Gas-metal Interface Research Articles

Clarification of steel refining mechanism with stream degassing

Removal of non-metallic oxide inclusions during stream degassing only proceeds as a result of their appearance at the metal–gas interface, i.e., as a result of a specific flotation effect.

Use of the Richtmyer-Meshkov Instability to Infer Yield Stress at High-Energy Densities

We use the Richtmyer-Meshkov instability (RMI) at a metal-gas interface to infer the metal's yield stress (Y) under shock loading and release. We first model how Y stabilizes the RMI using hydrodynamics simulations with a perfectly plastic constitutive relation for copper (Cu). The model is then tested with molecular dynamics (MD) of crystalline Cu by comparing the inferred Y from RMI simulations with direct stress-strain calculations, both with MD at the same conditions. Finally, new RMI experiments with solid Cu validate our simulation-based model and infer Y~0.47 GPa for a 36 GPa shock.

Silver loss during the oxidative refining of silver–copper alloys

The high temperature oxidative refining of molten silver–copper alloys is accompanied by silver losses to the slag. Typically, borosilicate slags are utilized as a flux and air or oxygen is injected into the molten alloy. The majority of the copper can be selectively oxidized to copper oxide, but some silver is also lost to the slag. In this research, the mechanism of silver loss has been investigated. Firstly, TGA and DTA studies of molten silver–copper alloys were performed, in order to elucidate the oxidation processes occurring at the gas–metal interface in the bubble. Secondly, the silver losses to the slag in the high temperature refining tests were quantified. Thirdly, the slag was characterized using XRD and the morphology of the silver in the slag was examined. Fourthly, a pseudo-equilibrium model of the refining process was developed and this was utilized to suggest methods for minimizing the silver loss to the slag. Finally, possible methods for recovering the silver from the slag are discussed.

Nitrogen Desorption in Molten Stainless Steel During Immersion Argon Blowing

The behavior of nitrogen desorption reaction in molten stainless steel for AISI 304 and 316 during immersion argon blowing through an immersed alumina nozzle with 3 mm in I. D. has been investigated by sampling method. Some kinetic parameters such as reaction order, rate constant and apparent activation energy of nitrogen desorption reaction for AISI 304 and 316 have been obtained. Results show that nitrogen desorption reaction from molten stainless steel for AISI 304 and 316 is the second order reaction. The rate constant at 1 550 °C and 1 580 °C for AISI 316 is 0. 084 07% −1 · min −1 and 0. 823 70% −1 · min −1, respectively. The rate constant at 1 550 °C for AISI 304 is 0. 416 6% −1 · min −1. The apparent activation energy E a of nitrogen desorption reaction for AISI 316 is 2136. 47 kJ/mol. This huge value of apparent activation energy verifies that the nitrogen desorption reaction has a complex and multistep reaction mechanism. The rate of nitrogen desorption reaction from molten stainless steel is mixed controlled by the desorption reaction of diatomic molecule nitrogen or of monatomic nitrogen from molten metal at the gas-metal interface and the mass transfer of nitrogen in molten metal. The rate equation of process for nitrogen desorption has been deduced.

Modelling of Physico-Chemical Phenomena between Gas inside a Bubble and Liquid Metal during Injection of Oxidant Gas

Gas liquid reactors are extensively used in many metallurgical processes involving the refining of liquid metals. In these processes, reactions leading to the oxidation of various solutes in liquid metal often compete with each other, which ultimately determine the liquid metal composition. In the present paper, a model has been proposed to simulate the evolution of solute contents in a metallic melt considering mass transfer of solutes in the melt in the vicinity of the bubble, equilibrium at the gas-metal interface and gas composition evolution in the bubble during its ascent through the melt. The composition of solutes at the metal-gas interface in principle can be altered by changing the injected gas composition.The model was applied to the case of oxygen injection through a lance into liquid steel-containing C and Cr, aiming sufficient decarburization without much oxidation of Cr to the slag. The Cr loss to the slag by oxidation is generally much more than that expected based on equilibrium thermodynamics applied to the bulk metal and gas. The actual Cr loss, as shown by the present model, is determined by the composition of solutes at the metal-gas interface rather than in the bulk. The effect of change of the partial pressure of oxygen in the bubble by replacing oxygen by carbon dioxide in the injected gas and the corresponding evolution of C and Cr contents in the melt was simulated. Some preliminary experiments were conducted to validate the model predictions. The frame work of the model is generic and can be extended to many gas-liquid metal reactors in liquid metal processing.

