Abstract
The apparent thermal conductivity λ of evacuated SiO 2-aerogel tiles was measured with our small guarded hot plate vacuum system LOLA II. In order to study the influence of the boundary emissivity on λ the plates (20 × 20 cm 2) were either used with their plasma-sprayed surfaces ( ε ≈ 0.5) or with low-emissivity aluminum ( ε ≈ 0.05) foils as covers. The difference in the apparent conductivity already showed at room temperature and rose to about 50% for radiative temperatures T r = 570 K. An important consequence is that superinsulating SiO 2-aerogel systems should always be provided with low-emissivity boundaries around the aerogel. The calorimetric results for λ are compared with radiative conductivity values derived from spectral i.r. transmission measurements.
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