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Formation enthalpy of intermetallic phases from Al–Fe system measured with solution calorimetric method
Intermetallics 24 (2012) 99e105
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Intermetallics journal homepage: www.elsevier.com/locate/intermet
Formation enthalpy of intermetallic phases from AleFe system measured with solution calorimetric method W. Ga˛sior, A. De˛ bski*, Z. Moser Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25, Reymonta Street, 30-059 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 September 2011 Received in revised form 31 January 2012 Accepted 1 February 2012 Available online 25 February 2012
The solution calorimetric method was used for the determination of the formation enthalpy of Al2Fe and Al5Fe2 intermetallic phases. The phases were prepared in a very pure Ar atmosphere by melting the calculated amounts of Al and Fe in alumina crucibles. Their crystal structure was confirmed with the Xray diffraction method. A very low amount of Al5Fe2 phase was found in the Al2Fe phase. The calorimetric experiments were carried out using an Al bath at temperature 1271 K. The formation enthalpies of the Al5Fe2 and Al2Fe phases obtained at room temperature were 30.5 and 27.8 kJ/mol of atoms, respectively. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Aluminides, miscellaneous B. Phase diagrams B. Phase identification B. Thermodynamic and thermochemical properties F. Calorimetry
1. Introduction Alloys of the AleFe system are characterized by a good oxidation resistance and good strength at high temperature, so they are promising for applications in many branches of industry. However, their thermodynamic properties have not been intensively studied for the last twenty years. Most of experimental works were conducted before 1990 year. The activity of Al in solid alloys were studied by Eldridge and Komarek [1], Radcliffe et al. [2] and Kleykamp and Glasbrenner [3] using the electromotive force measurements as well as by Belton and Fruehan [4], Bencze et al. [5,6] and Ichise et al. [7] applying the vapor pressure and Knudsen’s effusion mass spectrometer method. The formation enthalpy of solid alloys from the region of AlFe solid solution at 1073 K was measured by Breuer et al. [8] with the solution calorimetric technique. The same method was applied by Rzyman et al. [9] for the examinations of intermetallic phases and the AlFe (B2 cP2 Al40Fe60, Al45Fe55, Al50Fe50) solid solution and by Feutelais et al. [10]. Kubaschewski and Dench [11] conducted the formation enthalpy measurements at the melting temperature of Al by a direct reaction calorimetric method. Oelsen and Middel [12] obtained the formation enthalpy of numerous AlFe solid alloys of
* Corresponding author. E-mail address: [email protected] (A. De˛ bski). 0966-9795/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2012.02.001
Al content XAl between 0.06 and 0.75 measuring the heat effect of direct reaction of liquid Al and Fe at 293 K. The same method was used by Biltz [13] to obtain the formation enthalpy of Fe3Al (D03 cF16) phase at 298 K and Ferro [14] for the Al0.5Fe0.5 alloy at 301 K. Meschel and Kleppa [15e17] used the direct synthesis (reaction) calorimetry to obtain the formation enthalpy of Al0.5Fe0.5 alloy. However, information on structural analysis of samples after their preparation can be found only in the paper of Breuer and coauthors [8] and Meschel and Kleppa [15e17]. It should be noted that the formation enthalpy data of intermetallic phases from the AleFe system, obtained by the CALPHAD-type assessment, were published in Ref. [18e22]. Additionally, Lechermann et al. [23] carried out the calculations of the formation enthalpy of Al3Fe (mC102) and AlFe3 phases using the ab initio density functional theory (DFT) with the mixed-basis pseudo-potential code. Maugis et al. [24] and Gonzales-Ormeno et al. [25] performed the calculations for the AlFe and AlFe3 using the DFT combined with the projector augmented wave (PAW) method and the full potential-linear augmented plane wave (FPLAPW) technique, respectively. The calculations using the Miedema model were performed by deBoer et al. [26] for the Fe0.5Al0.5-B2, Al3Fe and Al2Fe phases. The AleFe phase diagram was of interest for many scientist groups, who presented their results in the literature [27e33], (Kattner and Burton [27] in Massalski [28], SGTE 2007 alloy database (FactSage) [29], Thermodata Nuclear Databas-DNucl (FactSage)
100
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
Fig. 1. The AleFe phase diagram presented in Ref. [27,28].
[30], Du et al. [31], Sundman et al. [32], Jacobs and SchmideFetzer [33]). They generally are similar and the differences concern the existence of a homogenous region of intermetallic phases. Only two: Al2Fe (aP18) and Al5Fe2 (hP28) out of the intermetallic phases were accepted in all cited works. Instead of the Al3Fe phase proposed in Ref. [27,28,30,32], the Al13Fe4 (mC102) was assumed in Ref. [29,31]. Also the Al5Fe4 suggested in Ref. [29,31] was substituted by the Al8Fe5 (cI52) [27,28,32] or Al3Fe2 [30], while the AlFe3 phase was not always taken into consideration. The other differences are shown in Figs. 1e6. Jacobs and SchmideFetzer [33] additionally analyzed the influence of the model used for the description of the aFe and FeAl phases at their equilibrium phase boundary (more details in Ref. [33]). The observed differences among the AleFe phase diagrams are most probably caused by serious experimental and computational problems and high complexity of the system. Unfortunately, the most results of the energetic effect accompanying the reaction in the direct reaction, solution and drop
calorimeter were not followed and confirmed by a structural analysis of the phases investigated by the authors (except of [8,15e17]). Therefore, the main aim of the work was measuring the formation enthalpies of Al2Fe and Al5Fe2 phases by the solution calorimetric method using the liquid aluminum as a solvent after their X-ray and scanning electron microscopy analysis. 2. Solution calorimetric method The measurement of the formation enthalpy of intermetallic phases has been based on the determination of energetic effects accompanying the dissolution of elements and the prepared phase in the solvent which, in many investigations, is aluminum [34,35]. The equation used in the calculation of formation enthalpy of AleFe intermetallic phases is as follows: ef ef ef Df H ¼ XAl DHAl þ XFe DHFe DHAl X
Al
Fig. 2. Microstructure of the Al5Fe2 alloy obtained with the back scattered electrons technique (BSE).
