Initial Stages Of Oxidation Research Articles

Initial Oxidation Behavior of Ferritic Stainless Steel Interconnect with Sputtered NiFe2 Alloy Coating

Initial oxidation behavior of ferritic stainless steel with a sputtered NiFe2 coating for solid oxide fuel cells interconnect application was investigated in air at 800 °C to understand the transformation process from the NiFe2 alloy coating to NiFe2O4 spinel layer. The results indicated that the NiFe2 coating was initially converted to a surface scale with a layered structure consisting of a top Fe2O3 layer followed by NiFe2O4 mid-layer and an NiO inner layer. Cr oxide started to form at scale/steel interface before the coating was completely oxidized. The preferential growth orientation of Fe2O3 on the surface varied with time during the initial oxidation stage. Steel preoxidation prior to coating not only accelerated the oxidation of NiFe2 coating and the growth of NiFe2O4 layer, but also suppressed the orientated growth of Fe2O3. The surface scales on the coated steels were electrically conductive. The oxidation mechanism of the coated steels is discussed.

Особенности роста поверхностной окалины в процессе окисления на воздухе сплава V-Cr-Ta-Zr

Investigation results of features of surface scale growth on samples of V-Cr-Ta-Zr vanadium alloy at a short duration of oxidation in air are presented. It is shown that at the initial stages of oxidation, regardless of the samples microstructure, the growth rate of surface scale can be an order of magnitude higher than with long-term processing. It has been established that scale is characterized by open porosity formed as a result of sticking of small plate-like V2O5 flakes together. It has been suggested that the decrease in oxidation rate is a consequence of an increase in the scale thickness, which helps to slow down the supply of oxygen to the sample surface on which the processes of nucleation and growth of scales occur, as well as diffusion saturation of the surface layer of the vanadium alloy with oxygen.

Application of High-Performance Liquid Chromatography/High Resolution Mass Spectrometry to the Investigation of the Biodegradation and Transformation of Phenanthrene by a Plasmid Bearing Rhizosphere Bacteria Pseudomonas aureofaciens

Mass spectrometry was applied to identify metabolites and estimate the efficiency of phenanthrene biodegradation and transformation by rhizosphere bacteria Pseudomonas aureofaciens BS1393. Strains P. aureofaciens BS1393(pOV17) and P. aureofaciens BS1393(NPL-41) bearing various naphthalene biodegradation plasmids were used in the work. The strain BS1393(pOV17) contains the pOV17 wild type naphthalene biodegradation plasmid that determines the oxidation of naphthalene to Krebs cycle metabolites. The strain BS1393(NPL-41) contains the mutant plasmid NPL-41 governing the initial stages of naphthalene oxidation into salicylic acid. The limiting stages of phenanthrene biodegradation in bacteria with various plasmids have been identified according to the accumulation of intermediates. When bacteria were grown on phenanthrene, the main metabolites were as follows: (a) 2-hydroxy-2H-benzo[h]chromene-2-carboxylic acid/trans-4-(1-hydroxynaph-2-yl)-2-oxobut-3-enoic acid, (b) 1-hydroxy-2-naphthoic acid, and (c) salicylic acid. In the strain BS1393(pOV17), metabolite (а) was observed during 1–14 days of cultivation. Unlike it, in the strain BS1393(NPL-41), an insignificant amount of this metabolite was found after only 14 days. The availability of metabolite (b) in the growth of both strains was an evidence of the limited rate of its further decarboxylation. Metabolite (c) as a final product was found in the growth of the strain BS1393(NPL-41). Contrastingly, in the strain BS1393(pOV17), this metabolite was not found, which indicates the complete oxidation of phenanthrene.

Micro-structural evolution of oxide scales formed on a Nb-Stabilizing heat-resistant steel at the initial stage in high-temperature water vapor

Early oxidation behavior of a Nb-Stabilizing heat-resistant steel in water vapor at 700 °C for 336 h was investigated. Micro-characterization methods including in-depth XPS, SEM/EDS, FIB were employed to acquire the composition and distribution of oxidation products. The results showed that the oxidation kinetics of this heat-resistant steel almost followed a parabolic law at 700 °C, indicating the oxidation was controlled by the ion diffusion. Surfaces of oxidation products on TP347HFG were gradually from compact to loose with a longer exposure. Oxide scales were mainly composed of layered (Mn, Fe)Cr2O4 and Cr2O3 and scattered Nb2O5. Contents of Mn at the surface were much higher than other positions, confirming that Mn diffuse much faster than Fe and Cr. During the initial oxidation stage, NbC was transformed into Nb2O5, which was covered by Fe–Cr oxide scales. The growth of oxide scales on TP347HFG is suggested.

