Investigating the Effect of pH on Corroding Magnesium by Dynamic pH Sweep Coupled with Electrochemical Measurements

A new experimental setup for controlling dynamically the pH of a sodium chloride solution during corrosion testing and electrochemical measurements on magnesium is presented. The setup comprises an electrochemical cell divided in two compartments such as ion exchange is possible between the two compartments, but macroscopic exchange of the NaCl solution is avoided. Each of the two compartment contains a graphite electrode, and a pH probe is immersed into one of the two compartment (named test cell) to acquire the value of pH. A controller, connected to a computer, adjusts the potential between the two inert electrodes, such as to develop hydrogen from one electrode and oxygen from the other. As a result, the pH in each compartment increases and decreases respectively. By sequentially measuring the pH and applying an adequate potential to the graphite electrodes, the pH in the test cell can be controlled precisely. In order to perform electrochemical measurement as a function of pH, an additional graphite counter electrode, an Ag/AgCl reference electrode, and a magnesium electrode are also placed in the test cell. As a result, it has been possible to perform pH sweep experiments and to obtain information on the variation of electrochemical behavior of magnesium as a function of the environment pH.