FeXFe
(1)
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
Fig. 3. Microstructure of the Al2Fe alloy obtained with the back scattered electrons technique (BSE).
Fig. 4. Diffraction pattern of Al5Fe2 intermetallic phase.
Fig. 5. Diffraction pattern of Al2Fe intermetallic phase. Small amount of Al5Fe2 was also detected.
101
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
102
Fig. 6. Formation enthalpies of solid alloys and phases obtained with different experimental methods (Fe-bcc and Al-fcc are reference states) [23]. 2005 Lec* reference state Al-fcc, Fe-fcc.
where: DfH denotes the formation enthalpy of intermetallic phase at room temperature, XAl and XFe, are mole fractions of the phase ef ; DH ef , are dissolution heat effects of one elements (Al, Fe), DHAl Fe ef mole atoms of aluminum and iron in the solvent and DHAl X
Al
FeXFe
is
the heat effect accompanying the dissolution of one gram-atom of intermetallic phase from the AleFe system in the aluminum bath at temperature T. The last quantity was each time determined from the measurements. In the present work the fcc solid aluminum and bcc iron were assumed to be the reference state. The investigations were carried out in a high temperature calorimeter whose construction and performance were presented in Ref. [35]. The calibration procedure was conducted in each measurement, by the dissolution of aluminum samples in the metal bath. They were immersed in the bath from the room temperature. The calorimetric constant was assessed based on the measurements of ten Al samples. The limiting enthalpy of solution of iron in aluminum at 1273 K (120 kJ/g-atom) was taken from earlier calorimetric investigations of alloys from the homogenous region of FeNi3 phase [34] which were carried out in the same conditions as in that study. Aluminum and iron purity used in the preparation of phases is shown in Table 1. 3. Preparation of phases The Al5Fe2 and Al2Fe phases were produced by melting of Al and Fe metals in the glove-box filled with a high purity Ar protective
atmosphere. In order to keep the level of impurities (O2, H2O and N2) in Ar very low, the circulation was conducted between the glove-box and purifying system with the catalytic copper, molecular sieve and Ti-sponge absorber. The metals were melted in alumina crucibles at temperature 1873 K (1600 C). After melting and fine mixing, the alloys were cooled together with the furnace to room temperature. The alloys of compositions of Al5Fe2 and Al2Fe intermetallic phases prepared in such a way were used for the X-ray and EDS analysis and calorimetric studies. 4. Results and discussion The prepared samples of phases were investigated with the scanning electron microscopy and X-ray diffraction to confirm their structure. The results of EDS (electron diffraction scanning) and Xray diffraction analysis are shown in Figs. 2e5 and in Tables 2 and 3. The microstructure of Al2Fe5 phase is presented in Fig. 2. The black areas are pores and the rest of the material has a homogeneous constitution. The microstructure of the second sample is shown in Fig. 3. This time the EDS analysis revealed also inclusions of the Al2Fe5 phase apart from the Al2Fe phase. The X-ray analysis of the Al2Fe5 and Al2Fe samples, shown in Figs. 4 and 5, confirmed the existence of the desired phases in the prepared samples. In the second sample, apart from the Al2Fe, also Table 2 Composition of Al5Fe2 intermetallic phase identified with EDS technique. Al5Fe2 phase
Table 1 Metals applied in the calorimetric study.
Mass.%
At.%
Notes
Metal
Purity [mass%]
Producer
Al
Fe
Al
Fe
Al Fe
99.99 99.97
Z.M. Trzebinia Alfa Aesar
52.06 52
47.94 48
69.21 69.15
30.79 30.85
Lighter zone Darker zone
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105 Table 3 Chemical composition of Al2Fe intermetallic phase obtained with EDS technique. Al2Fe phase % Mass
% At. Fe
Al
Fe
47.53 47.49 46.93 52.23 51.97 47.2 51.53
52.47 52.51 53.07 47.77 48.03 52.8 48.47
65.22 65.18 64.67 69.36 69.13 64.91 68.75
34.78 34.82 35.33 30.64 30.87 35.09 31.25
Matrix Matrix Matrix Inclusions Inclusions Inclusions Inclusions
Table 4 Lattice parameters of intermetallic phases from Al-Fe system. Phase
Lattice parameter [nm] a
b
c
References
Al2Fe
0.761 0.762 0.765 0.760
1.692 1.682 0.641 0.640
0.487 0.486 0.422 0.426
[37] This study [38] This study
Al5Fe2
Table 5 Formation enthalpy at 298 K and heat effect of dissolution of Al2Fe phase in the Al bath at temperature 1271 2 K. Phase
Al2Fe
Measurement temperature [K]
298
Sample number
1 2 3 4 5 Average value Standard deviation
Heat effect DHef [kJ/mol of atoms]
Formation enthalpy DfH [kJ/mol of atoms]
32.0 30.5 29.6 26.9 30.2 29.8 1.9
29.9 28.5 27.6 24.8 28.2 L27.8 1.9
