Modifying the Pore Size of Resorcinol Formaldehyde Aerogels for Fabrication of Hollow Spheres for Direct Drive ICF Exper
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1147-OO04-05
Modifying the Pore Size of Resorcinol Formaldehyde Aerogels for Fabrication of Hollow Spheres for Direct Drive ICF Experiments* R.R. Paguio1, C.A. Frederick1, J. Ilavsky2, J.F. Hund1, A. Nikroo1 and M.A. Thi1 1General
Atomics, P.O. Box 85608, San Diego, CA 92186-5608, U.S.A. National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, U.S.A.
2Argonne
ABSTRACT This work investigates an alternative way to modify the pore size of a 100 mg/cc resorcinol formaldehyde (R/F) aerogel without any significant change to the aerogel target density. This was successfully accomplished by an addition of hydrophilic polymer additive [Poly Vinyl Alcohol (PVA) or Poly Acrylic Acid (PAA)] to the R/F precursor solution which acts as an impurity in the reaction. The polymer can modify the cross linking or aggregation of the primary particles which can change the structure formation of the aerogel, thus changing the pore size. This paper will discuss this process modification and the fabrication of hollow, large pore R/F aerogel spheres that are used for direct drive inertial confinement fusion (ICF) cryogenic ice layering experiments at the University of Rochester Laboratory for Laser Energetics (LLE). The aerogels were characterized using scanning electron microscopy (SEM), nitrogen gas adsorption, and ultra small angle x-ray scattering (USAXS). INTRODUCTION Hollow spherical targets (shells) of resorcinol formaldehyde (R/F) aerogel are employed in direct drive inertial confinement fusion (ICF) experiments on the OMEGA facility at the University of Rochester Laboratory for Laser Energetics (LLE) and will be used in future experiments on the National Ignition Facility (NIF). The shells needed for OMEGA experiments have diameters of ~800–900 µm which are scaled down versions of the targets that are required for high gain wetted foam direct drive ignition designs on NIF [1]. The required wall thickness for these shells is 40–60 µm with an aerogel density of 100 mg/cc. The standard R/F aerogel used in these experiments is transparent due to its small pores of 0.5 µm) through reaction limited aggregation [2,3]. We will refer this as the low-catalyst method (LC method). A drawback to the LC method is that the final density was 30% lower than the calculated density [3]. The density reduction is due to less catalyst in the base catalysis part of this two-step polycondensation reaction, which forms less hydroxymethyl adducts due to unreacted monomer in the reaction. Another drawback was the instability of the precursor solution at room temperature (RT) and the gelation time at (the STD R/F precursor solution’s gelation temperature of) 70oC. This caused the solution to gel faster (10 min. at 70oC and 2–3 hours at RT) than the standard R/F solution (15–18 min. at 70oC and >12 hours at RT). Previous work showed that the gelation time of the precursor solution was key in producing hollow R/F shells, the process required the solution to be stable at room temperature for >6 hours, allowing consistent behavior of the R/F precursor thro
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