Study on corrosion resistance of palladium films on 316L stainless steel by electroplating and electroless plating

Palladium films with good adhesive strength were deposited on 316L stainless steel by electroless plating and electroplating. Scanning electronic microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, weight loss tests and electrochemical methods were used to study the properties of the films. The electroless plated palladium film mainly consisted of palladium, phosphorus and nitrogen, and the electroplated palladium film was almost pure palladium. XPS analysis indicated that palladium was present in the films as metal state. The palladium plated stainless steel samples prepared by both methods showed excellent corrosion resistance in strong reductive corrosion mediums. In boiling 20% dilute sulfuric acid solution, the corrosion rates of the palladium plated 316L stainless steel samples were four orders of magnitude lower than that of the original 316L stainless steel samples. In the solution with 0.01 M NaCl, the palladium plated samples also showed better corrosion resistance. In comparison, the electroplated samples showed slightly better corrosion resistance than electroless plated samples, which may be attributed to less impurities and thereby higher corrosion potential for the former.     

The semiconducting properties of passive films formed on AISI 316 L and AISI 321 stainless steels: A test of the point defect model (PDM)

The semiconductor properties of passive films formed on AISI 316L in 1 M H₂SO₄ in three temperatures and AISI 321 in 0.5 M H₂SO₄ were studied by employing Mott–Schottky analysis in conjunction with the point defect model (PDM). Based on the Mott–Schottky analysis in conjunction with PDM, it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. Also, the results indicated that donor densities increased with temperature. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficients of the donors for two stainless steels are calculated.     

Nanostructure and local properties of oxide layers grown on stainless steel in simulated pressurized water reactor environment

The morphology and local electrical resistance of duplex oxide films formed on 316L stainless steel at 325 °C in simulated primary coolant of pressurized water reactor have been investigated at the nanometre scale with Conductive Atomic Force Microscopy. The electrical resistance varies over ∼1 order of magnitude for most oxide grains and over 2–3 orders of magnitude locally at grains and grain boundaries. This is rationalized in terms of local variation of the composition and thus resistivity of the mixed Fe(II)–Cr(III) barrier inner layer of the oxide films with grain boundaries of the outer layer possibly promoting Cr(III) enrichment.     

不锈钢表面Cr-Pd合金电沉积及镀层在强还原性介质中的耐蚀性

通过选择络合剂、缓冲剂及采用方波脉冲电流和优化电镀工艺, 在酸性镀液中实现了Cr-Pd共镀, 并在不锈钢表面制备出均匀致密且与基体结合良好的Cr-Pd合金镀层. 通过改变镀液中铬盐和钯盐的相对含量, 可以大范围改变镀层成分. Cr-Pd合金镀层可显著提高不锈钢在高温还原性腐蚀介质中的耐蚀性, 在沸腾的20%(质量分数)H₂SO₄溶液中, Cr-Pd合金镀层使316L不锈钢的腐蚀速率降低了4个数量级以上. 镀层中的Cr和Pd对致钝具有协同促进作用, 当镀层中含有2.5%Pd(质量分数)时即具有明显的促进钝化效果, 含33.3%Pd镀层对不锈钢的保护效果与纯Pd镀层相当.     

316L不锈钢上电刷镀钯膜的组成与耐蚀性(英文)

利用电刷镀工艺在316L不锈钢上制备了结合力良好的钯膜。使用扫描电子显微镜、X射线能谱、X射线光电子能谱(XPS)、质量损失实验和电化学测试研究了膜层的性能。结果表明,电刷镀钯膜主要是由钯元素构成的;XPS分析表明,膜层中的钯为金属态。电刷镀钯后的不锈钢试样在沸腾的20%硫酸溶液和含0.005mol/L溴离子的甲酸和乙酸混合溶液中均显示了非常好的耐蚀性能。镀钯试样的腐蚀速率比不锈钢试样的下降了2个数量级。     

A comparative H2S corrosion study of 304L and 316L stainless steels in acidic media

H₂S corrosion of 304L and 316L in oxygen-free Na₂SO₄ + Na₂S solution at pH 3 and temperature of 60 °C were investigated by EIS, potentiodynamic polarisation, multi-component Pourbaix diagrams and microstructure characterization. At similar conditions, lower corrosion rate was observed on 316L, attributed to its denser (1.5 times) and smoother (6%) surface layer and confirmed by SEM micrograph. During polarisation, H₂S increases significantly the critical current density on 304L and passivation current density, i_p, on 316L. Higher i_p on 316L was associated to simultaneous FeS₂–MoS₂ preservation, confirmed by XRD examination. H₂S could have an inhibiting effect on 304L in passivity region.     