On diffusion, oxidation and condensation phenomena at the liquid metal–gas interface

The mass transfer phenomena between a liquid metal and the surrounding gas phase play an important role in several technological processes: the existence of oxygen fluxes can strongly affect the properties of the gas–liquid interface. Here, known kinetic criteria will be connected to saturation laws and arranged in a series of tests easily applicable to real cases in order to forecast the steady configuration of the phases. The case of tin will be discussed.

Non-Faradaic electrochemical activation of catalysis

The use of fuel cells for carrying out oxidation reactions with cogeneration of electrical power and chemicals led, upon cofeeding oxygen and fuel at the anode, to the discovery of the effect of non-Faradaic electrochemical modification of catalytic activity or electrochemical promotion of catalysis. This phenomenon has been studied already for more than 70 catalytic reactions, including oxidations, reductions and isomerizations and using a variety of metal catalysts, and solid electrolytes. In this work we summarize the main features of electrochemical promotion and discuss critically its currently accepted sacrificial promoter mechanism which involves electrochemically controlled migration (spillover-backspillover) of promoting species from the electrolyte to the catalytically active metal-gas interface. It is shown that the spillover ionic species (e.g., O(delta-), Na(delta+)) form an overall neutral double layer at the catalyst-gas interface which alters the catalyst work function and the binding energies of coadsorbed reactants and intermediates, thus causing very pronounced and reversible alterations in the catalytic activation energy and catalytic rate and selectivity. Recent efforts for the practical utilization of electrochemical promotion are also briefly discussed.

Bond-Selective Control of a Heterogeneously Catalyzed Reaction

Energy redistribution, including the many phonon-assisted and electronically assisted energy-exchange processes at a gas-metal interface, can hamper vibrationally mediated selectivity in chemical reactions. We establish that these limitations do not prevent bond-selective control of a heterogeneously catalyzed reaction. State-resolved gas-surface scattering measurements show that the nu1 C-H stretch vibration in trideuteromethane (CHD3) selectively activates C-H bond cleavage on a Ni(111) surface. Isotope-resolved detection reveals a CD3:CHD2 product ratio > 30:1, which contrasts with the 1:3 ratio for an isoenergetic ensemble of CHD3 whose vibrations are statistically populated. Recent studies of vibrational energy redistribution in the gas and condensed phases suggest that other gas-surface reactions with similar vibrational energy flow dynamics might also be candidates for such bond-selective control.

Surface Tension during Molten Metal Granulation

The surface tensions of a number of common commercial ferroalloys have been measured during their granulation in water. These measured values are significantly lower than would be expected from a normal metal-gas interface and are more typical of the interfacial tensions of slag-gas interfaces. This would seem to indicate that the slag-metal interface on the surface of a granule produces no significant interfacial tension. An electron microscope study on sections through the surface layers of granules showed that, in some cases, although not in all, emulsification had occurred at the slag-metal interface.

Interaction of Co thin films with SiO 2: Effect of Co loading

Electron microscopy studies of Co films (1 and 4 nm) supported on SiO 2 reveal how the morphology and composition of the system vary following heating at 500 °C in dependence on atmosphere (H 2, air) and Co loading. We have shown that for small Co loading, chemistry of the metal–gas interface strongly influences the metal-support interaction. After heating in H 2 at 500 °C of 1 and 4 nm thick Co films supported on SiO 2 layer we established formation of α-Co 2SiO 4 and Co particles, respectively.

