to locate and classify the damage and ascertain the overall health state of the structure. In this study, an advanced integration of measurement hardware, that is, sensors and actuators, within the laminate structure is investigated. Sensor integration into FML allows for improved and more sophisticated monitoring capabilities in comparison to measuring techniques like laser vibrometers, which are limited to measuring displacements on the surface of the structure. However, the integration of sensors and actuators yields the technical difficulty of distorting the wave‐fields and may result in an over‐ or underestimation of the damage. Similar to damage, the distortion of the wave‐field is caused by the changes in acoustic impedance resulting from different material properties. In a previous study, incorporating a functionally graded artificial interphase through acoustic impedance matching between the sensor and host material showed notable and significant outcomes. The current contribution extends the prior graded artificial interphase for an isotropic homogeneous material to an FML structure. This paper presents a comprehensive numerical simulation study on a two‐dimensional model of FML with integrated sensors. The interphases are designed based on impedance matching, which improves signal transmission and reduces disturbing reflections. The conducted investigations hold for several interphase configurations for a wide frequency range. The optimised integration of sensors demonstrates promising results for enhancing the reliability and accuracy of SHM systems. This research serves as a foundation for further experimental validation and the development of advanced sensor‐integrated FML structures with improved monitoring capabilities.

Three-dimensional phase field modeling, orientation prediction and stress field analyses of twin-twin, twin-grain boundary reactions mediated by disclinations in hexagonal close-packed metals

Crystalline defects, such as dislocations, disclinations, twins and grain boundaries, play critical roles in determining the mechanical properties of metals and alloys. In particular, with multiple competitive deformation modes activated, the mechanical behaviors of hexagonal close-packed metals are strongly influenced by the interactions and reactions of various types of defects. Despite extensive studies on the elastic interactions of defects, a theoretical framework capturing crystallographic reactions, especially reaction products and associated local stress concentration, is still unavailable. Here we suggest a disclination-based method to quantify defect reactions. By using a combination of crystallographic calculations and phase field modeling/simulations, twin-twin and twin-grain boundary reactions in hexagonal close-packed metals have been quantitatively analyzed. It has been found that partial disclinations, accompanied with other defects (e.g., {112¯6} and {112¯2} high-index twins), can be generated by defect reactions as typical byproducts. The orientation change and stress fields caused by disclination formation have been systematically calculated, which offers a rigorous mathematical foundation to explore twin-twin, twin-grain boundary reactions. By quantitatively determining defect reactions and local stress fields, our work provides new insights into the deformation mechanism and microstructure-property relationship in metallic materials.

Influence of local structure and metal-oxygen hybridization on the electrical and magnetic properties of alkaline earth metal (Mg2+, Ca2+, Sr2+) substituted LaFeO3 ceramics

Pristine and alkaline-earth metal-substituted LaFeO3 (La1−xAxFeO3−δ; x = 0 and 0.2; A = Mg2+, Ca2+, and Sr2+) sintered ceramics are prepared from nanoparticles synthesized via a low-temperature citrate sol–gel technique. X-ray diffraction studies confirm the formation of a phase-pure LaFeO3 structure without any secondary phases for all the La1−xAxFeO3−δ compositions. LaFeO3 and La0.8Mg0.2FeO3−δ ceramics show Raman active modes related to La vibration, oxygen octahedral tilting, bending, and stretching. The optical bandgap is estimated to be 2.34 eV for pure LaFeO3 and reduces to 2.23 eV for La0.8Mg0.2FeO3−δ ceramics. On the contrary, La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics show no features in Raman spectra, consistent with the observation of metallic nature and diffuse band edge without any indication of sharp band edge noted. X-ray absorption spectroscopy (XAS) studies on La-L3 and Fe-K-edges confirm the oxidation states of La3+ and Fe3+ in all these ceramics. Local structural distortions and formation of oxygen vacancies in La0.8A0.2FeO3−δ (A = Mg2+, Ca2+, and Sr2+) ceramics are discerned from XAS structure analysis compared to the pristine LaFeO3 ceramics. Magnetic measurements of La1−xAxFeO3−δ reveal weak ferromagnetic nature except for La0.8Mg0.2FeO3−δ, which shows a large magnetization of 4.6 (6.7) emu/g at 300 (5) K. The ferromagnetic behavior of La0.8Mg0.2FeO3−δ ceramics seems to originate from the modification of hybridization between Fe(3d)–O(2p), La(5d)–O(2p), and Fe(4sp)–O(2p) orbitals. An anomalous magnetic transition observed only in zero-field-cooled curves at 88 K in La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics is correlated to the formation of new electronic states containing O 2p character as discerned from pre-peak O-K-edge.

