Study of silica aerogel grain surfaces by using a positron age-momentum correlation technique

The effect of heat treatment on silica aerogel has been studied by a positron age-momentum correlation technique and infrared measurement. A difference was observed between the momentum distributions of the electrons on the first layers of the silica aerogel grain surfaces and the electrons in the grains in an as-supplied sample, but not in the sample heat treated at 800°C. A large change in the S parameter for the momentum distribution of the electrons on the first layer occurs around 200°C. This change correlates well with that of the infrared spectra, which show oxidation of the methoxyl groups at temperatures above around 200°C. This correlation reveals that those groups are mainly located on the first layer of the silica grains.