Oxide Growth Kinetics Research Articles

On the Estimation of Oxide Scale Growth in T22 Superheater and Reheater Tubes

In this paper, an iterative procedure was performed for the prediction of scale growth in T22 superheater and reheater tubes, which utilized empirical formulae for oxide-growth kinetics in steam and heat transfer analysis. Several expressions for oxide-growth kinetics and different thermal conductivities of scale were considered in calculations. The results indicate that the expression for oxide-growth kinetics can affect the estimated results significantly, and the thermal conductivity of scale has relatively small influence on the prediction of scale growth, but the influence degree increases with time.

Chemical stability and surface stoichiometry of vanadium oxide phases studied by reactive molecular dynamics simulations

Compositional stability of various vanadium oxides and oxide growth on vanadium surfaces have been studied using reactive molecular dynamics simulation methods. Vanadium dioxide (VO2), sesquioxide (V2O3), pentoxide (V2O5), and hexavanadium tridecaoxide (V6O13) are studied in bulk crystalline and thin film structures, investigating charge distribution and pair distribution functions of particle interactions. The stability is estimated to be pentoxide, hexavanadium tridecaoxide, sesquioxide, and dioxide respectively in decreasing order in thin film structures. We then analyze oxide growth kinetics on vanadium (100) and (110) surfaces. The oxidation rate, stoichiometry, charge distribution, and the effect of surface orientation on kinetic phenomena are noted. In the early stages of surface oxidation of our simulation configurations, sesquioxide is found to be the dominant component. The modeling and simulation results are compared with experiments where available.

Influence of surface orientation and defects on early-stage oxidation and ultrathin oxide growth on pure copper

We investigate oxidation and oxide growth on single-crystal copper surfaces using reactive molecular dynamics simulation. The kinetics of surface oxide growth are strongly correlated with the microstructure of the metal substrates. Simulating oxide layer growth along the (100), (110), and (111) orientations of crystalline copper, oxidation characteristics are investigated at temperatures of 300 K and 600 K. The oxidation kinetics are found to strongly depend on the surface orientation, ambient temperature, and surface defects. The effect of surface morphology on oxidation characteristics is analyzed by comparing oxygen adsorption on various sites and the structure factor. The surface oxide formed on (100) retains the initial crystal structure in the 300–600 K range. The (100) surface shows the highest oxidation rate at both temperature conditions but saturates, facilitating oxygen adsorption on hollow sites. The oxidation kinetics of the (100) orientation are found to be not significantly affected by surface defects. (110) shows modest oxidation at 300 K but the highest oxidation is observed at 600 K. By surface disorder and reconstruction, the oxide layer is produced continuously. The (111) surface is sensitive to ambient temperature and surface defects, showing that surface reconstruction is a key element for further oxidation. The charge distribution of oxidized Cu atoms indicates multiple groups of stoichiometric oxides, while the fraction of CuO-like characteristics increases significantly on the (110) and (111) orientations at higher temperature (600 K). The energetics and mechanisms of oxidation on Cu metal substrates at the nanoscale are discussed in detail, and comparisons with available experimental and other theoretical studies are presented wherever possible.

Corrosion of 9Cr Steel in CO2 at Intermediate Temperature III: Modelling and Simulation of Void-induced Duplex Oxide Growth

9Cr–1Mo steel forms in CO2 at 550 °C a duplex oxide layer containing an outer magnetite scale and an inner Fe–Cr rich spinel scale. The inner spinel oxide layer is formed according to a void-induced oxidation mechanism. The kinetics of the total oxide growth is simulated from the proposed oxidation model. It is found that the rate limiting step of the total oxide growth is iron diffusion through high diffusion paths such as oxide grain boundaries in the inner Fe–Cr rich spinel oxide layer. In the proposed oxidation model, a network of nanometric high diffusion paths through the oxide layer allows the very fast supply of CO2 inside pores formed at the oxide/metal interface. Its existence is demonstrated to be physically realistic and allows explaining several observed physical features evolving in the oxide layer with time.

Estimation of kinetic parameters of the corrosion layer constituents on steels in supercritical water coolant conditions

A model for the distribution of individual metallic constituents (Fe, Cr, Ni, Mn) in the corrosion layers on steels in supercritical water is proposed. A detailed description of the model concept and the calculation procedure is given. To verify and validate the model, its predictions are quantitatively compared to depth profiles of the oxides on ferritic–martensitic and austenitic steels as estimated by surface analytical techniques. Estimates of kinetic and transport parameters of the oxidation process for ferritic–martensitic and austenitic stainless steels in supercritical water are obtained. Predictive calculations of the growth kinetics of the respective oxides are presented and discussed.

