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1.
The corrosion behavior of an austenitic stainless steel (UNS S30400) has been characterized in a 10,000 h test conducted in hydrogenated, ammoniated water at 260 °C. The corrosion kinetics were observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 1.16 mg dm−2 h−1/2. X-ray photoelectron spectroscopy, in combination with argon ion milling and target factor analysis, was applied to provide an independent estimate of the rate constant that agreed with the gravimetric result. Based on the distribution of the three oxidized alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, it was found that: (a) corrosion occurs in a non-selective manner, and (b) the corrosion film consists of two spinel oxide layers--a ferrite-based outer layer (Ni0.2Fe0.8)(Fe0.95Cr0.05)2O4 on top of a chromite-based inner layer (Ni0.2Fe0.8)(Cr0.7Fe0.3)2O4. These compositions agree closely with the solvi phases created by immiscibility in the Fe3O4-FeCr2O4 binary, implying that immiscibility plays an important role in the phase separation process. 相似文献
2.
The corrosion behavior of Alloy 600 (UNS N06600) is investigated in hydrogenated water at 260 °C. The corrosion kinetics are observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 0.055 mg dm−2 h−1/2. A combination of scanning and transmission electron microscopy, supplemented by energy dispersive X-ray spectroscopy and grazing incidence X-ray diffraction, are used to identify the oxide phases present (i.e., spinel) and to characterize their morphology and thickness. Two oxide layers are identified: an outer, ferrite-rich layer and an inner, chromite-rich layer. X-ray photoelectron spectroscopy with argon ion milling and target factor analysis is applied to determine spinel stoichiometry; the inner layer is (Ni0.7Fe0.3)(Fe0.3Cr0.7)2O4, while the outer layer is (Ni0.9Fe0.1)(Fe0.85Cr0.15)2O4. The distribution of trivalent iron and chromium cations in the inner and outer oxide layers is essentially the same as that found previously in stainless steel corrosion oxides, thus confirming their invariant nature as solvi in the immiscible spinel binary Fe3O4-FeCr2O4 (or NiFe2O4-NiCr2O4). Although oxidation occurred non-selectively, excess quantities of nickel(II) oxide were not found. Instead, the excess nickel was accounted for as recrystallized nickel metal in the inner layer, as additional nickel ferrite in the outer layer, formed by pickup of iron ions from the aqueous phase, and by selective release to the aqueous phase. 相似文献
3.
Zinc treatment effects on corrosion behavior of Alloy 600 in high temperature, hydrogenated water 总被引:2,自引:0,他引:2
Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 °C were found to reduce the corrosion rate of Alloy 600 (UNS N06600) by about 40% relative to a non-zinc baseline test [S.E. Ziemniak, M. Hanson, Corros. Sci., in press, doi:10.1016/j.corsci.2005.01.006]. Characterizations of the corrosion oxide layer via SEM/TEM and grazing incidence X-ray diffraction confirmed the presence of a chromite-rich oxide phase and recrystallized nickel. The oxide crystals had an approximate surface density of 3500 μm−2 and an average size of 11 ± 5 nm. Application of X-ray photoelectron spectroscopy with argon ion milling, followed by target factor analyses, permitted speciated composition versus depth profiles to be obtained. Numerical integration of the profiles revealed that: (1) alloy oxidation occurred non-selectively and (2) zinc(II) ions were incorporated into the chromite-rich spinel: (Zn0.55Ni0.3Fe0.15)(Fe0.25Cr0.75)2O4. Spinel stoichiometry places the trivalent ion composition in the single phase oxide region, consistent with the absence of the usual outer, ferrite-rich solvus layer. By comparison with compositions of the chromite-rich spinel obtained in the non-zinc baseline test, it is hypothesized that zinc(II) ion incorporation was controlled by the equilibrium for
0.55Zn2+(aq)+(Ni0.7Fe0.3)(Fe0.3Cr0.7)2O4(s)?0.40Ni2+(aq)+0.15Fe2+(aq)+(Zn0.55Ni0.3Fe0.15)(Fe0.3Cr0.7)2O4(s) 相似文献
4.
