Test of wall coatings for controlled moist air experiments

Abstract

Various hydrophobic surface treatments were investigated to facilitate high humidity (relative and absolute) experiments with a millimeter wave spectrometer. There were 17 different cases tested for adsorption and desorption behavior of a vacuum chamber, employing various combinations of metal surfaces (stainless steel, aluminum, brass), coating materials (electropolish, gold plate, Teflon, HMDS, silicone, lacquer), and surface-to-volume ratios (0.3 to 1.7 cm-1). Test procedure and data are described together with a brief discussion of the findings. Trends are evaluated toward an effective reduction of the wall effect, which is a nemesis to all laboratory studies involved with polar gas molecules such as H2O in air.