Corrosion inhibitors for zinc in organic and inorganic acids

Some alkaloids of vegetable origin namely narcotine, papaverine, brucine, strychnine, cinchonidine, quinidine and ephedrine were examined by weight loss and polarization measurements with regard to their inhibitive effect on the corrosion of zinc in 1M solutions of tartaric, citric, acetic, propionic, mono-, di- and trichloracetic acids. In the hydroxy acids the opium and the nuxvomica alkaloids give inhibition efficiency ranging from 58 to 82%, papaverine leading the others. In the mono carboxylic acids the performance of all the alkaloids is poor except that of papaverine. In chloracetic acids narcotine, papaverine and brucine give inhibition efficiency of 70% or more at the higher concentrations only in monochloracetic acid. The polarization experiments of zinc in the systems giving more than 50% inhibition efficiency have also been carried out. The effect of cetyl trimethyl ammonium bromide (CTAB) and hexadecyl pyridinium chloride (HDPC) on the corrosion of zinc in hydrochloric and sulphuric acids has also been investigated. It has been observed that the performance of HDPC is better (I.E. 99.0%) than that of CTAB in both the media and this has been attributed to the presence of a pyridine ring in the former. From polarization experiments it is concluded that the inhibitive action of HDPC is under cathodic control as evidenced by appreciable cathodic polarization, whereas that of CTAB is under mixed control. The results are discussed