Experimental study of the ultrathin oxides on SiGe alloy formed by low-temperature ozone oxidation

The ultrathin oxides (<1.2 nm) on SiGe are formed by directly oxidizing SiGe surface in 10% O3/O2 mixture in Beneq TFS 200 ALD system. The oxide compositions are characterized using X-ray photoelectron spectroscopy technology as a function of processing conditions, including oxidation time, temperature, and pressure. It is found that the oxide composition is very sensitive to ozone partial pressure. That is, under a lower pressure, Ge atoms can't be oxidized even over a long time and the oxides are pure SiOx. Until the temperature is increased to 300 °C, about 54% of the Ge atoms of the outermost atomic layer of SiGe are oxidized in the initial oxidation stage. Nevertheless, a slight increase in ozone partial pressure cause a rapid changeover to the formation of oxide mixture containing Si oxide and Ge oxide at all temperatures investigated, i.e. 100 °C–300 °C. Moreover, the oxidation rate of Ge atoms maintains almost unchanged from 100 °C to 230 °C, and decreases at 300 °C.

Deformation, Cracking and Fracture Behavior of Dynamically-Formed Oxide Layers on Molten Metals

This study investigates the cracking behavior of oxide layers formed on molten metals and alloys including pure zinc, Zn–4 wt%Al (ZAMAK3) and Al–(0.5–2) wt%Ca in dynamic oxidation condition by injecting gas bubbles into the molten metal during the pouring process. The crack characteristics of the oxide layers were studied using a field emission scanning electron microscope. The results show that various stresses initiated from turbulence flow in the molten metal promote the deformation of the oxide layer, particularly at the initial stages of oxidation. Different coefficients of thermal expansion of the oxide layers and the metals can also result in deformation/cracking the oxide layers. Simultaneous aspiration of the molten metal and solidification phenomenon within the casting process may lead to various morphological changes, e.g. folded-, wrinkled- and cracked-oxide layers. In addition, a splitting and reforming phenomenon of multiple oxide layers is observed, called as strips of ‘ruffled tape’. An illustrative mechanism is suggested and discussed quantitatively for the formation of such phenomena. It is assumed that the unique appearance of these strips depends on the formation time and complex stress gradients on the oxide layers.

Effect of residual stress on the spallation of the thermally-grown oxide formed on NiCoCrAlY coating

In this study, the effect of residual stress in the NiCoCrAlY coating on the oxidation and spallation behavior of the thermally grown oxide (TGO) has been investigated. The surfaces of the NiCoCrAlY coatings were polished to a 0.1 μm finish before oxidation. The oxidation performed at 1150 °C shows that coating with compressive stress induced by grit blasting exhibits a higher oxidation rate, higher surface roughness and lower spallation resistance compared with coating with tensile stress. This is attributed to the significant interfacial rumpling induced by the relaxation of the compressive stress in the coating at the initial oxidation stage. The interfacial rumpling leads to the formation of the fast-growing spinel oxides and interfacial cracks, which are detrimental to the interfacial adherence.

Synthesis, structure, and properties of the high Nb–TiAl alloy after Ni coatings by plasma surface alloying technique

Ni coatings were prepared on the high Nb–TiAl alloy by the plasma surface alloying technique. The results found that surface morphology and microstructure exhibited a strong dependence on the deposited temperature. The elements diffusion during the metalizing stage leaded to the high hardness value and adhesion force between the Ni coating and substrate. The corrosion resistance of the Ni-coated specimens depended on the fabrication temperature related to the deposition and diffusion layers. For the oxidation, the weight gain rate was involved in the chemical reaction in the initial oxidation stage. The inter-diffusion among elements such as the nickel, titanium, and aluminum resulted in the high adhesion force after the oxidation, improving the bonding force between the Ni coating and substrate.

