An approach to improve initial pump-down speed of turbomolecular pumps by water-repellent coating on the blades

Abstract

Outgassing from turbomolecular pump (TMP) blades affects not only the ultimate pressure but also the initial rate of decrease of the inlet pressure. A longer evacuation time to attain a high vacuum is required for TMP than for a cryopump, because TMP's pumping speed for water, the dominant species of desorbed gases, is lower than that of the cryopump. The aim of this study is to develop a TMP which enables quick evacuation without the use of a cryotrap. The surface free energy or the water-repellent characteristics are considered to be important in the evacuation of water from surfaces. A special surface coating which has better water-repellent characteristics than an uncoated surface of aluminum alloy was developed, and outgassing from this surface was investigated.