small amounts of Al5Fe2 phase were detected. However, its influence on the final results of calorimetric measurement of the enthalpy of formation was very low. The results of calculation of lattice parameters for the Al2Fe and Al5Fe2 intermetallic phases are presented in Table 4 together with these obtained in Ref. [36,37] and the observed differences are lower than 1%. In the following step, the obtained phases were cut into small pieces suitable for using in the calorimeter. The experiments were conducted in the Al bath at 1271 K. The samples were dropped into the calorimeter from room temperatures (298 K, 300 K) what means that the formation enthalpies were determined at those temperatures. All results of investigations are presented in Tables 5, 6. The experiments of solution were carried out on five and six Table 6 Formation enthalpy at 300 K and heat effect of dissolution of Al5Fe2 phase in the Al bath at temperature 1271 2K. Phase Measurement Sample number temperature [K]
Heat effect Formation enthalpy DHef [kJ/mol DfH [kJ/mol of of atoms] atoms]
Al5Fe2 300
38.5 40.0 35.5 36.8 38.9 39.1 38.1 1.7
1 2 3 4 5 6 Average value Standard deviation
Table 7 Calculated and experimental enthalpies of formation of Al-Fe alloys. Alloy
DfH [kJ/mol T [K] of atoms]
Al0.67Fe0.33 Al0.71Fe0.29
27.8 30.5
Al0.3Fe0.7 Al0.325Fe0.675 Al0.35Fe0.65 Al0.3625Fe0.6375 Al0.36875Fe0.63125 Al0.375Fe0.625 Al0.3875Fe0.6125 Al0.39375Fe0.60625 Al0.4Fe0.6 Al0.425Fe0.575 Al0.45Fe0.55 Al0.475Fe0.525 Al0.5Fe0.5 Al0.06Fe0.94 Al0.1Fe0.9 Al0.15Fe0.85 Al0.18Fe0.82 Al0.24Fe0.76 Al0.27Fe0.73 Al0.32Fe0.68 Al0.34Fe0.66 Al0.49Fe0.51 Al0.5Fe0.5 Al0.67Fe0.33 Al0.71Fe0.29 Al0.75Fe0.25 Al0.3Fe0.7 Al0.4Fe0.6 Al0.4Fe0.6 Al0.5Fe0.5 Al0.667Fe0.333 Al0.714Fe0.286 Al0.75Fe0.25 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.45Fe0.55 Al0.4Fe0.6 Al0.75Fe0.25
27.15 27.23 27.83 28.35 28.61 31.19 30.53 30.52 30.82 33.12 34.10 35.72 36.29 3.4 6.3 9 11.9 14 15.6 19.4 19.4 24 25.6 27.4 27.8 28.1 15.7 19.9 20.1 25.1 26.2 28.7 27.9 26.7 27 22.9 22.5 27.2 23 19.9 26.2
Al0.5Fe0.5
42
Al0.5Fe0.5
23.5
Al0.55Fe0.45 Al0.75Fe0.25 Al0.67Fe0.33 Al0.71Fe0.29 Al0.64Fe0.36 Al0.5Fe0.5 Al0.26Fe0.74 Al0.5Fe0.5 Al0.67Fe0.33 Al0.75Fe0.25 Al0.5Fe0.5
19.958 28.5733 29.6492 30.0396 35.7 28.6 42.4 32 25 19 25.1
Notes
Al
30.9 32.3 27.8 29.1 31.2 31.4 L30.5 1.7
103
Method and remarks 298 Solutions 300 calorimetry. Reference state: Al-fcc, Fe-bcc. S** 1073 Solutions calorimetry Reference state: Fe(s, fcc) and Al(l). S**
Ref. This study
[8] 2001 Breuer
293 Drop direct calorimetry Data quoted in Ref. [11]. Reference state: Al-fcc, Fe-bcc.
[12] 1937 Oelsen
298 Direct reaction calorimetry. Reference state: Al-fcc, Fe-bcc.
[11] 1955 Kubaschewski
296 296 791 792 1029 296 296 298
Solutions calorimetry. Reference state: Al-fcc, Fe-bcc.
Acid solutions calorimetry Reference state: Al-fcc, Fe-bcc. 0 FLASTO Reference state Al-fcc, Fe-bcc. 298 Direct reaction calorimetry. Reference state: Al-fcc, Fe-bcc. S** 298 Calphad method. Reference state: Al-fcc, Fe-bcc.
900e1100 EMF Reference state: Al-Fcc, Fe-bcc. 1000 Miedema model. Reference state: Al-fcc, Fe-bcc. 298 Quoted in [39] Reference state: Al-fcc, Fe-bcc.
[9] 2001 Rzyman
[13] 1937 Biltz
[38],a
[17] 1994 Kleppa
[20] 1995 Ansara quoted in [21] [3] 1997 Kleykamp [26] 1988 deBoer [22], 1980 Chang
(continued on next page)
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
104 Table 7 (continued ) Alloy
DfH [kJ/mol T [K] of atoms]
Al0.28Fe0.72
24.645
Al0.5Fe0.5 Al0.25Fe0.75
27.9 18.6
Al0.5Fe0.5 Al0.25Fe0.75
31.3 20.2
Al0.05Fe0.95 Al0.1Fe0.9 Al0.15Fe0.85 Al0.2Fe0.8 Al0.25Fe0.75 Al0.3Fe0.7 Al0.35Fe0.65 Al0.4Fe0.6 Al0.45Fe0.55 Al0.5Fe0.5 Al0.52Fe0.48 Al0.55Fe0.45 Al0.6Fe0.4 Al0.65Fe0.35 Al0.67Fe0.33 Al0.7Fe0.3 Al0.72Fe0.28 Al0.74Fe0.26 Al0.76Fe0.24 Al0.05Fe0.95 Al0.1Fe0.9 Al0.15Fe0.85 Al0.2Fe0.8 Al0.25Fe0.75 Al0.3Fe0.7 Al0.35Fe0.65 Al0.4Fe0.6 Al0.45Fe0.55 Al0.5Fe0.5 Al0.52Fe0.48 Al0.6Fe0.4 Al0.67Fe0.23 Al0.7Fe0.3 Al0.75Fe0.25 Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
4.4 9.4 13.8 18.0 21.6 24.7 27.8 30.3 32.4 34.3 34.5 34.5 34.5 34.5 34.3 33.5 33.1 32.4 31.4 4.6 8.8 13.0 16.7 19.9 23.0 25.5 27.8 29.5 30.6 30.8 31.6 32.3 32.7 30.6 10.2 27.9 1.3
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
19.4 30 1.3
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
16.8 6.7 10.2
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
21.4 26.1 10.2
Al0.5Fe0.5
23.8
Table 7 (continued ) Method and remarks 298 Solutions calorimetry Tian-Calvet. Reference state: Al-fcc, Fe-bcc. 0 Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, without spin Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, with spin. 1173 EMF Reference state: Al-fcc, Fe-bcc.
