Фазовая диаграмма системы Be-O

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Be-O (Beryllium-Oxygen) H.A. Wriedt The equilibrium solid phases of the Be-O system are (1) the terminal solid solution, (aBe); (2) the terminal solid solution, (bBe); (3) the hexagonal oxide aBeO; and (4) the tetragonal oxide bBeO. No published diagram has been found for this system. The types of three-phase equilibria have not been established. A largely schematic diagram is shown for the range 0 to 50 at.% O. The phases (aBe) and (bBe) exist stably only at very small oxygen (O2) fugacities; at greater O2 fugacities, BeO is stable. At 0.1 MPa hydrostatic pressure, aBe is stable below 1270 C and bBe is stable from 1270 C to the melting point of bBe. Effects of O on the triple point and melting point have not been detected. The very small O concentrations in (aBe) or (bBe), that are in equilibrium with aBeO, and the (bBe) solidus have not been determined. At 0.1 MPa hydrostatic pressure and temperatures up to 2105 C, aBeO is stable; from 2105 C to the melting point (2550 C [78Cha]), bBeO is stable [62Bak, 64Smi]. Because the undetermined deviations in BeO composition from the stoichiometry are certainly small, the aBeO <259> bBeO transformation is probably not appreciably affected by variations in O2 fugacity. Determination of the exact temperature has been hindered by hysteresis. There is no information concerning the liquidus temperatures between the compositions 0 and 50 at.% O. There is no experimental information on the three-phase equilibrium involving ( aBe), (bBe), and aBeO, or on that involving L, aBeO, and bBeO, but their existence is required. For the former, either a eutectoid or a peritectoid reaction is possible; for the latter, either a peritectic or metatectic reaction is possible. The temperatures are very close to those of the transformations in pure Be and in BeO, respectively. L + (bBe) + aBeO is the only three-phase equilibrium for which any experimental study exists. [ 32Slo] suggested that it is a eutectic reaction. 32Slo: H.A. Sloman, J.Inst. Met, 49, 365-388 (1932). 62Bak: T.W. Baker and P.J. Baldock, Nature, 193, 1172 (1962). 64Smi: D.K. Smith, C.F. Cline, and S.B. Austerman, J. Nucl. Mater., 14, 237- 238 (1964). 78Cha: M.W. Chase, J.L. Curnutt, R.A. McDonald, and A.N. Syverud, J. Phys. Chem. Ref. Data, 7(3), 793-940 (1978). Published in Phase Diagrams of Binary Beryllium Alloys, 1987, and Bull. Alloy Phase Diagrams, 6(6), Dec 1985. Complete evaluation contains 1 figure, 3 tables, and 70 references. Special Points of the Be-O System