Zinc treatment effects on corrosion behavior of 304 stainless steel in high temperature, hydrogenated water 总被引:1,自引:0,他引:1
Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 °C were found to lower the corrosion rate of austenitic stainless steel (UNS S30400) by about a factor of five, relative to a non-zinc baseline test [S.E. Ziemniak, M. Hanson, Corros. Sci. 44 (2002) 2209] after 10,000 h. Characterizations of the corrosion oxide layer via grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy in combination with argon ion milling and target factor analysis, revealed that miscibility gaps in two spinel binaries—Fe(Fe1−mCrm)2O4 and (Fe1−nZnn)Fe2O4—play a significant role in determining the composition and structure of the corrosion layer(s). Although compositions of the inner and outer corrosion oxide layers represent solvus phases in the Fe3O4-FeCr2O4 binary, zinc(II) ion incorporation into both phases leads to further phase separation in the outer (ferrite) layer. Recrystallization of the low zinc content ferrite solvus phase is seen to produce an extremely fine grain size (∼20 nm), which is comparable in size to grains in the inner layer and which is known to impart resistance to corrosion. Zinc(II) ion incorporation into the inner layer creates additional corrosion oxide film stabilization by further reducing the unit cell dimension via the substitution reaction
0.2Zn2+(aq)+Fe(Fe0.35Cr0.65)2O4(s)?0.2Fe2+(aq)+(Zn0.2Fe0.8)(Fe0.35Cr0.65)2O4(s) 相似文献
5.
Fabrice GoutierStéphane Valette Etienne LabordePierre Lefort 《Journal of Alloys and Compounds》2011,509(7):3246-3251
From the early beginning of the oxidation of 304L stainless steel in carbon dioxide at 1273 K (1 min, for a weight gain of 0.02 mg cm−2), the surface of the alloy was entirely covered by oxides: magnetite Fe3O4, chromia Cr2O3 and traces of wüstite Fe1−xO. Later on, for weight gains approaching 1 mg cm−2, magnetite remained at the outer interface, with traces of hematite (Fe2O3), above a thick layer of wüstite Fe1−xO. Magnetite and wüstite may favour adhesion of thermal plasma protective coatings such as alumina. 相似文献
6.
A. G. Tyurin 《Protection of Metals》2000,36(1):61-68
The pH-potential diagram of the Ni−H2O system is refined, and similar diagrams of the Fe−Ni- and X18H10 alloy-H2O systems are constructed for a temperature of 25°C. It is shown that nickel may enter into a mixed, magnetite-base spinel
(Fe1-x Nix)Fe2O4 (in the case of iron-nickel alloys) or into an iron-chromite base spinel (Fe1-x Nix)(Cr2-y Fey)O4 (iron-chromium-nickel alloys), thus participating in the passivation of alloys. 相似文献
7.
The corrosion rate of electropolished 304 stainless steel surfaces (UNS S30400) is found to be lower by more than a factor of three relative to that determined previously for machined surfaces in mildly alkaline, hydrogenated water at 260 °C. This favorable result is attributed to significant changes in nanocrystallinity of the corrosion oxide layer caused by the removal of surface microstrain, which had been imparted during the machining process. In the absence of microstrain, a low-porosity, protective, corrosion layer forms that is composed of extremely small and uniformly-sized spinel oxide crystals. Application of scanning electron microscopy (FEG-SEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) in conjunction with ion milling and target factor analyses, found the corrosion layer to consist of micrometer-size crystals of a ferrite-based spinel oxide (non-protective) over-laying nanometer-size crystals of a chromite-based spinel oxide (protective). Composition of both phases is unchanged from that previously observed on corroded, machined surfaces and is representative of solvus phases in the immiscible Fe(Fe1−nCrn)2O4 spinel binary. The smaller size (10 vs. 26 nm) and greater surface density (∼10,000 vs. 835 μm−2) of the chromite-based crystals relative to those formed on machined (i.e., cold-worked) surfaces, however, is consistent with the absence of preferred high energy nucleation sites on strain-free surfaces. Therefore, electropolishing, which removes surface microstrain induced by cold-working, represents a preferred reference surface condition. 相似文献
8.
