Scale Growth Mechanism Research Articles

The Corrosion Behavior of Stainless Steel 316L in Novel Quaternary Eutectic Molten Salt System

AbstractIn this article, the corrosion behavior of stainless steel 316L in a low melting point novel LiNO3-NaNO3-KNO3-NaNO2 eutectic salt mixture was investigated at 695 K which is considered as thermally stable temperature using electrochemical and isothermal dipping methods. The passive region in the anodic polarization curve indicates the formation of protective oxides layer on the sample surface. After isothermal dipping corrosion experiments, samples were analyzed using SEM and XRD to determine the topography, corrosion products, and scale growth mechanisms. It was found that after long-term immersion in the LiNO3-NaNO3-KNO3-NaNO2 molten salt, LiFeO2, LiFe5O8, Fe3O4, (Fe, Cr)3O4 and (Fe, Ni)3O4 oxides were formed. Among these corrosion products, LiFeO2 formed a dense and protective layer which prevents the SS 316L from severe corrosion.

Development of growth and thermal stresses in NiO scale on nanocrystalline Ni without and with dispersion of CeO2 nanoparticles

The development of growth and thermal stresses in the NiO scale on a nanocrystalline (NC) Ni without and with the dispersion of CeO2 nanoparticles during isothermal oxidation in air at 800°C and subsequent cooling has been analyzed by using a two-sided oxidation deflection testing. The CeO2 dispersion causes the NC Ni to form a NiO scale which accommodates higher growth stresses during oxidation but lower thermal stresses during cooling. The result is interpreted by characterization of the effect of CeO2 dispersion on the growth mechanism and microstructure of the NiO scale on the NC Ni.

Assessment of a Mechanical Model Associated with Oxide Scale Growth on T91 Steel at 550 °C Under Wet Atmosphere

The Deflection Test in Monofacial Oxidation (DTMO) was used to assess the parameters of a phenomenological model aimed to represent the mechanical behavior of the martensitic T91 steel during oxidation at 550 °C under wet atmosphere. The constitutive equations of the mechanical model were determined from the knowledge of the growth mechanism of the oxide scale. Some model parameters were found in the literature and complementary data were obtained by the comparison between experimental DTMO curve and simulated results.

Effect of doping aluminum and yttrium on high-temperature oxidation behavior of Ni-11Fe-10Cu alloy

Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant (kp) of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX) analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.

High-temperature oxidation behavior of Ni-11Fe-10Cu alloy: Growth of a protective oxide scale

The oxidation of Ni-11Fe-10Cu alloys in air at high temperature was investigated. A parabolic kinetics was found at 750°C and a linear kinetics was shown at 850 and 950°C. The oxide scale formed at 750°C is compact and coherent possessing triplex oxide layers, i.e., a CuO external layer, a NiFe2O4 middle layer, and a NiO inner layer. A thin copper-rich layer sits between the scale and alloy substrate, functioning as a barrier for iron and nickel diffusing outwards from the alloy substrate and oxygen ion diffusing inwards. The growth mechanism of the multi-layer oxide scale was discussed.