Investigation of the effect of elbow pipes of Ti6Al4V, 304 stainless steel, AZ91 materials on erosion corrosion by finite element analysis

Corrosion is the degradation of metals caused by chemical or electrochemical reactions with their environment. As a result of these reactions, undesirable conditions occur in the physical, chemical, mechanical and electrical properties of metals. These conditions cause parts made of metallic materials to become unusable. Erosion corrosion is one of the most common types of corrosion in fluid transfer. There are several methods for preventing erosion corrosion. First of all, some precautions should be taken to prevent wear. Intervention is very important in terms of cost, especially at the design stage. Measures such as wide angle bends, wall thickness of wear-resistant material and corrosion allowance can be taken, especially in applications where the flow direction needs to be changed. The aim of this study was to determine the effect of liquid fluid on erosion corrosion in Ti6Al4V, 304 stainless steel and MgAz91 elbow pipes by using the computer aided and finite element based AnsysWorkbench Explicit Dynamics module. For the design of the elbow pipe, SolidWorks was used for 3D studies. In the analysis of the pipe, the suitability of the pipe for the 3D model was examined. The effect of fluid rotation on the pipe walls and the effect of the pipe material on the flow along the pipe were determined. The standard k-e model based on the velocity-pressure relationship in continuous and steady flow was used for the flow calculations. The flow simulation showed that for all models the flow accumulation after rotation was more concentrated on the opposite walls of the pipe, as expected. The results obtained showed that the deformation in MgAZ91 material had the highest value at 9.14 × 10−8 mm. This situation has been interpreted to mean that it may vary depending on the flow rate automation. Designs on the old designs in the erosion structure of the liquid that occurs in the pipes with a new product design in the analysis design.

Fabrication of CoM (M= Ni, Cu) alloys modified carbon electrocatalysts by pyrolysis of dual-metal-site metal-organic frameworks for efficient dye-sensitized solar cells

The regulation of interface properties of multi-component transition metals in carbon-based catalyst has been an effective method to boost the electrochemical performance of counter electrode (CE) catalysts for dye-sensitized solar cells (DSSCs). Herein, CoNi-metal-organic framework (MOF) and CoCu-MOF are fabricated through introducing Ni and Cu into the stable Co-MOF, and used as sacrificial precursor in the followed pyrolysis-alloying process. And then, the target product CoM (M=Ni, Cu)/N-doped polyhedron-like carbon (NC) are successfully obtained, in which CoNi and CoCu alloy nanoparticles are uniformly dispersed on the N-doped carbon skeleton. Such MOFs-derived carbon matrix can not only supply as conductive network, but also isolate the alloy nanoparticles to avoid agglomeration, ensuring more effective active sites. Meanwhile, the built-in electric field generated by the Mott-Schottky interface effect of CoM/NCs could regulate the electronic structure inside the catalysts, resulting in faster electron transfer ability. Significantly, the reduced work function due to the introduction of Cu atoms leads to stronger self-driven electron transfer at the heterogeneous interface of CoCu/NC, which helps to improve reaction activity and electrocatalytic efficiency. Among the tested catalysts, CoCu/NC displays a more satisfying power conversion efficiency (PCE) of 7.60 % when assembled into CE of DSSC, also superior to 7.19 % of Pt.

