Corrosion Properties of Mn-Based Alloys Obtained by Aluminothermic Reduction of Deep-Sea Nodules.

Šárka Msallamová,Pauline Miossec,Jaromír Kopeček,Darya Rudomilova,Alisa Tsepeleva,Pavel Novák,Jaroslav Fojt

doi:10.3390/ma14185211

Abstract

Deep-sea manganese nodules are polymetallic oxidic ores that can be found on a seabed. Aluminothermic reduction is one of the possibilities of manganese nodules processing. This process obtains the polymetallic alloy with a high content of Mn and a varying content of Al, depending on the ratio between aluminum and nodules. The corrosion behaviors of three experimental Mn-based alloys produced by aluminothermic reduction with a content of Mn > 50 wt % were studied. The electrochemical testing in potable water and model seawater was used to explain the corrosion mechanism of Mn-based alloys. The results showed that the corrosion rate of experimental Mn-based alloy decreases with the increase in aluminum content in both potable water and model seawater. It was observed that the uniform corrosion of experimental Mn-based alloys is changed with an increase in aluminum content in alloy to localized corrosion, which was caused by microcells in an environment of model seawater. In contrast, the formation of a semi-protective layer of corrosion products was observed on the surface of Mn-based alloys with a higher content of aluminum in potable water. Moreover, the pitting corrosion of tested Mn-based alloys was observed neither in potable water nor in model seawater.

Highlights

Deep-sea nodules are polymetallic oxidic ores, which can be found on a seabed.One of the main deposits of the deep-sea nodules is Clarion–Clipperton Fracture Zone in the Pacific Ocean
The aim of the study is to describe the corrosion behavior of polymetallic Mn-based alloys prepared by the aluminothermic reduction of deep-sea nodules in both potable water and model seawater
By the detailed analysis of the X-Ray Photoelectron Spectroscopy measurement (XPS) spectra, it was found that the natural layer of corrosion products formed predominantly by the aluminosilicate in the case of all alloys, while in the case of the alloy reduced in stoichiometric amount, there was the AlO(OH) phase as the constituent of the layer (Figure 1)

Summary

Introduction

Deep-sea nodules are polymetallic oxidic ores, which can be found on a seabed. One of the main deposits of the deep-sea nodules is Clarion–Clipperton Fracture Zone in the Pacific Ocean. There are about 100 billion tons of deep-sea nodules at a depth of. Deep-sea nodules have high porosity and a large specific surface. Their size ranges from a few millimeters to 30 cm [5,6]. There are several types of deep-sea nodules. The most interesting ones are the deep-sea manganese nodules. The rest of the manganese nodules contain clay, quartzite or zeolite, and amorphous hydrated ferric oxide [9,10]

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