Oxidation of magnesium alloys at elevated temperatures in air: A review

Tan, Qiyang; Atrens, Andrej; Mo, Ning; Zhang, Mingxing

doi:10.1016/j.corsci.2016.06.018

Cited by 151 publications

(75 citation statements)

References 163 publications

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“…(See reviews by Gusieva et al [24], Tan et al [25], Atrens et al [26] and Taheri et al [27].) There is a greater emphasis on corrosion in aqueous conditions, rather than in the relatively dry atmospheres in this study.…”

Section: Discussionmentioning

confidence: 97%

Corrosion of the alloys Magnox AL80, Magnox ZR55 and pure magnesium in air containing water vapour

et al. 2016

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms CORROSION OF THE ALLOYS MAGNOX AL80, MAGNOX ZR55 AND PURE MAGNESIUM IN AIR ABSTRACTUnderstanding the corrosion susceptibility of Magnox alloys during short-and long-term storage in moist air is important. Corrosion of Magnox AL80, Magnox ZR55 and magnesium has been studied in air containing water partial pressures between 200 vppm and ~80000 vppm, at temperatures of 46 °C to 96 °C.Specimens were exposed to air, with and without CO2, and argon gas. Metal consumption rates were measured and corrosion products characterised, using scanning electron and optical microscopy, energy dispersive x-ray microanalysis, x-ray diffraction and secondary ion mass spectrometry. Results show the importance of CO2 gas for suppressing breakaway corrosion in moist air. INTRODUCTIONOf the fleet of UK gas-cooled Magnox-type nuclear power stations that were designed, constructed and commissioned during the 1950s and 1960s, the last ceased generating electricity at the end of 2015 [1]. All the other reactors, most of which achieved a 40-year operating life, are now in various stages of decommissioning. The fuel elements in these first generation gas-cooled, graphite-moderated nuclear reactors consist of metallic uranium rods within sealed cans of Magnox AL80 alloy. This alloy is magnesium-based, nominally containing 0.80 wt% aluminium together with 50 ppm by weight beryllium.This alloy normally undergoes negligible corrosion in the dry carbon dioxide (CO2) gas used to cool the reactors at power. During reactor operation, the fuel cans achieve temperatures within the range 250 °C to 450 °C [2]. There are, however, occasions where Magnox alloy fuel elements are exposed to air. These include outages for maintenance, sometimes quite prolonged, and, most significantly, during defueling following the final shutdown of the reactor. In these circumstances, the temperature of the Magnox alloy cans is, at most, about 100 °C and the water vapour partial pressure is that of the ambient air outside the reactor, about 2000 Pa to 3000 Pa.To underwrite the safe storage of fuel in the shutdown condition, it is necessary to have an understanding of the extent and rate of corrosion of the Magnox alloy cans in moist air. In particular, it is essential to know whether the resulting corrosion product is protective. If it is, then the extent of corrosion can be neglected; if it is not, and the corrosion obeys a linear rate law; a significant quantity of corrosion product can be formed.During decommissioning, if the corrosion leads to penetration of a Magnox alloy can then the irradiated fuel will be exposed, with consequential safety implications. There are no data available that consider the corrosion of Magnox AL80 under these shutdown conditions. Friskney [3] has published data on the reaction in dry steam at a pressure of ~10 5 ...

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Section: Discussionmentioning

confidence: 97%

Corrosion of the alloys Magnox AL80, Magnox ZR55 and pure magnesium in air containing water vapour

et al. 2016

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“…Figure 2a. Additionally, the existence of MgO is attributed to the preferential oxidation of Mg atoms [22,23]. It could be figured out that as the NH 4 Cl content increases from 1 to 3 g gradually, the peaks of the Mg 17 Al 12 phase in the XRD pattern became smaller and smaller, which means a continuously reduced quantity of the intermetallic layer.…”