Experimental studies on mechanical properties of metal fused filament fabricated SS316L

Fused filament fabrication is a simple and commercially popular additive manufacturing (AM) technique for developing high-accuracy polymer-based materials. In this experiment, a retrofit type of setup was developed to manufacture stainless steel 316L–based products. The current study focuses on the encapsulation of stainless steel with polylactic acid to prepare the filament for 3D printing. The effects of printing parameters such as layer thickness, infill density, and extruder temperature on responses like density, surface roughness, micro-hardness, and material/filament consumption have been studied. A Box–Behnken design approach was employed to systematically evaluate 15 specimens under varying conditions. The results revealed that a maximum relative density of 97% was achieved with a layer thickness of 0.2 mm, an extruder temperature of 215°C, and a 100% infill density. Additionally, the optimized infill density demonstrated a significant effect on both hardness and surface roughness, confirming the importance of precise control over processing conditions for improving the performance of the printed parts. The findings contribute to the advancement of metal-polymer composite filaments in additive manufacturing, highlighting their potential for producing complex, high-performance components.

Improving the precision of work-function calculations within plane-wave density functional theory

Abstract Work function is a fundamental property of metals and is related to many surface-related phenomena of metals. Theoretically, it can be calculated with a metal slab supercell in density functional theory (DFT) calculations. In this paper, we discuss how the commensurability of atomic structure with the underlying fast Fourier transform (FFT) grid affects the accuracy of work function obtained from plane-wave pseudopotential DFT calculations. We show that the macroscopic average potential, which is an important property in work function calculations under the ‘bulk reference’ method, is more numerically stable when it is calculated with commensurate FFT grids than with incommensurate FFT grids. Due to the stability of the macroscopic average potential, work function calculated with commensurate FFT grids shows better convergence with respect to basis set size, vacuum length and slab thickness of a slab supercell. After we control the FFT grid commensurability issue in our work function calculations, we obtain well-converged work functions for Al, Pd, Au and Pt of (100), (110) and (111) surface orientations. For all the metals considered, the ordering of our calculated work functions of the three surface orientations agrees with experiment. Our findings reveal the importance of the FFT grid commensurability issue, which is usually neglected in practice, in obtaining accurate metal work functions, and are also meaningful to other DFT calculations which can be affected by the FFT grid commensurability issue.

Opportunities and Challenges in the Synthesis of Noble Metal Nanoparticles via the Chemical Route in Microreactor Systems.

The process of noble metal nanoparticle synthesis is complex and consists of at least two steps: slow nucleation and fast autocatalytic growth. The kinetics of these two processes depends on the reductant "power" and the addition of stabilizers, as well as other factors (e.g., temperature, pH, ionic strength). Knowing these parameters, it is possible to synthesize materials with appropriate physicochemical properties, which can be simply adjusted by the type of the used metal, particle morphology and surface property. This, in turn, affects the possibility of their applications in various areas of life, including medicine, catalysis, engineering, fuel cells, etc. However, in some cases, the standard route, i.e., the chemical reduction of a metal precursor carried out in the batch reactor, is not sufficient due to problems with temperature control, properties of reagents, unstable or dangerous intermediates and products, etc. Therefore, in this review, we focused on an alternative approach to their chemical synthesis provided by microreactor systems. The use of microreactors for the synthesis of noble metal nanomaterials (e.g., Ag, Au, Pt, Pd), obtained by chemical reduction, is analyzed, taking into account investigations carried out in recent years. A particular emphasis is placed on the processes in which the use of microreactors removed the limitations associated with synthesis in a batch reactor. Moreover, the opportunities and challenges related to the synthesis of noble nanomaterials in the microreactor system are underlined. This review discusses the advantages as well as the problems of nanoparticle synthesis in microreactors.

