Effect of Surface Pretreatments on the Accommodation Coefficients of Argon on Nickel

Abstract

The accomodation coefficients of argon at 305 1 K on nickel were determined by using a nickel ribbon at the temperature range from 345 to 5500K under the pressure of 2.v5 10- Torr of Argon. To elcidate the effect of surface conditions on the accommodation coefficierits, measurements were carried out on the surfaces which had been pretreated differently each other, and the thermal desqrption was measured at the surfaces before and after the measurements of the accommodatioh' coeficients to see the change of surface conditions owing to the measurements of the accomodation coedicients. As for surface pretreatment three methods were preferred; i.e. the exposure to hydrogen, the bombardment with argon ions and the treatment of oxidation and reduction.The values of the accommodation coefllicients obtained in the present experiments lay in the range from O.50 to O.99. As the temperature difference (a T) between argon and nickel became larger, the accommodation coefficients decreased no matter which pretreatment was taken, however the rate of decrease varied with surface conditions. At the surface bombatded with argon ions the rate of the decrease was the largest, and moreover the most remarkable change of thermal desorption curves before and after the measurements of the accomodation coeMcients was obtained in this case. As compared at the same d T, the accommodation coemcients were larger when the cleanliness on the surface was thought to be inferior. she value proposed by Eucken, 2 the difference between the heat of adsorption and the activation energy of energy transfer was seen to be influenced greatly by the surface pretreatments.