Crack propagation of Si nanofilm accompanied by initial stage of wet oxidation

Motivated by our recent research presenting the effect of dry oxidation on crack propagation of Si nanofilm, water environment was taken into account in this work to clarify how crack propagates accompanied by initial wet oxidation which is influential for nanoscale devices in aqueous environment. By Reactive force field molecular dynamics (ReaxFF MD) simulation, the fracture strength during crack propagation by simultaneous oxidation with water was calculated. The atomic configurations were tracked as well. It demonstrated that the initial wet oxidation improved fracture toughness and retarded crack propagation to some extent, although less obvious than that of dry oxidation. The initial stage oxidation of crack tip and the oxide structures have been analyzed, showing that hydrogen dissociated from water was attractive to bond with Si under tension. The number of absorbed oxygen into Si by water oxidant was lower than that with dry one at same temperature, accordingly forming less Si-O bonds which released the tension at crack tip to enhance the fracture strength in a minor way. The influence of initial wet oxidation on crack propagation investigated here could be helpful on deeply understanding the mechanical property of nanoscale devices under aqueous environment fabrication and application.

Influence of NiAl2O4 spinel formation on the oxidation behavior of the Ni50Al alloy at 1273 K in air

The influence of NiAl2O4 spinel formation on the oxidation behavior of the Ni50Al alloy at 1273 K in air was investigated. Pulsed electrodeposition was used to introduce a nano layer of Ni prior to the oxidation test of the Ni50Al alloy. Excluding the initial stage of oxidation, the oxidation mass gains of the coated sample significantly decreased, and the oxide scale growth rate was slower than that on the bare Ni50Al alloy sample. Peaks from the metastable Al2O3 phases were detected for the Ni-coated Ni50Al sample in X-ray powder diffraction (XRD) analysis even after 100 h oxidation. Multi-layered oxide scale of facet-NiO, fine-NiAl2O4 and dense Al2O3 has developed on the oxidized coated sample, in the order from outside to inside the oxide scale. NiO was consumed in the formation of denser NiAl2O4 spinel that hindered the oxidation kinetics of the Ni50Al alloy. The results confirmed that the slower growth rate of oxide on the coated sample might be attributed to the blocking effect of the NiAl2O4 spinel even though metastable Al2O3 phases still grow.

Insight into the oxidation mechanism of the intermetallic compound NbAl3: A first-principles study

The microscopic mechanisms of the early stage oxidation of the NbAl3(100) and NbAl3(110) surfaces were studied by the first-principles method and thermodynamics calculations. First, the relationship between the relative surface energy of those two surfaces and Al chemical potential was investigated. Then, the binding energy per oxygen atom on those two surfaces at various adsorption sites was calculated and the preferential sites were determined. Finally, the surface phase diagrams of the NbAl3(100) and NbAl3(110) systems with different defects and different oxygen coverages were built. The results show that the defect-free NbAl3(100) is the most stable surface before oxygen adsorption, while the NbAl3(110) with Al antisite defects is the favorable configurations. Moreover, the adsorption of oxygen on those two surfaces is in favor of the surface segregation of Al and then leads to the formation of a complete Al surface layer at the initial stage of oxidation. Additionally, according to the density of states analysis, the significant orbital hybridizations between the O and Al in the ranges from −10 to 0 eV would lead to the formation of strong AlO bonding. Consequently, the oxygen atoms prefer to be adsorbed at the sites of Al-rich region.

Investigation on the initial oxidation behavior of TiAl alloy

In this paper, the initial oxidation behaviors of α2, γ and β phase in the newly developed TNM alloy (Ti-44Al-4.0Nb-1.5Mo-0.1B-0.01Y) were investigated. The oxidation tests were performed at 800 °C for 3 min, 5 min, 20 min, 1 h, 2 h and 4 h respectively. The alloy has a good oxidation resistance below 800 °C. The antioxidant capacity of the three phases decreases as follow order: γ > α2 > β. Within the lamellar colony, the values of atom ratio (Ti/Al) in α2 lath and γ lath remain within the range of 1.11-1.16, indicating that atom diffusion occurs at the initial stage of oxidation. The microstructure observations also confirmed the segregation of Y element at grain boundaries of primary coarse α grains and segregation of Nb element in massive γ phases. The peeling off of the oxide from β phase and oxygen diffusion at grain boundaries are detrimental to the oxidation resistance of the alloy.