The corrosion behavior of mild steel has been investigated during the wet and dry cyclic transitions containing Cr3+ ion added as sulfate in order to gain a better understanding of the influence of Cr on the atmospheric corrosion of steels. The corrosion rate during drying is greatly suppressed by the existence of Cr3+ ion in the electrolyte covered with the surface. Lower corrosion rates are observed during drying even if the surface have been polarized to negative potentials below −200 mVSHE during the wet corrosion conditions in which the surface-covered electrolyte contains Cr3+ ion. This corrosion behavior is identical to the case of Cr-containing steel for the wet and dry cyclic transitions without the addition of Cr3+ ion. The composition of rust layer after the wet and dry cyclic transitions is composed of α-FeOOH, γ-FeOOH and Fe3−δO4 for both cases of non-Cr3+ and Cr3+-containing condition, and no significant difference in the mass fraction of the above rust substances between two conditions is observed by means of Mössbauer spectroscopy. The only difference in the rust layer is that the rust formed under the wet and dry cyclic transitions containing Cr3+ ion contains a certain amount of Cr near the steel/rust interface. Those results suggest that the role of Cr during the wet and dry cyclic transitions is the inhibition of the rust reduction and the formation of Fe2+-state intermediate by the existence of Cr in the rust layer. This can lead to the inhibition of the oxygen reduction during drying. 相似文献
9.
D.E. Hajas M. to Baben B. HallstedtR. Iskandar J. MayerJ.M. Schneider 《Surface & coatings technology》2011,206(4):591-598
The isothermal oxidation behavior of Cr2AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410 °C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr2AlC films form a dense continuous oxide scale consisting of α-Al2O3 on Cr carbides. The oxidation rates determined by thermo gravimetric analysis (TGA) were parabolic, indicating that diffusion through the scale is the rate limiting mechanism. The activation energy for oxidation was determined to be 348 kJ mol− 1 and the parabolic rate constant at 1230 °C was 7.1 × 10− 10 kg2 m− 4 s− 1. Hence, the oxidation behavior is comparable to NiAl in the temperature range and time intervals investigated. With increasing oxidation time voids form at the interface between oxide and Cr carbides and the amount of Cr7C3 increases at the expense of Cr3C2. Based on our thermodynamic calculations the oxygen partial pressure below the oxide scale increases as Al is depleted and Cr carbides oxidize, resulting in CO gas- and Cr2O3-formation. The formation of gas may together with the depletion of Al and Cr lead to the significant void formation observed in the Cr carbide interlayer. Observation of both Cr carbide precipitates and the formation of (Al,Cr)2O3 solid solution support this notion. For comparison bulk Cr2AlC was oxidized. It is argued that the absence of pores in oxidized bulk Cr2AlC is due to the considerably larger amount of Al available. 相似文献
10.
The nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni0.8Zn0.2Fe2O4 thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm−1 which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni0.8Zn0.2Fe2O4 thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm−2 and 19 F g−1, respectively. 相似文献
11.
The oxidation of an Fe-12% Ni alloy has been studied at 700–1000°C using thermogravimetric, metallographic, and electron probe microanalysis techniques. At all temperatures parabolic kinetics were observed and the activation energy for the process was 48±4 kcal mole–1. At 700°C Fe3O4 and Fe2O3 were present in the external scale and scaling was accompanied by a progressive Ni enrichment of the underlying alloy. When the Ni-enriched zone contained 50–60% Ni, this metal entered the spinel phase, eventually leading to the formation of NixFe3–xO4 where x had a value of 0.24 close to the alloy and <0.01 close to the Fe2O3 phase boundary. At higher temperatures (900–1000°C) Ni entered the spinel phase very early in the oxidation process. There was a buildup in Ni concentration in the NixFe3–xO4 phase to x values of 0.4 and at 900°C only this corresponded to a transition to a lower parabolic rate of oxidation. The internal oxide phase was identified as Ni0.7Fe2.3O4. The mechanism of oxidation of the alloy is discussed in the light of present knowledge concerning the Fe-Ni-O system. 相似文献
12.
The oxidation behaviour of single crystal PWA 1483 at 950 °C was investigated by means of XRD, SEM and EDS. The parabolic oxidation behaviour, as defined by mass gain and the respective oxide layer thicknesses, is characterized by a parabolic rate constant of about 4 × 10−6 mg2/(cm4 × s) and the formation of a multi-layered oxide scale. An outer scale contains a Ti-bearing thin film composed of TiO2 and NiTiO3 but mostly Cr in Cr2O3 and (Ni/Co)Cr2O4 besides NiTaO4. This outer scale is connected to a discontinuous layer of Al2O3 and an area of γ′-depletion within the base material. 相似文献
13.
