Oxide Growth Mechanism Research Articles

Role of Si in the Oxide Nucleation and Growth Mechanisms of 60Si2Mn Spring Steel: Experimental and First-Principles Study

Role of Si in the Oxide Nucleation and Growth Mechanisms of 60Si2Mn Spring Steel: Experimental and First-Principles Study

The Mechanism of Oxide Growth on Pure Aluminum in Ultra-High-Temperature Steam

A high-temperature water steam (H2O(g)) between 300 °C and 1000 °C reacted with the Al surface in this study. The Al surface states were characterized and analyzed using XRD °C, XPS, and SEM after and before the reaction, and the effects and mechanism of H2O(g) on the Al surface morphology and chemical composition were studied. The experiment showed that for an Al sheet reacting with H2O(g), its oxide layer morphology changed from nano-needle to flaky and granular oxides gradually with the rise of temperature, and finally the Al surface became porous as a whole. Its oxide crystals were amorphous and were determined to be aluminum oxide (Al2O3) using XPS. The needle-like oxide in the Al sheet surface tended to grow toward the surface, and no obviously inward oxidizing corrosion layer occurred in the aluminum substrate; the oxide layer between the oxide and Al sheet substrate was compact, and could effectively prevent the infiltration and corrosion of water molecules.

Growth mechanism of double cone-shaped nano zinc oxide prepared from zinc oxidation flue dusts by acid leaching

Cone-shaped nano zinc oxide was prepared by acid leaching-alkali precipitation using zinc oxidation flue dusts as raw materials. The dynamic conditions of acid leaching and the growth mechanism of ZnO crystal were also discussed. It was shown that the optimum acid leaching conditions were H2SO4 concentration 2 mol/L, liquid–solid ratio 20:1, reaction time 4 h, reaction temperature 90 °C and Zn leaching rate was 94.98%. Then, the nano ZnO was prepared by acid leaching solution in an open hydrothermal system at low temperature. The formation process of nano ZnO crystals undergoes crystallization-dissolution-recrystallization under low temperature and alkaline conditions. Double cone-shaped ZnO nanoparticles could be obtained at 62 °C with n(Zn2+)/n(OH−) ratio of 1:5 and reaction time of 1 h. The average size of ZnO nanoparticles was about 100 nm.

Understanding the growth mechanisms of TiO2/Al2O3 mixed scales formed on Al-depleted Ti2AlC at 1000–1200 °C

We present a detailed study of thermally grown oxide scales on a bulk Ti2AlC material and explore its oxide growth mechanisms at 1000 °C, 1100 °C and 1200 °C, respectively. The oxide scale predominantly consists of an outer TiO2-rich layer and an inner TiO2/Al2O3 mixed layer. The formation of such a duplex microstructure is caused by the phase transformation from Ti2AlC to TiC at the scale/substrate interface and the Al depletion due to the formation of impurities. The insufficient supply of Al to scale/substrate interface, together with the competition from growth of TiO2, prevents formation of a continuous Al2O3 scale.

Oxidation and electrochemical characterization of oxide formed on Ti-Al-Zr in a neutral steam environment

The study focuses on the oxidation and the electrochemical behavior of the oxide formed on an alpha titanium alloy, Ti-Al-Zr, in a neutral steam environment. The alloy was exposed in a static autoclave at 400 °C, 10 MPa for durations up to 90 days. The oxidation kinetics and the rate laws were established by the discontinuous gravimetric method. The characterization of the oxide was done by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), glow discharge optical emission spectroscopy (GDOES) and Raman spectroscopy. The electrochemical characterization of the high-temperature oxide film was done by a potentiodynamic polarization experiment and ex-situ electrochemical impedance spectroscopy (EIS) measurement. The defect density of the oxide was calculated using the Mott-Schottky (M-S) analysis. A physical model was developed based on the impedance response, within the framework of point defect model (PDM) theory. The oxidation kinetics followed a nearly fourth power rate law followed by a linear rate law. The oxide consisted of an inner barrier layer and an outer layer containing crystallized grains. The transition in the oxidation kinetics was attributed to the recrystallization of the outer layer. The defect density for all the oxidized specimens was of the order of 1021 cm−3. The EIS study, in conjunction with the PDM, established that the oxidation kinetic was controlled by both titanium interstitials and oxygen vacancies. A correlation between the oxidation kinetics and the kinetics of the interfacial reactions was established and the oxide growth mechanism in the steam environment is discussed.

