Synthesis of Resorcinol Formaldehyde Aerogel Using Photo-Acid Generators for Inertial Confinement Fusion Experiments
- PDF / 3,289,140 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 214 Views
Synthesis of Resorcinol Formaldehyde Aerogel Using Photo-Acid Generators for Inertial Confinement Fusion Experiments K.M. Saito, R.R. Paguio, J.F. Hund, and R. M. Jimenez General Atomics, PO Box 85608, San Diego, California 92186-5608, U.S.A. ABSTRACT Traditionally, the synthesis of resorcinol formaldehyde (R/F) aerogels consists of a 2-step (base/acid catalysis) polycondensation reaction. Since the acid catalyst in the reaction controls the gelation time, the replacement of the acid catalyst with a non-ionic photo-acid generator decreased the gelation time from hours, down to a few minutes at room temperature using a UV light source. The reaction rate was not only fast, but the liquid precursor was stable for several hours prior to UV exposure. After drying, the resulting aerogel porosity was characterized by scanning electron microscopy (SEM) and confirmed the internal structure of the aerogel was similar to the original R/F pore structures. This paper will discuss the modifications made to the traditional R/F formulation, as well as the benefits of a fast gelation time for aerogel casting applications such as thin films, cylinders, and solid and hollow microspheres. INTRODUCTION Resorcinol formaldehyde aerogels were used in a variety of inertial confinement fusion (ICF) experiments in the form of solid and hollow spheres, cylinders, and thin films. R/F aerogels were synthesized using the traditional 2-step polycondensation reaction devised by Pekala [1]. The 2-step polycondensation reaction consisted of a base and acid catalysis step to form the R/F aerogel. During the first step of the reaction, the base catalysis step creates the hydroxymethyl aggregates; the aggregates react with one another to form the primary particles of R/F. The second step of the reaction, the acid catalysis step binds the primary particles together by methylene ether bridges to form the hydrogel. For the duration of the base catalysis step, small amounts of acid were generated, causing the gelation of the R/F [1]. Without the acid catalysis step, the reaction would take significantly longer (hours to days), and not optimal for the experimental working time. Heat was also used throughout the reaction to speed up the process, allowing the gel to setup in the time frame of a typical working day for these experiments. The primary use and design for R/F aerogels in ICF experiments was in the form of hollow microspheres (spherical shells), as shown in figure 1, containing hydrogen isotope fuel (deuterium-tritium or tritium). The R/F shell was a concept for future direct and indirect drive targets at the National Ignition Facility (NIF), as well as the inertial fusion energy (IFE) power plant [2,3]. The issue with fabricating R/F shells was meeting the wall uniformity specification. Investigations and process improvements at General Atomics (GA) have been made to the traditional R/F shell fabrication process, developed by Lambert et al. [4], to improve the yields of intact shells to 90% [5] and wall uniformity specification of 50% [6,7]. Even t
Data Loading...
