Synthesis of Resorcinol Formaldehyde Aerogel Using UV Photo-Initiators for Inertial Confinement Fusion Experiments
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Synthesis of Resorcinol Formaldehyde Aerogel Using UV Photo-Initiators for Inertial Confinement Fusion Experiments R.R. Paguio1, K.M. Saito1, J.F. Hund1, and R. M. Jimenez1 1 General Atomics, PO Box 85608, San Diego, California 92186-5608, U.S.A. ABSTRACT Resorcinol formaldehyde (R/F) aerogels have been used in a variety of laser targets for Inertial Confinement Fusion (ICF) experiments in the form of thin films, cast shapes such as cylinders and cubes, and hollow and solid microspheres. Besides ICF experiments, R/F aerogel can be used for capacitors, batteries, thermal insulation, absorption/filtration media, and chromatographic packing applications. Traditionally, R/F aerogel is synthesized using a 2-step (base/acid catalysis) polycondensation reaction. We have developed a novel process to synthesize the R/F aerogel using free radical UV initiator at room temperature in 10 minutes using a UV light source. This paper will review this process, which was developed to synthesize R/F aerogels using UV-free radical initiators. Scanning electron microscopy results will also be discussed to show that the aerogel pore structure is similar to traditional R/F aerogels. Fabrication of solid and hollow microspheres for ICF experiments using this R/F aerogel synthesis technique and the technique’s limitations will also be discussed. INTRODUCTION Resorcinol formaldehyde (R/F) aerogel is a low-density solid-state material derived from a gelation and liquid extraction process. This material can be used for capacitors, batteries, thermal insulation, absorption/filtration media, and chromatographic packing applications [1]. R/F aerogels have also been used in a variety of laser targets for Inertial Confinement Fusion (ICF) experiments in the form of thin films, cast shapes such as cylinders and cubes, and hollow and solid microspheres. Traditionally, these R/F aerogels are synthesized using a 2-step (base/acid catalysis) polycondensation reaction developed by Pekala et al. [2]. One of the main uses and designs for R/F in ICF experiments is in the form of hollow microspheres (shells) for future direct and indirect drive targets at the National Ignition Facility (NIF) and the High Average Power Laser (HAPL) programs pilot Inertial Fusion Energy (IFE) power plant [3,4]. These shells are a scaled-up version of foam cryogenic targets currently used at the OMEGA facility at the University of Rochester Laboratory for Laser Energetics (LLE). Depending on the experimental design these spheres can have a diameter that can range from 900 to 4500 µm. A picture showing the variety of R/F shell sizes and the design that they are used for is shown in figure 1. One of the issues with the R/F aerogel shells has been the yield that meets the wall uniformity specification. Ongoing research at General Atomics (GA) have been made to the traditional R/F shell fabrication process that was first developed by Lambert et al. [5] to improve the yield of intact shells to 90% [6] and the shells that meet the wall uniformity specification to 50% [7,8]. Though th
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