Section: Ammonium Chloride Could Keep the Surface Of The Magnesium Almentioning

confidence: 97%

“…It is reported that [22] at the beginning of the oxidation process of magnesium alloys, a compact layer would emerge at the magnesium alloy surface, and such a dense layer could separate the diffusion source from the magnesium alloy matrix, thus the diffusion of active metal atoms and the growth of the intermetallic layer on magnesium alloy surface is interfered by a dense film as illustrated in Figure 4.…”

Section: Ammonium Chloride Could Keep the Surface Of The Magnesium Almentioning

confidence: 99%

The Role of Ammonium Chloride in the Powder Thermal Diffusion Alloying Process on a Magnesium Alloy

Meng

Zhang

et al. 2019

Coatings

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The powder thermal diffusion alloying method could be utilized to fabricate Al-rich intermetallic coatings on magnesium alloys in the air. While the role of ammonium chloride powder in the diffusion alloying source is still to be investigated. This research took the AZ91D magnesium alloy as the substrate. Diffusion sources with various powders were utilized as the diffusion source. Microstructure observation and phase identification were enrolled to investigate the role of the ammonium chloride powder in the diffusion alloying process. Results indicate that HCl gas could turn some solid Al powder into gaseous AlCl3 to enhance the transport of active Al atoms, moreover, it reacts with the dense MgO film and converts it to a loose one, which enables the AlCl3 gas to penetrate MgO and arrive the matrix to form a protective coating. Furthermore, the ammonium chloride content should be confined to 10 wt. % of the diffusion alloying source. Too much ammonium chloride powder would result in a worse intermetallic coating.

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“…[7] These together with other issues inhibit the widespread application of Mg-alloys. [8][9][10] Therefore, significant efforts have been directed to understand oxidation mechanisms in Mg-alloys and to develop practical approaches to minimize their negative effects, [11][12][13][14][15] as has been reviewed recently by Czerwinski [16] and Tan et al [17] Extensive practical methods were proposed to either retard or eliminate oxidation. These include the prevention of ignition and burning by applying a flux or protective gas during casting, [18,19] the addition of reactive elements to enhance the oxidation resistance through the formation of protective oxide films, [16,20] the application of melt cleaning techniques and innovative die filling to ensure the casting quality and mechanical properties of Mg-alloys.…”

Section: Introductionmentioning

confidence: 99%

The Nature of Native MgO in Mg and Its Alloys

Wang

Ramasse

et al. 2020

Metall Mater Trans A

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Native MgO particles in Mg-alloy melts have been recently exploited as potential substrates for heterogeneous nucleation during solidification, leading to significant grain refinement of various Mg-alloys. However, our current knowledge of the nature of the native MgO particles is still limited. In this work, we study both the physical and chemical nature of the native MgO in commercial purity Mg and Mg-9Al alloy by means of advanced electron microscopy. We found that as oxidation products MgO aggregates exist in the alloy melt in three different forms: dominantly young oxide film, occasionally old oxide film and ingot skin, all consisting of discrete nano-sized MgO particles. Detailed analysis shows that the native MgO particles have an octahedral or cubic morphology, a nano-scale particle size and a log-normal size distribution. The mechanisms underlying the formation of the two types of MgO were investigated, and we found that octahedral MgO is formed by oxidation of Mg melt and cubic MgO by oxidation of Mg vapor. With a large lattice misfit with a-Mg, the native MgO particles are impotent for heterogeneous nucleation, but can be made effective for grain refinement.

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Oxidation of magnesium alloys at elevated temperatures in air: A review

Cited by 151 publications

References 163 publications

Corrosion of the alloys Magnox AL80, Magnox ZR55 and pure magnesium in air containing water vapour

Corrosion of the alloys Magnox AL80, Magnox ZR55 and pure magnesium in air containing water vapour

The Role of Ammonium Chloride in the Powder Thermal Diffusion Alloying Process on a Magnesium Alloy

The Nature of Native MgO in Mg and Its Alloys

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