Gas-metal Interactions Research Articles

On the quantum dynamical treatment of surface vibrational modes for reactive scattering of H2 from Cu(111) at 925 K.

We construct the effective Hartree potential for H2 on Cu(111) as introduced in our earlier work [Dutta et al., J. Chem. Phys. 154, 104103 (2021), and Dutta et al., J. Chem. Phys. 157, 194112 (2022)] starting from the same gas-metal interaction potential obtained for 0K. Unlike in that work, we now explicitly account for surface expansion at 925K and investigate different models to describe the surface vibrational modes: (i) a cluster model yielding harmonic normal modes at 0K and (ii) slab models resulting in phonons at 0 and 925K according to the quasi-harmonic approximation-all consistently calculated at the density functional theory level with the same exchange-correlation potential. While performing dynamical calculations for the H2(v = 0, j = 0)-Cu(111) system employing Hartree potential constructed with 925K phonons and surface temperature, (i) the calculated chemisorption probabilities are the highest compared to the other approaches over the energy domain and (ii) the threshold for the reaction probability is the lowest, in close agreement with the experiment. Although the survival probabilities (v' = 0) depict the expected trend (lower in magnitude), the excitation probabilities (v' = 1) display a higher magnitude since the 925K phonons and surface temperature are more effective for the excitation process compared to the phonons/normal modes obtained from the other approaches investigated to describe the surface.

Rational design of the PEBA2533 mixed matrix membrane containing metallo-supramolecular polymers for efficient CO2/H2 separation

Mixed-matrix membranes (MMMs) are an effective method for overcoming the trade-off limitations of conventional polymeric membranes and are attractive for CO2/H2 separation. However, major challenges remain in achieving high gas separation performance and long-term stability owing to undesirable polymer/filler interfaces. In this study, a novel metallo-supramolecular polymer (F127-Tpy-M) was designed and selected to engineer a polymer/filler interface. Benefiting from strong intermolecular interactions, F127-Tpy-M dispersed well in the PEBA2533 matrix with a defect-free interface. By synergistically combining the dipole–quadrupole effect of the ethylene oxide groups in F127 and gas–metal interactions, MMMs could significantly improve the gas separation performance. In comparison with the pristine membrane, the MMM with 60% F127-Tpy-M loading exhibited 175–194% and 215–259% increases in CO2/H2 selectivity and CO2 permeability, respectively, which far surpass the 2008 Robeson upper bound. The molecular dynamics simulations supported the experimental data, confirming that F127-Tpy-M is a promising candidate for designing next-generation high-performance MMMs.

Refining at the impact and emulsion zones of basic oxygen steel making process – a fundamental study

ABSTRACT Insights into the kinetics occurring during the combined blown (top and bottom blowing) oxygen steelmaking process, particularly at the impact and emulsion zones within separate reactors, can provide a deeper understanding of the refining mechanism in steelmaking. A dynamic model has been developed that can predict the contributions of various refining processes such as decarburization, desiliconization, demanganization, and dephosphorization. The model considers gas–metal interactions at the impact zone and slag–metal–gas interactions at the emulsion zone in an oxygen steelmaking converter. The model includes sub-models for lime dissolution and heat loss calculation. FactSage™ software and its macro programming facility were employed to integrate thermochemical and kinetic information into the model. The model predicts the temperature, composition, and volume of several phases involved in the process. The model predictions transient metal and slag compositions and metal bath temperature, were found to be consistent with the plant data.

In situ identification of the metallic state of Ag nanoclusters in oxidative dispersion

Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions.

Activity of Ti and V in iron melts

Thermodynamic data regarding the formation of the nitrides TiN and VN in iron melts were obtained by Ser’eznov at Moscow Institute of Steel and Alloys on improved Sieverts equipment by a compensation method of measuring the pressure and gas volume using a highly sensitive pressure sensor. The use of this very reliable method to investigate gas–metal interactions was first proposed by Ponomarev and implemented at Chelyabinsk Research Institute. The experimental data obtained in the present work are used to calculate the activity coefficients of Ti and V in dilute solutions based on iron. Refined reference data regarding the Gibbs energy of vanadium-nitride formation from its elements are employed here. The results for the activity coefficients γ Ti.1873 ∞ = 0.055 and γ V.1873 ∞ = 0.24 are in good agreement with literature values.