Growth Kinetics of Self-Assembled Indium Hydroxide and Oxide in Electrolytic Alkali Halide Solution

Introduction of a critical amount of different alkali halides in an otherwise identical aqueous synthesis condition was found to produce different morphologies of indium hydroxide from an In metal source. In this study, synthesis in KCl medium leads to polycrystalline bundled rodlike morphology whereas KI medium leads to a single-crystalline sheetlike morphology of indium hydroxide, which upon being annealed at 250 °C transforms to oriented mesocrystals of cubic and hexagonal indium oxide phases, respectively. The difference in the morphology is likely due to the change in the pressure at the interface of the solution and the product, which is controlled by the structure and interactions of the monomers, similar to that observed for block copolymers. The evolution of the polymorphs comes with some interesting thermodynamics of decomposition, which is evident in the thermal studies. This study also indicates the role of crystallinity and dimensionality of indium hydroxide in the formation of different poly...

Numerical modeling of oxygen diffusion in the wall thickness of Low-Tin Zircaloy-4 fuel cladding tube during high temperature (1100–1250 °C) steam oxidation

A new numerical tool has been developed by coupling the diffusion code “EKINOX” (Estimation Kinetics Oxidation) and the thermodynamic database “ZIRCOBASE” using TQ (ThermoCalc program interface). The aim of this tool is to calculate the oxygen diffusion during oxidation of Zr based alloys. The simulation results of the oxide growth kinetics and the induced oxygen diffusion profiles in the [1100–1250 °C] temperature range, at different times, are presented and compared to previous experimental results. An estimation of the diffusion coefficient in the α phase is deduced from this comparison. The results are discussed in comparison to previous models based on an analytical treatment and the influence of the choice of the thermodynamic data set on the final oxygen diffusion profile is explored. Finally, it is shown that the present modeling is able to predict quite accurately the “critical” oxidation time corresponding to the overall ductile-to-brittle transition of the high temperature (HT) oxidized clad.

Effect of Surface Roughness on the Oxidation Behavior of the Ni-Base Superalloy ME3

Ni-base superalloys are used in applications, such as jet aircraft engines and power production facilities that require excellent elevated temperature oxidation resistance. This present work evaluated the effect of surface roughness on the oxidation behavior of the Ni-base superalloy ME3. Isothermal oxidation tests were performed in air at different times to investigate the oxide growth kinetics. The surface oxides were also characterized using scanning electron microscopy and x-ray diffraction. The surface roughness was measured using a linear scanning profilometer. The surface roughness measurements were correlated to the oxidation rates and an empirical model is proposed to describe the effect of surface roughness on the oxidation behavior.

A Growth Kinetics Model for the Radical Oxidation of Silicon

The silicon oxide growth kinetics were investigated for single wafer rapid thermal (RTP) and large batch vertical furnace radical oxidation processes under varying conditions. An oxidation model is proposed in which the oxidation rate of hydrogen–assisted radical oxidation is a combination of constant–rate low pressure wet oxidation and an oxygen radical driven process decaying with increasing oxide thickness. The model parameters for selected RTP and batch furnace oxidation processes are extracted and discussed. The implications of this model are compared to observed properties of the radical oxidation process like lattice orientation, stress independence, bird’s beak formation and thickness uniformity.

Composition effects on the early-stage oxidation kinetics of (001) Cu–Au alloys

An in situ environmental transmission electron microscopy study of the nucleation and growth of oxide islands during the early-stage oxidation of (001) Cu1−xAux alloys (x⩽38at.%) was undertaken in order to investigate the effects of alloying on oxide island nucleation behavior and growth kinetics. The kinetic data reveal that Au enhances the nucleation density of oxide islands and suppresses their growth rate. Our results provide insight into reasons for the decreased passivation properties of Cu when alloyed with Au.

Fractal growth modelling of [formula omitted] nanoparticles

The kinetics of iodine oxide aerosol production and growth was studied in an aerosol flow reactor by the photolysis of I 2 in an excess of O 3 , at a temperature of 295 K and a total pressure of 1 atm. The time-resolved evolution of the particle size distribution was fitted using a model which assumes that the initial period of particle growth (in the free molecular flow regime) is dominated by collision-coalescence, maintaining spherical shape and compact structure. This leads to the formation of primary particles of about 3 nm radius, which trigger fractal (agglomerative) growth in the transition regime resulting in particle aggregates characterised by lower mass fractal dimensions ( D f ) in the range 2.2–2.5. Enhancement of the particle pair collision kernels due to competing van der Waals and hydrodynamic forces is treated within the model. The densities of the fractal aggregates are lower than that of the bulk material, recently identified as I 2 O 5 [Saunders, R. W., & Plane, J. M. C. (2005). Formation pathways and composition of iodine oxide ultrafine particles. Environmental Chemistry, 2, 299], as a result of internal void space within the aggregate structures.

