Фазовая диаграмма системы Ce-La

К оглавлению: Другие диаграммы (Others phase diargams)

Ce-La (Cerium-Lanthanum) K.A. Gschneidner, Jr. and F.W. Calderwood The assessed phase diagram for the Ce-La system is based on the liquidus and fcc <259> bcc transformation data of [54Vog]. Ce and La form a continuous series of solid solutions. The melting points of the pure metals have been adjusted to the accepted values [Gschneidner]. La undergoes two phase transformations on heating: (1) from the dcph form to the fcc form at 310 C and (2) from the fcc to the bcc form at 865 C. Ce exhibits only the latter transformation at 726 C, because it is normally fcc at room temperature. On cooling, the fcc <259> dcph transformation occurs at lower temperatures (-16 C for Ce, 260 C for La) than the dcph <259> fcc transition on heating. Because Ce and La form a continuous series of solid solutions and are adjacent elements in the periodic table, the liquidus and solidus and the heating and cooling lines of the fcc = bcc transformation, respectively, were drawn as single straight line connecting the two melting or the two transformation points of Ce and La. No information is available concerning the dcph = fcc transformation for any Ce-La alloys, only for the pure elements. Thus, a dashed line has been drawn connecting the heating and cooling transformation temperatures of b <259> g in Ce and a <259> b in La. In a study of the magnetic and electrical properties of some Ce-La alloys, [ 78Pet] found that, at room temperature, alloys containing 30 to 70 at.% La contained at least some of the fcc phase, whereas alloys containing 0 to 30 at. % La and 70 to 100 at.% La could be prepared as the pure dcph phase (bCe and aLa, respectively). These alloys were prepared by normal melting followed by low-temperature (<25 C) cycling procedures. This suggests that the dcph = fcc transformation lines may go through a minimum in the center of the diagram. However, the inability to prepare the dcph alloys between 30 and 70 at.% La may be a kinetics problem and not a lowering of the fcc to dcph transformation temperature. In this particular system, the plot of weight percent against temperature cannot be distinguished from a plot of atomic percent against temperature due to the small difference in atomic weights. 54Vog: R. Vogel and H. Klose, Z. Metallkd., 45, 633 (1954). 78Pet: T.S. Peterson, S. Legvold, K.A. Gschneidner, Jr., T.-W.E. Tsang, and J. O. Moorman, J. Appl. Phys., 49, 2115 (1978). Published in Bull. Alloy Phase Diagrams, 2(4), Mar 1982. Complete evaluation contains 2 figures and 15 references. 1