Evaluation of Pb–17Li compatibility of ODS Fe-12Cr-5Al alloys

The Dual Coolant Lead Lithium (DCLL: eutectic Pb–17Li and He) blanket concept requires improved Pb–17Li compatibility with ferritic steels in order to demonstrate acceptable performance in fusion reactors. As an initial step, static Pb-17at.%Li (Pb-17Li) capsule experiments were conducted on new oxide dispersion strengthened (ODS) FeCrAl alloys ((1) Y2O3 (125Y), (2) Y2O3+ZrO2 (125YZ), (3) Y2O3+HfO2 (125YH), and (4) Y2O3+TiO2 (125YT)) produced at ORNL via mechanical alloying (MA). Tests were conducted in static Pb–17Li for 1000 h at 700 °C. Alloys showed promising compatibility with Pb–17Li with small mass change after testing for 125YZ, 125YH and 125YT, while the 125Y alloy experienced the highest mass loss associated with some oxide spallation and subsequent alloy dissolution. X-ray diffraction methods identified the surface reaction product as LiAlO2 on all four alloys. A small decrease (∼1 at.%) in Al content beneath the oxide scale was observed in all four ODS alloys, which extended 60 μm beneath the oxide/metal interface. This indicates improvements in alloy dissolution by decreasing the amount of Al loss from the alloy. Scales formed on 125YZ, 125YH and 125YT were examined via scanning transmission electron microscopy (S/TEM) and revealed incorporation of Zr-, Hf-, and Ti-rich precipitates within the LiAlO2 product, respectively. This indicates an inward scale growth mechanism. Future work in flowing Pb–17Li is needed to further evaluate the effectiveness of this strategy in a test blanket module.

Effect of yttria(Y2O3) coating for high temperature oxidation resistance of 9Cr-1Mo steel

This paper investigates the effect of yttria (Y2O3) coating on high temperature oxidation behaviour of low alloy 9 Cr–1Mo steel. The superficial coating is Y2O3 was prepared for experimental investigation. The isothermal corrosion study of uncoated and coated specimens was carried out in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterized in SEM, EDS and XRD. The results clearly indicate that Y2O3 coated specimen improves the high temperature oxidation resistance than uncoated specimens. The improvement of oxidation resistance in presence of Y2O3 coating can be attributed to the changed mechanism of scale growth from outer cation migration to inner anion migration and enhancement of scale adhesion with the substrate. Further, enhancement of scale adhesion with the substrate in case of Y2O3 coating also improves the oxidation resistance. The detail mechanism of the oxidation of Y2O3 coated and uncoated specimen is further discussed in this paper.

Oxide phases and residual stresses in scales formed at early stages of oxidation of β‐NiAl at 1473 K and the effect of implanted yttrium

Oxide phases formed at early oxidation stages on unmodified and yttrium‐implanted β‐NiAl intermetallic compound were studied with the aid of photoluminescence spectroscopy in scales developed at 1473 K for oxidation periods of up to 4 h. Two‐stage‐oxidation exposures with 18O2‐tracer were applied. The PLS method was also used to assess the residual stresses in α‐Al2O3 scale at consecutive stages of its development. It was found that scale formation occurs in a very local way, related to inhomogeneous distribution of Cr in substrate: sometimes distances as short as 10–15 μm were sufficient to observe entirely different phases in the scale. In general, implanted yttrium was found to retard the formation of a stable and protective layer of α‐Al2O3. Oxidation for 4 h was necessary for no transient aluminum oxides (mostly θ and/or δ) to be detected, while on non‐implanted material they were not found after only 26 min exposure. Only compressive stresses were found in α‐alumina scales. They were rather high, reaching even 5 GPa. However, their dependence on the regions in the scale and the scale evolution stage was observed. The results indicate that patches frequently observed in scales on β‐NiAl are regions where the phase transformation of transient aluminas to the α phase occurs preferentially. Ridges, which fill the transformation‐related cracks, consisted only of α‐Al2O3. Combination of these results with those obtained using SIMS distribution analyses of oxygen isotopes as well as with SEM/EDX, enabled very precise conclusions to be inferred concerning the scale growth mechanism. In particular, the local nature of the scale development can be described in more detail.

Effect of Plasma Sprayed Yttria Stabilized Zirconia(YSZ) Coating for High Temperature Oxidation Resistance of Low Alloy Steel

This paper investigates the influence of YSZ coating on high temperature oxidation behaviour of low alloy 2.25 Cr-1 Mo steel. The YSZ powder was plasma sprayed coated over 2.25 Cr-1 Mo steel substrate. The isothermal oxidation test of the coated and uncoated specimen was carried in air oxidation environment at 900°C. The weight changes of the specimen were measured at different intervals. The oxidation rate and reaction kinetics were studied and the post corroded scales were characterized in SEM, EDS and XRD. The results clearly indicate that YSZ coated specimen significantly improves the oxidation resistance as compared to uncoated specimen. The improvement of oxidation resistance in presence of YSZ coating can be attributed to the changed mechanism of scale growth from outer cation migration to inner anion migration. The detail mechanism of the oxidation behaviour in presence of YSZ coated and uncoated specimen is discussed in this paper.

