Calorimetric study of the aluminium–titanium system

Journal of Alloys and Compounds 350 (2003) 151–154

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Calorimetric study of the aluminium–titanium system a a a, b M. Nassik , F.Z. Chrifi-Alaoui , K. Mahdouk *, J.C. Gachon a

´ ´ , Universite´ Ibn Zohr, Faculte´ des Sciences, B.P. 28 /S, Agadir, Morocco Laboratoire de Thermodynamique et Corrosion et Rheologie des Materiaux b ´ , UMR 7555, Service de Thermodynamique Metallurgique ´ , Faculte´ des Sciences, Laboratoire de Chimie du Solide Mineral ` Nancy Cedex, France Universite´ Henri Poincare´ , Nancy 1, B.P. 239, F-54506 Vandœuvre les Received 13 July 2002; accepted 23 July 2002

Abstract The intermetallic compounds of the Al–Ti system were investigated by direct reaction calorimetry at high temperatures. New enthalpies of formation were determined and compared with the available experimental values based on calorimetric measurements and with the predicted values from Miedema’s semi-empirical model. X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA) were used to check the crystal structure and the homogeneity of the calorimetric products.  2002 Elsevier Science B.V. All rights reserved. Keywords: Aluminium; Titanium; Enthalpy; Calorimetry

1. Introduction

2. Experimental methods

In the course of our program concerning the interactions of aluminium with transition metals we have investigated the aluminium–titanium system. The purpose was to provide reliable experimental results usable in theoretical studies as well as in phase diagram computations. We present, in this paper, the enthalpies of formation of the Al 3 Ti, Al 2 Ti, AlTi and AlTi 3 compounds as determined by direct reaction calorimetry at high temperatures. This work constitutes part of a general study of the Al–Ni–Ti ternary system. This system deserves investigation because of its interesting high temperature properties. The Al 5 Ti 2 phase, which was not formed homogeneously in the calorimeter, was not considered. Results are compared with experimental data available in the literature and with predicted values from Miedema’s semi-empirical model. Results of X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA) performed on calorimetric products are discussed and compared with literature data.

Fine powders of Al and Ti were mixed in suitable proportions and compressed at room temperature under purified argon in a glove box. The samples still at room temperature were then dropped under argon into the crucible of a calorimeter, which was kept at a temperature chosen in order to induce the interdiffusion of the components, but below the melting point or peritectic decomposition of the compound under scrutiny. The global thermal effect measured by the calorimeter, Q, is the sum of pure metal heat contents, H TT 10 (i) between room (T 0 ) and calorimeter (T 1 ) temperatures and of the enthalpy of formation, D f H, of the compound at T 1 [1].

*Corresponding author. Tel.: 1212-48-220-957; fax: 1212-48-220100. E-mail addresses: [email protected] (K. Mahdouk), [email protected] (K. Mahdouk).

As the enthalpy increments of the components, H TT 10 (i), are known [2] we can deduce the enthalpy of formation D f H of the solid compound from the components in their equilibrium state at the reaction temperature. The calorimeter calibration was achieved by dropping cold alumina samples (50–100 mg) into the working crucible, the corresponding enthalpy increments being taken from

0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00975-1

M. Nassik et al. / Journal of Alloys and Compounds 350 (2003) 151–154

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the work of the NIST group [3]. After each experiment XRD and EPMA were used to check structure and composition of the products. XRD were performed with molybdenum Ka 1 radiation ( l 50.070926 nm) on samples crushed into powder. The chemical compositions were determined by wavelength dispersive spectroscopy (WDS) on a Cameca microprobe (Service Commun de Mi´ Nancy 1, France). croanalyse, Universite´ Henri Poincare, The starting materials were aluminium powder (2–5 mm, .99 wt.% pure) from Prolabo and titanium (,44 mm, 99 wt.% pure) from Alpha Ventron.

Table 2 Enthalpies of formation of ternary alloys based on the AlTi 3 phase Alloy

Temperature of reaction T (K)

Our measurements (standard deviation)

Table 1 summarises the experimental enthalpies of formation at high temperature of Al 0.75 Ti 0.25 (Al 3 Ti), Al 0.67 Ti 0.33 (Al 2 Ti) and Al 0.50 Ti 0.50 (AlTi). The reference states for the experiments were solid titanium and liquid aluminium. A change of reference states has been made to get enthalpies of formation relative to solid Al (fcc) and Ti (hcp) at the reaction temperatures. This helps to facilitate the comparison with the literature data relative to the Al–Ti system. In Table 2 we give the enthalpies of formation, at 1081 K, of three ternary alloys: Al 0.23 Ni 0.02 Ti 0.75 , Al 0.27 Ni 0.02 Ti 0.71 , and Al 0.37 Ni 0.02 Ti 0.61 , based on the binary AlTi 3 phase. We did not find any experimental result in the literature to compare with our values for these ternary compositions.

