Fluorescent impact cavities in a titanium-doped Al2O3–SiO2 aerogel: implications for the velocity resolution of calorimetric aerogels

Silica aerogels have been shown to be superior at capturing hypervelocity projectiles with minimal alteration. On the basis of what is known about the abundance of natural projectiles in low Earth orbit (LEO), aerogel collectors flown in LEO should collect numerous scientifically interesting extraterrestrial dust particles, including interstellar dust grains. However, to date, only a few extraterrestrial dust grains have been found and not a single contemporary interstellar dust grain has ever been identified or analyzed in the laboratory. This lack of success is due to the fact that when using conventional aerogels it is very difficult, if not impossible, to reconstruct the velocity of captured natural projectiles. To address this problem, we are currently developing aerogel collectors/detectors that passively record the kinetic energy of an impacting projectile. In our previous work, we demonstrated that (Gd, Tb)-doped alumina aerogels may transform into a fluorescent phase(s) as a result of the rapid shock heating experienced by the capture of hypervelocity projectiles and that the amount of fluorescence excited, using a UV light source, is an increasing function of the projectile’s kinetic energy. However, our previous work did not demonstrate the accuracy of this ‘calorimetric’ technique in reconstructing the impact velocity of projectiles. In this paper, we report on the production of fluorescent impact cavities in a Ti-doped (5%) SiO2–Al2O3 aerogel monolith that resulted from the capture of 4.37 km s−1 20 μm glass beads. In addition we demonstrate that the dispersion of the fluorescent response of this aerogel implies that we should be able to reconstruct the velocity of a captured projectile with a resolution of 20% or better.