Electroplated and Plasma Enhanced Magnetron Sputtered Ta and Cr Coatings for High Temperature and High Pressure Operation

AbstractFor A723 steel large caliber gun barrel applications, high pressure (∼700MPa), rapid cyclic heating-cooling (∼1250°C), and aggressive propellant gases (CO, CO2, H2O, H2, N2, NH3, CH4, H2S etc) operational environment can cause severe wear and erosion damages to the bore, reducing the service life of the component. Refractory bore coatings can help protect the steel bore to extend service life. Cr electroplating process is currently being widely used in industry and in the military, but toxic wastes from the process are difficult and expensive to dispose. Plasma enhanced magnetron sputtering techniques are being developed for potential replacement of the Cr electroplating process. In this work, we compared A723 steel specimens coated with electroplated Cr and plasma enhanced magnetron sputtered Ta and Cr coatings. The specimens were subjected to analytical testing, including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, metallography; and adhesion testing, including groove test, a pulsed laser heat test to simulate cyclic thermal environment of the bore, and actual firing test. Steel samples electroplated with HC (high contraction) Cr showed extensive pre-deposition cracks, it also showed cohesive failures under groove adhesion test. When subjected to cyclic high pressure and temperature operation, gas-metal interactions led the as-deposited cracks to grow wider and new cracks to develop, allowing hot pressurized propellant gases to penetrate the cracks and erode the steel substrate. Plasma enhanced sputtered Ta and Cr coatings on steel were harder and denser compared to conventional magnetron sputtered coatings. Under groove testing, they showed no cracks, no cohesive and no adhesive failures. When subjected to cyclic pulsed laser heating simulation at 1490°K, thick sputtered Ta showed no crack, no delamination, and no failures. A heat affected zone was observed in steel, which was caused by tempered to untempered martensite conversion. Our data also showed that Ta sputtered in Ar consisted of minimum interface meta-stable tetragonal Ta fingers, which converted to bcc Ta in the heat affected zone; Ta sputtered in Kr consisted of 100% stable bcc Ta under similar experimental conditions.

Kinetics of microstructure evolution during gaseous thermochemical surface treatment

The incorporation of nitrogen or carbon in steel is widely applied to provide major improvements in materials performance with respect to fatigue, wear, tribology, and atmospheric corrosion. These improvements rely on a modification of the surface-adjacent region of the material by the (internal) precipitation of alloying element nitrides/carbides or by the development of a continuous layer of iron-based (carbo-) nitrides. The evolution of the microstructure during thermochemical treatments is not only determined by solid-state diffusion, but in many cases also by the kinetics of the surface reactions and the interplay with mechanical stress. In the present article a few examples, covering research on the interaction of carbon and/or nitrogen with iron-based metals, are included to illustrate the various aspects of gas-metal interactions.

Kinetic Regularities of Interaction of Metals and Semiconductors with Active Gases

A kinetic theory of the interaction of metals and semiconductors with active gases is given for a wide temperature range and different gas pressures. Equations describing the kinetics of primary direct gas–metal interaction are derived with due allowances for the effect of hot spots caused by heat of a chemical reaction. A dynamic model of the growing film of reaction products, taking into account transient stages of the process, as well as point defect concentration, is raised. An asymptotic parabolic equation derived in terms of transient kinetics describes the growth of the film, starting from its onset and till the formation of thick films at different temperatures. A reverse problem of determining diffusion parameters of the oxidation process and the concentration and types of the point defects from experimental kinetic data is also solved. These equations are verified by the example of silicon–oxygen system.

