|
Abstract
|
In this study, the formation of Fe3O4 nanoparticle coatings on gray cast iron was investigated. Two blackening
methods, including a hot alkaline (open system) and a hydrothermal method (closed system), were employed.
The hot alkaline method faced challenges due to the presence of near-surface graphite, leading to the formation
of a porous and defective coating containing significant amounts of hematite (Fe2O3), as confirmed by thermodynamic
calculations. In contrast, a dense and uniform high-quality Fe3O4 coating was produced by the
hydrothermal method, and the issues related to surface graphite were effectively resolved by converting it into
carbon-based nanomaterials inside the autoclave. Quantitative comparison showed that the hot alkaline coated
specimens had icorr = (2.11 ± 0.04) × 10 6 A cm 2, bond strength = 1.34 ± 0.04 MPa, and Ra ≈ 1.42 ± 0.36 μm,
whereas the hydrothermally treated samples exhibited icorr = (1.54 ± 0.03) × 10- 6 A cm- 2, bond strength = 2.56
± 0.03 MPa, and Ra ≈ 40.36 ± 1.2 nm, indicating markedly improved corrosion resistance, adhesion, and surface
quality. The resulting coatings were characterized using XRD, Field Emission Scanning Electron Microscopy (FESEM),
Atomic Force Microscopy (AFM), Pull-off adhesion test, and corrosion tests, including Open Circuit Potential
(OCP), potentiodynamic polarization, and Electrochemical Impedance Spectroscopy (EIS).
|