CHLORINE ADSORPTION AT A TITANIUM SURFACE - SEGREGATION FROM BULK CRYSTAL - INTERACTION WITH CHLORINE GAS

It was discovered that although the impurity level of chlorine and sulfur in the bulk crystal are less than 1 ppm, these elements segregate from the bulk to the crystal surface at elevated temperatures with a segregation coefficient similar 10**5 to 10**6. Above 600 C sulfur displaces the chlorine from the surface. Segregation coefficients and diffusion coefficients are measured for chlorine as a function of temperature. Adsorption of chlorine gas on a clean Ti surface occurs as a nonactivated process with a sticking coefficient similar 0. 05. The adsorption isotherms are consistent with dissociation of the molecular chlorine to atomic chlorine. It is concluded that at room temperature the diffusion coefficient and segregation coefficient are much too low to allow chlorine to segregate to the surface at a crack tip during stress corrosion cracking unless the stress and increased local temperature are sufficient to lower the diffusion activation energy.