Abstract:
The processes of helium diffusion and solubility in $\gamma$-$\mathrm{Al_2O_3}$ crystals have been investigated using high-temperature helium defectoscopy. The flows of desorbing helium have been measured in the range of $200$–$450^\circ$C, temperature dependencies of diffusion coefficients have been calculated, and the effective diffusion activation energy of $0{,}068$ eV has been obtained. The found diffusion coefficients of the order of $10^{-16}$ cm$^2$/s are too low for an interstitial diffusion mechanism. Helium solubility in $\gamma$-$\mathrm{Al_2O_3}$ samples reaches $4 \times 10^{18}$ cm$^{-3}$ at a temperature of $500^\circ$C and a saturation pressure of $50$ atm. The observed low rate of helium desorption at $200^\circ$C, about a day, indicates its strong interaction with the aluminum oxide crystal lattice, and cation vacancies appear to be preferred positions for helium dissolution. At the same time, the discrepancy between the degassing process times and the desorption flow approximation results indicate the need to develop and use more complex theoretical models to describe helium mass transfer processes in $\gamma$-$\mathrm{Al_2O_3}$.
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