Ref.
Alloy
DfH [kJ/mol T [K] of atoms]
[10] 2001 Feutelais
Al0.3Fe0.7 Al0.325Fe0.675 Al0.325Fe0.675 Al0.35Fe0.65 Al0.375Fe0.625 Al0.4Fe0.6 Al0.45Fe0.55 Al0.4Fe0.6 Al0.45Fe0.55 Al0.48Fe0.52 Al0.51Fe0.49 Al0.32Fe0.68 Al0.33Fe0.67 Al0.34Fe0.66 Al0.45Fe0.55
23.15 25.81 25.63 27.8 29.8 32.03 35.5 34.03 34.78 35 36.14 23.6 24.4 22.7 36.6
Al0.5Fe0.5
24.4
Al0.5Fe0.5 Al0.25Fe0.75
32.2 19.3
[25] 2002 Gonzales
[2] 1961 Radcliffe
Method and remarks
Ref.
1140e1600 Vapor pressure and [5] 2003 Knudsen’s effusion Bencze mass spectrometer method. Reference state: Fe(s, fcc) and Al(l).
1180e1508 1100 Calphad Method Reference state: Al-fcc, Fe-bcc. 0 Ab initio density functional theory (DFT). Reference state :Al-fcc, Fe-bcc.
[6] 2006 Bencze [18] 1981 Ansara quoted in [9] [24] 2006 Maugis
S** e Structural characterization was performed. a R. E. Watson e quoted in Ref. [9].
1173 Isopiestic method. Reference state: Al-fcc, Fe-bcc.
0 Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, spin unpolarized calculations. Reference state: Al-bcc, Fe-bcc, spin polarized calculations. Reference state: Al-fcc, Fe-fcc, spin unpolarized calculations. Reference state: Al-fcc, Fe-fcc, spin polarized calculations. 298 Direct reaction calorimetry. Reference state Al-fcc, Fe-bcc.
[1] 1964 Eldrich
[23] 2005 Lechermann
samples for Al2Fe and Al5Fe2 phases, respectively (Tables 5 and 6). The determined values of formation enthalpy were 27.8 kJ/mol of atoms for the Al2Fe intermetallic phase and 30.5 kJ/mol of atoms for the Al5Fe2 one. The set of experimental data of the formation enthalpy of AleFe solid alloys obtained with different calorimetric techniques, recalculated using the EMF data, results of partial pressure measurements and calculated using different models are shown in Table 7 and Fig. 6. This comparison shows that the differences between these data reach even about 20 kJ/mol of atoms especially in the concentration region from 0.4 up to 0.8 mole fraction of Al. The data obtained for the Al2Fe phase using the calorimetric technique [11,12] are very close to the value measured in this study and the results obtained from the EMF and partial pressure measurements [1,2] are by 4e7 kJ/mol of atoms lower than these measured by the calorimetric method in Ref. [11,12], this study. The formation enthalpy of the Al66Fe34 phase calculated based on the Miedema model [26] is by about 2 kJ/mol of atoms less exothermic, while the enthalpy reported in [19e21] is more exothermic in comparison to the data measured in this study. The value of formation enthalpy of Al5Fe2 phase observed in this work is almost the average value of the data given in Ref. [1,2,11,12] and the observed differences oscillate around 2.5 kJ/mol of atoms and it is only 0.5 kJ/mol of atoms lower than the value measured in this work. The formation enthalpy of Al3Fe phase obtained from Miedema model [26] and ab-initio calculations [23] are much more endothermic than these derived experimentally and differ by about 10e20 kJ/mol of atoms. 5. Conclusions
[14] 1963 Ferro
The results of the X-ray structural and scanning analysis showed that the preparation procedure of Al2Fe and Al5Fe2 intermetallic phases proved to be correct. The measured values of formation enthalpies of Al2Fe and Al5Fe2 phases are in reasonable agreement with the data from earlier
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
calorimetric studies. The observed deviations oscillate around 2.5 kJ/mol of atoms. The formation enthalpies obtained by Calphad method for the Al5Fe2 phase are almost identical and for the Al2Fe by 2 kJ/mol of atoms more exothermic in comparison with the values measured in this work. The formation enthalpy of Al2Fe phase calculated with the Miedema model is by 2.7 kJ/mol atoms less exothermic in comparison with the value obtained in this study. The formation enthalpy of AleFe alloys calculated from the data obtained by the electromotive force and vapor pressure methods are in most cases more exothermic than these obtained with the calorimetric technique. The formation enthalpy of Al3Fe intermetallic phase calculated from the Miedema model and ab-initio calculations are much more endothermic in comparison with the experimental data. The AleFe system due to its high complexity is still a serious challenge as far as the experiment and modeling of the phase equilibria. Acknowledgments This study was carried out in the frame of the European Project “COST Action 535: Thermodynamics of Alloyed AluminideseTHALU”. Financial support from Polish Ministry of Science and Informatics of project Nr 62/E-88/SPB/COST/T-08/DWM 122/2004-2007 is gratefully acknowledged. References [1] [2] [3] [4] [5]
Eldridge J, Komarek KL. Trans AIME 1964;230:226e33. Radcliffe SV, Averbach BL, Cohen M. Acta Metal 1961;9:169e76. Kleykamp H, Glasbrenner H. Z Metallkd 1997;88:230e5. Belton GR, Fruehan RJ. Trans AIME 1969;245:113e7. Bencze L, Raj DD, Kath D, Oates WA, Herrmann J, Singheiser L, et al. Metall Mater Trans A 2003;34:2409e19. [6] Bencze L, Markus T, Dash S, Raj DD, Kath D, Oates WA, et al. Metall Mater Trans A 2006;37:3171e81. [7] Ichise E, Yamauchi T, Mori T. Tetsu-to-Hagane 1977;63:417e24. [8] Breuer J, Grün A, Sommer F, Mittemeijer EJ. Metall Mater Trans B 2001;32: 913e8.
