Фазовая диаграмма системы Mg-N

К оглавлению: Другие диаграммы (Others phase diargams)

Mg-N (Magnesium-Nitrogen) H.A. Wriedt No published diagram for the Mg-N system was found, and because quantitative data are lacking, the assessed diagram is undetailed. Although evidence was published for the existence of three polymorphs of Mg3N2, this is unsupported by several other investigations and is not accepted in this assessment. The solubility of nitrogen in (Mg) apparently has not been determined, but probably is small. At room temperature, (Mg) with 9 x 10-4 at.% N exhibited numerous inclusions of Mg3N2 [80Sim], which indicates that this concentration exceeds the saturation value. Internal nitridation in an alloy of Mg with a small content of Zr when it was exposed to N2 gas at 590 C [64Sif] is evidence that appreciable solubility of nitrogen in (Mg) exists at this temperature. In the condensed system, nitrogen-saturated (Mg) is in equilibrium with Mg3N2; no intermediate nitride has been reported. In a narrow temperature range near 650 C, the nitrogen-saturated (Mg) + L + Mg3N2 equilibrium and the location of (Mg) solidus are undetermined. Mg3N2 forms in the reaction of N2 or NH3 with Mg. The range of Mg3N2 compositions has not been determined; it is probably narrow and essentially stoichiometric. The existence of polymorphs of Mg3N2 other than the well-documented cubic type first was asserted by [49Mit]. No investigator other than [49Mit] has observed these phases; thus, the assessed diagram shows only one type of Mg3N2. The melting point of Mg3N2 has not been determined. Determination is hindered by the high dissociation pressure, which exceeds 0.1 MPa at about 1500 C. The occurrence of fusion was not mentioned in the work of [66Bra] at 4.6 GPa for temperatures up to 2000 or 2300 C; only recrystallization was mentioned at temperatures up to 1800 C. MgN6 is included tentatively among the equilibrium phases of the binary system, because it is the highest nitride known, but it has not been observed in equilibrium coexistence with Mg3N2 or any other Mg nitride. It is mildly explosive when heated [54Wib, 59Vol], but there is no quantitative data on equilibrium N2 pressures in decomposition. Its lack of volatility at room temperature [54Wib] is probably not an equilibrium observation. The (Mg) and Mg3N2 liquidus curves apparently are undetermined, but probably are located at low nitrogen concentrations. 49Mit: D.W. Mitchell, Ind. Eng. Chem., 41(9), 2027-2031 (1949). 54Wib: E. Wiberg and H. Michaud, Z. Naturforsch. B, 9, 501-502 (1954) in German. 59Vol: A.E. Vol, Handbook of Binary Metallic Systems. Structure and Properties, Vol. 1, Gosudarstrennoe Izdatel›stvo Fiziko-Matematicheskoi Literatury, Moscow, 572-573 (1959) in Russian; TR: Israel Program for Scientific Translation, Jerusalem (1966). 64Sif: R. Sifferlen, C. R. Acad. Sci. (Paris), 259(8), 1520-1523 (1964) in French. 66Bra: R.S. Bradley, D.C. Munro, and M. Whitfield, J. Inorg. Nucl. Chem., 28, 1803-1812 (1966). 71Dav: J. David, Y. Laurent, and J. Lang, Bull. Soc. Fr. Mineral. Cristallogr., 94(4), 340-346 (1971) in French. 80Sim: C.J. Simensen and B. Oberl„nder, Prakt. Metallogr., 17, 125-136 (1980). Published in Phase Diagrams of Binary Magnesium Alloys, 1988. Complete evaluation contains 1 figure, 3 tables, and 22 references. Special Points of the Mg-N System