Shiro Matsuda

Passive and transpassive films on FeCr alloys in acid and neutral solutions

Abstract Passive and transpassive films on FeCr alloys containing 5 – 6% chromium in 1 mol l −1 Na 2 SO 4 solutions of pH 2 and pH 6 have been investigated by in situ ellipsometry coupled with electrochemical measurements. The optical constants of film-free surfaces of the alloys, which were determined by ellipsometry in dehydrated methanol immediately after stripping the surface films in a bromine-methanol solution, were used in the calculation of the thickness and optical constants of these films. It was found that the thickness and the real parts of the optical constants of the films decreased with increasing chromium content of the alloy and decreasing pH of the solution. In the case of the passive films this was most pronounced for chromium contents in the range 5–20% which indicates the occurrence of substantial variations in the nature and composition of the films. The transpassive film thickness, the rate of film growth with the potential and the real part of the optical constant were usually found to be larger than those of the passive films.

In-situ ellipsometric determination of thickness and optical constants of passive and transpassive films on alloy 600 in neutral solution

Abstract In-Situ ellipsometric measurements coupled with electrochemical techniques have been performed on Alloy 600 in a neutral solution at various temperatures ranging from 293 to 368K. Three characteristic potential regions, that is, the passive, the primary transpassive and the secondary transpassive regions were observed on film thickness versus potential curves. The effect of temperature on the thickness end the optical consant for films was remarkable in the primary and the secondary transpassive regions.