Potentiodynamic Corrosion Testing

Summary

Here, we present a protocol to set up and run an in vitro potentiodynamic corrosion system to analyze pitting corrosion for small metallic medical devices.

Abstract

Different metallic materials have different polarization characteristics as dictated by the open circuit potential, breakdown potential, and passivation potential of the material. The detection of these electrochemical parameters identifies the corrosion factors of a material. A reliable and well-functioning corrosion system is required to achieve this.

Corrosion of the samples was achieved via a potentiodynamic polarization technique employing a three-electrode configuration, consisting of reference, counter, and working electrodes. Prior to commencement a baseline potential is obtained. Following the stabilization of the corrosion potential (E_corr), the applied potential is ramped at a slow rate in the positive direction relative to the reference electrode. The working electrode was a stainless steel screw. The reference electrode was a standard Ag/AgCl. The counter electrode used was a platinum mesh. Having a reliable and well-functioning in vitro corrosion system to test biomaterials provides an in-expensive technique that allows for the systematic characterization of the material by determining the breakdown potential, to further understand the material's response to corrosion. The goal of the protocol is to set up and run an in vitro potentiodynamic corrosion system to analyze pitting corrosion for small metallic medical devices.

Introduction

Electrochemical techniques provide a quick and relatively inexpensive method to obtain the electrochemical properties of a material. These techniques are based predominately on the ability to detect corrosion of a metal by observing the response of the charge-transfer process to a controlled electrochemical disturbance ^1-5. Corrosion of metal implants within a body environment is critical due to the adverse implications on biocompatibility and material integrity ⁶. The main factor contributing to corrosion of implants within the body is the dissolution of the surface oxide leading to an increased release of metallic ions ^7-11. This res....

Protocol

1. Construction of the Sample Holder

1. Construct the sample holder from stainless steel spacers and a M3 stainless steel threaded screw, held in place with a M3 hexagonal nut.
2. Remove the head of the threaded screw using pliers and polish the cut segment to maintain the thread pattern.
3. When all individual components are ready, assemble the electrode holders. Each electrode holder contains three spacers joined together by the M3 screws resulting in an 11.5 cm handle. Place the hexagonal nuts at the junction of the screw and spacers to lock the connection.
4. Solder (60/40% Sn/Pb) a toothless alligator clip onto the screw at the end o....

Results

At the conclusion of the procedure an in vitro corrosion system is setup to conduct corrosion studies. Specific procedures such as the cleaning of the corrosion vessel and the Faraday cage were introduced into the protocol to improve noise performance. The fundamental concept of a good polarization scan is to identify the electro-physical conditions of the material providing valuable information in order to understand the corrosion susceptibility of a metallic material. The proce.......

Discussion

Polarization scans produced from the stainless steel samples showed clean continuous plots correlating with scans seen in literature indicative of a well functioning corrosion system which is both reliable and reproducible ²⁹. Poor reproducibility of potentiodynamic pitting potentials is identified with a spread of a few hundred millivolts, with pitting potential being characterized by a stochastic process ²⁹. This is commonly due to the variables of temperature, halide content and potential (V); th.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Potentiostat	Metrohm	PGSTAT101
Ag/AgCl reference electrode, shielded	Metrohm	6.0729.100
Electrode shaft	Metrohm	6.1241.060
Polisher Forcipol 1v	Metkon	3602
Clindrical flask 700 ml	SciLabware	FR700F
Reaction lid	SciLabware	MAF2/41
Dichloromethane	Sigma-Aldrich	MKBR7629V	Use under a fumehood. Wear protective clothing.
Thermo / HAAKE D Series Immersion Circulators	Haake