The Influence of Casein Coatings on the Corrosion Behavior of Mg-Based Alloys.

Aneta Kania,Paulina Smolarczyk,Łukasz Reimann,Zbigniew Brytan,Katarzyna Cesarz-Andraczke

doi:10.3390/ma15041399

Abstract

This article discusses the influence of conversion casein coatings with a thickness of about 20 µm on the structure and the corrosion behavior of two magnesium alloys: MgCa2Zn1 and MgCa2Zn1Gd3. Casein is a protein that, along with whey protein, is a part of milk. Casein coatings are appropriate for bone growth because they contain high amounts of calcium and phosphorus. In this work, casein coatings and casein-free coatings were applied on Mg-based alloys using the conversion process. The structure and topography observations were presented. The corrosion behavior was determined by electrochemical and immersion tests, and electrochemical impedance spectroscopy (EIS) in chloride-rich Ringer solution. The obtained results show that conversion casein coatings effectively protect Mg-based alloys against corrosion. This was confirmed by higher corrosion potentials (Ecorr), polarization resistances (Rp) derived from Tafel’s and EIS analysis, as well as low hydrogen release. The volume of hydrogen released after 216 h of immersion for casein coatings applied to MgCa2Zn1 and MgCa2Zn1Gd3 alloys was 19.25 and 12.42 mL/cm2, respectively. The improvement in corrosion resistance of casein coatings was more significant for Mg alloy dopped with gadolinium. The lower corrosion rate of casein conversion coatings is explained by the synergistic effect of the addition of Gd in the Mg-based alloy and the formation of dense, tight conversion casein coatings on the surface of this alloy.

Highlights

In the field of medicine, magnesium alloys are currently being studied for their use in implantology, mainly in orthopedics
Constraints related to the release of too high a level of H2 from Mg-based alloys can be reduced by controlling the degradation rate of a resorbable implant [3,4]
The corrosion resistance of magnesium alloys can be significantly improved with conversion protective coatings, the idea of applying two different coatings with casein (CN) and without casein (NZ) to the MgCa2Zn1 and MgCa2Zn1Gd3 alloys

Summary

Introduction

In the field of medicine, magnesium alloys are currently being studied for their use in implantology, mainly in orthopedics. The biocompatibility of magnesium alloys, i.e., the chemical composition of metals present in the human body and the possibility of obtaining appropriate mechanical properties for implantology applications, is the main premise for continuous research in this respect. Designed Mg alloys are very promising materials for orthopedic implants. The development of this type of implant would eliminate the need to reoperate to remove the implant, and reduce postoperative costs, including the costs of patient rehabilitation. Constraints related to the release of too high a level of H2 from Mg-based alloys can be reduced by controlling the degradation rate of a resorbable implant [3,4]

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