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Mechanical Properties and Gas Permeability of Polyimide Shells Fabricated by the Vapor Deposition Method

F.-Y. Tsai, E. L. Alfonso, S.-H. Chen, D. R. Harding

Fusion Science and Technology / Volume 38 / Number 1 / July 2000 / Pages 83-89

Technical Paper / Thirteenth Target Fabrication Specialists’ Meeting

Spherical polyimide (PMDA-ODA) shells with high aspect ratio (OD = 900 to 1020 μm and wall thickness = 0.7 to 8.0 μm) were successfully fabricated by the vapor deposition method. These shells were characterized in terms of gas permeability, Young’s modulus, tensile strength, and ultimate elongation. The measured properties of the shells agreed with those of commercial films (Kapton®). Post-coating treatments of the shells, including thermal imidization in air and biaxial expansion, effectively increased gas permeability. Air-curing resulted in shells that were more brittle and twice as permeable as those cured in nitrogen. Since no difference in chemical composition was found between the N2- and air-cured shells, the effect of air-curing may be attributed to morphological or microstructural changes due to oxygen or water vapor in air. Shells that were expanded plastically showed over 300-fold increase in gas permeability, while retaining half of the original Young’s modulus. The effect of expansion on permeability may have arisen from localized plastic deformation. Both treatments will be useful for preparing ICF targets that allow a rapid fill with DT fuel for cryogenic experiments.

 
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