Oxidation induced strain and defects in magnetite crystals

Area of Science:

• Geochemistry
• Environmental Science
• Materials Science

Background:

• Magnetite (Fe3O4) oxidation is crucial in geochemistry, environmental, and materials science.
• Understanding strain fields and defect evolution during oxidation is key to elucidating reaction mechanisms.

Purpose of the Study:

• To visualize internal strain distributions and morphology of nano-sized magnetite crystals during oxidation.
• To investigate the impact of different oxidation conditions (acidic dissolution vs. thermal oxidation) on strain evolution.

Main Methods:

• Utilized Bragg coherent diffractive imaging (BCDI) to spatially resolve strain fields in individual ~400 nm magnetite crystals.
• Compared strain evolution under oxidative dissolution in acidic solutions versus oxidation at elevated temperature in air.

Main Results:

• Oxidative dissolution in acidic solutions significantly increased the magnitude and heterogeneity of internal strains.
• Observed heterogeneous strain likely arises from Fe(II) diffusion, causing lattice distortions and creating compressive/tensile strain domains.
• Strain evolution was less pronounced during high-temperature air oxidation.

Conclusions:

• Magnetite oxidation, particularly oxidative dissolution, induces complex strain and defect structures.
• This strain heterogeneity is a significant factor contributing to the high reactivity of magnetite particles in aqueous environments.