Фазовая диаграмма системы Hg-La

К оглавлению: Другие диаграммы (Others phase diargams)

Hg-La (Mercury-Lanthanum) C. Guminski The assessed La-Hg phase diagram at constrained vapor pressure is redrawn from [Moffatt], with review of the data of [36Par], [76Bru], [77Bul], [82Sag], and [ 86Sag]. Several details concerning this system are difficult to reconcile with this diagram. In the La-rich part of the diagram, a similarity to the Pr-Hg system was presumed. Above 250 C, the liquidus line was drawn according to the results of [76Bru]. Below this temperature, the liquidus demarcation line was positioned on the basis of solubility determinations of La in liquid Hg. Most of these determinations, carried out by various methods, yielded concordant results. An extrapolation of these data to higher temperatures leads to liquidus composition values which are in perfect agreement with rough estimates of [ 66Kir] and about ten times lower than those recorded by [76Bru]. Presumably, this discrepancy could be explained by the formation of a compound with Hg content higher than LaHg~6.5, but such a possibility is excluded because no Hg- richer compounds have been identified [36Par, 76Bru]. Between 0 and 60 C, the mean results of [36Par], [77Bul], [82Sag], and [86Sag] are suggested for construction of the recommended liquidus line. The solubility results of [61Bow] at 250 C fit well with the selected data, whereas the values at 150 and 20 C seem to be too high. All four stable intermetallic compounds are characterized by very narrow homogeneity ranges [51Ian2, 66Kir], below 1% of relative changes. Precise analysis of [79Mer] disclosed that the exact formula of LaHg4 is La11Hg45. LaHg is the most stable compound in this system. At constrained pressure, LaHg is formed by a congruent reaction at 1078 C [76Bru]. At normal pressure, the compound decomposes at 580 C [66Kir]. [76Bru] detected no intermetallic compounds with La content greater than 50 at. % La. However, [51Ian2] previously suggested formation of La3Hg. Moreover, [ 64Fla] noticed that at 1000 C (82 C over the melting point of La) the La phase still contained 13 at.% Hg. A very slow decomposition of LaHg could explain this phenomenon; if not, this would seriously discredit the assessed phase diagram. Because [64Fla] gives very little information on the experimental conditions, this information might be disregarded. According to [66Kir], the mutual solubilities of (La) and (Hg) are below the detection limit from -100 to +20 C. As with Pr, one may expect a solubility of (Hg) in(La) of several at.% Hg at temperatures higher than 500 C. 36Par: W.G. Parks and J.L. Campanella, J. Phys. Chem., 40, 333-341 (1936). 51Ian1: A. Iandelli and R. Ferro, Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis. Mat. Nat., 8, 48-52 (1951) in Italian. 51Ian2: A. Iandelli and R. Ferro, Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis. Mat. Nat., 11, 85-93 (1951) in Italian. 60Ian: A. Iandelli, Atti Accad. Naz. Lincei, Rend. Cl. Sci. Fis. Mat. Nat., 29, 62-69 (1960) in Italian. 61Bow: D.F. Bowersox and J.A. Leary, Rep. LAMS-2518, U.S. AEC (1961). 64Fla: D. Flad and F. Matthes, Z. Chem., 4, 466 (1964) in German. 66Kir: H.R. Kirchmayr and W. Lugscheider, Z. Metallkd., 57, 725-728 (1966) in German. 68Ian: A. Iandelli and A. Palenzona, J. Less-Common Met., 15, 273-284 (1968). 73Sag2: K.Zh. Sagadieva, A.I. Zebreva, and B. Zheldybaeva, Izv. V.U.Z. Khim. Tekhnol., 16, 47-50 (1973) in Russian. 76Bru: G. Bruzzone and F. Merlo, J. Less-Common Met., 44, 259-265 (1976). 77Bul: V.A. Bulina, A.I. Zebreva, and R.Sh. Enikeev, Izv. V.U.Z. Khim. Tekhnol. , 20, 959-961 (1977) in Russian. 79Mer: F. Merlo and M.L. Fornasini, J. Less-Common Met., 64, 221-231 (1979). 82Sag: K.Zh. Sagadieva, G.L. Badavamova, and A.I. Zebreva, Izv. Akad. Nauk Kaz. SSR, Ser. Khim., (2), 59-61 (1982) in Russian. 86Sag: K.Zh. Sagadieva, G.L. Badavamova, and A.I. Zebreva, Izv. Akad. Nauk Kaz. SSR, Ser. Khim., (1), 20-22 (1986) in Russian. 89Gum: C. Guminski, J. Mater. Sci., 24, 2661-2676 (1989). Submitted to the APD Program. Complete evaluation contains 2 figures, 4 tables, and 26 references. Special Points of the La-Hg System