Effects of multilayer MoS2 coating on the mechanical properties of metals: A competition between external force and interfacial adhesion

Molybdenum disulfide (MoS2) is a two-dimensional material that exhibits unique interfacial interactions with metals, making it potential coating material for improving material properties of metals. In this work, the effects of multilayer MoS2 coating on the mechanical properties and deformation behaviours of copper (Cu) and gold (Au) substrates are investigated by nanoindentation experiments and molecular dynamics (MD) simulations. Specifically, our experimental results indicate that the MoS2 coating greatly increases the Young's modulus and hardness of Au substrate throughout the indentation process. In the MoS2/Cu system, however, the MoS2 coating exhibits inverse effects at diffident indentation depths, which, specifically, has the weakening and enhancing effects at the early and late stages of the indentation process, respectively. MD simulations indicate that the different effects of the MoS2 coating on the mechanical properties of Au and Cu substrates are attributed to the different interfacial adhesion properties between the MoS2/Cu and MoS2/Au systems, as the binding energy of the MoS2/Au system is much larger than that of its MoS2/Cu counterpart. Moreover, it is also revealed in MD simulations that the load-bearing area of metal substrates can be significantly enlarged by the MoS2 coating, which leads to the dense dislocations distributed in metal substrates and thus the strain-hardening in MoS2/metal composites.

Microstructure and stress mapping in 3D at industrially relevant degrees of plastic deformation

Strength, ductility, and failure properties of metals are tailored by plastic deformation routes. Predicting these properties requires modeling of the structural dynamics and stress evolution taking place on several length scales. Progress has been hampered by a lack of representative 3D experimental data at industrially relevant degrees of deformation. We present an X-ray imaging based 3D mapping of an aluminum polycrystal deformed to the ultimate tensile strength (32% elongation). The extensive dataset reveals significant intra-grain stress variations (36 MPa) up to at least half of the inter-grain variations (76 MPa), which are dominated by grain orientation effects. Local intra-grain stress concentrations are candidates for damage nucleation. Such data are important for models of structure-property relations and damage.

Effects of stabilized heat treatment on stress rupture properties of high Si-bearing austenitic stainless steel weld metal

The 15Cr-9Ni-Nb austenitic stainless steel weld metal with a Si content of 3.5 wt% was prepared via gas tungsten arc welding and then held at 900 °C for 3 h for the stabilized heat treatment (SHT). The stress rupture properties of the as-welded (AW) and SHT weld metals at 550 °C were evaluated via the Larson-Miller parameter. The microstructure evolution was discussed during the 550 °C stress rupture process. The coarse σ-phase and relatively fine G-phase formed on the δ-ferrite during aging at 550 °C. In the AW weld metal, the continuous δ-ferrite with a large amount of coarse σ-phase led to the formation and expansion of cracks during the stress rupture process, which accelerated the eventual rupture and damaged the stress rupture properties. The SHT decreased the δ-ferrite content and formed a large amount of nanoscale NbC precipitated in the matrix. The decreased δ-ferrite content avoided the rapid formation and expansion of cracks and the nanoscale NbC blocked the dislocation movement during the stress rupture process, which improved the stress rupture properties.

A mechanical TiAl/TiAlN multinanolayer coating model based on microstructural analysis and nanoindentation

A finite element model reproducing the mechanical behaviour during nanoindentation tests on Ti0.67Al0.33/Ti0.54Al0.46N multilayer coatings was developed. Coatings with two different nanoperiods (10 and 50 nm) were deposited by radio-frequency magnetron sputtering from a single sintered titanium/aluminium target using the reactive gas pulsing process. X-ray diffraction and transmission electron microscopy confirmed the multilayer stacking of the coatings. The finite element models of coatings with these two stacking periods were built considering successive hypotheses: equal thicknesses for metal and nitride nanolayers stacked without transition layer, equal thicknesses stacking with a transition layer between each metal and nitride nanolayer and finally imbalanced thicknesses stacking with a transition layer. The elastic and plastic properties of the stacked nanolayers were determined on thick monolithic coatings of metal and nitride using indentation testing and the finite element model updating method respectively. The elastic-plastic properties of the interface were introduced in the multilayer model as a rule of mixtures of the metal and nitride properties using two hypotheses: parallel or serial. For 50 nm-period film, the interface has a negligible effect on the overall indentation response. On the other hand, for the 10 nm period, the imbalanced stacking model with precise knowledge of the transition layer thickness obtained by N K-edge electron energy loss spectroscopy is required to reproduce the experimental indentation curve. Compared to classical analytical models accounting for hardness, not only the hardnesses but also the indentation moduli appear to be well predicted and evaluated in this work.