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25–60 °C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i_G values at 60 °C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H₃PO₄ media from a corrosion point of view for all the temperatures analysed.     

Interfacial morphology and corrosion resistance of Fe–B cast steel containing chromium and nickel in liquid zinc

The interfacial morphology and corrosion resistance of low carbon Fe–B cast steels in zinc bath at 520 °C were investigated. The results show Fe–B cast steel containing high Cr and Ni exhibits the best corrosion resistance to liquid zinc. The corrosion layers are composed of Γ-Fe₃Zn₁₀, δ-FeZn₁₀, ξ-FeZn₁₃ and η-Zn. The corrosion behaviour of Fe–B cast steels includes the following processes: the preferential leach and dissolution of Cr and Ni, the formation of Fe–Zn compounds controlled by zinc atom diffusion, and the spalling of borides without the supporting role of α-(Fe, Cr) matrix corroded by liquid zinc.     

Dissolution mechanism of 316L in lead–bismuth eutectic at 500 °C

In the frame of the Accelerator Driven System (ADS) cooled by liquid lead–bismuth eutectic (LBE), the austenitic stainless steel 316L is considered as a possible structural material for the reactor. However, the corrosion of 316L in this liquid alloy environment can be substantial, especially when a dissolution process occurs. In order to understand the dissolution process and to obtain a modelling of the 316L corrosion rate by LBE, an experimental dissolution kinetics of 316L is carried out in stagnant LBE at 500 °C up to 3000 h. A Ni preferential dissolution of the 316L is observed, leading to the formation of a ferritic layer at the 316L surface. A discussion on the various steps occurring in dissolution process leads to the conclusion that only the Ni dissolution reaction rate can control the 316L dissolution kinetics. The dissolution reaction rate constant, k_d, calculated from this study experimental points is equal to 4.2 × 10⁻¹¹ mol cm⁻² s⁻¹.     

The electroplated palladium-copper alloy film on 316L stainless steel and its corrosion resistance in mixture of acetic and formic acids

Palladium-copper alloy films (Cu 2.93-5.66 at.%) were deposited on 316L stainless steel by electroplating. The films showed good adhesive strength and increased surface micro-hardness. In boiling mixture of 90% acetic acid + 10% formic acid + 400 ppm Br⁻ under stirring (625 r/min), the Pd-Cu films showed better corrosion resistance than Pd film. The Pd-5.66%Cu films showed the lowest corrosion rate almost three orders of magnitude lower than that of 316L matrix. The increased corrosion resistance of Pd-Cu films was attributed to the improved passivity, better barrier effect, increased surface hardness and the effect of Cu to resist pitting.     

Fabrication of continuous mesoporous organic–inorganic nanocomposite films for corrosion protection of stainless steel in PEM fuel cells

The organic–inorganic composite film was deposited on the 304 stainless steel as bipolar plate material for proton exchange membrane fuel cells by spin-coating method. As shown by XRD, N₂ adsorption–desorption and TEM, the composite films exhibit ordered mesoporous structures. The corrosion tests in 0.5 M H₂SO₄ system displayed that, compared with 304SS, the composite films made corrosion potential shifted to positive direction by 250–1000 mV (SCE) and corrosion current decreased by 1–3 orders of magnitude. Wherein, the C-50–60% composite film showed the optimal protective performance, its corresponding potentiostatic polarization process was extremely stable in the simulated fuel cells environment.     

Metal release and formation of surface precipitate at stainless steel grade 316 and Hanks solution interface - Inflammatory response and surface finishing effects

The influence of surface finishing (polishing and passivation) on the release of Cr, Fe, Ni from the stainless steel 316 implant materials to Hanks solution with or without H₂O₂ (simulating a body inflammatory response) was investigated. The surfaces were characterized by means of SEM EDXS, XPS and Kelvin Probe measurements before and after exposure to the synthetic body fluids. The total metal ions release rates are more than 10 times higher in the presence of H₂O₂, independently of the surface finishing. In the absence of H₂O₂, formation of a surface layer consisting mainly of Ca₃(PO₄)₂ was observed, most likely it was responsible for the observed decrease of the release rates.     

Corrosion and passivation mechanism of chromium diboride coatings on stainless steel

The corrosion resistance of fully crystalline CrB₂ coatings magnetron sputtered onto AISI 316L stainless steel was tested in acidic solutions. CrB₂ coatings showed excellent corrosion protection, but suffered a breakdown when an anodic potential of greater than about +1 V (SHE) was applied to the surface in a 1 M HCl electrolyte. The coating failure at high potentials is attributed to transpassive dissolution of the coating at volume defects, enabling the electrolyte to reach the underlying 316L substrate, resulting in its rapid corrosion and subsequent fracturing of the coating. Electrochemical data and potential-pH (Pourbaix) diagrams, constructed from thermodynamic data, indicate that the corrosion resistance of CrB₂ is due to the formation of a Cr(III) oxide passive film in the absence of activation corrosion.     

