Reduction in helium thermal conductivity by 1 mg/cc silica aerogel foam.

Ultralow density 1 mg/cc aerogel foam reduces the thermal conductivity of pure helium gas by about a factor of 3 at 1 Torr and 20 K, with smaller reductions at higher temperatures and pressures. The measurements were made using the dc hot wire method over temperatures ranging between 15 and 300 K and pressures ranging from 0.05 to 100 Torr. The results are generally consistent with a simple model that accounts for a reduction in the He mean free path due to the foam. [ABSTRACT FROM AUTHOR]