Acoustical measurement of energy and momentum accommodation coefficients on polycrystalline platinum

Abstract

The acoustical method of measuring energy (EAC), and tangential momentum (TMAC) accommodation coefficients [F. Douglas Shields, J. Chem. Phys. 62, 1248–1252 (1975)] has been used to measure the accommodation coefficients of Ne and He on vacuum flashed Pt and on Pt after exposure to O2, N2, CO, and CO2. Vacuum flashing the Pt at 1400 K in the presence of misch metal getter resulted in a surface that was reproduced a number of times after exposure to various adsorbants. The combined value of TMAC + EAC for this surface was 0.80 ± 0.04 for Ne and 0.64 ± 0.04 for He. These values are significantly greater than values measured earlier in a similar way for W [F. Douglas Shields, J. Chem. Phys. 72, 3767 (1979); 76, 3809 (1982); 76, 3814 (1982)]. Exposing the flashed surface to O2 raised the combined values of TMAC + EAC to 1.28 for Ne and 1.00 for He. Flashing the surface at 1100 K removed some of the O2 and flashing at 1400 K restored the original AC values. In contrast to this, exposure to N2 did not change th...