Liquidus Projection of the B-Fe-U Diagram: The Fe-Rich Corner
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TERNARY uranium compounds from the U-Fe-X systems (X = element belonging to III and IV groups) often show unusual physical behavior.[1,2] Albeit poorly studied, interesting properties are expected for borides of the B-Fe-U system, where the introduction of boron, an interstitial element with high electronegativity, can decrease the hybridization between the 5f and 3d states. Previous studies on the B-Fe-U ternary diagram were reported by Valyovka et al.,[3,4] who identified the UFeB4 and UFe3B2 compounds. Recent systematic investigations on the isothermal section at 1223 K (950 C) revealed the existence of three other ternary compounds: (i) UFe4B, with a hexagonal structure closely related to the CeCo4B-type structure (a = 0.4932(1) nm and c = 0.7037(2) nm[5]); (ii) U2Fe21B6, with the cubic Cr23C6-type structure (a = 1.0766(4) nm[5]); and (iii) UFe2B6 with the orthorhombic CeCr2B6-type structure (a = 0.3137(6) nm, b = 0.6181(11) and c = 0.8225(17) nm[6]). A detailed knowledge of the B-Fe-U ternary phase diagram is essential for a comprehensive understanding of M. DIAS, Po´s-Doc, is with the IST/ITN, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa, Estrada Nacional 10, 2686-953 Sacave´m, Portugal, and also with the ICEMS, Departamento de Bioengenharia, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal. Contact e-mail: [email protected] P.A. CARVALHO, Researcher, is with the ICEMS, Departamento de Bioengenharia, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa. U.V. MARDOLCAR, Researcher, is with the Departamento de Fı´ sica, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal, and also with the Centro de Cieˆncia Moleculares e Materiais, Faculdade de Cieˆncias da Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugal. O. TOUGAIT and H. NOE¨L, Researchers, are with the Institut des Sciences Chimiques de Rennes, Chemie du Solide et Mate´riaux, UMR CNRS 6226, Universite´ de Rennes 1, Avenue de Ge´ne´ral Leclerc, 35042 Rennes, France. A.P. GONC¸, Researcher, is with the IST/ITN, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa. Manuscript submitted August 21, 2012. Article published online December 13, 2012 2270—VOLUME 44A, MAY 2013
the alloys’ solidification behavior, which is necessary for an optimized selection of the preparation and/or single crystal growth method suitable for each boride. A preceding investigation has established the liquidus projection of the B-rich corner of this diagram,[7] which comprehends two ternary compounds, UFeB4 and UFe2B6, and six ternary invariant reactions, as shown in Figure 1. Another work has defined a cascade of peritectic reactions along the U:(Fe,B) = 1:5 vertical section of the B-Fe-U system (as presented in Figure 2, based on Reference 8). However, limited information is known on the remaining regions of this complex diagram. In the case of compounds with high melting temperature, such as borides, and especially when
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