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[9] Rzyman K, Moser Z, Miodownik AP, Kaufman L, Watson RE, Weinert M. Calphad 2000;24:309e18. [10] Feutelais Y, Legendre B, Guymont M, Ochin P. J Alloys Compd 2001;322: 184e9. [11] Kubaschewski O, Dench WA. Acta Metall 1955;3:339e46. [12] Oelsen W, Middel W. Eisenforschung 1937;19:1e26. [13] Biltz W. Z Metallkd 1937;29:73e9. [14] Ferro R. Atti Acc Naz Lincei e Sc Fis Mat Nat 1963;36:653e8. [15] Meschel SV, Kleppa OJ. In: Faulkner JS, editor. Metallic alloys: experimental and theoretical perspectives. Dordrecht, The Netherlands: Kluwer Academic Publishers; 1994. [16] Meschel SV, Kleppa OJ. J Alloys Compd 2001;321:183e200. [17] Kleppa OJ. J Phase Equilb 1994;15:240e63. [18] Ansara I. Commission des communautes Europennes: CECA No.7210-CA/3/ 303; 1981. [19] Ansara I, . Dinsdale AT, Rand MH, editors. Cost 507, thermochemical data for light metal alloys. European Communities; 1988. [20] Ansara I, editor. Thermochemical database for light metal alloys, concerted action on materials science. Brussels and Luxembourg: ECSC-EEC-EAEC; 1995. [21] Fries SG, Jantzen T. Thermochim Acta 1998;314:23e33. [22] Chang JA, Neumann JP. Prog Solid State Chem 1980;71:398. [23] Lechermann F, Fähnle M, Sanchez JM. Intermetallics 2005;13:1096e109. [24] Maugis P, Lacaze J, Besson R, Morillo J. Metall Mater Trans 2006;37A: 3397e401. o PG, Petrilli HM, Schön CG. Calphad 2002;26:573e82. [25] Gonzales-Ormen [26] deBoer FR, Boom R, Mattens WCM, Miedema AR, Niessen AK. Cohesion in metals, transition metal alloys, ed; 1988. North-Holland. [27] Kattner UR, Burton BP. AleFe (AluminumeIron). In: Okamoto H, editor. Phase diagrams of binary alloys. ASM International; 1993. p. 12e28. [28] Massalski TB. Binary alloy phase diagrams. 2nd ed. ASM International Materials Information Society; 1990. [29] http://www.crct.polymtl.ca/fact/phase_diagram.php?file¼Al-Fe. jpg&dir¼SGTE2007. [30] http://www.crct.polymtl.ca/fact/phase_diagram.php?file¼Al-Fe. jpg&dir¼TDnucl. [31] Du Y, Schuster JC, Liu ZK, Hu R, Nash P, Sun W, et al. Intermetallics 2008;16: 554e70. [32] Sundman B, Ohnuma I, Dupin N, Kattner UR, Fries SG. Acta Mater 2009;57: 2896e908. [33] Jacobs MHG, SchmideFetzer R. Calphad 2009;33:170e8. [34] Ga˛ sior W, Moser Z, De˛ bski A. J Alloys Compd 2009;487:132e7. [35] Moser Z, Ga˛ sior W, Rzyman K, De˛ bski A. Arch Metall Mater 2006;51:605e8. [36] Ellner M, Mayer J. Scripta Metall Mater 1992;26:501e4. [37] Bastin G, van Loo FJJ, Vrolijk JWGA, Wolff LR. J Cryst Growth 1978;43:745e51. [38] R.E. Watson private communications. [39] Gomozov PA, YuZasypalov V, Mogutnov BM. Russ J Phys Chem 1986;60: 1865e7.