Computational Study of Fluid Flow Inside a Concentric Reducer

Scale growth in pipe fittings is a major problem for an alumina refinery. Investigation into the scale growth mechanism at an alumina refinery found almost 60% more scale growth in concentric reducer when compared with the connecting straight pipe sections for similar flow conditions. The current study is an attempt to characterise the fluid flow inside a concentric reducer, especially streamwise and crossflow fluctuations using computational fluid dynamics methodology. The present study shows that streamwise component of instantaneous velocity fluctuation decreased and cross component of the instantaneous velocity fluctuation increased inside the concentric reducer. Present Computational results have shown good agreement with the experimental data.

Turbulent boundary layer flow with a step change from smooth to rough surface

A direct numerical simulation (DNS) dataset of a turbulent boundary layer (TBL) with a step change from a smooth to a rough surface is analyzed to examine the characteristics of a spatially developing flow. The roughness elements are periodically arranged two-dimensional (2-D) spanwise rods, with the first rod placed 80θin downstream from the inlet, where θin denotes the inlet momentum thickness. Based on an accurate estimation of relevant parameters, clear evidence for mean flow universality is provided when scaled properly, even for the present roughness configuration, which is believed to have one of the strongest impacts on the flow. Compared to previous studies, it is shown that overshooting behavior is present in the first- and second-order statistics and is locally created either within the cavity or at the leading edge of the roughness depending on the type of statistics and the wall-normal measurement location. Inspection of spatial two-point correlations of the streamwise velocity fluctuations shows a continuous increase of spanwise length scales of structures over the rough wall after the step change at a greater growth rate than that over smooth wall TBL flow. This is expected because spanwise energy spectrum shows presence of much energetic wider structures over the rough wall. Full images of the DNS data are presented to describe not only predominance of hairpin vortices but also a possible spanwise scale growth mechanism via merging over the rough wall.

Ceria (CeO2) based coating for high temperature corrosion protection of 9Cr-1 Mo steel

Ceria (CeO2) based high temperature coating was developed over 9Cr-1 Mo steel substrate. The coating is produced by plasma spray coating method by using robotic arm. Isothermal corrosion study of the CeO2 coated and uncoated specimen was conducted at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterized in SEM, EDS and XRD. The results clearly indicate that ceria (CeO2) coated specimen improves the high temperature oxidation resistance than uncoated specimens. The kinetic behaviour of both coated and uncoated specimen follows approximate parabolic growth rate which further indicates that the corrosion is diffusion controlled growth. The post corroded scale of the coated specimen shows fine grained oxide scale with no scale cracking and detachment. The improvement of oxidation resistance in presence of CeO2 coating can be attributed to the formation of fine grained oxide on the scale, changed mechanism of scale growth from outer cation migration to inner anion migration and enhancement of scale adhesion with the substrate. The detail mechanism of the oxidation of CeO2 coated specimen and uncoated specimen is further discussed in this paper.

Effect of thermal treatment on the corrosion resistance of Type 316L stainless steel exposed in supercritical water

There are still unknown aspects about the growth mechanism of oxide scales formed on candidate stainless steel fuel cladding materials during exposure in supercritical water (SCW) under the conditions relevant to the Canadian supercritical water-cooled reactor (SCWR). The tendency for intermetallic precipitates to form within the grains and on grain boundaries during prolonged exposure at high temperatures represents an unknown factor to corrosion resistance, since they tend to bind alloyed Cr. The objective of this study was to better understand the extent to which intermetallic precipitates affects the mode and extent of corrosion in SCW. Type 316L stainless steel, used as a model Fe–Cr–Ni–Mo alloy, was exposed to 25MPa SCW at 550°C for 500h in a static autoclave for this purpose. Mechanically-abraded samples were tested in the mill-annealed (MA) and a thermally-treated (TT) condition. The thermal treatment was conducted at 815°C for 1000h to precipitate the carbide (M23C6), chi (χ), laves (η) and sigma (σ) phases. It was found that although relatively large intermetallic precipitates formed at the scale/alloy interface locally affected the oxide scale formation, their discontinuous formation did not affect the short-term overall apparent corrosion resistance.

