Study on the Pickling Inhibitors

A quantitative relation between the cathode potential rise with the addition of inhibitor and its inhibition efficiency is suggested and proved. The difference in functions between nitrogen-contai fling organic inhibitors and inorganic inhibitors is pointed out. The function of inorganic inhibitors may beto due not only the high hydrogen overvoltage of deposited metal which covers the original cathode by replacement, but also. the formation of various cathode films such as metastable Sb4O3 (OH)3Cl3 in antimony trichloride-containing hydrochloric acid solution at higher temperature. The inhibition efficiency increases with the concentration of inhibitor in solution. Thiourea may be the more useful and efficient inhibitor than monoaliphatic amines and nitrogen-containing aromatic compounds of the short hydrocarbon chains.