New sight on the oxide film growth mechanism in a single crystal Ni-based superalloy with a ground surface signature

The oxide film characteristics and growth mechanism of a single crystal Ni-based superalloy were studied under the ground surface signature. In the transient oxidation, oxygen atoms invaded the substrate along with the γ ´ phases, resulting in the Ni-Al spinels and alumina with nanosize formed simultaneously. Moreover, the outer layer of NiAl2O4 obeyed a liner law (with n ≈ 1) and was controlled by the outward diffusion of Ni and Al cations (with Q= 1.13 eV), whereas the inner Al2O3 layer followed a parabolic law(with n ≈ 0.5) and was determined by the inward diffusion of oxygen (with Q= 1.43 eV).

Isothermal Oxidation TGO Growth Behaviors of Laser-Remolten LZO/YSZ Thermal Barrier Coatings

Laser scanning modification was applied to secondarily melt the top ceramic coating surface of lanthanum zirconate/yttria-stabilized zirconia double ceramic thermal barrier coatings (LZO/YSZ TBCs) to reduce the gas oxygen diffusion and improve the TBCs service life. Isothermal oxidations with different times were carried out on the as-sprayed (AS) TBCs and laser-remolten (LR) TBCs at 1100 °C to investigate thermally growth oxide (TGO)growth mechanisms and isothermal oxidation behaviors. The results showed that the laser-remolten top-ceramic-coating dense layer with a columnar crystal structure of LR TBCs presented a 96.3% and 59.1% lower surface roughness and porosity, respectively, than those of the top ceramic coating of AS TBCs, and the TGO growth rate of LR TBCs decreased by 46.2% compared to that of AS TBCs. The mixed-oxides appearance time of LR TBCs (50 h) was later than that of AS TBCs (25 h). After 100 h of isothermal oxidation, the total TGO thickness of LR TBCs was only 77.2% of that of AS TBCs, and the effects of the laser-remolten TBCs on gas oxygen diffusion inhibition and high-temperature oxidation resistance were promising in LZO/YSZ TBCs.

Nucleation and growth mechanism of cuprous oxide electrodeposited on ITO substrate

The electrodeposition mechanisms of cuprous oxide (Cu2O) from copper nitrate solutions on indium tin oxide (ITO) were investigated using the cyclic voltammetry and the chronoamperometry methods. Then the kinetics parameters, nucleation and growth mechanism were explored. The CV measurement showed that the electrodeposition of Cu2O takes place by cathodic reduction at potential −0.5 V versus saturated calomel electrode (SCE). Furthermore, the voltammograms at different scan rates revealed that the electrodeposition reaction of Cu2O is a quasi-reversible reaction controlled by the diffusion of copper ions. Moreover, the deposition mechanism of Cu2O on the ITO substrate determined by the Astley approach and confirmed by the Scharifker-Hills models follows an instantaneous three-dimensional (3D) nucleation controlled by diffusion with an average diffusion coefficient D of 0.549 10-6 cm2 s−1. The X-ray diffraction pattern of Cu2O film was indexed to cubic crystal structure. The scanning electron microscopy analysis indicated that the average size of the cuprous oxide particles is about 1.408 µm. The optical energy band gap (Eg) was calculated by Tauc’s plot for Cu2O is 2.16 eV. The theoretical analyses reveal that Cu2O has an energy band gap of 2.25 eV, which corresponds to experimental results.

A reactive molecular dynamics simulation study on corrosion behaviors of carbon steel in salt spray

Corrosion behaviors, charge distribution, and oxide growth mechanisms of carbon steel have been studied by using reactive molecular dynamics simulations. The corrosion kinetics of carbon steel with a carbon content of 0.1% has been investigated in the 35‰ salinity salt spray with different densities of 1.03, 0.52, and 0.10 g/ml at different temperatures, respectively. The results show that the corrosion is massive in normal density (1.03 g/ml) salt spray system and pitting in dilute density (0.52 g/ml and 0.10 g/ml) salt spray systems. Iron crystal lattice defects on the carbon steel surface will arouse O, H, and Cl particles in the salt spray to migrate inward, causing deep oxidation. The density of salt spray is found to take a dominant position in the carbon steel corrosion. Therefore, the influence of temperature on oxidation kinetics in normal density salt spray is much greater compared to dilute density. In addition, the “decarburization” phenomenon of carbon steel has been observed and verified that the carbon content in the decarburized layer continues to decrease as the oxidation deepens. In the long-term simulation of the 1.03 g/ml salt spray system, the oxide growth and corrosion behavior are found to occur mainly before 600 ps, and the corrosion rate at this time is determined by the chemical reaction rate. After 600 ps, the corrosion rate depends on the electron diffusion rate. Furthermore, the activation energy is calculated to estimate the oxidizing property of different salt spray systems by fitting the consumption rate of water molecules into Arrhenius equation. When the concentration of salt spray decreases, the activation barrier tends to increase and the oxidizing ability of salt spray becomes weaker.