High Temperature Oxidation of Ultra-Low-Carbon Steel

An oxide scale layer always forms at the strip surface during the hot rolling process. Its properties have a large impact on surface quality. The most important features of the oxide layer are its thickness, composition, structure, adherence and coherence. Temperature, time and gas atmosphere determine the growth of oxide layers. In this paper, the high temperature oxidation properties of ultra low carbon steels are discussed in terms of oxide growth mechanism, kinetics and phase morphology. The oxidation kinetics of ultra-low carbon steel (ULC) in air, its scale structure and composition were investigated over the temperature range 923-1473K. Oxidation experiments were performed either under controlled atmosphere or in air, to analyse the oxidation process during strip production. A first series of experiments was carried out in an electric furnace at temperatures ranging from 923 to 1473K, for times between 16 and 7200s. A second series was carried out in a device especially designed to control the atmosphere. After heating under pure nitrogen, the samples were oxidised in air at temperatures between 923-1323K for various oxidation times. Thus treated specimens were characterised by metallography and their scale thickness was measured under the optical microscope. Scale morphology was studied and scale composition confirmed by EDS (Energy Dispersive Spectroscopy) and EBSD (Electron Backscattered Diffraction) analysis. Results show that scale growth under controlled atmosphere is significantly faster than under non controlled conditions, additionally the adherence of the scale formed in the laboratory device was significantly better than the other one. It is clear that scale thickness and constitution depend strongly on the oxidation potential of atmosphere. Computed parabolic activation energies (Ea) values are in good agreement with those found in the literature.

Rate-Limiting Reactions of Growth and Decomposition Kinetics of Very Thin Oxides on Si(001) Surfaces Studied by Reflection High-Energy Electron Diffraction Combined with Auger Electron Spectroscopy

The growth and decomposition kinetics of very thin oxides on Si(001) surfaces were investigated by reflection high-energy electron diffraction combined with Auger electron spectroscopy (RHEED–AES) to monitor the reaction rates of oxide growth and decomposition in real time, and changes in surface structure and interface morphology simultaneously. The oxides prepared by stopping the second oxide layer growth at various coverages following the first oxide layer growth by Langmuir-type adsorption at 500 °C under an O2 pressure of 2.6×10-4 Pa were isothermally annealed by increasing temperature from 500 to 666 °C at the same time that O2 gas was quickly evacuated. It was observed that (1) oxide thickness continued to decrease significantly as measured on the basis of changes in O KLL Auger electron intensity ΔIO-KLL before voids appeared at a nucleation time tN as recognized by the appearance of half-order spots in RHEED patterns, (2) the SiO2/Si interface morphology was considerably roughened corresponding to ΔIO-KLL during void nucleation as observed by the evolution of the RHEED intensity of bulk diffraction spots ΔIbulk, (3) the ratio of ΔIbulk to ΔIO-KLL was almost constant, and (4) oxide decomposition rate during void nucleation, which was approximately given by ΔIO-KLL/tN, showed a good linear correlation with the second oxide layer growth rate α immediately before starting the decomposition reaction. The good correlation between ΔIO-KLL/tN and α clearly indicates that the rate-limiting reaction of the second oxide layer growth is closely related to that of the oxide decomposition during void nucleation. All the above-mentioned observations can be comprehensively interpreted using a reaction model proposed for the rate-limiting reactions of oxide growth and decomposition, in which the point defect generation (emitted Si atoms + vacancies) caused by the strain due to the volume expansion of oxidation plays a crucial role because of the high reactivity of the emitted Si atoms and vacancies with dangling bonds. Under an O2 atmosphere, both emitted Si atoms and vacancies are the preferential adsorption sites of O2 molecules in the oxide and at the SiO2/Si interface, respectively. The oxide can be decomposed by the emitted Si atoms to produce SiO molecules, which desorb from the surface, leading to oxide removal in vacuum with SiO2/Si interface morphology roughening, but may be oxidized within the oxide under an O2 atmosphere.

Growth Kinetics and Electrical Properties of Ultrathin Silicon Dioxide Layers

In this paper, the growth kinetics and electrical properties of ultrathin silicon-dioxide layers are reviewed. Topics discussed here include the onset of oxide growth, the effects of temperature, substrate orientation, dopant type and concentration, and stress on oxide growth kinetics. The use of in situ real-time ellipsometry to control the rapid- thermal oxidation of silicon will be presented. The electrical properties of the ultrathin silicon-dioxide layers will be discussed, especially the contact potential difference in MOS devices and its dependence on the processing history and substrate orientation which will be explained in terms of the role of partial-charge-transfer dipoles at the oxide/silicon interface. Finally, gate tunneling considerations in MOSFET design, modeling, characterization, and circuit performance will be briefly presented.

