Influence of The KF Concentration on The Coating Process And Properties of Potentiostatic Deposited Fluoride Conversion Film on AZ31 Mg Alloy

Jie Dong

doi:10.4172/2321-6212.1000131

Abstract

The dependence of coating process and properties of the fluoride conversion film on AZ31 Mg alloy on the concentration of deaerated KF solutions was studied by anodic potentiostatic deposition, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The results show that the film deposited in 0.05 M KF solution is a monolayer consisting of amorphous Mg(OH)2 and MgF2, while amorphous Mg(OH)2 and MgF2 and crystallized KMgF3 as a double layer formed in 0.1 M~0.5 M KF solutions. The composition of inner layer is same as that of the monolayer, while the outer layer is composed of Mg(OH)2 and MgF2 and KMgF3. Continually increasing KF concentration reduces the content of KMgF3 in the outer layer, shortens the coating duration, and reduces the film thickness. The corrosion resistance of FCF coatings is closely correlated with the content of KMgF3 and the film thickness

Highlights

Magnesium (Mg) and its alloy have closer density and elastic modulus (density: 1.7–2.04 g/cm-3, Young's modulus: 41–45 GPa) to those of natural bone (density: 1.8–2.1 g/cm-3, Young's modulus: 10–30 GPa) than traditional implants such as 316L stainless steels, Ti6Al4V alloys, Co-Cr based alloys, when implanted they can minimize the stress shielding effect that can cause delay in healing process of damaged bones and implant loosening . [1,2,3] Mg can be excreted in terms of soluble MgCl2 through urine, and Mg is considered as a beneficial element in maintaining the normal function of the human metabolism and the growth of new bone tissue . [2,3] Mg can totally degrade in the physiological system (pH 7.4-7.6), eliminating the need for secondary surgery . [1,2,3,4,5] These intriguing characteristics make Mg and its alloys have great potential in orthopaedic application
All of the current decay curves can be divided into three stages, in which the first stage (S1) corresponds to the sum of the charging process of the electric double layer and electrode reactions, the second stage (S2) describes to the coating process of fluoride conversion film (FCF) layer, and in the third stage (S3), the metal surface is protected by the coating film
The variation of the surface morphologies is indicative of the variation of the chemical composition of the film . [28] A comparison of Figure 5b, 5f and 5i with the surface morphology of the AZ31 Mg alloy polarized in 0.1 M KF solution for 16000 s [30] shows that KMgF3 deposited in 0.1 M KF solution has the greatest size and optimal crystallinity, increasing the KF concentration causes a decrease in the size and crystallinity of KMgF3 and decreasing the KF concentration results in no formation of KMgF3

Summary

Introduction

Magnesium (Mg) and its alloy have closer density and elastic modulus (density: 1.7–2.04 g/cm-3, Young's modulus: 41–45 GPa) to those of natural bone (density: 1.8–2.1 g/cm-3, Young's modulus: 10–30 GPa) than traditional implants such as 316L stainless steels, Ti6Al4V alloys, Co-Cr based alloys, when implanted they can minimize the stress shielding effect that can cause delay in healing process of damaged bones and implant loosening . [1,2,3] Mg can be excreted in terms of soluble MgCl2 through urine, and Mg is considered as a beneficial element in maintaining the normal function of the human metabolism and the growth of new bone tissue . [2,3] Mg can totally degrade in the physiological system (pH 7.4-7.6), eliminating the need for secondary surgery . [1,2,3,4,5] These intriguing characteristics make Mg and its alloys have great potential in orthopaedic application.

Results

Conclusion