Фазовая диаграмма системы Na-Sr

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Na-Sr (Sodium-Strontium) A.D. Pelton The assessed phase diagram for the Na-Sr system is based primarily on the work of [64Rob] and [76Bus], with review of the work of [57Rem] and [66Pet]. The phase boundaries were generated from thermodynamic analysis. The (aSr + bSr) phase boundaries, as well as the invariant at 453 C (shown as dashed lines), were also calculated from thermodynamic analysis and thus should be regarded only as rough estimates. No intermetallic compounds have been detected by X- ray diffraction, thermal analysis, or electrodiffusion. The Na-Sr system exhibits complete miscibility in the liquid state. [64Rob] reported up to 12.5 at.% solubility of Na in solid (Sr). No detectable change was observed in the lattice parameter of (Na) with Sr additions as determined by X-ray diffraction, thereby indicating negligible solubility. The melting point of Sr is increased by the presence of hydrogen. Starting at pure Sr, the liquidus of [64Rob] parallels the liquidus of the present diagram closely, to about 3 at.% Na. Experimental points in the range of 3 to 12 at.% Na lie somewhat above the thermodynamically smoothed liquidus. This may be the result of Na losses by volatilization. A peritectoid reaction in the H-Sr system involving "(bSr)," "(gSr)," and the hydride H2Sr was observed by [66Pet] at 620 C, whereas a eutectoid reaction involving "(aSr)," "(bSr)," and H2Sr was observed near 240 C. These temperatures correspond closely to the a <259> b and b <259> g transformation temperatures of Sr reported by [64Rob]. It is now believed that the intermediate (cph) phase of Sr reported by [64Rob] was stabilized by the presence of hydrogen and that pure Sr exhibits no cph allotrope. Using thermal analysis on very pure Sr, [66Pet] discovered one thermal arrest at 557 C, which was taken to be the allotropic transformation temperature. Although the existence of a cph phase in pure Sr has not been ruled out, if it does exist it is most likely stable only over a much narrower temperature range than was previously thought. The accepted transformations for pure Sr are the melting point at 769 C and the b <259> a (bcc <259> fcc) transformation at 547 C. 57Rem: H. Remy, G. Wolfrum, and H.W. Hasse, Naturwissenschaften, 44, 534-535 ( 1957) in German. 64Rob: W.O. Roberts, Ph.D. thesis, Syracuse University, NY (1964), University Microfilms, Ann Arbor, MI, No. 65-3434, 91 p; see also W.O. Roberts, U.S. At. Energy Comm. TID-20639, 99 p (1964). 66Pet: D.T. Peterson and R.P. Colburn, J. Phys. Chem., 70, 468-471 (1966). 76Bus: P.R. Bussey, P. Hubberstey, and R.J. Pulham, J. Chem. Soc. Dalton Trans. , 22, 2327-2329 (1976). Published in Bull. Alloy Phase Diagrams, 6(1), Feb 1985. Complete evaluation contains 1 figure, 1 table, and 6 references. 1