CeO2 based coating for high temperature oxidation protection

This paper investigates the influence of ceria (CeO2) coating on high temperature oxidation behaviour of 2·25Cr–1Mo steel. The superficial coating of CeO2 powder was prepared for experimental investigation. The isothermal corrosion study of uncoated and coated specimens was carried out in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterised in scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. The results clearly indicate that CeO2 coated specimen improves the high temperature oxidation resistance than uncoated specimen. The improvement of oxidation resistance in presence of CeO2 coating can be attributed to the formation of fine grained oxide on the scale, changed mechanism of scale growth from outer cation migration to inner anion migration and enhancement of scale adhesion with the substrate. The detail mechanism of the oxidation of CeO2 coated and uncoated specimen was further discussed in this paper.

Plasma sprayed Cr3C2–Ni–Cr coating for oxidation protection of 2·25Cr–1Mo steel

This paper investigated the influence of Cr3C2–Ni–Cr coating on high temperature oxidation behaviour of 2·25Cr–1Mo steel. The coating of Cr3C2–NiCr was made by plasma spray coating method. The isothermal corrosion test was carried in air oxidation environment at 973 K for 72 h and the weight change of the specimen during corrosion was measured at different interval. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterised in SEM, EDS and XRD. The results clearly indicated that Cr3C2–NiCr coated specimen significantly improved the oxidation resistance. The improvement of oxidation resistance in presence of coating could be attributed to the formation of protective Cr2O3 layer and changed mechanism of scale growth from outer cation migration to inner anion migration. The detail mechanism of the oxidation behaviour of Cr3C2–NiCr coated and uncoated specimen was discussed in this paper.

Oxidation behavior of Zr-containing Ti2AlNb-based alloy at 800 °C

The oxidation behavior of Ti–22Al–(27–x)Nb–xZr (x=0, 1, 6) alloys at 800 °C for exposure time up to 100 h was examined. It is shown that oxidation rate of experimental alloys obeys the parabolic kinetics. Ti–22Al–26Nb–1Zr alloy demonstrates more excellent oxidation resistance than the other two alloys. The main oxidation products are TiO2, Al2O3 and AlNbO4 phases for all these alloys. For the Ti–22Al–26Nb–1Zr alloy, Zr addition can modify the growth mechanism of oxide scale, which can effectively hinder the diffusion of oxygen. Whereas, reaction of Zr with oxygen leads to the formation of ZrO2 precipitates for the Ti–22Al–21Nb–6Zr alloy, which promotes the oxygen ingress into the substrate. Meanwhile, oxidation affected zones, including internal-oxidation layer and oxygen-enriched zone, are present beneath the outmost oxide scale. The difference in these zones is derived from the phase constitution in the starting Ti–22Al–(27–x)Nb–xZr (x=0, 1, 6) alloys.

High temperature oxidation behaviour of yttria ( Y2O3) coated low alloy steel

This paper investigates the effect of yttria (Y2O3) coating on high temperature oxidation behaviour of low alloy 2·25Cr–1Mo steel. The superficial coating is Y2O3, which was prepared for experimental investigation. The isothermal corrosion study of uncoated and coated specimens was carried out in air oxidation environment at 973 K for 8 h. The corrosion rate and reaction kinetics were studied and the post-corroded scales were characterised by SEM, Energy-dispersive X-ray spectroscopy and X-ray diffraction. The results clearly indicate that Y2O3 coated specimen improves the high temperature oxidation resistance than uncoated specimen. The improvement of oxidation resistance in presence of Y2O3 coating can be attributed to the modification of grain structure of the scale, changed mechanism of scale growth and enhancement of scale adhesion with the substrate. The detailed mechanism of the oxidation of Y2O3 coated and uncoated specimen is further discussed in this paper.

