Фазовая диаграмма системы Ca-La

К оглавлению: Другие диаграммы (Others phase diargams)


Ca-La (Calcium-Lanthanum) K.A. Gschneidner, Jr. and F.W. Calderwood The assessed La-Ca phase diagram is based on the work of [58Sav], who used 98. 5% (wt.?) pure La that contained 0.75% Pr and 0.04% Fe as major impurities and Ca of 99.98% (wt.?) purity. The melting temperature of La was given as 885 C, whereas that of their Ca was given as 850 C, which is 8 C higher than the accepted melting point. An extensive liquid immiscibility ranging from 32 to 38 at.% Ca to 97% Ca was observed. Solubilities of La in (Ca) and of Ca in (La) were reported not to exceed 10 to 15 at.% at the eutectic temperature of 705 C. Pure Ca occurs in two stable forms. The low-temperature form, aCa, has the fcc structure of the Cu-type and is stable below 443 C. Above this temperature, bCa has the bcc structure of the W type. Because the melting temperature of La metal was reported to be 885 C instead of the accepted value of 918 C, the monotectic temperature in the assessed diagram has been raised 33 C (from 765 to 798 C) to maintain the same difference between the monotectic and the melting point of La. On the other side of the phase diagram, the temperature of the eutectic between bCa and La has been dropped 10 C from the reported temperature (705 C), to maintain the same difference that [58Sav] reported between this eutectic and the melting point of Ca metal. The three transformation temperatures (aLa = bLa at 310 C on heating, bLa = gLa at 865 C, and aCa = bCa at 443 C) are shown in the present phase diagram, but boundaries for the phase fields cannot be drawn due to lack of experimental evidence. 58Sav: E.M. Savitskii and V.F. Terekhova, Zh. Neorg. Khim., 3, 756 (1958) in Russian. Published in Bull. Alloy Phase Diagrams, 8(6), Dec 1987. Complete evaluation contains 1 figure, 1 table, and 2 references. 1