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Formation enthalpy of intermetallic phases from AleFe system measured with solution calorimetric method W. Ga˛sior, A. De˛ bski*, Z. Moser Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25, Reymonta Street, 30-059 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 September 2011 Received in revised form 31 January 2012 Accepted 1 February 2012 Available online 25 February 2012
The solution calorimetric method was used for the determination of the formation enthalpy of Al2Fe and Al5Fe2 intermetallic phases. The phases were prepared in a very pure Ar atmosphere by melting the calculated amounts of Al and Fe in alumina crucibles. Their crystal structure was confirmed with the Xray diffraction method. A very low amount of Al5Fe2 phase was found in the Al2Fe phase. The calorimetric experiments were carried out using an Al bath at temperature 1271 K. The formation enthalpies of the Al5Fe2 and Al2Fe phases obtained at room temperature were 30.5 and 27.8 kJ/mol of atoms, respectively. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Aluminides, miscellaneous B. Phase diagrams B. Phase identification B. Thermodynamic and thermochemical properties F. Calorimetry
1. Introduction Alloys of the AleFe system are characterized by a good oxidation resistance and good strength at high temperature, so they are promising for applications in many branches of industry. However, their thermodynamic properties have not been intensively studied for the last twenty years. Most of experimental works were conducted before 1990 year. The activity of Al in solid alloys were studied by Eldridge and Komarek [1], Radcliffe et al. [2] and Kleykamp and Glasbrenner [3] using the electromotive force measurements as well as by Belton and Fruehan [4], Bencze et al. [5,6] and Ichise et al. [7] applying the vapor pressure and Knudsen’s effusion mass spectrometer method. The formation enthalpy of solid alloys from the region of AlFe solid solution at 1073 K was measured by Breuer et al. [8] with the solution calorimetric technique. The same method was applied by Rzyman et al. [9] for the examinations of intermetallic phases and the AlFe (B2 cP2 Al40Fe60, Al45Fe55, Al50Fe50) solid solution and by Feutelais et al. [10]. Kubaschewski and Dench [11] conducted the formation enthalpy measurements at the melting temperature of Al by a direct reaction calorimetric method. Oelsen and Middel [12] obtained the formation enthalpy of numerous AlFe solid alloys of
* Corresponding author. E-mail address: [email protected] (A. De˛ bski). 0966-9795/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2012.02.001
Al content XAl between 0.06 and 0.75 measuring the heat effect of direct reaction of liquid Al and Fe at 293 K. The same method was used by Biltz [13] to obtain the formation enthalpy of Fe3Al (D03 cF16) phase at 298 K and Ferro [14] for the Al0.5Fe0.5 alloy at 301 K. Meschel and Kleppa [15e17] used the direct synthesis (reaction) calorimetry to obtain the formation enthalpy of Al0.5Fe0.5 alloy. However, information on structural analysis of samples after their preparation can be found only in the paper of Breuer and coauthors [8] and Meschel and Kleppa [15e17]. It should be noted that the formation enthalpy data of intermetallic phases from the AleFe system, obtained by the CALPHAD-type assessment, were published in Ref. [18e22]. Additionally, Lechermann et al. [23] carried out the calculations of the formation enthalpy of Al3Fe (mC102) and AlFe3 phases using the ab initio density functional theory (DFT) with the mixed-basis pseudo-potential code. Maugis et al. [24] and Gonzales-Ormeno et al. [25] performed the calculations for the AlFe and AlFe3 using the DFT combined with the projector augmented wave (PAW) method and the full potential-linear augmented plane wave (FPLAPW) technique, respectively. The calculations using the Miedema model were performed by deBoer et al. [26] for the Fe0.5Al0.5-B2, Al3Fe and Al2Fe phases. The AleFe phase diagram was of interest for many scientist groups, who presented their results in the literature [27e33], (Kattner and Burton [27] in Massalski [28], SGTE 2007 alloy database (FactSage) [29], Thermodata Nuclear Databas-DNucl (FactSage)
100
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
Fig. 1. The AleFe phase diagram presented in Ref. [27,28].
[30], Du et al. [31], Sundman et al. [32], Jacobs and SchmideFetzer [33]). They generally are similar and the differences concern the existence of a homogenous region of intermetallic phases. Only two: Al2Fe (aP18) and Al5Fe2 (hP28) out of the intermetallic phases were accepted in all cited works. Instead of the Al3Fe phase proposed in Ref. [27,28,30,32], the Al13Fe4 (mC102) was assumed in Ref. [29,31]. Also the Al5Fe4 suggested in Ref. [29,31] was substituted by the Al8Fe5 (cI52) [27,28,32] or Al3Fe2 [30], while the AlFe3 phase was not always taken into consideration. The other differences are shown in Figs. 1e6. Jacobs and SchmideFetzer [33] additionally analyzed the influence of the model used for the description of the aFe and FeAl phases at their equilibrium phase boundary (more details in Ref. [33]). The observed differences among the AleFe phase diagrams are most probably caused by serious experimental and computational problems and high complexity of the system. Unfortunately, the most results of the energetic effect accompanying the reaction in the direct reaction, solution and drop
calorimeter were not followed and confirmed by a structural analysis of the phases investigated by the authors (except of [8,15e17]). Therefore, the main aim of the work was measuring the formation enthalpies of Al2Fe and Al5Fe2 phases by the solution calorimetric method using the liquid aluminum as a solvent after their X-ray and scanning electron microscopy analysis. 2. Solution calorimetric method The measurement of the formation enthalpy of intermetallic phases has been based on the determination of energetic effects accompanying the dissolution of elements and the prepared phase in the solvent which, in many investigations, is aluminum [34,35]. The equation used in the calculation of formation enthalpy of AleFe intermetallic phases is as follows: ef ef ef Df H ¼ XAl DHAl þ XFe DHFe DHAl X
Al
Fig. 2. Microstructure of the Al5Fe2 alloy obtained with the back scattered electrons technique (BSE).
FeXFe
(1)
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
Fig. 3. Microstructure of the Al2Fe alloy obtained with the back scattered electrons technique (BSE).
Fig. 4. Diffraction pattern of Al5Fe2 intermetallic phase.
Fig. 5. Diffraction pattern of Al2Fe intermetallic phase. Small amount of Al5Fe2 was also detected.
