Materials and Corrosion-werkstoffe Und Korrosion最新文献

Cover:

SEM-EDS analysis of edge section of tube # 9 (Kanthal ® APMT). A type of grain boundary related attack is observed in this specimen. The bright spots correspond to RE elements.

More detailed information can be found in: Maria Asuncion Valiente Bermejo, Alice Moya Núñez, Rikard Norling, Metal loss and corrosion attack of FeCrAl overlay welds on evaporator tube shields of a waste-fi red power plant, Materials and Corrosion 2024, 75, 950.

The corrosion behavior of 304 stainless steel in wet CO₂ gas with or without CO and CO plus 400 ppmv SO₂ was investigated in this study. Corrosion kinetics was studied by thermogravimetric analysis at 710°C for 100 h under three gas conditions. After isothermal exposure, the corroded coupons were characterized in detail by X-ray diffraction, scanning electron microscopy, an electron probe microanalyzer, and transmission electron microscopy. CO addition to wet CO₂ resulted in lower oxygen partial pressure and lower oxide growth kinetics. It also suppressed iron-rich oxide nodule formation, as compared to the wet CO₂ gas environment. A Cr-depletion zone was observed underneath the oxide scale in the substrate, but no obvious internal carburization was observed in all three gas environments. A thin, protective oxide scale consisting of an outer layer of a Cr-rich spinel and an inner Cr-rich chromia layer was developed in CO-containing gas conditions, with or without SO₂. The effect of CO on oxidation and scale formation is discussed in comparison with that in wet CO₂ conditions.

The high-temperature corrosion behavior of Ni–xFe–5Cr alloys (x = 0, 10, or 30 wt.%) was investigated in air containing alkali salt vapor at 570°C to clarify the effect of Fe on the corrosion resistance. Fe addition to Ni–5Cr was found to improve the corrosion resistance under the present conditions. In the case of Ni–5Cr, NiCl₂ was formed beneath the NiO scale during the initial stage of corrosion, and it grew thicker over time and then evaporated. The formation and evaporation of NiCl₂ resulted in a porous scale that underwent spallation resulting in mass loss. In the Fe-containing alloys, (Fe, Ni, Cr)₃O₄ spinel and Fe₃O₄ decreased the partial pressures of oxygen and chlorine and thus prevented the generation of NiO and NiCl₂, leading to superior corrosion resistance compared with Ni–5Cr.

The bonding strength and LBE corrosion resistance of the Fe15Cr11Al2Si, Fe15Cr11Al0.5Y, and Fe15Cr11Al2Si0.5Y coatings heat-treated at 500–650°C for 500 h were investigated. The results showed that the as-deposited Fe15Cr11Al0.5Y coating has the strongest bonding strength with the F/M steel cladding tube compared with the Fe15Cr11Al2Si and Fe15Cr11Al2Si0.5Y coatings. Heat treatment deteriorates the bonding performance of the coatings, and obvious enrichment of Cr and Al elements appeared. The consumed Al element inside the heat-treated coatings promotes the formation of Fe₃O₄ on the surface of the coatings after the corrosion test. The Y element can inhibit the enrichment of elements and the formation of Fe₃O₄. The bonding strength of the heat-treated coatings can be improved after the corrosion test. The underlying mechanism of the evolution of microstructure and properties of the coatings after heat treatment and corrosion test was discussed.

This work focuses on archaeological analogues as a way of obtaining long-term data for assessing the lifetime of a spent nuclear fuel canister. An analysis of the environment around the excavated artefacts is presented, followed by geochemical modelling of the likely corrosion products and subsequent comparison with real phases in the corrosion layer estimated by X-ray diffraction. A total of 16 archaeological sites with fine clay soils and the potential for long-term flooding were evaluated. Although the soil pore solution contained high levels of silicates, no such phases with iron in the corrosion products were confirmed. Carbonate corrosion products, typical of bentonite environments, were also not observed. Although oxygen access is very limited in the environments of all sites, even low concentrations shifted the equilibrium of corrosion products formed in favour of (hydroxy)oxides.

