The ternary system: Uranium – Zirconium – Silicon

Abstract

Phase equilibria in the system U-Zr-Si were established at 1273 K by optical microscopy, X-ray micro analyses (XMA) and X-ray diffraction. One novel ternary compound was observed, U2-xZr3+xSi4 (x~1), extending at 1273 K from U8Zr47.6Si44.4 to U12Zr43.6Si44.4 (in at% from XMA). The crystal structure was elucidated by X-ray single crystal data refinement and found to be isotypic with the tetragonal Sc2−xRe3+xSi4-type (space group P41212). Uranium atoms partially and randomly occupy (~0.5 U+0.5 Zr) only the Zr-site 8b (~0, 0.35, 0.21) of the Sc2−xRe3+xSi4-type structure. UZr4Si4 is in equilibrium with all the many modifications of defect uranium disilicide (AlB2-type; U3Si5−x derivative structures) and forms a series of three-phase triangles, which characterize phase equilibria in the U-Zr-Si system at 1273 K: UZr4Si4 + (U1−xZrx)3Si2 (3 at% Zr, x~0.05) + L (~10 at% Si, 1 at% Zr), UZr4Si4 + (γU~90βZr~10) + (Zr1−xUx)3Si2 (3 at% U, x~0.05). Mutual solid solubilities are small and reside below about 3 at% for Zr in U3Si2 and U in Zr3Si2. Due to the equilibrium tie-lines, Zr3Si2 + (γU,βZr) and Zr2Si + (γU,βZr), no compatibility exists between the U-rich silicides U3Si or U3Si2 and zirconium metal.