The corrosion protection of RE-iron-boron magnets by a phosphate treatment

The effect of a phosphate treatment as a corrosion inhibitor for a RE-iron-boron magnet has been investigated. The corrosion characteristics of the magnet in a phosphate solution, which consisted of 0.15 M NaH/sub 2/PO/sub 4/, were analyzed by electrochemical impedance and electrochemical noise measurements. The immersion of the magnet in the phosphate solution resulted in the formation of a passive layer on its surface causing a prolonged corrosion protection, after removal from the solution. The protective layer was found to consist of phosphate/pyrophosphate and oxide by XPS analysis.