AVS 45th International Symposium
    Manufacturing Science and Technology Group Thursday Sessions
       Session MS-ThP

Paper MS-ThP2
Surface Cleaning on Aluminum for UHV using Supercritical Fluid CO@sub 2@ including NaCl and H@sub 2@O as Impurities

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Manufacturing Science and Technology Group Poster Session
Presenter: T. Momose, Miyagi National College of Technology, Japan
Authors: T. Momose, Miyagi National College of Technology, Japan
H. Yoshida, Miyagi National College of Technology, Japan
Z. Sherverni, National Industrial Research Institute of Tohoku, Japan
T. Ebina, National Industrial Research Institute of Tohoku, Japan
Y. Ikushima, National Industrial Research Institute of Tohoku, Japan
Correspondent: Click to Email
Ozone treatment has been applied to several metals for UHV to improve outgassing rate. The surface of the ozone treated Al and superconducting Nb cavity @footnote 1@ showed the low adsorption characteristics and low density of hydroxide in the surface. These suggest that removal of the native oxide and the treatment without water can improve vacuum characteristics of the surface. Conventional surface treatments cause inhomogeneity and need water cleaning process. Therefore, we investigated the treatment with supercritical CO@sub 2@ because supercritical CO@sub 2@ can readily dissolve nonpolar compounds. Before the removal of surface oxide and ozone treatment, supercritical CO@sub 2@ was applied to the UHV material such as Al to clean the surface. A sample was a half piece of a swagelok cylinder (10.8 mm in diameter and 8.5 mm in length) cut along the axis with hard almite coating. CO@sub 2@ was supplied from a tank and charged into a syringe pump (HPB-350) via a cooler at about -10 °C. Liquefied CO@sub 2@ was transferred into a high pressure chamber made of stainless steel 316 cylinder with inner diameter of 50 mm, inner length of 50 mm and thickness of 20 mm. The surface analysis was carried out by XPS. The cleaned level was evaluated by the density (at%) of carbon (C) determined from the ratio of convoluted area of Al2p, O1s, and C1s peaks. The C density of untreated Al was 87 %. The C density of Al treated by supercritical CO@sub 2@ at 70 °C and 94 atm for 2 hours was 65 %. Furthermore, the C density of the surface treated by the addition of H@sub 2@O of 0.5 cc and NaCl of 0.05 g to supercritical CO@sub 2@ at 100 °C and 150 atm for 2 hours decreased to 13 %. The treatment with the same fluid showed no C density (13-25 %) dependence on pressure ranging from 100 to 250 atm. The treatment also showed the black surface which was locally oxidized with the aid of the contact potential with the chamber. Similar results were observed on the almite coating of the sample. @FootnoteText@ @Footnote 1@T. Momose. et. al., Vacuum, 47, No4, 319-324.