Laser pulse heating of gun bore coatings

The authors have developed laser pulse heating (LPH) as a tool for studying erosion processes at gun bore surfaces and for evaluating candidate coatings for bore protection. During firing, the bore coating and steel substrate experience thermal shock from rapid heating and cooling. Thermal pulse durations are in the millisecond range. Despite the short thermal pulse durations, severe coating and substrate degradation processes can occur; these include melting, gas–metal reactions, metallurgical transformations, interface reactions, transformational stresses, and thermal stresses. The degradation processes lead to coating cracking and spallation, which, in turn, allow erosion of the vulnerable underlying steel. Gas–metal interactions may also enhance fracture propagation in the steel. LPH is particularly convenient for performing multiple tests on coupon specimens for early evaluations of candidate bore coatings. This allows initial screening of candidate coatings without the difficulty and expense of testing in an actual gun or in a vented combustor. LPH was applied to gun steel that was electroplated with high-contractile chromium, which is the conventional coating for gun bores. LPH was also applied to low-contractile electroplated chromium and bare steel to provide baseline information. In the present LPH experiments, samples were repeatedly pulse heated to simulate the effects of multiple gun firings. The samples were then sectioned through the pulse-heated areas and examined to assess the resulting degradation. The results validate the approach. LPH reproduces the many features of thermal damage from actual gun firing: recrystallization and grain growth in the chromium, development of major cracks in the chromium, a heat-affected zone in the substrate steel, interface degradation, white layer formation (carburization and/or nitriding), and gray layer formation (rapid oxidation) in the steel.

Comparison of hydrogen gas–, atom– and ion–metal interactions

In the first part of the paper, we describe in more detail the dissociative chemisorption model, presented by Wang for the gas–metal interaction and then developed by Pick and Sonnenberg for the atom–metal interaction, in order to show the important factors which were not taken into account by previous authors. One of these factors is the initial sticking coefficient s 0 which can be less than unity even for a clean surface and can strongly influence the plasma-driven permeation and inventory. Then, we extend the dissociative chemisorption model on the case of the interaction of hydrogen molecular gas and fast hydrogen atoms with a multi-layer metal, and we verify the validity of the model by comparison of experimental data with calculations. Although in recent theoretical papers [Richards; Pisarev and Ogorodnikova] it was shown that Baskes’ model has an error, many authors apply Baskes’ recombination coefficient for their calculations till now. Experimental measurements show that the plasma-driven permeation and inventory are a function of the sticking coefficient which is very sensitive to any surface contamination that is in contradiction with Baskes’ model. Finally, on the basis of the dissociative chemisorption model, the assessment of the plasma-driven permeation through martensitic steel MANET covered by some plasma-facing metals (copper, beryllium and beryllium oxide) is presented. We show that the experimental data of hydrogen isotope permeation and inventory measured for the gas–metal interaction cannot be applied for the plasma-driven permeation and inventory. The analysis of the existing database of the sticking coefficient s updates those estimates for endothermic metals which can be applied for the fusion reactor.

New opportunities in soft X-ray absorption to characterise the adsorbate bonding

A useful and necessary step to understand the complexity of catalysis is to first study the simple prototype systems which involve elements active in such reactions. Studies throwing light on gas–metal interaction are of vital importance. The X-ray absorption spectroscopy can provide vital information for catalysis as one probes the system on a very local scale. We present state of the art surface EXAFS measurements of carbon, nitrogen and oxygen adsorbed on well characterised metal surfaces (Ni and Cu). The present contribution highlights from experimental measurements supported by improved theoretical calculations that temperature and angular dependent studies are essential for a reliable structural analysis and to gain an insight into absorbate–substrate bonding and kinetics. The low Z metal systems were found suitable to detect unambiguously the photoelectron backscattering by interstitial charge densities.

Ab-initio adiabatic noble gas–metal interaction: the role of the induced polarization charge

Within an ab-initio DFT–LDA framework, we have investigated the polarization induced on He and Ne atoms by a jellium (Al-like) surface. It is shown that the displaced charge of the gas–metal system is spherically distributed around Ne. It is polarized instead for He with a dipole moment having the negative lobe towards the jellium surface. A relationship between the two different polarizations of He and Ne with corrugating and anti-corrugating behavior is discussed.

