Site-Specific Hydroxide Formation and Corrosion on Mg Nanocrystals

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Magnesium alloys are attractive for various applications due to their low density.
• However, rapid corrosion and poorly understood initiation mechanisms limit magnesium's widespread use.
• Developing corrosion-resistant magnesium is crucial for aerospace, transportation, and biomedical fields.

Purpose of the Study:

• To investigate the intrinsic corrosion behavior of magnesium using a defect-free model system.
• To elucidate the early-stage mechanisms of magnesium corrosion initiation.
• To identify potential strategies for enhancing magnesium's corrosion resistance.

Main Methods:

• Utilized single-crystalline Mg nanocrystals as a model system.
• Employed quasi in situ Transmission Electron Microscopy (TEM) and 3D reconstruction.
• Analyzed the role of the magnesium hydroxide (Mg(OH)2) layer and interfacial properties.

Main Results:

• The Mg(OH)2 hydration layer initially protects magnesium but loses stability beyond a critical thickness (10-20 nm).
• Corrosion initiates at exposed crystal corners and propagates along incoherent Mg(OH)2/Mg interfaces.
• Chloride ions preferentially attack these interfaces, leading to localized matrix corrosion and interfacial rupture.

Conclusions:

• Corrosion initiation in magnesium is strongly linked to interfacial coherence and hydroxide film stability.
• Localized attack at incoherent interfaces, rather than bulk dissolution, drives early corrosion.
• Interfacial engineering presents a promising strategy to enhance the corrosion resistance of magnesium and similar lightweight metals.