Continuous cooling transformation diagrams for the heterogeneous nucleation of Sn-5 mass%Pb droplets catalyzed by surface oxidation

A model was developed that permits computation of CCT diagrams for surface oxidation catalyzed heterogeneous nucleation of alloy droplets from a few experimental data. The model addresses the progress of droplet surface oxidation during continuous cooling in terms of oxide nucleation and growth kinetics. Avrami-corrected surface oxidation kinetics are adopted to account for the impingement of oxide islands growing on the droplet surface during continuous cooling. The model predicts droplet nucleation kinetics in relation to the oxidation potential in the atmosphere, droplet diameter, cooling schedule and four temperature-independent constants. CCT diagrams were computed for Sn-5 mass%Pb droplets cooling in nitrogen atmospheres with various oxidation potentials using nucleation data and cooling simulation of traveling mono-size droplets. Calculated CCT diagrams show that droplet surface oxidation sharply increases the droplet nucleation temperature particularly at high cooling rates. Computation can be extended to predict CCT curves for droplet nucleation in industrial thermal spraying processes.

Effect of Polymeric Media on the Kinetics of Nanocluster Nucleation and Growth

The effect of a polymeric medium on the nucleation and growth kinetics of iron oxide (γ-Fe2O3) clusters is studied. We show that the kinetics in both poly(methyl methacrylate) and polystyrene are d...

Enhanced Nucleation and Decreased Growth Rates of Cu2O in Cu0.5Au0.5 (001) Thin Films During in situ Oxidation

The initial oxidation behaviors of Cu–50 at.% Au (001) single-crystal thin film were studied by in situ ultra-high-vacuum transmission electron microscopy to model nano-oxidation of alloys with one oxidizing component and one inert component. The oxidation behaviors such as incubation time, oxide nucleation rate, oxide growth kinetics as well as nucleation activation energy were greatly changed by the addition of nonoxidizing Au. The reasons for these changes, such as Au segregation to the top surface, a decrease in Cu activity, and reduced lattice mismatch due to the addition of Au, were discussed, and a qualitative analysis of nucleation energetics was given.

Atomistic Modeling of Cation Transport in the Passive Film on Iron and Implications for Models of Growth Kinetics

Atomistic modeling has been used to study the structure and transport properties of surface oxide films on pure iron. These calculations have been used to constrain parameters in two common models for oxide growth kinetics, i.e., the high-field model and diffusion-limited growth. Empirically determined parameters for these models are not consistent with the atomistic modeling. However, if cation transport is dominated by grain-boundary diffusion, these growth models can be reconciled with the atomistic modeling.

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2 : N2O. IV: Oxide structure and growth kinetics in the monolayer regime

The structure and growth kinetics of the oxide resulting from exposure of hydrogen-terminated single-crystalline (100) silicon to diluted N2 : N2O atmospheres at moderate temperatures (in the interval 750–850 °C) have been studied byX-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (TEM), and secondary-ion mass spectrometry (SIMS). Under these conditions, the data suggest that the substoichiometric interface region is extremely narrow, and they point to O2 (resulting from N2O decomposition) as the major oxidizing species after monolayer completion.

The Effect of Grain-Boundary Diffusion on the Oxidation of Low-Chromium Steels

Even though the oxidation behavior of steels is generally considered as to be widely understood, a closer look reveals some open questions, e.g. regarding the influence of the substrate grain size on the overall oxidation kinetics. At temperatures below 570°C the main constituent of the oxide scale formed on top of low alloy steels is magnetite. As shown by gold marker experiments it grows outward and inward at the same time, the latter exhibiting a gradual transition to the more stable spinel compound FeCr2O4. As indicated by intergranular-oxidation attack below the superficial scale, inward oxide growth seems to be driven by oxygen transport along the grain boundaries serving as fast diffusion paths. This is supported by thermogravimetric oxidation tests in air on low-Cr steels with varying grain size: The smaller the grains the higher the oxidation rate. Recently, a numerical model for the diffusive transport processes based on the finite-difference approach has been developed, which distinguishes between fast grain-boundary diffusion and bulk diffusion. Qualitatively, it is capable to predict the relationship between substrate grain size and inward oxide growth kinetics. Together with the thermodynamic tool ChemApp and in combination with a data set for the Fe-Cr-O system the mechanism-based simulation of the overall oxidation process of low-Cr steels is possible.