Revisiting Andrews method and grain boundary resistivity from a computational multiscale perspective

The effective material response as observed at a macro level is a manifestation of the material microstructure and lower scale processes. Due to their distinct atomic arrangement, compared to bulk material, grain boundaries significantly affect the electrical properties of metals. However, a scale-bridging understanding of the associated microstructure–property relation remains elusive so that phenomenological approaches such as the Andrews method are typically applied. In the present contribution we revisit Andrews method from a computational multiscale perspective to analyse its limits and drive concepts to go beyond. By making use of homogenisation techniques we provide a solid theoretical foundation to the Andrews method, discuss its applicability and tacit assumptions involved, and resolve its core limitations. To this end, simplistic analytical examples are discussed in a one-dimensional setting to show the fundamental relation between the Andrews method and homogenisation approaches. Building on this knowledge the importance of the underlying microscale morphology and associated morphology-induced anisotropies are in the focus of investigations based on simplified microstructures. Concluding the analysis, scaling laws for isotropic microstructures are derived and the transferability of the results to realistic, (quasi-)isotropic polycrystals is shown.

Orientation-related and temperature-dependent continuous grain boundary migration in multi-principal element alloys

Grain boundaries (GBs) significantly affect the mechanical properties of metals and alloys. In this study, we investigated using molecular dynamic simulations the migration behavior of Σ25 (710), Σ5 (310), and Σ37 (750) [001] symmetric tilt GBs in CoCrCuFeNi multi-principal element alloy (MPEA) and Cu samples subjected to shear deformation. In Cu, the migration of the GBs exhibits a coupled migration pattern, consistent with the Cahn model; while in MPEA, the migration pattern varies with GB angle and temperature. Both Σ25 (710) and Σ37 (750) GBs, along with higher temperatures, induce GB roughening and continuous migration in the MPEA samples. Further investigation to the effects of GB angle and temperature was conducted through microstructure evolution tracing and quantitative analysis. A model was developed to describe the temperature-dependent continuous GB migration and average flow stress in MPEA samples with Σ25 (710) or Σ37 (750) GBs. This work can help understand the mechanical behavior of GB in MPEA and provide valuable insights for the development of high-performance materials.

DETERMINATION OF CHANGES IN MECHANICAL PROPERTIES OF METAL OF FEEDWATER PIPELINES BENDS AND “HOT” STEAM OF THE SECOND POWER UNIT OF PIVDENNOUKRAINSK NPP FOR THE SECOND 100,000 h OF OPERATION

An analysis of the results of periodic testing of hardness of metal of pipelines bends of power unit No. 2 of Pivdennoukrainsk Nuclear Power Plant (PNPP) after ~100,000 and ~200,000 h of operation was carried out. It is shown that during the operation of feedwater and “hot” steam pipelines during the second 100,000 h of operation, the aging of the metal is observed, which is manifested in a partial, at least in their surface layers, uneven decrease in the strength of the metal. An increased rate of aging of the metal of pipeline bends is observed in areas where the metal was subjected to the greatest plastic deformation during the pipe manufacturing process (compressed and stretched sides of the bends). The critical parameter among the normalized mechanical properties of bending metal is the tensile strength, which is the first to reach a critical level when extrapolating the obtained data. While maintaining the rate of change in the mechanical properties of the metal at the level of the second 100,000 h of operation for post-project operation, the projected residual resource of metal bends of feedwater pipelines and "hot" steam is ~590,000 and ~380,000 h, respectively.