Mechanisms of Graphene Growth on Metal Surfaces: Theoretical Perspectives

Graphene is an important material with unique electronic properties. Aiming to obtain high quality samples at a large scale, graphene growth on metal surfaces has been widely studied. An important topic in these studies is the atomic scale growth mechanism, which is the precondition for a rational optimization of growth conditions. Theoretical studies have provided useful insights for understanding graphene growth mechanisms, which are reviewed in this article. On the mostly used Cu substrate, graphene growth is found to be more complicated than a simple adsorption-dehydrogenation-growth model. Growth on Ni surface is precipitation dominated. On surfaces with a large lattice mismatch to graphene, epitaxial geometry determin a robust nonlinear growth behavior. Further progresses in understanding graphene growth mechanisms is expected with intense theoretical studies using advanced simulation techniques, which will make a guided design of growth protocols practical.

A comparative study of pure nickel and the Ni–CeO2 nanocrystalline coatings: microstructural evolution, oxidation behavior, and thermodynamic stability

In the present work, a novel method of ultrasonic-assisted double-pulsed electro deposition was innovatively used to prepare nanocrystalline Ni coatings from a modified Watts–Nickel electrolyte without and with the addition of CeO2 nanoparticles. The dynamic oxidation kinetics of pure nickel and the Ni–CeO2 coatings was conducted in air at 650 and 850 °C. To clarify the beneficial effects of CeO2 addition on surface morphologies, phase composition and microstructural evolution, the as-received coatings were investigated using various analytical techniques of FE-SEM, XRD, XPS, and HR-TEM observations. In addition, both EDX maps and TG–DSC scans were also carried out for further evaluating the effective bonding effect that generated from the Ce-rich precipitated phase on the inhibition of coarsening growth and textural transformation. Meanwhile, an analytical model for predicting the growth mechanism of oxide scales was successfully validated for the comparison of their different oxidation behaviors. Experimental results illustrated that interfacial boundaries existed in nanocrystalline Ni coatings were favorable for embedding CeO2 nanoparticles to make dispersion strengthening. The existence of well-distributed CeO2 phase in the coating was beneficial to achieve finer-grained size of Ni grains for improvements of structural densification. It exhibited super oxidation resistance of the Ni–CeO2 coatings as compared to that of pure nickel, which was mainly attributed to the Ce-rich oxide scales that acted as a passive layer to fully cover on the coating surface. Furthermore, the precipitation of the Ce-rich phase along high-angle grain boundaries would make great contributions to promote the bonding interactions with high-energy defective regions for effectively completing those cracking boundaries, thereby achieving denser microstructure attached with excellent thermodynamic stability of the Ni–CeO2 coatings.

Gas Corrosion of Chromium-Manganese Steel in Atmospheres with Low Oxygen Partial Pressure

Studies were conducted on the kinetics and mechanism of oxidation of chromium-manganese steel under partial oxygen pressure pO2from 10-11to 10-2Pa at a temperature of 1173 K. The low oxygen partial pressure was produced in a gas mixture of CO-CO2and helium containing 0.2 ppm of oxygen. The kinetics of oxidation was examined by thermogravimetry using a thermobalance made by Setaram Company. Scale growth mechanism was determined with the use of markers. The oxidation products were analyzed by scanning electron microscopy (SEM, EDS). It was found that at low partial pressure of oxygen, MnO oxide was forming on the steel surface. From an analysis of the curves of the steel weight growth per unit surface in function of time it followed that the oxidation assumed a parabolic course. A relationship has been determined between the coefficient of self-diffusion of manganese in MnO and the oxygen partial pressure.