Passivation of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys in 1 M H2SO4 and 1 M NaOH solutions

The corrosion mechanisms of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al–Cr–Fe surface is exhibited from 1 M H₂SO₄ to 1 M NaOH solutions, which was confirmed by ICP-OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy-hydroxide film. Although Al–Cu–Fe–Cr showed passivation during potentiodynamic polarization, heavy active corrosion at OCP was revealed by ICP-OES. For the Al–Cu–Fe–Cr alloy, the 10% content of Cr is insufficient to maintain a protective “chemically stable” Cr oxide/hydroxide.     

The mechanism of oxide film formation on Alloy 690 in oxygenated high temperature water

Oxide films formed on Alloy 690 exposed to 290 °C water containing 3 ppm O₂ were investigated. It was found that Cr rich oxides form initially through solid-state reactions. Ni–Fe spinels gradually develop on surface layer by precipitation with increasing immersion time. Initially formed Cr rich oxides react with outwards diffusing Ni and Fe to form small spinel particles which then vanish gradually. An inner layer develops from oxide/matrix interface through inward diffusion of oxidant. Cr is preferentially oxidized and tends to dissolve into solution. The resultant inner layer consists of predominant NiO which cannot serve as a protective barrier layer.     

Oxidation behaviour of Ti–Al–C films composed mainly of a Ti2AlC phase

This paper addresses the oxidation behaviour of Ti–Al–C films composed mainly of a Ti₂AlC phase. The films exhibited rather low oxidation rates at 600 and 700 °C, with an oxygen-rich zone or a thin oxide layer appearing on the film surfaces. Much faster oxidation rates were observed at 800 and 900 °C. The Ti₂AlC phase was quickly consumed by oxidation. From the film surface to the inner zone, TiO₂-rich layer, Al₂O₃-rich layer, and TiO₂ + Al₂O₃ mixed layer was observed, respectively. The oxidation mechanism of the Ti–Al–C film is discussed based on the experimental results.     

XPS analysis of manganese in stainless steel passive films on 1.4432 and the lean duplex 1.4162

Passive films were compared on two stainless steels: the recent lean duplex EN 1.4162 and EN 1.4432 (316L). For alloys with significant amount of manganese and nickel, the Mn 2p_3/2 peak will overlap with the Ni-LMM. To resolve this overlap, Ni 2p_3/2 to Ni-LMM intensity ratios were recorded on 1.4432, compensated for overlayer thickness, and then used to fix the Ni-LMM intensities in the Mn 2p spectra on the duplex material. Manganese was found in oxidation states II and V/VI; its film content was not dependent on the bulk composition.     

Oxidation of 316 stainless steel in supercritical water

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.     

XPS analysis of the passive film formed on austenitic stainless steel coated with conductive polymer

Improvement of the passivation behavior of Type 304 austenitic stainless steel (SS) by coating with conductive polymers (CPs), like polyaniline (PANI) and poly(o-phenylenediamine) (PoPD), followed by exposure in an acid solution has been demonstrated. The passive films formed on SSs (after peeling off the polymer layer) are compared with those formed during anodic polarization under the same exposure condition. The passive films beneath the CPs are thicker and less hydrated than those formed on uncoated stainless steel. The polymer layer enhances the enrichment of chromium and nickel in the entire passive oxide, forming a more protective film than that formed during anodic polarization. The elemental distribution within the passive film is different in the two modes of passivation. The type of the polymer influences on the composition of the passive film. The best passivation is obtained by PoPD, with the passive film resulting in significant resistance of the SS to pitting corrosion in the 3% NaCl solution. The oxide film of this steel is characterized, in its inner and outer layers, by the highest ratio of Cr(OH)₃/Cr₂O₃ and the lowest content of iron species.     

High temperature carburization behaviour of Mn–Cr–O spinel oxides with varied concentrations of manganese

Mn–Cr–O spinel often formed on austenitic alloys is an oxide phase that could be protective against high temperature carbonaceous attack. In this research, various Mn–Cr–O samples were tested in carburization environments with controlled oxygen partial pressures. The stoichiometric MnCr₂O₄ shows better resistance to carburization and coke formation than the Mn-rich Mn–Cr–O and the Cr-rich Mn–Cr–O samples because of its highest thermodynamic stability as compared with MnO and Cr₂O₃. (Mn,Cr)₇C₃ formed after carburization is catalytic to coke formation, and was found instable at higher levels of H₂O/oxygen and may form volatile phases in the presence of H₂O, leading to a continuous reduction in sample weight.