Nanosized Porphyrinic Metal–Organic Frameworks for the Construction of Transparent Membranes as a Multiresponsive Optical Gas Sensor

The well‐known and excellent colorimetric sensing capacity of porphyrins, along with the exceptional structural properties of metal–organic frameworks (MOFs), make porphyrin‐based MOFs, such as PCN‐222, ideal candidates for the construction of a chemical sensor based on absorbance. However, to the best of authors’ knowledge, no high‐quality porphyrin‐based MOF gas sensors have been developed to date, most likely due to the difficulties in: 1) preparing nanosized porphyrin‐MOFs to minimize scattering in absorbance measurements; and 2) incorporating MOFs into transparent membranes for practical use. Herein, a simple and fast microwave‐assisted method for preparing high‐quality nanosized PCN‐222 crystals and their metalated derivatives PCN‐222(M) is reported to finely tune the sensing response. Next, the successful dispersion of these PCN‐222(M) nanoparticles into poly(dimethylsiloxane) to create flexible and transparent membranes is demonstrated. This integration yields a multiresponsive optical gas sensor exhibiting excellent sensitivity and the ability to discriminate between various volatile organic compounds via pattern recognition identification.

Liquid thermophysical properties of Ag-Si alloy based on deep learning potential

The knowledge of the thermophysical properties of liquid metals and alloys is essential for expanding the materials database and designing materials with good properties. In this work, we developed an interatomic potential using a deep neural network (DNN) algorithm for liquid Ag-Si alloys. Compared with ab initio molecular dynamics (AIMD) results, the DNN potential provided a good description of the information of energy, force, and structure features of the system in the simulated temperature range. Through this potential, we can obtain the thermophysical properties of different compositions of liquid alloys by simulation way. The computed thermophysical properties are in excellent agreement with the reported experimental data. The analysis of local structure indicates that the liquid ordering and stability strengthen upon cooling at the atomic level, eventually leading to an increase in thermophysical properties.

Investigating nanostructure-property relationship of WTaVCr high-entropy alloy via machine learning optimized reactive potential

In spite of the promising prospects of the WTaVCr refractory high-entropy alloy (RHEA), the nanoscale structure-property relationship remains largely unexplored. This study introduces a supervised machine learning (ML) framework to develop a charge-transfer ionic potential (CTIP) for the W/Ta/V/Cr/O multi-component system. This novel approach demonstrates exceptional advantages in optimizing numerous parameters of a highly flexible yet physically rigorous potential, leveraging a modified distributed breeder genetic algorithm (DBGA) to balance search comprehensiveness and efficiency. The robustness of developed potential is verified through cross-validation against first-principles predictions on various properties of metals, alloys and oxides. Subsequently, dynamic simulations of annealing, mechanical loading, surface oxidation and radiation collision are conducted utilizing CTIP. Results of these simulations align with previous experiments about nanoscale chemical ordering, plastic deformation behavior, oxidation mechanisms and radiation tolerance. These findings not only further corroborate the reliability of CTIP potential, but also uncover atomic-scale insights that are experimentally unattainable, thereby enhancing the understanding of the nanostructure-property relationship.

Perspective—Concerning a New Mechanistic Model Toward the Catalytic Ammonia Synthesis

A reasonable catalytic mechanistic model should refer to a widely range of catalytic reaction. We believe that all types of catalytic reaction on heterogeneous catalysis should follow a general mechanism, and it is our opinion that with the hall-filled valence orbitals, the atom of catalysts could convert the reactant into reactive radical and/or support the formation of new chemical bond between two reactants via radical dimerization. In our recent publications this new mechanistic model on the catalytic Fischer-Tropsch reaction (the conversion of CO and H<sub>2</sub> to hydrocarbons), electrochemical hydrogen evolution reactions, and hydrogen combustion in various metal catalysts is discussed, and which seems to provide a reasonable interpretation to those catalytic reactions. In the present work it is discussed that this new mechanistic model is suitable to the Haber-Bosch process (catalytic ammonia synthesis) on various transition metal catalysts, and a reasonable explanation is provided on the catalytic property of various transition metal for ammonia synthesis.