Growth Rate of Frost Heave in Helium and Mass Transport in Solid 4He

Frost heave phenomena have been studied in 4He on porous vycor glass, in which 4He in the pores remained supercooled fluid below the bulk melting temperature, T m . When we cool a bulk solid at T below T m on the vycor, the bulk solid sucks the supercooled liquid in the pores and grows. We measured the maximum frost heave pressure over bulk melting pressure, P m , as a function of ΔT=T m −T. When temperature was suddenly lowered, the frost heave pressure increased in time to a next equilibrium pressure and we measured the time constant and derived the frost heave rate. The frost heave rate was measured as a function of temperature and decreased very rapidly as temperature was lowered. We propose models to explain the mass transport in solid either by vacancy or by amorphous solid between bulk solid 4He and vycor. From measured temperature dependence of the rate in comparison with our model, we conclude the frost heave rate is determined by mass flow in solid 4He due to thermally-activated vacancy diffusion.