To meet the application requirements of electronic connectors, a trivalent chromium process (TCP) conversion coating was prepared on the Zn–Ni alloy plating of 2024 aluminium alloy. The composition of the TCP solution was as follows: 45 g/L Cr(NO₃)₃, 14 g/L CoCl₂, 1.3 g/L NiCl₂, 10 g/L citric acid, 10 g/L succinic acid and 1 g/L sodium dodecyl sulphate. The properties of TCP were characterised by a range of techniques, including macroscopic observations, scanning electron microscope, energy-dispersive X-ray spectrometer, three-dimensional (3D) morphometry, electrochemical impedance spectroscopy, polarisation curves and conductivity tests. The TCP prepared in this experiment exhibits a uniform black colour and bright appearance, predominantly composed of Zn, Ni, O, Cr and Co. The TCP enhances the impedance of Zn–Ni alloys, reduces the corrosion current to 1.99 × 10⁻⁵A/cm² and maintains a flatter surface 3D morphology and less surface roughness following electrochemical testing. It has better corrosion resistance. Following the preparation of the TCP on a suitably sized shell sample, the shell resistance was 1.2 mVDC with good electrical conductivity, which meets the requirements for electrical connector applications.

Novel sacrificial zinc-rich organic coatings, with varying additions of aluminium, were prepared and tested for anticorrosion performance. Electrochemical measurements (potential vs. time and electrochemical impedance spectroscopy) were carried out to investigate cathodic protection and barrier performance while neutral salt spray and immersion experiments tested long-term performance. Analytical scanning electron microscopy and X-ray diffraction were used to characterize coatings before and after testing. Formulations containing aluminium significantly outperformed the standard 100% zinc-rich coating with the greatest improvement occurring at 10%–15% aluminium by volume in the dry film. This improvement was caused by the dispersal of aluminium between zinc particles, which improved packing and enabled greater efficiency in zinc consumption resulting in extended galvanic protection times for steel substrates. The expected zinc corrosion product (basic zinc chloride, simonkolleite) was present within the coating as well as a Zn–Al layered doubled hydroxide. The latter's presence demonstrates that dissolution of aluminium contributed to the longevity of the galvanic action. The new Zn–Al formulations are extremely promising alternatives to standard zinc-rich epoxy coatings, significantly reducing zinc loading and increasing the sacrificial lifetime.

The alloying contents with the same Zn/Ca atomic ratio of 0.13 on the corrosion behavior of Mg-Zn-Ca (ZX) alloys were investigated. The second phases in ZX10, ZX20, ZX30, and ZX51 alloys were identical with a majority of Mg₂Ca and very few Ca₂Mg₆Zn₃ and their distribution changed from isolated to continuous state in ZX30 and ZX51. ZX10 had the lowest corrosion rate of 0.55 mm/year after 168 h immersion in simulated body fluid solution due to the smallest number of sites of galvanic corrosion. The corrosion rate of ZX30 alloy was the highest (0.72 mm/year), while though ZX51 alloy had the most Mg₂Ca, its corrosion rate was reduced to 0.69 mm/year, resulting from the small size and thin Mg₂Ca. In situ microstructure observation demonstrated the high fraction Mg₂Ca phase and continuous Mg₂Ca with bulky size were the main reason for the fast corrosion rate.

The isothermal oxidation behavior of the Cu-11.35Al-3.2Ni-3.5Mn (wt.%) shape-memory alloy (SMA) in the temperature range of 500–900°C in oxygen was studied using the thermogravimetric (TG) method. TG curve showed that the alloy has parabolic isothermal oxidation characteristics. The effect of oxidation on the surface morphology and chemical composition of the Cu–Al–Ni–Mn alloy was determined by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The oxidation rate of SMA increases up to 700°C, remains stable at 800°C, and increases again up to 900°C. The XPS analysis identified that the corrosion products mainly contained MnO₂, MnO/Mn₂O₃, and Al₂O₃.