The quantum effects in the kinetics of ⁴He sorption by mesoporous materials

The sorption and the desorption of 4He by the mesoporous silicate MCM-41 material have been investigated in the temperature interval 1,5-290 K. It is shown that at T = 25-290 K the thermal activation mechanism is dominant in the kinetics of the sorption of ⁴He atoms by the MCM-41 sample. Its activation energy was estimated to be E approx 164,8 K. At T = 12-23 K the diffusion of the ⁴He atoms in the MCM-41 was practically independent of temperature, which typically occurs when the tunnel mechanism of diffusion dominates over the thermal - activation one. The mobility of the ⁴He atoms in the MCM-41 channels changed at T = 6-12 K which may be indicative of the formation on cooling (or decay on heating) of the monolayer and subsequent ⁴He layers at the inner surfaces of the channels. Below 6 K the diffusion coefficients of ⁴He are only slightly dependent on temperature, which may be attributed to the behavior of the quantum ⁴He liquid in the MCM-41 channels covered with several layers of ⁴He atoms.