N‐heterocyclic amines and derivatives as corrosion inhibitors for iron in perchloric acid

Work reported in the present paper investigated the inhibiting properties of a number of N‐heterocyclic amines in 0.1 mol/l HClO₄. An attempt also was made to correlate some molecular parameters of these compounds with their corrosion inhibitor efficiency.

The test series included piperidine (pip), 2‐methylpiperidine (2mp), 3‐methylpiperidine (3mp), cis‐2,6‐dimethylpiperidine (26dp), 3,5‐dimethylpiperidine (35dp), 3‐hydroxy piperidine (3hp), 4‐hydroxypiperidine (4hp), 4‐aminopiperidine (4ap), piperazine (pz), 2‐methylpiperazine (2mpz) and cis‐2,6‐dimethylpiperazine (26dpz). The inhibiting effect was investigated in 0.1& mol/L HClO₄ by potentiodynamic polarization (DC) and electrochemical impedance spectroscopy (EIS).

The results show that these compounds suppressed both cathodic and anodic processes of iron corrosion in 0.1 mol/l HClO₄ by adsorption on the surface, which followed a Langmuir adsorption isotherm. Experimental observations indicated that basic piperidine and piperazine were better corrosion inhibitors than were their derivatives. The inhibition properties of N‐heterocyclic amines were found to be related to the charge on the nitrogen atom and the sum of the net charge of the all six atoms from the cyclic ring.

This paper provides useful information relative to corrosion inhibition efficiency of the group of N‐heterocyclic amines. It is concerned with a theoretical explanation between electronic and structural characteristics of these compounds and their inhibitor efficiency.