Фазовая диаграмма системы Hf-Si

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Hf-Si (Hafnium-Silicon) A.B. Gokhale and G.J. Abbaschian The assessed phase diagram for the Hf-Si system is based primarily on the work of [68Bru], considered to be the most reliable because of thoroughness of the investigation, comprehensive experimental techniques utilized, and the number of alloys used in the determination of phase equilibria. The maximum terminal solid solubility of Si in (bHf) is less than 1 at.%; that of Hf in (Si) has not been determined, but is likely to be very small. A peritectoid reaction was included tentatively in the Hf-rich side of the assessed diagram. This is based on the observation of [68Bru], who indicated the presence of a thermal arrest on the Hf-rich side at ~1770 C (above the allotropic transformation temperature of Hf at 1743 C). This suggests that the addition of Si increases the allotropic trasformation temperature of Hf, possibly through a peritectoid-type reaction. The incipient melting temperatures indicated by [68Bru] are temperatures at which an appreciable amount of liquid was present in the samples. Because these temperatures are considerably higher than those at which the first liquid forms, the liquidus was not determined reliably by [68Bru]. [60Now], [60Vic], and [71Shu] reported the presence of "Hf5Si3" whereas [68Bru] showed that the phase occurs only when stabilized by oxygen, nitrogen, or carbon. This finding is supported by data of [58Kie] and [58Now]. The phase appears to be ternary or higher order and consequently has been excluded from the assessed diagram. According to [60Vic], the electrical resistivities of Hf2Si, HfSi, ("Hf6Si5"), and HfSi2 increase linearly with temperature in the range 30 to 800 C. They reported the Seebeck coefficients for Hf2Si, Hf5Si4 ("Hf4Si3"), and HfSi2 at 30 C to be 35, 22, 18, and 30 mv/C, respectively. The heat of formation of HfSi2, estimated on the basis of volume contraction, was found to range between -167 and -209 kJ/mol [57Smi]. 57Smi: J.F. Smith and D.M. Bailey, Acta Crystallogr., 10, 341-342 (1957). 58Kie: R. Kieffer and F. Benesovsky, Powder Metall., 1/2, 145-171 (1958). 58Now: H. Nowotny, E. Laube, T. Kieffer, and F. Benesovsky, Monatsh. Chem., 89, 701-707 (1958) in German. 60Now: H. Nowotny, H. Braun, and F. Benesovsky, Radex Rundsch., 6, 367-372 ( 1960) in German. 60Vic: R.C. Vickery and H.M. Muir, Tech. Rep. Research Chemicals, No. RC-145, AD 258218, Dept. of the Navy, Bureau of Ships, Washington, DC, 88 p (1960). 68Bru: C.E. Brukl, Tech. Rep. AFML-TR- 65-2, Air Force Materials Lab., WPAFB, OH, 72 p (1968). 69Kar: O.G. Karpinsky and B.A. Evseev, Russ. Metall., 3, 128-130 (1969). 71Shu: A.K. Shurin and N. Todorov, Metallogzika, 33, 100-102 (1971) in Russian. Published in Bull. Alloy Phase Diagrams, 10(4), Aug 1989. Complete evaluation contains 1 figure, 4 tables, and 16 references.