Abstract
Radiotracer techniques were used to study the sorption of sulfur vapor by silicone and epoxy polymers and to obtain information on the diffusion of sulfur in these materials. Sulfur was found to enter silicone polymers solely by a physical solution process which obeys Henry's law. The heat of solution is large (−0.43 eV) and at room temperature the solubility coefficient is at least five orders of magnitude greater than for many fully gaseous solutes, a result which fits an empirical rule relating the solubility coefficient of a given solute to its boiling point. Sorption of sulfur by a flexibilized anhydride-cured diglycidyletherbisphenol-A (DGEBA) epoxy is somewhat more complicated and appears to involve a double process of physical solution and chemical reaction. The rapid diffusion of sulfur in silicone rubber necessitated measurements of the diffusion coefficient D by a vacuum desorption technique. The activation energy Q and pre-exponential constant D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> are found to be 0.74 eV and 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /s, respectively. Corresponding values for the epoxy, as determined by a steady state permeation method, are 1.06 eV and 3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /s. These relatively large activation energies and pre-exponential factors are thought to reflect the large size of the S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf> molecule. Near room temperature, the difference in the activation energies causes sulfur diffusion to occur at least four orders of magnitude more slowly in the epoxy, which makes this material much more attractive for encapsulation applications requiring an effective diffusion barrier to elemental sulfur present as a pollutant of the atmosphere.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.