ZnO Thin Films as Promising Corrosion Protection on Mg-Based Alloys.

Area of Science:

• Materials Science
• Biomaterials Engineering
• Corrosion Science

Background:

• Magnesium alloys are promising for biodegradable implants due to their mechanical properties.
• However, their rapid corrosion in physiological environments limits clinical application.
• Protective coatings are essential to control degradation rates.

Purpose of the Study:

• To investigate the effect of ZnO thin film thickness on the microstructure and corrosion resistance of MgCa4Zn1Gd1 and MgCa2Zn1Gd3 alloys.
• To evaluate the suitability of ZnO coatings deposited by atomic layer deposition (ALD) for biodegradable magnesium implants.

Main Methods:

• ZnO thin films of varying thicknesses (42.5, 95.4, 133.7 nm) were deposited on MgCa4Zn1Gd1 and MgCa2Zn1Gd3 alloys using ALD.
• Coating characterization involved X-ray diffraction (XRD), Raman spectroscopy, SEM/EDS, AFM, and FTIR.
• Corrosion resistance was assessed via potentiodynamic polarization and immersion tests in Ringer solution at 37 °C.

Main Results:

• XRD and Raman confirmed crystalline ZnO formation with homogeneous morphology.
• Surface roughness decreased with increasing ZnO thickness, with the smoothest surface (R_a = 7.65 nm) on MgCa2Zn1Gd3 with 1500 cycles.
• Thicker ZnO coatings improved corrosion resistance, evidenced by reduced hydrogen evolution (20.89 mL·cm^-2) for the 1500-cycle coated MgCa2Zn1Gd3 alloy.
• FTIR analysis identified Mg(OH)₂ and MgCO₃ as primary corrosion products, with ZnO coating remaining intact after 100 h immersion.

Conclusions:

• The 1500-cycle ZnO coating deposited by ALD on the MgCa2Zn1Gd3 alloy offers superior corrosion protection.
• This ZnO-coated magnesium alloy demonstrates significant potential as a material for biodegradable medical implants.
• Optimizing ZnO coating thickness is crucial for enhancing the in vivo performance of magnesium-based implants.