The effect of surface sulfur on the oxidation of zirconium

Abstract

Abstract In order to examine the effect of surface sulfur on the oxidation of zirconium, we have tried to make a quantitative analysis of sulfur segregation on Zr and made a study of the oxidation of sulfur segregated Zr. Depth profiles of the S-segregated Zr surface determined after high temperature annealing in vacuum show that the saturated surface concentration of sulfur has an S/Zr atomic ratio of about 1 and the total amount of segregated S is about 1 monolayer. These values do not depend on the annealing time. The S-segregated surface is exposed to an oxygen atmosphere in a pressure range of 10 −6 −10 −5 Pa up to a total exposure of 9000 L at RT. Changes of the surface concentration of S, O and Zr are monitored by in situ AES analysis. Depth profiling of O, S and Zr for the oxidized specimen is also carried out. Surface oxidation is clearly delayed by segregated sulfur. This effect, however, is not so significant as for the SFe system, and three oxidation stages are clearly distinguished in the same manner as in the oxidation of clean Zr surfaces. This is because S is simultaneously oxidized and removed in the form of a volatile oxide such as SO or SO 2 .