Zn-Mg and Zn-Ag Degradation Mechanism Under Biologically Relevant Conditions

Abstract

Zinc (Zn) alloys form a promising new class of biodegradable metals that combine suitable mechanical properties with the favorable degradation properties of pure zinc. However, the current understanding of the influence of alloying elements on the corrosion of zinc alloys, in biologically relevant media, is limited. The authors studied the degradation of three alloys, zinc-4 wt% silver (Ag), zinc-0·5 wt% magnesium (Mg) and zinc-3 wt% magnesium by in situ electrochemical impedance spectroscopy (EIS). After exposure for 1 h or 30 d, the samples were characterized by infrared spectroscopy and scanning electron microscopy. The presence of secondary phases in the alloy microstructure induced selective corrosion and increased the degradation rate. EIS analysis revealed an increase in surface inhomogeneity already at short (hours) immersion times. The microgalvanic corrosion of the zinc-silver alloy resulted in enrichment of the AgZn 3 phase at the sample surface. The enrichment of silver and potential release of AgZn 3 particles may result in complications during the tissue regeneration. The zinc-magnesium alloy surface was depleted of the magnesium-rich phase after 8-12 d. The selective dissolution caused local precipitation of corrosion products and a thicker corrosion layer with larger pore size consistent with increased corrosion rate.

Zinc/Silver Particle (Zn/AgP) Composite Coatings: Evaluation of Corrosion in Physiological Environments and Antibacterial Activity against P. aeruginosa

“…This result is consistent with that reported by Punith et al [42], who studied the corrosion of Zn/Ag composites in NaCl saline solutions and associated the lower corrosion rate of Zn/Ag composites with respect to Zn because the Ag particles occluded in the coating minimize defects in the coating, which are active sites for corrosion. However, the trend of our results is contrary to those reported by Sikova-Jasenska et al [18], who found that by increasing the Ag content in Zn-Ag alloys formed by smelting at 650 • C, the values of j corr and CR were slightly increased when using Hank's solution as electrolyte, and those of Törne et al [17], who reported increases in the corrosion rate of Zn-4Ag alloys (4 wt.% Ag) (formed by smelting at 550 • C) with respect to pure Zn. The observed differences can be explained taking into account that in the Zn-Ag alloy obtained by heat treatment the formation of intermetallic compounds as AgZn 3 of low corrosion resistance is favoured, contrary to what happens with Zn/AgP composite electrodeposited coatings in which these types of compounds are not formed.…”

“…In this sense, Niu et al [16] proposed a Zn-Cu alloy as a biodegradable material for application in vascular stents. Törne et al [17] studied the degradation mechanism of Zn-Mg and Zn-Ag alloys obtained by smelting at 550 • C, immersed in Ringer's solutions. The microgalvanic corrosion of the Zn-Ag alloy causes the accumulation of the AgZn 3 phase on the surface, and this accumulation could cause complications in the regeneration of the tissue.…”

Zinc-based alloys for degradable vascular stent applications

“…Indeed, AgZn 3 particles act as sites for disruption of any oxide/hydroxide film covering the Zn-Ag alloys’ surfaces. Recently, Torne et al [90] carried out an investigation on the degradation mechanism of as-cast Zn-4.0Ag alloy in a Ringer’s solution. Microstructural characterization on samples after 30 days of immersion showed selective corrosion surrounding AgZn 3 dendrites, leaving the AgZn 3 phase at the implant surface; nevertheless, no evident sign of corrosion pits was observed.…”

“…It was speculated that Mg 2 Zn 11 particles promote a more aggressive activity of macrophages in an attempt to metabolize this alloy phase known for increased corrosion resistance. An enrichment of intermetallic particles in the corrosion product layer during in vivo degradation of zinc alloys and their effect on tissue regeneration is of concern [90] and has not been addressed yet.…”

Advancements in Copper Nanowires: Synthesis, Purification, Assemblies, Surface Modification, and Applications

“…Moreover, their morphology, chemical composition and dimension severely affect the corrosion processes. Apart from oxidation, atmospheric sulfidation process also occur via reacting with reduced sulfur ligands, forming a silver sulfide corrosion layer . However, S‐containing species are rare (H 2 S 0.3 ppb, COS 0.6 ppb) in air, which are much lower than the oxidation content (around 20.95%) .…”