THE EFFECT OF SULFUR ON THE PASSIVATION OF IRON IN CALCIUM NITRATE

Electrochemical polarization experiments in conjunction with surface a nalyses using ultrahigh vacuum transfer showed that the presence of S, above a certain threshold amount, accelerated the corrosion of Fe whe n polarized at a normally passive potential in 55 weight percent Ca(NO 3)2 solution at 60-degrees-C. Above the threshold amount, the corrosio n rate did not depend on the S content. During corrosion, much of the S remained in the corrosion product film, and a large portion of the c harge passed contributed to film growth. Similiarities between the eff ects of S and those of P reported previously may help explain the simi lar influences of S and P as grain boundary impurities on the intergra nular stress corrosion cracking of Fe.