Tailored Oxidation Barrier Coatings for Mo-Hf-B and Mo-Zr-B Alloys.

The cyclic oxidation response of Mo-14Hf-23B and Mo-14.8Zr-26B (compositions in at. %) was investigated in air at 800 °C, which is a critical temperature for Mo-based alloys because of the pesting phenomenon. Rapid oxidation was observed for the unprotected samples, and an oxidation protection coating was developed based on a preceramic polymer with silicon and boron as particulate fillers. Cyclic oxidation tests of the coated samples showed excellent oxidation protection: no Mo, Hf or Zr oxides were found after testing and a small mass gain in the initial stage of oxidation indicated the formation of a glassy protection layer on the alloys surfaces after exposure to air at 800 °C.

XPS Study of the Process of HgCdTe Oxidation in a Glow Discharge Oxygen Plasma

Initial stages of HgCdTe oxidation in a glow discharge plasma in O2 atmosphere are first studied using the XPS method. The chemical composition of the growing native oxide layer is investigated and the oxidation kinetics is revealed. It is experimentally established that the mechanism of HgCdTe oxidation changes as the oxide thickness reaches 2-3 nm due to the change of the limiting stage of the chemical reaction. The composition of the formed oxide is varies with depth and is characterized by low mercury content. It is suggested that the diffusion of oxygen to the oxide–semiconductor interface and its predominant interaction with tellurium are the main mechanism of the native MCT oxide growth, so that the oxide region bordering the substrate is ∼10% oxygen depleted. The obtained results are discussed and compared with previously reported data on MCT oxidation in RF plasma and in liquid electrolytes.

Investigation of the initial stage of iron oxidation in the air. Part 1. Temperature range 250-400 ºС

Iron oxidation in the case of formation of thin oxide films on the surface of iron plates as a result of their oxidation in air by a logarithmic law has been studied. Experimental studies of kinetics and thermodynamics of the oxidation of chemically pure iron in a horizontal tubular quartz glass furnacehave been performed. The samples were heated by a bifilar winding at both ends of the tube. The temperature was measured by the calibrated chromel-alumel thermocouples. The time of occurrence of colors was averaged over three plate, on each of which at least 4-5 measurements were taken. The experimental determination of the thickness of the oxide film depending on time is based on the method of occurrence of variability colors on the surface of the oxidized iron plate. With an increase in the thickness of the oxide filmits color as a result of light's interference will consistently vary according to the series: yellow, orange, red, purple, violet and blue.As a result of the study, it was found that oxidation at 253 ° C significantlydiffers from the results obtained at temperatures of 300-375 ° C. The oxidation at 253 ° C is more complex, since two types of oxides are formed. It has been assumedthat the rate of oxidation depends on the index of the faces of the crystal lattice. Dependences of the thickness of the film (by color) on the time of its formation in a heated furnace at a constant temperaturehave been obtained. It has been shown that in the temperature range 250 - 400 oС the law of the change in the thickness of the film is logarithmic. In this case, the oxidation constant in this law changes with the temperature according to the Arrhenius law. For the first time, an oxidation constant for pure iron was evaluated at the initial oxidation stage. Its dependence on the temperature was obtained and the corresponding values of the activation energy were found.

Investigation of the initial stage of iron oxidation in the air. Part 2. Temperature range 400-625 ºС

Iron oxidation in the case of formation of thin oxide films on the surface of iron plates as a result of their oxidation in air by a parabolic law at temperatures above(400-550 ºС) and below (575 – 600 ºС) the Shadronpoint (575 ºС)has been studied.Studies are performed on the experimental plant described in the first part of the article, published in this issue of the journal.The experimental determination of the thickness of the oxide film depending on time is based on the method of occurrence of "variability" colors on the surface of the oxidized iron plate. With an increase in the thickness of the oxide film its color as a result of light's interference will consistently vary according to the series: yellow, orange, red, purple, violet and blue. This corresponds to the range of the oxide film's thickness from 46 to 72 nm.In the temperature range of 400-550 °C, a stable oxide Fe3O4 (magnetite) appears on the iron’s surface. It was shown that the dependences lnh of lnτ for all investigated temperatures are linear and have tangents of inclination angles equal to 0.5. The obtainedvalue of the activation energyis constant and equal to E = 43.0 kJ/mol.The oxygen diffusion coefficient D = 1.73 · 10–13 m2/s was obtained according to the oxidation model of a metal plate, which is based on the determinant role of oxygen diffusion through an oxide film.In the temperature range of 550 - 625 ºC, the change in the rate of the constant of the interaction between iron and oxygen from the air is due to the stable formation ofawustiteFeO. All of the oxidation isotherms can be described by the linear dependence in the coordinates lnh and lnτ. It was shown that the index of degree in the oxidation law at the temperatures below the Shadronpoint is equal to 2 (the parabolic law), and above the Shadron point it increases with increasing temperature of the process in accordance with the obtained dependence n = 2 + 0.008 (T-823).

