The efficiencies of o-, m-, p-phenylenediamine as corrosion inhibitors for ASTM-A-179 steel in 1.0 N HC1 at room temperature are investigated and the possibility that these efficiencies depend on the amine groups' (NH 2)position on the benzene ring is explored. One of the more and the least effective inhibitors are tested in galvanic corrosion cells of ASTM-A-179 steel and type 405 stainless steel.
Two laboratory experimental methods, which are the electrochemical and weight loss methods, were used in accordance with ASTM G 1-81, ASTM G 3-74, ASTM G 5-82, ASTM G 46-76, and ASTM G 59-78 standards.
It is found that the efficiency of o-phenylenediamine ranges from 25% to 80% inhibition by using a concentration range of 10 ppm to 200 ppm. Similarly, the efficiency of m-phenylenediamine ranges from 65% to 80% by using a concentration range of 10 ppm to 200 ppm. This is a clear indication that the efficiency of this inhibitor does not depend strongly on its concentration, making it a good practical inhibitor. The efficiency of p-phenylenediamine range from 5% to 30% by using a concentration range of 100 ppm to 200 ppm. This inhibitor is harmful to ASTM-A-179 when the concentration is below 100 ppm.
It is found that the efficiencies of phenylenediamines depend on the amine groups' (NH 2) position on the benzene ring and the efficiency of these inhibitors decreases in the order of m > o > p.
It is found that o-phenylenediamine has a higher efficiency than that of p-phenylenediamine in preventing the corrosion of ASTM-A-179 steel while it is in the galvanic cells with type 405 stainless steel.