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

Abstract Enthalpies of the hcp–bcc transformation Δ tr H and melting Δ m H of Be were measured by anisothermal calorimetry which gave Δ tr H =6100 J/mol and Δ m H =7200 J/mol. The high value of Δ tr H 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 Al 5 Fe 2 at 870°C. The phases AlFeBe 4 and Al 2 FeBe 2.3 were not observed. The Be–C–Si system is marked by two two-phase equilibria Be 2 C–Si and Be 2 C–SiC at 900°C. The phase diagram of the pseudo-ternary BeO–Li 2 O–SiO 2 system was established on the basis of in-pile Be–BeO–Li 4 SiO 4 –Li 2 SiO 3 compatibility studies at about 450°C. The system is characterised by Li 2 BeSiO 4 which is in equilibrium with BeO, Be 2 SiO 4 ,SiO 2 ,Li 2 Si 2 O 5 ,Li 2 SiO 3 and Li 4 SiO 4 . The latter phase is also in equilibrium with Li 2 Be 2 O 3 .