Technical note: Cyclohexylamine carbonate as vapor phase inhibitor for Nd-Fe-B magnet

The efficiency of cyclohexylamine carbonate (CHC) as a vapor phase inhibitor for a Nd-Fe-B magnet in the simulated atmospheric environments as well as under thin electrolyte layers was investigated using scanning electron microscopy (SEM) and electrochemical methods. SEM results suggested that CHC was an effective vapor phase inhibitor for Nd-Fe-B subjected to a 7-day exposure in the simulated atmospheric environments, and the Nd-rich phase was also soundly protected. Polarization and electrochemical impedance spectroscopy (EIS) measurements indicated that CHC was an anodic type of inhibitor for Nd-Fe-B, and the inhibition efficiency can reach a relatively high value. The corrosion inhibition mechanism was studied through IR spectroscopy and the potential of zero charge (PZC) measurements. IR spectra analysis demonstrated that physisorption played a main role in the process of adsorbing CHC. PZC tests indicated that the Nd-Fe-B surface carried negative charges at free corrosion potential. The corrosion inhibition of CHC was achieved by physisorption of protonated amine on the negatively charged Nd-Fe-B surface via electrostatic attraction.