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

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

Nucleation and growth mechanism of manganese oxide electrodeposited on ITO substrate

Metal nanoparticles usually show different oxidation dynamics from bulk metals, which results in various oxide nanostructures because of their size-related surface effects. In this work, we have found and investigated the chain-like nucleation and growth of oxides on the aluminum nanoparticle (ANP) surface, using molecular dynamics simulations with the reactive force-field (ReaxFF). After nucleation, the chain-like oxide nuclei could stay on the ANP surface and continue growing into an oxide shell, extend outward from the surface to form longer oxide chains, or detach from the ANP to generate independent oxide clusters, which is highly dependent on the oxygen content, temperature, and nanoparticle size. Our results emphasize the complicated interplay between the surface structure of nanoparticles and the environmental conditions in determining the formation of oxides, which provides insights into the atomic-scale oxidation mechanism of metal nanoparticles.

Specimen of Fe-18Cr(-10Ni) (wt.-%) were isothermally oxidized in dry and wet high p(O2) gas at 900°C. The morphology and microstructural evolution of the chromia scales formed were analysed by SEM-EBSD. At high pO2 test gas containing O2 and H2O, the pO2 is independent of the H2O content of the test gas. However, both types of oxygen species, i.e. O2 as well as H2O contribute to the chromia scaling reaction. The effect of specimen thickness on chromia scaling allows the change of the concentration of the intrinsic defects and their diffusivities in thermally grown chromia scales independently from the test gas applied. Chromia scales are under pressure during scale growth. For thermodynamic reasons the concentration and diffusivity of the intrinsic, native defects in oxides under hydro-static pressure varies with the amount of pressure applied. Ion beam polished oxide cross-sections were analysed in terms of oxide grain growth and nucleation rates of new oxide at the oxide-gas interface. Chromia scales formed on the various substrates at high p(O2) test gas grew at different rates, and microstructures formed on Fe18Cr(-10Ni) differ in grain shape and size. The chromia growth kinetic was found to be depending on the thickness of the specimens used, the H2O content of the gas, and its Ni content. The scale growth mechanism consists of two interlinked levels. At the meta-level oxide nucleation and oxide grain growth are affected by the cation flux in the oxide scale formed and the nature of the oxygen species in the gas. This fixes the number, size and shape of the oxide grains as well as the number of oxide grain boundaries available as short-circuit diffusion paths. The lattice level denotes the atomic level. Hereby the cation flux in the single grain by lattice diffusion and cation vacancy condensation are linked. The defect structure in the oxide lattice is important. The factors affecting it are the Cr diffusion in the substrate and the presence of Ni in the alloy, local p(O2), H-defects and oxide growth stress. The experimental findings will be discussed with strong focus on the oxide growth mechanism, the chromia microstructure of the scales formed under the various conditions and the concentration and mobility of the native defects in the chromia scales and its interactions with H-containing species originating from water vapour in the test gas. Furthermore, the role of Fe as base and Ni as alloying element in the metal substrate will be discussed. This is done by considering the differences between the Ni-Cr-O and Fe-Cr-O phase diagrams and the consequence of the existence of the Fe3+ ion on the miscibility of the oxides formed by the various cations.

Unveiling the nucleation and growth of Zr oxide precipitates in internally oxidized Nb3Sn superconductors

Nucleation and growth mechanism of cuprous oxide electrodeposited on ITO substrate

Oxidation of iron surfaces and oxide growth mechanisms have been studied using reactive molecular dynamics. Oxide growth kinetics on Fe(100), (110), and (111) surface orientations has been investigated at various temperatures and/or an external electric field. The oxide growth kinetics decreases in the order of (110), (111), and (100) surfaces at 300 K over 1 ns timescale while higher temperature increases the oxidation rate. The oxidation rate shows a transition after an initial high rate, implying that the oxide formation mechanism evolves, with iron cation re-ordering. In early stages of surface oxide growth, oxygen transport through iron interstitial sites is dominant, yielding non-stoichiometric wüstite characteristics. The dominant oxygen inward transport decreases as the oxide thickens, evolving into more stoichiometric oxide phases such as wüstite or hematite. This also suggests that cation outward transport increases correspondingly. In addition to oxidation kinetics simulations, formed oxide layers have been relaxed in the range of 600-1500 K to investigate diffusion characteristics, fitting these results into an Arrhenius relation. The activation energy of oxygen diffusion in oxide layers formed on Fe(100), (110), and (111) surfaces was estimated to be 0.32, 0.26, and 0.28 eV, respectively. Comparison between our modeling results and literature data is then discussed. An external electric field (10 MV cm(-1)) facilitates initial oxidation kinetics by promoting oxygen transport through iron lattice interstitial sites, but reaches self-limiting thickness, showing that similar oxide formation stages are maintained when cation transport increases. The effect of the external electric field on iron oxide structure, composition, and oxide activation energy is found to be minimal, whereas cation outward migration is slightly promoted.