The oxidation behavior and the oxide microstructure on Fe-3 wt. % Cr alloy were investigated at 800°C in dry air at atmospheric pressure. Two distinct oxidation rate laws were observed: initial parabolic oxidation was followed by nonparabolic growth. The change in the oxidation kinetics was caused by microchemical and microstructural developments in the oxide scale. Several layers developed in the oxide scale, consisting of an innermost layer of (Fe,Cr)3O4 spinel, an intermediate layer of (Fe,Cr)2O3 sesquioxide, and two outer layers of Fe2O3 hematite, each with different morphologies. Wustite (Fe1–xO) and distorted cubic oxide (-(Fe,Cr)2O3) were observed during the iniital parabolic oxidation only. 相似文献
14.
The oxide scales of 316 stainless steel (316 SS) have been examined after exposure to supercritical water (SCW) with 2.0% H2O2 for up to 250 h. The exposed samples were analyzed using weight measurement, scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). It was found that mass gain of all samples increased with increasing temperature and exposure time. Higher temperature SCW resulted in rougher surfaces and thicker oxide scales. Duplex layer oxide structures with Ni-enrichment at the oxide/metal interface developed on all samples exposed to SCW, which were identified as Fe2O3/Fe3O4 + spinel/Cr2O3/Ni-enrichment/316 SS from the outer to inner layer. The possible oxidation mechanisms are also discussed. 相似文献
15.
Pure Fe, Cr and Fe-Cr binary alloys were corroded in O2 containing 298 ppm KCl vapour at 750 °C. The corrosion kinetics were determined, and the microstructure and the composition of oxide scales were examined. During corrosion process, KCl vapour reacted with the formed oxide scales and generated Cl2 gas. As Cl2 gas introduced the active oxidation, a multilayer oxide scales consisted of an outmost Fe2O3 layer and an inner Cr2O3 layer formed on the Fe-Cr alloys with lower Cr concentration. In the case of Fe-60Cr or Fe-80Cr alloys, monolayer Cr2O3 formed as the healing oxidation process. However, multilayer Cr2O3 formed on pure Cr. 相似文献
16.
The addition of Ni leads to the formation of protective rust layer on steel and subsequently high corrosion resistance of steel in Cl−-containing environment. α-FeOOH, β-FeOOH, γ-FeOOH and Fe3O4 are formed mainly on steels exposed to Cl−-containing atmosphere. It is expected that systematic investigation of the effect of Ni(II) on the formation process of each oxide in solution should lead to elucidation of the role of Ni in the formation of anticorrosive oxide layer. This study reports the oxidation behavior of NixFe1−x(OH)2 in Cl−-containing solution at two different pH regions (condition I under which solution pH is allowed to decrease and condition II under which solution pH is maintained at 8) where γ-FeOOH and Fe3O4 are predominantly formed, respectively, upon the oxidation of Fe(OH)2. In the presence of Ni(II) in the starting solution, the formation of Ni(II) doped β-FeOOH with very low crystalline was facilitated and the formation of γ-FeOOH was suppressed with increasing Ni(II) content and with increasing oxidation rate of Fe(II). Ni(II) was found to have Fe3O4-suppressing effect under condition II. 相似文献
17.
The oxidation behavior in air of Fe-19.6Cr-15.1Mn was studied from 700 to 1000°C. Pseudoparabolic kinetics were followed, giving an activation energy of 80 kcal/mole. The scale structure varied with temperature, although spinel formation occurred at all temperatures. At both 700 and 800°C, a thin outer layer of -Mn2O3 formed. The inner layer at 700°C was (Fe,Cr,Mn)3O4, but at 800°C there was an intermediate layer of Fe2O3 and an inner layer of Cr2O3 + (Fe, Cr,Mn)3O4. Oxidation at 900°C produced an outer layer of Fe3O4 and an inner layer of Cr2O3+(Fe,Cr,Mn)3O4. Oxidation at 1000°C caused some internal oxidation of chromium. In addition, a thin layer of Cr2O3 formed in some regions with an intermediate layer of Fe3O4 and an outer layer of (Fe,Mn)3O4. A comparison of rates for Fe3O4 formation during oxidation of FeO as well as for the oxidation of various stainless steels, which form spinels, gave good agreement and strongly suggests that spinel growth was rate controlling. The oxidation rate of this alloy (high-Cr) was compared with that of an alloy previously studied, Fe-9.5Cr-17.8Mn (low-Cr) and was less by about a factor of 12 at 1000°C and by about a factor of 100 at 800°C. The marked differences can be ascribed to the destabilization of wustite by the higher chromium alloy. No wustite formation occurred in the high-Cr alloy, whereas, extensive wustite formed in the low-Cr alloy. Scale structures are explained by the use of calculated stability diagrams. The mechanism of oxidation is discussed and compared with that of the low-Cr alloy. 相似文献
18.