101
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102
Fig. 6. Formation enthalpies of solid alloys and phases obtained with different experimental methods (Fe-bcc and Al-fcc are reference states) [23]. 2005 Lec* reference state Al-fcc, Fe-fcc.
where: DfH denotes the formation enthalpy of intermetallic phase at room temperature, XAl and XFe, are mole fractions of the phase ef ; DH ef , are dissolution heat effects of one elements (Al, Fe), DHAl Fe ef mole atoms of aluminum and iron in the solvent and DHAl X
Al
FeXFe
is
the heat effect accompanying the dissolution of one gram-atom of intermetallic phase from the AleFe system in the aluminum bath at temperature T. The last quantity was each time determined from the measurements. In the present work the fcc solid aluminum and bcc iron were assumed to be the reference state. The investigations were carried out in a high temperature calorimeter whose construction and performance were presented in Ref. [35]. The calibration procedure was conducted in each measurement, by the dissolution of aluminum samples in the metal bath. They were immersed in the bath from the room temperature. The calorimetric constant was assessed based on the measurements of ten Al samples. The limiting enthalpy of solution of iron in aluminum at 1273 K (120 kJ/g-atom) was taken from earlier calorimetric investigations of alloys from the homogenous region of FeNi3 phase [34] which were carried out in the same conditions as in that study. Aluminum and iron purity used in the preparation of phases is shown in Table 1. 3. Preparation of phases The Al5Fe2 and Al2Fe phases were produced by melting of Al and Fe metals in the glove-box filled with a high purity Ar protective
atmosphere. In order to keep the level of impurities (O2, H2O and N2) in Ar very low, the circulation was conducted between the glove-box and purifying system with the catalytic copper, molecular sieve and Ti-sponge absorber. The metals were melted in alumina crucibles at temperature 1873 K (1600 C). After melting and fine mixing, the alloys were cooled together with the furnace to room temperature. The alloys of compositions of Al5Fe2 and Al2Fe intermetallic phases prepared in such a way were used for the X-ray and EDS analysis and calorimetric studies. 4. Results and discussion The prepared samples of phases were investigated with the scanning electron microscopy and X-ray diffraction to confirm their structure. The results of EDS (electron diffraction scanning) and Xray diffraction analysis are shown in Figs. 2e5 and in Tables 2 and 3. The microstructure of Al2Fe5 phase is presented in Fig. 2. The black areas are pores and the rest of the material has a homogeneous constitution. The microstructure of the second sample is shown in Fig. 3. This time the EDS analysis revealed also inclusions of the Al2Fe5 phase apart from the Al2Fe phase. The X-ray analysis of the Al2Fe5 and Al2Fe samples, shown in Figs. 4 and 5, confirmed the existence of the desired phases in the prepared samples. In the second sample, apart from the Al2Fe, also Table 2 Composition of Al5Fe2 intermetallic phase identified with EDS technique. Al5Fe2 phase
Table 1 Metals applied in the calorimetric study.
Mass.%
At.%
Notes
Metal
Purity [mass%]
Producer
Al
Fe
Al
Fe
Al Fe
99.99 99.97
Z.M. Trzebinia Alfa Aesar
52.06 52
47.94 48
69.21 69.15
30.79 30.85
Lighter zone Darker zone
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105 Table 3 Chemical composition of Al2Fe intermetallic phase obtained with EDS technique. Al2Fe phase % Mass
% At. Fe
Al
Fe
47.53 47.49 46.93 52.23 51.97 47.2 51.53
52.47 52.51 53.07 47.77 48.03 52.8 48.47
65.22 65.18 64.67 69.36 69.13 64.91 68.75
34.78 34.82 35.33 30.64 30.87 35.09 31.25
Matrix Matrix Matrix Inclusions Inclusions Inclusions Inclusions
Table 4 Lattice parameters of intermetallic phases from Al-Fe system. Phase
Lattice parameter [nm] a
b
c
References
Al2Fe
0.761 0.762 0.765 0.760
1.692 1.682 0.641 0.640
0.487 0.486 0.422 0.426
[37] This study [38] This study
Al5Fe2
Table 5 Formation enthalpy at 298 K and heat effect of dissolution of Al2Fe phase in the Al bath at temperature 1271 2 K. Phase
Al2Fe
Measurement temperature [K]
298
Sample number
1 2 3 4 5 Average value Standard deviation
Heat effect DHef [kJ/mol of atoms]
Formation enthalpy DfH [kJ/mol of atoms]
32.0 30.5 29.6 26.9 30.2 29.8 1.9
29.9 28.5 27.6 24.8 28.2 L27.8 1.9
