The ternary system: silicon–uranium–vanadium

Abstract

Phase equilibria in the system Si–U–V were established at 1100 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed, U 2V 3Si 4 and (U 1− x V x ) 5Si 3, for which the crystal structures were elucidated by X-ray powder data refinement and found to be isotypic with the monoclinic U 2Mo 3Si 4-type (space group P2 1/ c; a = 0.6821(3), b = 0.6820(4), c = 0.6735(3) nm, β = 109.77(1)°) and the tetragonal W 5Si 3-type (space group I4/ mcm, a = 1.06825(2), c = 0.52764(2) nm), respectively. (U 1− x V x ) 5Si 3 appears at 1100 °C without any significant homogeneity region at x ∼ 0.2 resulting in a formula U 4VSi 3 which corresponds to a fully ordered atom arrangement. DTA experiments clearly show decomposition of this phase above 1206 °C revealing a two-phase region U 3Si 2 + V 3Si. At 1100 °C U 4VSi 3 is in equilibrium with V 3Si, V 5Si 3, U 3Si 2 and U(V). At 800 °C U 4VSi 3 forms one vertex of the tie-triangle to U 3Si and V 3Si. Due to the rather high thermodynamic stability of V 3Si and the corresponding tie-lines V 3Si + liquid at 1100 °C and V 3Si + U(V) below 925 °C, no compatibility exists between U 3Si or U 3Si 2 and vanadium metal.