High-vacuum setup for permeability and diffusivity measurements by membrane techniques

Abstract

The knowledge of the permeability and diffusivity (the diffusion coefficient) of materials to different gases is essential for a wide range of applications, such as food packaging, gas separation techniques, and vacuum technology. In this paper, we describe a versatile high-vacuum apparatus for permeation measurements, based on a membrane technique, with the aim of increasing the reliability of results and allowing measurements of permeability of different materials whose permeability spanning several orders of magnitude. The apparatus is equipped with a residual gas analyzer for measurements of partial and total pressure, a spinning rotor gauge for accurate determination of pressure, a calibrated leak to determine pumping speed and capacitance diaphragm gauges for accurate pressure measurements greater than 10−2 Pa. The apparatus works in a static or a dynamic mode. Its performance is tested on polydimethylsiloxane with N2 and Viton® with He as tracer gases. The lower measurement limit of the apparatus depends mainly on the degassing of the inner walls of the chamber. With the procedure described in this paper, it is possible measured permeability from 10−5 cm2/s to 10−10 cm2/s.