Literature Experimental

Al 0.23 Ni 0.02 Ti 0.75 Al 0.27 Ni 0.02 Ti 0.71

1081

Al 0.37 Ni 0.02 Ti 0.61

3. Results and discussion

Molar enthalpy of formation (kJ mol 21 )

(a)

(b)

220.3 (0.5) 226.4 (0.4) 233.1 (1.3)

217.9 (0.5) 223.6 (0.4) 229.3 (1.3)

225.161* [5] 23061 [ [5] 7

(a) Relative to liquid Al and solid Ti (hcp) at the reaction temperatures. (b) Relative to solid Al (fcc) and solid Ti (hcp) at the reaction temperatures. *For Al 0.25 Ti 0.75 . [ For Al 0.35 Ti 0.65 .

3.1. Al0.75 Ti0.25 (Al3 Ti) The enthalpy of formation of Al 0.75 Ti 0.25 after five measurements at 1073 K was: D f H (Al 0.75 Ti 0.25 ; 1073 K) 5 2 47 00061800 J mol 21 Our value is more exothermic than the experimental ones from the published literature [4–7], all based on calorimetric measurements. The difference between our value and that of Meschel

Table 1 Enthalpies of formation of intermetallic compounds in the Al–Ti system Compound

Temperature of reaction T (K)

Molar enthalpy of formation (kJ mol 21 ) Our measurements (standard deviation)

Literature

(a)

(b)

Al 3 Ti (Al 0.75 Ti 0.25 )

1073

247 (1.8)

239.2 (1.8)

Al 2 Ti (Al 0.67 Ti 0.33 ) AlTi (Al 0.50 Ti 0.50 )

1073

244 (0.9) 240.2 (0.5)

237.1 (0.9) 235.1 (0.5)

1173

(a) Relative to liquid Al and solid Ti (hcp) at the reaction temperatures. (b) Relative to solid Al (fcc) and solid Ti (hcp) at the reaction temperatures. *Standard enthalpies of formation at 25 8C. [ Enthalpies of formation for an average temperature of 548 K. **Enthalpies of formation for temperatures between 573 and 623 K. 1 For Al 0.5925 Ti 0.4075 . 2 For Al 0.60 Ti 0.40 .

Experimental

Calculated*

236.661.1 [ [4] 235.561 ** [5] 237* [6] 236.661.2* [7] 240.961 [1 [4] 238.861 ** 2 [5] 240.161 [ [4] 236.461 ** [5]

238.5 [8] 239 [9]

242 [8] 250 [9] 233.8 [15] 234.4 [8] 261 [9]

M. Nassik et al. / Journal of Alloys and Compounds 350 (2003) 151–154

and Kleppa [7], who have used the direct reaction calorimetry technique, can be interpreted as due to the difference between the heat contents of the components and the compound. Indeed, according to the heat contents, of the pure metals and the Al 3 Ti compound, taken from Barin and Platzki [2] we found an enthalpy increment of 30 600 J mol 21 for the mixture 25at.%Ti175at.%Al and 21 780 J mol 21 for the Al 3 Ti compound between 298 and 1073 K. Thermodynamically D f H(298 K) 1

E

1073

Cp(compound)dT

298

must be the same as D f H(1073 K) 1

E

1073

Cp(0.25Ti 1 0.75Al)dT,

298

so it appears that between our value and that of Meschel and Kleppa the difference is about 1580 J mol 21 which is of the same order of magnitude as the experimental errors. Our experimental result, referred to solid Al (fcc) and Ti (hcp), is also in good agreement with the value deduced by Kattner et al. [8] from phase diagram calculations and with the predicted value from Miedema’s semi-empirical model [9]. XRD analysis confirmed the tetragonal structure of Al 3 Ti [10]. The EPMA results showed that both homogeneity and stoichiometry (73.760.4 at.%Al) were correct.

3.2. Al0.67 Ti0.33 (Al2 Ti) The enthalpy of formation of Al 0.67 Ti 0.33 after five measurements at 1073 K was: D f H (Al 0.67 Ti 0.33 ; 1073 K)5 244 0006900 J mol 21 . With solid Al (fcc) and Ti (hcp) as references this value becomes: 237 1006900 J mol 21 . This result is in good agreement (Table 1) with the earlier calorimetric value determined by Kubaschewski and co-workers [4,5] using calorimetric methods, although the value reported by Kubaschewski and Heymer (238.861000 kJ mol 21 ) [5] is less exothermic than that reported by Kubaschewski and Dench (240.961 kJ mol 21 ) [4]. Note that this is the case for every intermetallic compound of the Al–Ti system. On the other hand, both calculated values from Miedema’s semi-empirical model (250 kJ mol 21 ) [9] and phase diagram optimization by Kattner et al. (242 kJ mol 21 ) [8] are more exothermic than our experimental one. Examination of the products by X-rays confirmed the tetragonal Ga 2 Hf-type structure [11–14]. EPMA analysis showed that both homogeneity and stoichiometry were correct (66.660.8 at.%Al). However, small amounts of Al 3 Ti and AlTi phases were detected.

