POLARIZATION AND CORROSION OF STEEL IN SOLUTIONS OF SODIUM PHOSPHATE ON PRESENCE OF CHLORIDE-ION
The present work on polarization and corrosion of steel is undertaken to investigate the hydrogen overvoltage, cathodic and anodic polarization and corrosion of specimens in inhibited and noninhibited solutions. 
Hydrogen overvoltage-log current density relationships on specimens have been measured. The results are shown in Fig. 3, and for each current densitiey, the hydrogen overvoltage on the steel in 0.1 N HCl decreases as corrosion proceeds. But it increases markedly during the addition of sodium phosphate as inhibitor up to a concentration of 0.78.10-1 M which is believed to be an optimum concentration (Fig. 4). 
The anodic and cathodic polarization curves of the specimens in solu-tions of 0.1 N hydrochloric acid containing 1.0·10-1 M sodium phosphate with pH 8.6 and of 0.1 N alkalinized sodium chloride with same pH, are studied and compared. At current density 0.4 mA/cm2 the magnitude of △, the difference between steady state potential and potential of cathodic polarized electrode, in former solution is 577 mv greater than that in the later. The presence of sodium phosphate shifts the steady state potential in the anodic direction. There has been no change in weight, and no local corrosion could be detected by microscopic examination when steel specimens are exposed to this inhibited solution for fourteen days (Fig. 9, d). 
In solutions of lesser sodium phosphate concentration, corrosion be-havior of steel has been investigated. Although the passivation occurs in time-corrosion curves as shown in Fig. 8, microscopic examination still reveals local corrosion on its surface (Fig. 9, a, b). 
The extend to which corrosion is inhibited and the increase in △ are closely related, and run approximately parallel to each other.