New technique for the measurement of adsorbed moisture concentration on a solid surface

We have established a new measurement method to evaluate the adsorbed moisture concentrations on solid surfaces exposed to the atmosphere having high moisture content ranging from 100 ppm to a few percent. The technique is based on the variation of the electric conductivity of anhydrous hydrogen fluoride. It has been found that the amount of adsorbed moisture on electropolished 316L stainless steel surface in an atmosphere with moisture concentration of 1% and 3% at 25 °C (relative humidity of 32% and 96% respectively) are 2.5× 1016 and 1.25×1017 molecules/cm2, respectively. This represents 25 and 125 molecule layers of water. The adsorbed moisture has been confirmed to reach an equilibrium level within an exposure time of 1 s.