XPS study of oxide nucleation and growth mechanisms on a model FeCrNiMo stainless steel surface

High resolution X-ray photoelectron spectroscopy analysis has been used to investigate, in-situ, the mechanisms for oxide nucleation and growth on a FeCrNiMo single crystal alloy. Ultra-high vacuum conditions provided the ideal environment in which an oxide-free surface could be oxidised in a controlled manner, using extremely low pressures and step-wise exposures of oxygen. In-situ snapshot measurements, which records an XPS spectrum every 10 s, provided insight into the mechanisms of chromium and nitrogen segregation during annealing of the sample. High resolution XPS spectra was used to follow the evolution of the key elements at step-wise intervals, allowing for detailed insights into the nucleation and growth mechanisms. Angular XPS analysis provided further information on the in-depth distribution and stratification of the oxide film.

A three-dimensional finite element model for the oxide growth mechanism and growth-induced stress within thermal barrier system

Thermal barrier coating is subjected to out-of-plane displacements and possible in-plane cracks as thermally grown oxide (TGO) grows at high temperatures. Three different schemes of TGO growth are carried out in a three-dimensional thermal barrier coating model, in order to discuss the growth mechanism of the TGO film and to analyze the growth-induced stress within the top-coat. They are respectively 1) that the TGO film uniformly thickens along the whole thickness; 2) that the TGO film uniformly thickens along the bottom; 3) and that the TGO film linearly thickens at the bottom. The TGO film is found to possess the maximum thickness at the crest and the minimum one at the middle. The difference between the maximum and minimum thicknesses reflects the irregularity of TGO thickness distribution, which causes significant displacement incompatibility within the top-coat. The displacement incompatibility makes the top-coat subjected to out-of-plane compression around the crest and out-of-plane tension around the middle. The TGO growth scheme affects the TGO thickness distribution and the out-of-plane stress within the top-coat. Additionally, the lengthening-to-thickening ratio is employed to study the effect of the lengthening strain rate on the TGO thickness and the top-coat stress. The top-coat stress is very sensitive to the lengthening strain rate, and reducing the lengthening strain rate is helpful in enhancing the lifetime of thermal barrier system.

Oxidation kinetics of transition metals exposed to molecular and atomic oxygen

In this work we analyze the oxidation of 30 nm polycrystalline transition metals films (Hf, Ta, Mo and Ru) at low temperatures (298 K to 473 K) upon the exposure to two different species: molecular oxygen and atomic oxygen. Using in-situ spectroscopic ellipsometry and in-vacuum X-ray photoelectron spectroscopy, we verify the oxide growth kinetics and the final stoichiometry after each exposure condition for the four metals, and explore the particularities present in each oxide growth mechanics. The temperature-dependent analysis enabled to experimentally obtain the dissociation energy of molecular oxygen at polycrystalline O covered surfaces. By applying the principles of coupled currents and the Cabrera-Mott oxide growth mechanism, we extract values of the energy barrier for oxidation and the field formed in both oxygen molecule-metal and atom-metal interaction, exploring the differences between both exposure conditions. We demonstrate that in oxide growth at low temperatures two key points should be highlighted: (i) the strong dependence of surface potential on reactive oxygen coverage; (ii) the interrelation between exposure conditions and crystalline oxide formation. The obtained results and analysis contribute to the understanding of oxidation processes at low temperatures, advancing the knowledge required for the design and synthesis of thin metal and oxide films.

Effect of water vapor on the oxide growth in FeCrAl-based oxide dispersion-strengthened fuel cladding material at 1100 ℃ and 1200 ℃

As a potential accident-tolerant fuel cladding material, the high-temperature oxidation behavior of Fe-13Cr-4.5Al-oxide dispersion-strengthened alloy was investigated in dry air and moist air at 1100–1200 ℃. The specimens were examined using a combination of gravimetry and several surface-analytical techniques, including X-ray diffraction, scanning electron microscopy, electron probe microanalysis, focused ion beam, and transmission electron microscopy. The oxidation occurred rapidly at first and then slowed down as the protective oxide layer developed. A typical two-layer alumina grain structure was observed in both environments. An oxide growth mechanism of the Fe-13Cr-4.5Al-ODS alloy is proposed, emphasizing the effect of water vapor.