Noble gas temperature control of metal clusters: A molecular dynamics study

We use classical molecular dynamics simulations to investigate temperature control of unsupported clusters using a noble gas atmosphere. The simulations are performed using a many-body interaction scheme for the intra-cluster potential, while a pairwise Lennard-Jones potential is used to model the interaction between the noble gas and the clusters. In order to isolate different parameters determining the energy exchange efficiency, we have studied the energy transfer with respect to (i) impact parameter, (ii) cluster temperature, (iii) noble gas temperature, (iv) gas–metal interaction strength, (v) metal potential, and (vi) noble gas mass. With these results, we are able to estimate the number of collisions needed to equilibrate a cluster at a given gas temperature. Our estimates are confirmed by simulations of cluster cooling in a noble gas atmosphere.

New Opportunities in the Soft X-Ray Absorption to Characterize the Adsorbate Bonding

One of the important applications of XAS in the soft X-ray regime is the ability to measure the EXAFS of light elements, like carbon, nitrogen, etc. up to sulfur and chlorine. These elements, adsorbed on metal surfaces, are the most important constituents for the investigation of gas-metal interactions. One decade ago, the surface EXAFS world was harmonic, the nearest neighbor distances were determined within the harmonic approximation, R did not change with temperature, and the coordination number N was determined from measurements at a single temperature. Recently, SEXAFS data were taken as a function of T and at various angles of X-ray incidence. This advance, in combination with multiple scattering analysis and full simulation computer codes, allows to routinely determine the pair distribution function up to the third moment. We relate in general terms the Einstein temperature, the local static disorder and thermal expansion to the ionic versus covalent bonding, shape of effective pair potentials and adsorbate induced surface reconstruction. Furthermore, these low Z systems are ideal candidates to detect unambiguously the photoelectron backscattering by interstitial charge densities (AXAFS).

Pressure build-up at the metal delivery tube orifice in ultrasonic gas atomization

The effects of geometry (diameter and tip design) and position (relative to the gas nozzles) of the metal delivery tube in an ultrasonic gas atomization (USGA) device on the pressure condition in the gas-metal interaction zone at the tube orifice have been studied. Simulation of ultrasonic gas (argon or nitrogen) atomization has been conducted, both at low (3.5 to 14 atm) and high (15 to 75 atm) atomization pressures. Low gas atomization pressures are generally used in spray deposition processes such as liquid dynamic compaction (LDC), while high pressures are used for powder production. Depending on the experimental conditions, i.e. the shape and angle of the taper at the metal delivery tube orifice or its position with respect to the nozzles' gas exit common plane, either partial vacuum (equivalent to downward aspiration of the melt) or overpressures (equivalent to back-pressurization of the melt) at the metal delivery tube was detected. Underpressure and overpressure effects were found to increase with gas atomization pressure. The maximum pressure differences measured with respect to the atomization chamber pressure were about 0.15 to 0.25 atm for the low-pressure experiments, and 0.50 to 0.60 atm for the high-pressure experiments. Underpressures or overpressures of these magnitudes have a large effect on the metal flow rate during gas atomization, either enhancing or reducing it, and thus changing significantly the gas to metal flow ratio. Because this is a crucial parameter for both the USGA and the LDC processes, the state of pressure at the delivery tube's orifice has to be monitored carefully, in order to ensure optimal processing conditions.

Effects of geometry and position of the metal delivery tube on ultrasonic gas atomization

The effects of the geometry and the position of the metal delivery tube on the pressure condition in the gas-metal interaction zone were studied. The measurements were performed under conditions which simulated ultrasonic gas atomization experiments, but at low gas atomization pressures (50–200 psig, 345–1380 kPa). Low gas atomization pressures are used in spray atomization and deposition processes such as liquid dynamic compaction (LDC), and Osprey. Depending on the experimental conditions, either underpressure or overpressure in the metal delivery tube was detected. The magnitude of the underpressures and overpressures was found to increase with the gas atomization pressure; the maximum pressure differences with respect to the atomization tank pressure were about 3 psi (21 kPa) when argon was used as an atomization gas with a pressure of 200 psig (1380 kPa). Underpressure or overpressure effects of such magnitude have a large effect on the metal flow rate during gas atomization. The large pressure differences measured in the present work result from using an atomizer with gas jet diameters larger than those used in previous investigations. Using a large ultrasonic atomizer, argon gas flow rates of about 5 kg/min can be obtained for atomization pressures of 200 psig (1380 kPa).

