Selected thermal properties of beryllium and phase equilibria in beryllium systems relevant for nuclear fusion reactor blankets

Enthalpies of the hcp–bcc transformation ΔtrH and melting ΔmH of Be were measured by anisothermal calorimetry which gave ΔtrH=6100 J/mol and ΔmH=7200 J/mol. The high value of ΔtrH is explained by the strongly reduced c/a-axis ratio of the hcp modification. Maximum solubilities of the metallic impurities Al, Cr, Fe, Mg and Si in different Be qualities which annealed at about 800°C are 0.01 mol% or less in each case. In the Al–Be–Fe system, Be(Al, Fe) is in equilibrium with Al5Fe2 at 870°C. The phases AlFeBe4 and Al2FeBe2.3 were not observed. The Be–C–Si system is marked by two two-phase equilibria Be2C–Si and Be2C–SiC at 900°C. The phase diagram of the pseudo-ternary BeO–Li2O–SiO2 system was established on the basis of in-pile Be–BeO–Li4SiO4–Li2SiO3 compatibility studies at about 450°C. The system is characterised by Li2BeSiO4 which is in equilibrium with BeO, Be2SiO4,SiO2,Li2Si2O5,Li2SiO3 and Li4SiO4. The latter phase is also in equilibrium with Li2Be2O3.