A.A. BirajdarSagar E. Shirsath R.H. KadamS.M. Patange K.S. LoharD.R. Mane A.R. Shitre 《Journal of Alloys and Compounds》2012,512(1):316-322
A series of ferrite samples with the chemical formula Ni0.7Zn0.3CrxFe2−xO4 (x = 0.0-0.5) were prepared by a sol-gel auto-combustion method and annealed at 600 °C for 4 h. The resultant powders were investigated by various techniques, including X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and permeability studies. The prepared samples have a cubic spinel structure with no impurity phase. As the Cr3+ content x increases, bulk density and crystallite size decrease, whereas porosity increases. The saturation magnetization decreases linearly from 58.31 to 42.90 emu/g with increasing Cr3+ content. However, coercivity increases with increasing Cr3+ substitution. The magnetic moments calculated from Neel's molecular-field model are in agreement in the experiment results. The initial permeability (μi) decreases with increasing Cr3+ substitution. The decrease in initial permeability (μi) is attributed to decrease in magnetization on addition of Cr3+. The real part of the permeability decreases gradually with increasing frequency in accordance with Snoek's law. The Curie temperature decreases linearly with increasing Cr3+ content. 相似文献
19.
The effects of molybdate and dichromate anions on pit propagation of mild steel in bicarbonate solution containing Cl− were investigated by electrochemical measurements. MoO42− ion suppressed both pit nucleation and propagation. Cr2O72− ion suppressed pit nucleation, but stimulated pit growth. The different effects of the two anions on pit propagation were explained by the opposite effects on pH value within pits. The pH value in molybdate-containing solution increased as a result of polymerization of MoO42−, while in dichromate-containing solution, pH value decreased due to hydrolysis of Fe3+ and Cr3+ which are the products of oxido-reducing reactions between Cr2O72− and Fe2+ ions. 相似文献
20.
The corrosion behavior of eight low and high alloy steels was investigated under simulating the conditions at the cathode of a molten carbonate fuel cell at 650°C. Different Li-containing iron oxides (LiFeO2 and LiFe5O8) were formed in contact with the eutectic (Li, K)-carbonate melt depending on the Cr-content of the steel. These oxides show low solubility in the melt and protect the metallic material against further corrosive attack last growing scales of Fe3O4 and LiFe5O8 were observed on the low alloy ferritic steel 10 CrMo 9 10. Higher alloy steels form LiFeO2 in contact with the melt and mixed Fe-Cr-spinels underneath. Steels with Cr-contents over 20 wt.% Cr form a mixed LiCr1-xFexO2 and LiCrO2 layer in contact with the metal. Marker experiments on the commercial steel 1.4404 (X2 CrNiMo 17 13 2) show that the outer LiFeO2 layer grows mainly by outward diffusion of iron ions (Fe3+), whereas the inner (Fe,Ni)Cr2O4 spinel layer grows inward. After 500 hours, LiFe5O8 was formed between the spinel and the LiFeO2 layer, but it had disappeared after several thousand hours of exposure as it was fully transformed to LiFeO2. Co-containing LiFeO2 was found after 500 hours on the high Co-containing steel 1.4971 (X12 CrCoNi 21 20), but is not stable after several thousand hours exposure. Co diffuses outward to form a protective LiCoO2 layer of a few microns in thickness. Protective Cr2O3 layers were not observed on steels with high Cr-content (≥ 25 wt.% Cr) due to peroxide ions in the melt, which cause oxidation Cr2O3 and flux to chromate, which is highly soluble in the melt. Further quantitative investigations on total corrosion considering the chromate formation have shown that high alloy steels with high amounts of Cr form mainly K2CrO4. 相似文献