Microstructure and Oxidation Behavior of Anti-Oxidation Coatings on Mo-Based Alloys through HAPC Process: A Review

Mo and Mo-based alloys are important aerospace materials with excellent high temperature mechanical properties. However, their oxidation resistance is very poor at high temperature, and the formation of volatile MoO3 will lead to catastrophic oxidation failure of molybdenum alloy components. Extensive research on the poor oxidation problem has indicated that the halide activated pack cementation (HAPC) technology is an ideal method to solve the problem. In this work, the microstructure, oxide growth mechanism, oxidation characteristics, and oxidation mechanism of the HAPC coatings were summarized and analyzed. In addition, the merits and demerits of HPAC techniques are critically examined and the future scope of research in the domain is outlined.

Unusual layer-by-layer growth of epitaxial oxide islands during Cu oxidation

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. However, current epitaxial oxide growth methods are based on macroscopic empirical knowledge, lacking fundamental guidance at the nanoscale. Using correlated in situ environmental transmission electron microscopy, statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu2O nano-island growth on Cu is layer-by-layer along Cu2O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. Growth kinetics show cubic relationships with time, indicating individual oxide monolayers follow Frank-van der Merwe growth whereas oxide islands follow Stranski-Krastanov growth. Cu sources for island growth transition from step edges to bulk substrates during oxidation, contrasting with classical corrosion theories which assume subsurface sources predominate. Our results resolve alternative epitaxial island growth mechanisms, improving the understanding of oxidation dynamics critical for advanced manufacturing at the nanoscale.

Sub-nano to nanometer wear and tribocorrosion of titanium oxide-metal surfaces by in situ atomic force microscopy

Wear and tribocorrosion of passive oxide film covered metals have been studied at the micro and macroscopic scales. Recent advances in nanotechnology have contributed to breakthroughs in understanding of fundamental friction and wear mechanisms of atomically thin 2D materials at the nanoscale. However, for metals and materials without ultra-flat surfaces, a gap in knowledge exists at or below a few nanometers, which is too small for continuum mechanics theories and experiments including conventional atomic force microscopy (AFM) methods, due to resolution limits arising from surface roughness. Here, we report the near-atomic-scale wear of titanium in air and physiological solution from a single atomic layer to beyond the full oxide thickness using an AFM-based tribology method. Sub-nano to nanometer wear of titanium was revealed with different stages of contact pressure dependent wear regions identified as wear depth increased, featured by a transition from atomic wear (below 2.4 GPa) to elasto-plastic driven wear (above 3.6 GPa) at its oxide thickness (3.8 nm) in air. Higher stress was required to generate a similar wear penetration process in PBS compared to air. Tribocorrosion at this scale was grain orientation and voltage-dependent. Our study opens up a new method to achieve reliable angstrom-level resolution wear quantification to advance the understanding of wear and tribocorrosion of metals at the nanoscale. Statement of significanceExperimental tests of wear for metallic biomaterials at the nanoscale are difficult because engineered metal surfacesare never perfectly atomically flat, limiting the resolution of precise wear measurements to a few nanometers scale or more. To systematically address this problem, we have introduced the AFM ‘image-wear-image’ tribology method and obtained quantitative stress dependent measurement of the near-atomic-scale wear of titanium surfaces in air and tribocorrosion in physiological solution from a single atomic layer to beyond the full oxide film thickness. This allowedto measure sub-nano scale wear by partial removal of oxide. Nanoscale wear has been found to be grain orientation-dependent above the ‘atomic scale’ wear region. The nano-tribocorrosion of CP-Ti across scales and voltage effects on oxides in physiological solution was studied. Our study opens up a new method for future studies to advance the understanding of sub-nanoscale and nanoscale wear and tribocorrosion phenomenon as well as oxide growth mechanism of metallic biomaterials.

