Graduate Thesis Or Dissertation
 

Potential Additive-Manufacturing of Ablative Thermal Protection Systems

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hq37vw99k

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  • Electrodeposition is a versatile polymer deposition technique to create nano-microscale materials using an electrical field generated from a charged droplet of solution and a grounded collector. Electrospinning or electrospraying can occur during electrodeposition, leading to the creation of nanofibers or bead-like materials depending on the process parameters. Photopolymerization of the electrodeposited solution has been used to cure the material during the flight of the charged droplets and/or produce a core-shell morphology of different polymer compositions. Acrylate monomers have been used in photopolymerization reactions due to their fast reaction time and reduction of moisture sensitivity. One drawback of acrylate monomers is the increase in oxygen-sensitivity, which requires an inert environment. The primary focus of using photopolymerization in this manuscript’s evaluation was to cure the acrylate monomers during flight, in of hopes of producing a distinct film morphology. The purpose of this manuscript’s evaluation, which was conducted in collaboration with Nanovox, LLC on a NASA funded project, was to utilize electrospinning as a manufacturing method for the production of thermal protection systems (TPS). The main goal of this manuscript’s evaluation was to optimize the electrodeposition process. The materials’ properties obtained from the electrodeposited films were observed to determine if electrodeposition was a viable way to produce a TPS. Previous methods of manufacturing TPS are more labor intensive and expensive due to material costs. Electrospinning was investigated as an environmentally friendly alternative manufacturing technique to solve the intensive labor and material cost issues with the added benefit of possibly controlling the overall morphology of the film. The products generated in the electrospinning process were fully cured polymer films with high thermal stability and non-porous film morphology. The most successful set-up was a vacuum chamber, which allowed for a N2 (g) rich environment with a light vacuum applied to keep the chamber gas pressure close to atmospheric. The shape of the films was determined by the distance from the collector. As the distance increased, a higherdegree of arcing was observed. The most consistent surface morphology that was observed was a non-porous film with bumpy ridges. Upon closer inspection under the SEM, the non-porous surface appeared to have droplets that were deposited in a bead-like shape rather than a fiber-like shape, which was more indicative of electrospraying, although some indication of electrospinning was observed sporadically. A comparative analysis of the reinforced composites found few differences between the control and reinforced films due to the lack of filler deposited. Fillers are used within TPS to provide additional structural and thermal reinforcement. The fillers aid in the production of the char layer for insulation and pores in order to allow the pyrolysis gas to travel to the surface. The majority of the filler was observed to be trapped within the plastic body of the needle before reaching the metal portion when processing the electrodeposited samples. The design of the needle’s plastic body led to a reduction in the filler distribution for the reinforced composite films. The thermal behavior of the reinforcement composite films was similar to the control because the filler distribution in the composite film was uneven. The HGMB showed a slight improvement in the thermal stability and char residual from the cast samples created. Cure-inflight electrodeposition was shown to have successfully produced a fully cured film that exhibited high thermal stability. Electrodeposition showcased its capabilities to photopolymerize the polyhedral oligomeric silsesquioxane/aliphatic urethane acrylate monomers in flight, which is a more environmentally friendly method. While some issues did arise with the production of the reinforcement composite films, overall, electrodeposition can produce a reinforced composite film.
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  • This work was funded by the National Aeronautics and Space Administration under contract number 80NSSC20C0300.
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