High-temperature oxidation response of Mo–Si–B composites with TiO2W/SiCW addition

Abstract In this study, TiO2W addition improved the oxidation resistance of the Mo–Si–B composite at 1300 °C. The TiO2 partially dissolved in SiO2 modified the network structure of the SiO2 glass and improved its fluidity at the initial oxidation stage. This favored to a continuous scale cover on the surface of the Mo–Si–B composite rapidly. The residual TiO2W promoted the formation of a passivated multilayer borosilicate scale at current temperature, which could impede the MoO3 volatilisation and O diffusion at the stable oxidation stage. The SiCW addition, compared to the TiO2W, especially could ensure the Mo–Si–B–SiC composite withstand a higher temperature such as 1400 °C. Its oxidation and the more intermetallics in the composite could increase the number of active sites of the SiO2 glass, thereby supplying the borosilicate scale with a relatively sufficient Si element. Thus, the transient oxidation stage was minimised and the initial mass loss was reduced, which indicated a continuous borosilicate scale had formed quickly at the initial stage. Finally, the improved viscosity of the borosilicate due to a lower B/Si ratio, could obviously decreased the oxygen diffusion and enabled the formation of a protective borosilicate layer at or above 1400 °C.

Microstructure and its high temperature oxidation behavior of W-Cr alloys prepared by spark plasma sintering

W-10 wt.% Cr (W-10Cr) and W-20 wt.% Cr (W-20Cr) alloys were fabricated through mechanical alloying and spark plasma sintering technology. The microstructure of W-Cr alloys was characterized by XRD, SEM, TEM. The W-20Cr alloy significantly increased the microhardness from 333.5 HV of pure W to 961.3 HV. Oxidation experiments at 800 °C and 1000 °C confirmed that W-20Cr alloy shows better oxidation resistance. A suitable amount of Cr content is favorable for the formation of the oxide scale Cr2O3 and the quality assurance at the initial stage of oxidation, which is able to slow down the oxidation rate. The quality of the oxide scale CrWO4 is better than that of Cr2WO6, indicating that the formation of the oxide scale CrWO4 is beneficial to weaken the further oxidation of the W-20Cr alloy.

Model for Thermal Oxidation of Silicon

Nanometer-thick silicon oxide films are needed for miniaturization and increase in the working rate of electronic devices. Interpretation of the initial stages of silicon oxidation is necessary for fabrication of such structures. A theoretical model of the thermal oxidation of thin silicon monolayers that takes into account an increase in the stress in the transition (oxide–substrate) layer due to oxygen accumulation therein is proposed.

Role of M23C6 carbide on the corrosion characteristics of modified 9Cr-1Mo steel in N2-O2-CO2-SO2 atmosphere at 650 °C

In this study, the oxidation and sulfidation characteristics of modified 9Cr1Mo steels according to Cr-rich M23C6 distributed in grain boundaries in the N2-O2-CO2-SO2 atmosphere at 650 °C were analyzed. The oxidation kinetic was obeyed by the parabolic law. The oxide layer presented a three-layer structure consisting of hematite, magnetite, and FeCr spinel from the outside. In the initial oxidation stage, Cr-rich M23C6 exposed to the surface acted as nuclei of Cr-rich oxide. However, it is thought to hardly effect on the growth of the outer oxide layer. The Cr-rich M23C6 distributed in grain boundaries preferentially formed a Cr2O3 layer at the oxide/matrix interface, and internal oxidation characteristics were shown to be different depending on the presence or absence of SO2 in the atmosphere.