Kinetics of Oxygen Refining Process for Ferromanganese Alloys

The present analysis of the experimental data by Yamamoto et al. permitted to determine the rate controlling mechanisms for the decarburization and evaporative manganese loss concurrently taking place during the oxygen refining process of ferromanganese melt.When oxygen is supplied by a top lance blowing mode, the decarburization reaction takes place by three different mechanisms in sequence. The chemical reaction at the melt-gas interface controls the rate of decarburization during the first period, the rate of oxygen supply through the boundary layer in gas during the second period, and the mass transfer rate of carbon in melt during the third period when the carbon content is less than 2 mass%.Manganese is lost primarily by evaporative reaction, but its dynamics are affected by the prevailing excess oxygen after accounting for CO formation. The excess oxygen and manganese vapor establish counter-current flux and form MnO mist at some distance away from the metal-gas interface. This creates two diffusion boundary layers, one for the flux of manganese vapor adjacent to the melt-gas interface and the other for the flux of excess oxygen in the gas phase. When the vapor pressure of manganese at the metal-gas interface is low, the rate of manganese vapor loss is controlled by the flux of excess oxygen. Otherwise, it is determined by the flux of manganese vapor.

Change of Nitrogen Content in the Molten Steel during CaO Powder Blowing

The rates of nitrogen desorption from molten steel were measured with the blow of CaO powder or argon gas onto the melts under reduced pressure. 15kg of electrolytic iron was melted in a MgO crucible by a high frequency induction furnace and the temperature of the melt was held at 1873 K. A mathematical model was developed with the consideration of the chemical reaction between sulphur in molten steel and CaO powder and the desorption of nitrogen at gas-metal interface. The calculated results were in good agreement with the measured ones. The apparent rate constant of nitrogen desorption and the rate controlling step were examined.

Diffusion of oxygen in liquid copper and nickel

The diffusivities of oxygen in liquid copper and nickel were determined from 1300°C to 1560°C by a capillary gas-reservoir method. A diffusion cell designed to behave as if of semi-infinite length and consisting of liquid copper or nickel held in an alumina capillary was used. A H2O-H2 gas mixture maintained a constant oxygen potential at the metal-gas interface. A controlled furnace hot zone of 15 cm was obtained with six separate windings of Pt-10%Rh wire. To prevent convection the top of the diffusion cell was adjusted to be hotter than the bottom. The solidified diffusion columns were sectioned and analysed for oxygen by vacuum fusion analysis. Oxygen diffusivities, D, were calculated through use of a solution of Fick's second law. For copper D is 1.52 × 10-8 m2/s at 1295°C and 3.78 × 10-8 m2/s at 1560°C; for nickel D is 3.12 × 10-8 m2/s at 1450°C and 3.39 × 10-8 m2/s at 1580°C. The results for copper can be represented by the Arrhenius relationship ln D equals -19570/RT + 3.21 where E and R are in calories or -81900/RT + 3.21 where E and R are in joules (1350-1560°C) and where the numerator, E, is oxygen diffusion activation energy/mol K and R is the gas constant.

Raman Scattering of Surface Plasmons at a Gas–Metal Interface: Possible Application to Surface Chemical Reactions

We propose a conceptually novel method for studying surface reactions at a metal surface bordering a gas of reactant molecules under equilibrium conditions. We investigate theoretically Raman scattering of a surface plasmon in the visible spectral range assuming that the vibrational transition of the reactant molecules is saturated by an infrared surface plasmon. Due to the vibrational deexcitation at the surface, the desorbing molecules are in the ground state and contribute to the Stokes intensity only. Their flux is dictated by the probability for a molecule to enter a reactive channel. As a result, this quantity can be determined by measuring the ratio of the intensities of the Stokes and anti-Stokes components. The method can be used up to high pressures of reactants and thus could bridge the “pressure gap” in catalysis.

