1989 年 29 巻 7 号 p. 560-567
Surface segregation behaviors of several important metals which are proposed to be used as first wall material of the fusion reactor are briefly reviewed. Examples of such phenomena are presented for nickel, vanadium and stainless steel as were experimentally observed by the present authors. As experimental results showed, the surface phenomena of these metals were characterized initially by the segregation of impurity sulfur. But, in the case of nickel, as sulfur was depleted in the course of experiments due to ion bombardment, the surface was predominated by oxygen which was believed to have been adsorbed from the gas phase. This impurity segregation and adsorption also played an important role on the surface of stainless steel.
The presence of surface impurities due to segregation and/or adsorption is shown here to affect the hydrogen isotope permeation behaviors of these metals. Especially sulfur and oxygen seem to have significant influence on the permeation rate. Strictly speaking, the presence of these impurities are considered to inhibit ''hydrogen recombination'' process at the surface. And with their strong electronegative properties, some kind of electronic effects must be responsible for lowering recombination coefficient kR, where it is demonstrated that accumulation of these impurities decreased kR by orders of magnitude.