153

3.3. Al0.50 Ti0.50 (AlTi) Our attempt to synthesise the AlTi phase, at 1073 K showed an incomplete reaction. However, at 1173 K, we obtained a complete reaction and the enthalpy of formation of Al 0.50 Ti 0.50 after five measurements was: D f H (Al 0.50 Ti 0.50 ; 1173 K)5 242 3006500 J mol 21 . With liquid Al and solid Ti (hcp) reference states [2], this value becomes: 240 2006500 J mol 21 . Whereas with solid metal reference states, Al (fcc) and Ti (hcp) [2] the enthalpy of formation becomes: 235 1006500 J mol 21 . The experimental value (Table 1) reported by Kubaschewski and Heymer (236 40061000 J mol 21 ) [5] is in excellent agreement with our result, whereas Kubaschew21 ski and Dench’s value [4] (240 10061000 J mol ) is slightly more exothermic. This difference may arise from the effects of the impurities of the titanium powder (98.3% pure) used by these authors. These impurities can involve, indeed, a relatively high amount of additional heat, particularly at high titanium contents. The tight-binding theory of Pasturel et al. [15] predicts, for the equiatomic compound, an enthalpy value (233 800 J mol 21 ), which is in excellent agreement with our result, whereas, we found a significant disagreement with the predicted value from the semi-empirical model of Miedema and co-workers (261 000 J mol 21 ) [9]. It is worth noting that this model predicts a parabolic variation of the enthalpy of formation versus the concentration with a maximum very near x550 at.% (for equiatomic alloys) but this is not really always true. According to the heat contents of pure metals and the AlTi compound, taken from Barin and Platzki [2], we found an enthalpy increment of 33 300 J mol 21 for the mixture 50 at.%Al150 at.%Ti and 25 450 J mol 21 for the AlTi compound between 298 and 1173 K. Thus we can deduce the standard enthalpy of formation of AlTi, referred to Al (cfc) and Ti (hcp), at 298 K: D f H (Al 0.50 Ti 0.50 ; 298 K)5 234 450 J mol 21 . Note that this value is nearly the same as the enthalpy of formation at 1173 K referred, of course, to Al (cfc) and Ti (hcp). XRD analysis confirmed the tetragonal AuCu-type structure [16]. EPMA results showed that the product was a single phase.

3.4. The AlTi3 phase In the course of this study we have not considered the binary AlTi 3 phase. Only ternary alloys containing 2 at.% of Ni, corresponding to the (z) ternary phase [17,18], were studied. The enthalpies of formation were determined, at 1081 K, for the following alloys: Al 0.23 Ni 0.02 Ti 0.75 , Al 0.27 Ni 0.02 Ti 0.71 , and Al 0.37 Ni 0.02 Ti 0.61 . Results are summarised in Table 2. We did not find any experimental result in the literature for comparison with our values for these

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154

Fig. 1. Concentration dependence of the enthalpy of formation in the solid Al–Ti system and comparison with literature data.

ternary compositions. These values are reported in Fig. 1 together with those obtained for the binary phases.

References [1] J.C. Gachon, J. Hertz, Calphad 7 (1983) 1. [2] I. Barin, G. Platzki, in: Thermochemical Data of Pure Substances, 3rd Edition, VCH, Weinheim, 1995, Parts I and II. [3] D.A. Ditmars, S. Ishihara, S.S. Chang, G. Bernstein, E.D. West, J. Res. N.B.S. 87 (1982) 159. [4] O. Kubaschewski, W.A. Dench, Acta Met. 3 (1955) 339. [5] O. Kubaschewski, G. Heymer, Trans. Faraday Soc. 56 (1960) 473. [6] J.M. Stuve, J.M. Ferrante, US Bureau of Mines Report Invest. No. 7834, 1974. [7] S.V. Meschel, O.J. Kleppa, NATO ASI Ser., Ser. E 256 (1994) 103.

[8] U.R. Kattner, J.C. Lin, Y.A. Chang, Metall. Trans. A 23A (1992) 2081. [9] F.R. de Boer, R. Boom, W.C.M. Mattens, A.R. Miedema, A.K. Niessen, in: Cohesion in Metals, North Holland, Amsterdam, 1988. [10] P. Norby, A. Norlund, Acta Chem. Scand., Ser. A 40 (1986) 157. [11] A. Raman, K. Schubert, Z. Metallkd. 56 (1965) 99. [12] F.J.J. Van Loo, G.D. Rieck, Acta Metall. 21 (1973) 73. [13] R. Miida, M. Kasahara, D. Watanabe, Jpn. J. Appl. Phys. 19 (11) (1980) 1707. [14] H. Mabuchi, T. Asai, Y. Nakayama, Scripta Metall. 23 (1989) 685. [15] A. Pasturel, D. Nguyen Manh, D. Mayou, J. Phys. Chem. Solids 47 (1986) 325. [16] H.R. Ogden, D.J. Maykuth, W.L. Finlay, R.J. Jafee, Trans. AIME 191 (1951) 1150. [17] K.J. Lee, P.G. Nash, J. Phase Equilibria 12 (5) (1991) 551. [18] P.G. Nash, V. Vejins, W.W. Liang, Bull. Alloy Phase Diagrams 3 (3) (1982) 367.