ZnO nanowire arrays were grown by potentiostatic cathodic electrodeposition on aluminum anodic oxide template (AAO) from dimethyl sulfoxide (DMSO) solutions containing zinc chloride and molecular oxygen as precursors. The nanowires presented high aspect ratio and exhibited a very high crystallinity with a wurtzite crystal structure with preferential orientation along the (0001) crystallographic axis. Chronoamperometric experiments were performed on gold bulk electrodes in order to model this preferential mode growth of ZnO nanowires, which has not been previously reported for similar precursors in DMSO solution. The analysis of the corresponding chronoamperograms revealed that chloride ions influence the oxide nucleation and growth mechanism. It was found that in the absence of KCl as a supporting electrolyte, the data fitted an instantaneous three-dimensional diffusion-controlled (IN-3D)diff nucleation and growth mechanism (NGM). The presence of KCl, instead favored a progressive three-dimensional (PN-3D)diff NGM. With these results, a model for the more complex nanowire’s growth inside the pores of the AAO template is proposed.

For the protection of high-temperature alloys against corrosion, a slowly growing, dense, well-adherent scale must be formed. At elevated to high temperatures either chromia (Cr2O3) or alumina (Al2O3) can act as such a protective scale. Surface and interface phenomena in the nucleation, growth and adherence of oxide scales have been studied, mainly by AES; these phenomena are described and their mechanisms are discussed. Various positive effects on nucleation, growth and adherence are exerted by alloying with reactive elements (i.e. Ce, Y, La, Ti, Zr …) in small concentrations. They are acting in their oxidized state, segregated on the metal surface in oxide nucleation and segregated in oxide grain boundaries in the oxide growth mechanism. Non-metal elements such as nitrogen and carbon can enhance Cr2O3 nucleation by intermediate co-segregation with chromium, in contrast sulphur impedes chromia formation. Segregation of sulphur to the surface of voids and cracks forming at the metal/oxide interface deteriorates the scale adherence. The detrimental sulphur can be scavenged in precipitates formed by the reactive elements (oxides and oxysulphides) and at their interfaces. Copyright © 2000 John Wiley & Sons, Ltd.

To predict the fate of aqueous pollutants, a better understanding of heterogeneous Fe(III) (hydr)oxide nucleation and growth on abundant mineral surfaces is needed. In this study, we measured in situ heterogeneous Fe(III) (hydr)oxide nucleation and growth on quartz, muscovite, and corundum (Al2O3) in 10(-4) M Fe(III) solution (in 10 mM NaNO3 at pH = 3.7 ± 0.2) using grazing incidence small-angle X-ray scattering (GISAXS). Interestingly, both the fastest heterogeneous nucleation and slowest growth occurred on corundum. To elucidate the mechanisms, zeta potential and water contact angle measurements were conducted. Electrostatic forces between the charged Fe(III) (hydr)oxide polymeric embryos and substrate surfaces-which affect local saturations near the substrate surfaces-controlled heterogeneous growth rates. Water contact angles (7.5° ± 0.7, 22.8° ± 1.7, and 44.8° ± 3.7 for quartz, muscovite, and corundum, respectively) indicate that corundum has the highest substrate-water interfacial energy. Furthermore, a comparison of structural mismatches between the substrates and precipitates indicates a lowest precipitate-substrate interfacial energy for corundum. The fastest nucleation on corundum suggests that interfacial energies in the solution-substrate-precipitate system controlled heterogeneous nucleation rates. The unique information provided here bolsters our understanding of nanoparticle-mineral surface interactions, mineral surface modification by iron oxide coating, and pollutant transport.

The internal oxidation of AgCu alloys with atomic percentage 0.8, 3.3, 6.3 and 9.5 of Cu in air at 750 degrees C and 850 degrees C has been studied. It was found that CuO particles precipitated homogeneously on the surface ai AgCu alloys except for Ag-9.5% (atomic percentage) Cu. The latter exhibited the agglomerated precipitation of CuO particle cluster on the surface. The experimental results also revealed that the nucleation and growth of CuO oxide evidently varied with the change of Cu contents or oxidation temperature. When both Cu content and exposure temperature were low, the precipitation and the growth of internal CuO oxide were consistent with the prediction by the classical Bohm-Kahlweit mode, but the abnormal phenomenon of nucleation and growth of the CuO oxide was observed when the Cu content or the exposure temperature was increased. As a result of investigation of the atomic structure of different internally oxidized AgCu alloys, it is proposed that the stacking fault tetrahedra(SFT), which were found in the oxidized alloys, promoted the nucleation of CuO internal oxide.

The kinetics of oxidation and oxide growth mechanisms on Zr(0001)

The nucleation and initial stages of growth of aluminium oxide deposited on two different polymer surfaces [poly(ethylene terephthalate), (PET) and amorphous polypropylene, (PP)] have been studied by atomic force microscopy (AFM). The permeation of water vapor and oxygen through the films has been measured. The initial stages of the growth of the oxide consisted of separated islands on the polymer surface. Further growth of oxide depends strongly on the surface morphology and chemical nature of the polymer surface. Growth on PET follows a layer-by-layer mechanism that maintains the native surface roughness of the polymer substrate. Growth on PP, however, follows an island mode, which leads to an increase in surface roughness. This may be due to a lack of chemical bonding between the polymer and the arriving metal-oxygen particles. The oxide layer on PET grows more densely than on PP, providing superior barrier to gas permeation. (C) 2000 John Wiley & Sons, Inc.

The initial interactions of beryllium with O 2 and H 2O vapor at elevated temperatures

Aluminum oxide nucleation in the early stages of atomic layer deposition on epitaxial graphene