Phase relationships of the La–Al–Sb system at 773 K from 0 to 50.0 at.% Sb

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Abstract

The La–Al–Sb phase diagram between 0 and 50.0 at.% Sb at 773 K was investigated by means of X-ray powder diffraction (XRD), Rietveld method and scanning electron microscopy (SEM) techniques. A new binary compound La2Al was found, it crystallizes in the tetragonal structure with a = 17.0942 (1) Å, c = 5.3790 (3) Å. The results show that this section consists of 14 single-phase regions, 25 two-phase regions and 12 three-phase regions. None of these phases in this system revealed a remarkable homogeneity range at 773 K.

Introduction

The rare earth (R) alloying is interesting not only from a fundamental point of view, but also because of possible technological applications. A possible example can be found in the rare earth additions to Al-based alloys. The beneficial effects on tensile strength, heat resistance and corrosion resistance have been described [1], [2], [3].

Attention has also been dedicated to the glass forming capability of several R–Al alloys and their ternary derivatives. Preparation, properties and applications of several R–Al–Me alloys have been described and discussed [4], [5], [6]. The phase diagram is an important basis for materials research and materials application. For the R–Al–Sb systems, the phase relations have not been investigated except the Y–Al–Sb [7], Pr–Al–Sb [8], Al–Nd–Sb [9] and Dy–Al–Sb [10] ternary system. In this work, we investigated the phase relationship in the La–Al–Sb ternary system at 773 K.

The binary phase diagrams of the La–Al, Al–Sb, La–Sb systems have been investigated previously and summarized in Ref. [11]. At 773 K, there is one intermetallic phase AlSb in the Al–Sb system, four compounds La2Sb, La3Sb2, LaSb and LaSb2 in the La–Sb system, and five intermetallic phases La3Al, LaAl, LaAl2, La Al3, La3Al11 in the La–Al system. In addition the existence of Al4La5 [12], La5Sb3 [13] and La4Sb3 [14] have been reported in literature.

Section snippets

Experimental details

For sample preparation, the ingots of lanthanum (99.5 wt.%), aluminum (99.95 wt%) and antimony (99.9 wt%) were used. Samples were prepared by arc melting on a water-cooled copper crucible with a non-consumable tungsten electrode under high pure argon atmosphere. The alloys were re-melted three times in order to achieve complete fusion and homogeneous composition. As-cast samples were sealed in vacuum quartz tubes and annealed at 773 K for 30 days, then quenched into liquid nitrogen. The

Binary compounds

In this work, we have studied the binary systems Al–La, La–Sb and Al–Sb at 773 K to identify binary compounds before the ternary phase analysis. In the Al–Sb system, one binary compound AlSb was confirmed. In the La–Sb system, the binary compound La3Sb2 was not observed. We identified four compounds La2Sb, La5Sb3, La4Sb3 and LaSb (0–50 at.% Sb). This result is in good agreement with that reported in Refs. [16], [17]. In the Al–La system, a new binary compound La2Al was found and the existence of

Conclusion

Partial isothermal section of the phase diagram of the Al–La–Sb ternary system at 773 K (up to 50 at.% Sb) has been determined. There are 12 binary compounds and no ternary compound. A new binary compound La2Al was found. Its XRD pattern has been indexed with tetragonal structure and a = 17.0942 (1) Å, c = 5.3790 (3) Å. None of the phases found in this system has a remarkable homogeneity range at 773 K.

Acknowledgements

This work was jointly supported by the National Natural Science Foundation of China (Grant No. 50961002) and the Natural Science Foundation of Guangxi (No. 0832027)

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