Acoustic study of the liquid-vapor critical point of neon and helium in aerogel

We used low-frequency acoustic resonators to study the liquid-vapor coexistence curve and critical behavior of simple fluids in low-density silica aerogels. Resonators provide direct measurements of sound speed at low frequency. Sound speeds exhibit sharp kinks at the liquid-vapor phase boundary that allow us to map out coexistence curves near the critical point. Our previous measurements showed that neon in 95% aerogel exhibits a narrowed coexistence curve shifted to higher fluid density, but were complicated by a significant quantity of bulk neon present in the cell. We discuss results from our current experiments on two different fluids (neon and helium). Results are compared to our earlier measurements and to studies by other groups. (C) 2003 Elsevier Science B.V. All rights reserved.