Oxide growth characteristics on Al (100), (110), and (111) surfaces: A chemo-mechanical evaluation

The oxide growth mechanism on Al (100), (110) and (111) and the corresponding oxide film properties were examined using all-atom molecular dynamics simulations. The growth kinetics of the aluminum oxide film at a constant dose rate of oxygen were analyzed. Al (110), with a structurally unstable surface and a high surface energy, showed the highest oxide growth rate, oxygen adsorption rate, and adsorption energy. However, as the crystallinity of the surface structure collapsed as oxidation progressed, the reaction energy of Al (110) with atomic oxygen converged to the same value as that of Al (100) and (111). Instead, a high anisotropic residual stress remained in the oxide layer on Al (110) with the aid of high surface energy and anisotropic surface structure. The results suggest that although the chemical bonding features of the as-prepared oxide layers were similar, the intermediate process of oxide film formation and the resultant mechanical properties were highly dependent on surface crystallinity. The oxidation kinetics model presented in this work showed consistency with other reported ab initio calculations. Moreover, it also successfully reproduced the experimental fact that the formation speed of oxygen islands on Al (100) is more delayed than that on Al (111).

One-dimensional ZnO micro/nanostructures: deep insight into the growth mechanism and fine control of the microscopic morphology.

One-dimensional zinc oxide arrays with various finely controlled microscopic morphologies are grown on fluorine-doped tin oxide substrates by a hydrothermal method. The relationship between the microscopic morphologies and the reaction conditions are studied deeply. It is found that although all the studied reaction parameters, like reaction time, pH value, concentration of the reactants and so on, can affect the microstructures of the resultant products, what they affect, in essence, is the concentration of free Zn2+ ions of the solution. By exploring the evolution of the microstructure of the one-dimensional zinc oxide crystals, it is proved that the formation of the various microscopic morphologies is a result of the competition between the kinetic control and the thermodynamic control during the crystal growth, which in turn is mainly determined by the concentration of the free Zn2+ ions in the solution. The in-depth exploration of the growth mechanism of zinc oxide and the fine control of its microscopic morphologies is expected to provide advanced materials for current and future cutting-edge applications of zinc oxide. It is also expected that the growth mechanism reported here can provide theoretical support for achieving other oxide materials whose microstructure can be finely controlled.

Unipolar plasma electrolytic oxidation: Waveform optimisation for corrosion resistance of commercially pure titanium

AbstractThis study deals with the anodisation of titanium grade 2 in 0.5‐M sulphuric acid using a pulsed signal in a unipolar regime. The electrical parameters investigated are voltage, frequency and duty cycle. The use of duty cycles with a high percentage of anodic polarisation (90%), combined with high frequencies (1000 Hz) and the higher voltage tested (220 V), favoured the establishment of a plasma regime involving strong dielectric discharges, allowing the growth of thicker oxides but with rough architecture. The corrosion resistance of the formed film has been characterised by potentiodynamic tests in 0.5‐M NaBr for localised corrosion resistance and by immersion tests in 10% v/v sulphuric acid solution for a uniform corrosion assessment. Current–time curves, visual observations and electron microscope analysis (scanning electron microscopy, energy‐dispersive X‐ray spectroscopy) were the tools selected to provide a correlation between technological parameters and oxide growth mechanism. For localised and uniform corrosion, anodisation at 220 V with a high level of anodic polarisation (90%) and frequency (1000 Hz) was verified to be particularly advantageous.

Investigation of β‐Ga2O3 Film Growth Mechanism on c‐Plane Sapphire Substrate by Ozone Molecular Beam Epitaxy

Growth mechanism and temperature of monoclinic gallium oxide (β‐Ga2O3) films grown by ozone molecular beam epitaxy (MBE) are investigated herein. Phase‐pure () β‐Ga2O3 films can be grown on c‐plane sapphire substrates when the growth temperature exceeds 500 °C, and the grain size increases with the increase in the growth temperature. Sixfold rotational domains are obtained based on the epitaxial relationships (Ga2O3 < 010>//Al2O3<> and Ga2O3 < 102>//Al2O3 < 110>). For the film grown at 700 °C, the threefold facets are observed for the first time, which are resulted from the easy‐cleaved (100) plane and rotational domains. In addition, the cathodoluminescence spectra of the β‐Ga2O3 films show that the proportion of ultraviolet emission increases with the increase in the growth temperature, which is attributed to the modulation of defect. Finally, the growth rate can be modulated by the ratio of Ga flux and ozone pressure. A reference is provided for heteroepitaxy of β‐Ga2O3 films and better understanding of the ozone MBE growth mechanism of oxides.