Phase relations and stabilities at 900 °C in the U–Fe–Si ternary system

Abstract

A systematic study of the U–Fe–Si ternary system was carried out in the whole concentration range, by means of scanning electron microscope observations, associated with energy dispersive X-ray spectroscopy analyses and X-ray powder diffraction measurements performed on as-cast and annealed samples. At 900 °C, the phase diagram is characterized by the existence of nine ternary compounds: U 2FeSi 3 with the AlB 2-type, UFe 2Si 2 with the ThCr 2Si 2-type, U 3Fe 2Si 7 with the La 3Co 2Sn 7-type, U 2Fe 3Si with the MgZn 2-type, UFeSi with the TiNiSi-type, U 1.2Fe 4Si 9.7 with the Er 1.2Fe 4Si 9.7-type, U 2Fe 3Si 5 with the Lu 2Co 3Si 5-type, U 6Fe 16Si 7 of the Mg 6Cu 16Si 7-type and UFe 5Si 3 with its own type of structure. Two intermediate solid solutions, U 2Fe 17− x Si x (3.2 < x < 4) structurally related to the Th 2Ni 17-type and UFe 12− x Si x (1 < x < 3) structurally related to the ThMn 12-type are formed and two extensions of binaries into the ternary system, UFe x Si 2− z− x (0 < x < 0.2) and UFe x Si 1− x (0 < x < 0.05) are observed. The homogenous ranges are formed by Si/Fe mechanisms of substitution. Analyses on as-cast samples revealed the formation of two additional ternary phases which were found to be stable only at high temperature, UFe 1− x Si 2 with x = 0.8 and a novel ternary compound with a 18(1)U:59(1)Fe:23(1)Si estimated atomic ratio.