Interaction of Hydrogen Isotopes with Stainless Steel 316 L

The parameters of gas-metal interaction solubility S, diffusivity D and permeability of protium and deuterium in stainless steel 316L have been determined in the temperature range from 600 to 900 K...

Excitation and emission of metal electrons in atom-surface collisions

Electron-hole pair excitation and ionization probabilities are calculated for atomic collisions with metal surfaces at high incident energies. The method adopted is based on a Sudden Collision Approximation, and a realistic model is employed for the bound and continuum electronic states involved. The parameters used in the calculations are for Ar, He, H atoms impinging on a Li surface at 300 eV. The main results are: (1) Only single electron-hole pair excitations are important; multiple pair contributions are small. (2) The transitions are dominated by the behavior of the electronic wavefunctions in the tunneling region and may serve as a probe of this regime. (3) The excitation efficiency is in the order H ⪢ Ar ⪢ He, the effectiveness of hydrogen being due to its stronger, longer-range coupling. (4) The maximum excitation probabilities are for electrons ejected with relatively low excess energies. (5) Total transition probabilities are about 0.5 per collision for H, and about 0.1 for Ar, indicating that these are important, easily detectable processes. Experiments in this field should provide important information on electronic wavefunctions at the metal-gas interface, and on gas-metal interactions at high energies.

Mechanism of chemical and physical gas-metal interactions in very high shearing regimes

Very high shearing flows of high pressure, hot gases over metal surfaces produce chemicaland physical gas metal interactions (i.e., combustion, oxidation, and melting) which differ markedly from those produced by quiescent and low flow conditions. Such situations are encountered, e.g., in gun barrels, turbines, vents and nozzles, and can result in severe erosion of the metal. An analytical model hypothesizes that the high shearing flows limit the build-up of protective oxide layers on the surface, thus exposing the metal to a more direct chemical attack and establishing heterogeneous surface reactions even in cases in which the metal would burn in the gas phase under quiescent atmosphere. When melting is involved, metal mass loss is mainly due to melt generation and removal, which depend on surface heating rate. Surface heating is greatly enhanced by exothermic surface reactions. The existence of a melt layer on the solid surface lowers the heat transfer to the unmelted metal. Comparisons of calculated results to experimental results, in which steel was subjected to short pulses (∼2 ms) of high pressure (∼350 MPa) hot (∼2500 K) air flow, exhibit good agreement and reveal that gas phase combustion is unlikely, the reaction rate is diffusion controlled, melting rates enhanced by chemical heating can exceed direct chemical consumption rate three-fold, and a few micrometer thick melt layer reduces the calculated mass loss by about 13%.

Corrosion behaviors of inconel 617 in hydrogen base gas mixture

The corrosion behavior of Inconel 617, a candidate for the structural material of heat exchanger in the high temperature gas-cooled reactor (HTGR), has been investigated at elevated temperatures in the hydrogen base gas mixture (80 pct H2 + 15 pct CO + 5 pct CO2). This gas mixture simulates the reducing gas in the direct steel making system that uses heat from HTGR in Japan. This gas has relatively high oxidizing and carburizing potentials. In the temperature range of 650 to 1000 °C Inconel 617 oxidized to form a Cr2O3 scale containing titanium oxide. The activation energy for this process is estimated to be 50 to 60 kcal/mol. The time dependence of the growth of the surface oxide scale was parabolic. The aluminum in Inconel 617 was internally oxidized. The time dependence of the internal oxidation was noticed to obey a 0.4 power rate law. Carburization was noticed at 650 and 900 °C. At 900 °C, carbides containing Si, Ti, and Mo precipitated beneath the oxide scale for gas exposure times up to 200 h. After 200 h, the formation and growth of the surface scale suppresses carburization. The thermodynamic analysis of gas atmosphere proposed by Gurry could be applied successfully to the experimental results. Some inconsistency existed mainly because of the scale formation and direct gas-metal interactions.