The effect of ligands on contact exchange in the NdFeB–Cu2+–P2O74-–NH4+ system

Abstract

Peculiarities of open-circuit interaction between the surface of electronegative NdFeB magnet and electrolytes containing pyrophosphate and ammonia complexes of copper are studied. It is shown that in the first minutes of the magnet immersion, the rate of open-circuit contact exchange in the pyrophosphate- ammonia electrolyte is close to its value in the pyrophosphate electrolyte (0.98 and 0.90 mA/cm², respectively) being gradually halved. Although the contact-exchange rate in pyrophosphate-ammonia electrolyte is higher as compared with the ammonia electrolyte, the contact exchange does no become the reason for the loss of adhesion of the deposited copper-containing coatings to the substrate. This is associated with both the formation of a strongly adhered copper layer on cathodic domains of the magnet surface and the absence of poorly soluble products of magnet dissolution formed on the surface of anodic sites.