Raman Scattering of Surface Plasmons at a Gas–Metal Interface: Possible Application to Surface Chemical Reactions

Raman Scattering of Surface Plasmons at a Gas–Metal Interface: Possible Application to Surface Chemical Reactions

The metal–solution interface

This article reviews our present understanding of the metal–solution interface, drawing comparisons between it and the metal–gas interface. The chief difference between these two systems is the solvent, which has a profound effect on the physics and chemistry of the interface. The solvent is never entirely inert, and if polar, as water is, will adsorb on the metal surface and stabilise ions in solution. However, the presence of ions in solution allows a current to be passed between two electrodes inserted in the solution, and one of these electrodes can be the metal under investigation. This is the field of electrochemistry, and much of our knowledge of the metal–solution interface is derived from electrochemical measurements. Complementary information is gained from many of the techniques used to study the metal–gas interface. The first type of electrochemical system to be considered is one in which the application of a potential across the interface does not lead to charge transfer. Such a system behaves as a capacitance due to the formation of a complex double layer. The effects of various types of adsorption is then described. The deposition of metals on the electrode surface is next considered, and this is followed by a discussion of the reverse metal dissolution reaction. The final section concerns the formation of films on the metal surface, a reaction which has its parallel in metal–gas reactions.

The Rate of Nitrogen Desorption from Liquid Iron by Blowing Argon Gas under the Condition of Non-inductive Stirring.

The nitrogen desorption reaction by blowing argon gas onto the surface of liquid iron containing various oxygen contents has been studied in a resistance furnace. Using a periscopic high temperature lens the Marangoni convection was qualitatively observed in the process of nitrogen desorption. In terms of the experimental results and gas-liquid metal reaction kinetic theory, the procedure of the nitrogen desorption is discussed. The nitrogen desorption from liquid iron under the condition of non-inductive stirring exhibits a 1.5th order dependence with respect to the nitrogen concentration in the melt regardless of oxygen content. The rate of nitrogen desorption is controlled by three mixed rate-controlling steps of gas-and liquid-phase mass transfers and chemical reaction at the gas-metal interface and mainly by the latter two steps. It was deduced that the decrease of the nitrogen desorption rate which accompanies the increment of oxygen concentration was mainly attributed to the attenuation of Marangoni convection and the increase of chemical reaction resistance at the interface in the present study.

Transition from parabolic to linear kinetics in the high-temperature nitridation of niobium

The nitridation behavior of pure niobium wasinvestigated in nitrogen gas over the pressure range of10-2 to 1 torr and over the temperature range1600-2000°C. A surface layer of Nb2Nformed at 1 and 10-1 torr, obeying parabolickinetics for the former and linear kinetics for thelatter. This transition in time dependency firstmanifested itself at 1 torr in nonlinear plots ofln(Kc) vs. 1/T, consistent with an adsorption-controlledreaction. An evaluation of the flux of nitrogen acrossthe gas-metal interface is presented, comparing thekinetics of gas arrival based on the kinetic theory of gases with gas removal because of inwarddiffusion into the metal. Data from the literature areused to estimate these adsorptive and diffusive fluxesand justify the observed behavior. Nitridation ofniobium at 10-2 torr resulted in gasdissolution only, with no nitride layer beingformed.

Investigation of surface destruction of construction materials under intense periodic heat transfer

The study simulates the surface destruction of structural steel elements in power installations as a result of interaction with periodic high-temperature chemically active flows. The system of equations of thermoelasticity with two spatial observations is used. The existence of high tangential and axial compressive stresses is established in a thin layer near the metal-gas interface.

Structure of Electrified Interfaces

The objective of this book is to provide a state-of-the-art description of the structure of electrified interfaces with particular emphasis on the structure of the metal-solution interface. During the past decade, a molecular picture of the interface has emerged, superseding the notions of metal and solution as electronic and dielectric continua respectively. This book discusses the newest developments, including the progress in surface science, where the structure of the metal surface at the metal-gas interface has become resolved down to the picometer scale.