Aluminium-Barium-Silicon (Rainer Schmid-Fetzer)
Introduction
The pseudobinary systems BaSi2-Al, BaAl4-BaAl2Si2() and Si- and -Ba have been studied by DTA, metallography and microhardness measurements on samples prepared from the pure elements in corundum crucibles under inert gas, remelted several times and checked by chemical analysis [76Gan, 78Gan]. An isothermal section at 500°C was investigated by additional X-ray studies [78Gan]. The same authors have also presented their data in the form of one liquidus surface for the entire system, without distinguishing between the areas of primary crystallizations of the various solid phases [77Vak]. The interpolation mathematics employed for this purpose by [77Vak] smears out all the individualities of the separate surfaces into one conglomerate which is not reproduced here. The existence of the ternary compound BaAl2Si2() [76Gan, 78Gan] was confirmed by electron probe microanalysis of samples prepared from BaSi2+Al in the presence of Si [84Pev]. A sample of composition BaAl1.5Si0.5 was found to consist of two phases, Ba7Al13 and a ternary phase isotypic with AlB2, by X-ray analysis [75For1], which confirms the existence of a Ba(AlxSi1-x)2 ()-phase [78Gan]. The ternary phase Ba3Al2Si2() has been prepared by fusing the component elements in corundum crucibles under argon at 1200°C for 4 h and slowly cooling to room temperature within 12 h [77Wid]. Single crystals were taken from that sample, checked by wet chemical analysis, the structure was determined by X-ray diffraction and atomic coordinates are given.
This -phase, however, was not found by [78Gan] and its decomposition or melting temperature is unknown.
Binary Systems
The binary systems Al-Ba, Al-Si and Ba-Si from [Mas] are accepted, with the exception of the phases BaAl2 and BaAl. Crystal structure studies have shown these phases to be Ba7Al13 [75For1] and Ba4Al5 [75For2].
Solid Phases
Data on the solid phases are given in Table 1.
Pseudobinary Systems
The pseudobinary systems BaSi2-Al, BaAl4- and -Ba are given in Figs. 1-4 [78Gan]. The decomposition temperature of Ba3Al2Si2() in Fig. 4 is speculative.
Isothermal Sections
The isothermal section at 500°C, Fig. 5, is based upon [78Gan] and was adapted in order to implement the Ba7Al13 and Ba3Al2Si2() phases. The possibility of the existence of a liquid region between the binary Ba-Ba7Al13 eutectic (528°C, 72 at.% Ba) and the Ba- eutectic (545°C, 73 at.% Ba, Fig. 4) may not be ruled out. The magnified Al-corner of the 500°C isothermal section, given by [78Gan], with the solubility limits of the (Al) phase is in conflict with the basic rules of heterogeneous equilibria and also with the accepted Al-Ba binary system and, therefore, it is not presented here.
Miscellaneous
The effect of Si additions to BaAl4 on the Ba vapor pressure and thermodynamic functions have been studied [72Plo, 72Vig]. The enthalpy of mixing of liquid Al-Ba-Si alloys has been investigated at 777°C [86Yat].
References
[72Plo] YU.V. PLOTNIKOV, A.V. VAKHOBOV and V.N. VIGDOROVICH, "The Effect of Si Additions on the Stability of Al-Ba Alloys" (in Russian), Dokl. Akad. Nauk Tadzh. SSR, 15, 36-39 (1972) (Thermodyn., Experimental, 2)
[72Vig] V.N. VIGOROVICH, A.V. VAKHOBOV and YU.V. PLOTNIKOV, "Physicochemical Study of Al-Ba-System Alloys and the Development of Getter Alloys" (in Russian), Sb. Nauch. Tr. Probl. Mikroelektron., Mosk. Inst. Elektron. Tekh, 11, 5-19 (1972) (Thermodyn., Experimental, 15)
[75For1] M.L. FORNASINI and G. BRUZZONE, "The Crystal Structure of the Ba7Al13 Phase", J. Less-Common Met., 40, 335-340 (1975) (Crys. Structure, Experimental, 9)
[75For2] M.L. FORNASINI, "The Crystal Structure of Ba4Al5", Acta Crystallogr. Sect. B, 31, 2551-2552 (1975) (Crys. Structure, Experimental, 6)
[76Gan] I.N. GANIEV, A.V. VAKHOBOV and T.D. DZHURAEV, "Study of Phase Equilibrium and Analysis of Intermolecular Interaction of Barium-Aluminium-Silicon Ternary System", Russ. J. of Phys. Chem., 50, 1850-1853 (1976), translated from Zh. Fiz. Khim., 50, 3115-3118 (1976) (Equi. Diagram, Experimental, #, 13)
[77Vak] A.V. VAKHOBOV, T.D. DZHURAEV and I.N. GANIEV, "Construction of Phase Diagrams for Sr-Al-Si and Ba-Al-Si by Simplex Designing Method", translated from Zavodshaya Laboratoriya, 43, 73-75 (1977) (Equi. Diagram, Experimental, #, 13)
[77Wid] A. WIDERA and H. SCHÄFER, "Preparation and Crystal Structure of A3Al2Si2 (A = Ca, Sr, Ba)" (in German), Z. Naturforsch., 32B, 1349-1351 (1977) (Crys. Structure, Experimental, 3)
[78Gan] I.N. GANIEV, A.V. VAKHOBOV and T.D. DZHURAEV, "The Ba-Al-Si Phase Diagram", Russ. Metall., (4), 183-185 (1978), translated from Izv. Akad. Nauk SSSR, Met., (4), 247-250 (1978) (Equi. Diagram, Experimental, #, *, 6)
[84Pev] V.D. PEVLOTSKII, "Phase Composition of Silicobarium" (in Russian), Izv. V.U.Z. Chernaya Metall., 4, 12-14 (1984) (Experimental, 3)
[86Yat] S.P. YATSENKO, V.D. BUSHMANOV, V.G. POSTOVALOV and E.I. YUR'EVA, "Enthalpy of Formation of Liquid Alloys of Aluminium with Silicon and Barium" (in Russian), Esvetnye Metally, 2, 38-40 (1986) (Thermodyn., Experimental, 10)
Phase / Temperature Range (°C) | Pearson Symbol/ Prototype | Lattice Parameters (pm) | Comments |
Al | cF4 Cu | a = 404.96 | [Mas] |
Ba | cI2 W | a = 502.3 | [Mas] |
Si | cF8 C-diamond | a = 543.06 | [Mas] |
BaAl4 | tI10 BaAl4 | a = 456.6 c = 1125.0 | [P], dissolves ~ 3 at.% Si at 500°C [78Gan] |
Ba7Al13 | hP20 Ba7Al13 | a = 609.9 c = 1726.9 | [78For1] |
BaSi | - | - | [C] |
BaSi2 | hP3 (AlB2) | a = 439 c = 483 | [P], dissolves ~ 4 at.% Al at 500°C [78Gan] |
* α, BaAl2Si2 | - | - |
|
* β, Ba(AlxSi1-x)2 | tetragonal (AlB2) | a = 437 c = 514 | solubility range [78Gan], lattice parameters in equilibrium with BaAl2 [75For] |
* γ, Ba3Al2Si2 | oI14 Ta3B4 | a = 420.4 b = 1957.0 c = 508.1 | ordered variant of Ta3B4 structure type analogous to Ba3Al2Ge2 [77Wid] |