small amounts of Al5Fe2 phase were detected. However, its influence on the final results of calorimetric measurement of the enthalpy of formation was very low. The results of calculation of lattice parameters for the Al2Fe and Al5Fe2 intermetallic phases are presented in Table 4 together with these obtained in Ref. [36,37] and the observed differences are lower than 1%. In the following step, the obtained phases were cut into small pieces suitable for using in the calorimeter. The experiments were conducted in the Al bath at 1271 K. The samples were dropped into the calorimeter from room temperatures (298 K, 300 K) what means that the formation enthalpies were determined at those temperatures. All results of investigations are presented in Tables 5, 6. The experiments of solution were carried out on five and six Table 6 Formation enthalpy at 300 K and heat effect of dissolution of Al5Fe2 phase in the Al bath at temperature 1271 2K. Phase Measurement Sample number temperature [K]
Heat effect Formation enthalpy DHef [kJ/mol DfH [kJ/mol of of atoms] atoms]
Al5Fe2 300
38.5 40.0 35.5 36.8 38.9 39.1 38.1 1.7
1 2 3 4 5 6 Average value Standard deviation
Table 7 Calculated and experimental enthalpies of formation of Al-Fe alloys. Alloy
DfH [kJ/mol T [K] of atoms]
Al0.67Fe0.33 Al0.71Fe0.29
27.8 30.5
Al0.3Fe0.7 Al0.325Fe0.675 Al0.35Fe0.65 Al0.3625Fe0.6375 Al0.36875Fe0.63125 Al0.375Fe0.625 Al0.3875Fe0.6125 Al0.39375Fe0.60625 Al0.4Fe0.6 Al0.425Fe0.575 Al0.45Fe0.55 Al0.475Fe0.525 Al0.5Fe0.5 Al0.06Fe0.94 Al0.1Fe0.9 Al0.15Fe0.85 Al0.18Fe0.82 Al0.24Fe0.76 Al0.27Fe0.73 Al0.32Fe0.68 Al0.34Fe0.66 Al0.49Fe0.51 Al0.5Fe0.5 Al0.67Fe0.33 Al0.71Fe0.29 Al0.75Fe0.25 Al0.3Fe0.7 Al0.4Fe0.6 Al0.4Fe0.6 Al0.5Fe0.5 Al0.667Fe0.333 Al0.714Fe0.286 Al0.75Fe0.25 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.5Fe0.5 Al0.45Fe0.55 Al0.4Fe0.6 Al0.75Fe0.25
27.15 27.23 27.83 28.35 28.61 31.19 30.53 30.52 30.82 33.12 34.10 35.72 36.29 3.4 6.3 9 11.9 14 15.6 19.4 19.4 24 25.6 27.4 27.8 28.1 15.7 19.9 20.1 25.1 26.2 28.7 27.9 26.7 27 22.9 22.5 27.2 23 19.9 26.2
Al0.5Fe0.5
42
Al0.5Fe0.5
23.5
Al0.55Fe0.45 Al0.75Fe0.25 Al0.67Fe0.33 Al0.71Fe0.29 Al0.64Fe0.36 Al0.5Fe0.5 Al0.26Fe0.74 Al0.5Fe0.5 Al0.67Fe0.33 Al0.75Fe0.25 Al0.5Fe0.5
19.958 28.5733 29.6492 30.0396 35.7 28.6 42.4 32 25 19 25.1
Notes
Al
30.9 32.3 27.8 29.1 31.2 31.4 L30.5 1.7
103
Method and remarks 298 Solutions 300 calorimetry. Reference state: Al-fcc, Fe-bcc. S** 1073 Solutions calorimetry Reference state: Fe(s, fcc) and Al(l). S**
Ref. This study
[8] 2001 Breuer
293 Drop direct calorimetry Data quoted in Ref. [11]. Reference state: Al-fcc, Fe-bcc.
[12] 1937 Oelsen
298 Direct reaction calorimetry. Reference state: Al-fcc, Fe-bcc.
[11] 1955 Kubaschewski
296 296 791 792 1029 296 296 298
Solutions calorimetry. Reference state: Al-fcc, Fe-bcc.
Acid solutions calorimetry Reference state: Al-fcc, Fe-bcc. 0 FLASTO Reference state Al-fcc, Fe-bcc. 298 Direct reaction calorimetry. Reference state: Al-fcc, Fe-bcc. S** 298 Calphad method. Reference state: Al-fcc, Fe-bcc.
900e1100 EMF Reference state: Al-Fcc, Fe-bcc. 1000 Miedema model. Reference state: Al-fcc, Fe-bcc. 298 Quoted in [39] Reference state: Al-fcc, Fe-bcc.
[9] 2001 Rzyman
[13] 1937 Biltz
[38],a
[17] 1994 Kleppa
[20] 1995 Ansara quoted in [21] [3] 1997 Kleykamp [26] 1988 deBoer [22], 1980 Chang
(continued on next page)
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
104 Table 7 (continued ) Alloy
DfH [kJ/mol T [K] of atoms]
Al0.28Fe0.72
24.645
Al0.5Fe0.5 Al0.25Fe0.75
27.9 18.6
Al0.5Fe0.5 Al0.25Fe0.75
31.3 20.2
Al0.05Fe0.95 Al0.1Fe0.9 Al0.15Fe0.85 Al0.2Fe0.8 Al0.25Fe0.75 Al0.3Fe0.7 Al0.35Fe0.65 Al0.4Fe0.6 Al0.45Fe0.55 Al0.5Fe0.5 Al0.52Fe0.48 Al0.55Fe0.45 Al0.6Fe0.4 Al0.65Fe0.35 Al0.67Fe0.33 Al0.7Fe0.3 Al0.72Fe0.28 Al0.74Fe0.26 Al0.76Fe0.24 Al0.05Fe0.95 Al0.1Fe0.9 Al0.15Fe0.85 Al0.2Fe0.8 Al0.25Fe0.75 Al0.3Fe0.7 Al0.35Fe0.65 Al0.4Fe0.6 Al0.45Fe0.55 Al0.5Fe0.5 Al0.52Fe0.48 Al0.6Fe0.4 Al0.67Fe0.23 Al0.7Fe0.3 Al0.75Fe0.25 Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
4.4 9.4 13.8 18.0 21.6 24.7 27.8 30.3 32.4 34.3 34.5 34.5 34.5 34.5 34.3 33.5 33.1 32.4 31.4 4.6 8.8 13.0 16.7 19.9 23.0 25.5 27.8 29.5 30.6 30.8 31.6 32.3 32.7 30.6 10.2 27.9 1.3
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
19.4 30 1.3
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
16.8 6.7 10.2
Al0.25Fe0.75 Al0.5Fe0.5 Al0.75Fe0.25
21.4 26.1 10.2
Al0.5Fe0.5
23.8
Table 7 (continued ) Method and remarks 298 Solutions calorimetry Tian-Calvet. Reference state: Al-fcc, Fe-bcc. 0 Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, without spin Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, with spin. 1173 EMF Reference state: Al-fcc, Fe-bcc.
Ref.
Alloy
DfH [kJ/mol T [K] of atoms]
[10] 2001 Feutelais
Al0.3Fe0.7 Al0.325Fe0.675 Al0.325Fe0.675 Al0.35Fe0.65 Al0.375Fe0.625 Al0.4Fe0.6 Al0.45Fe0.55 Al0.4Fe0.6 Al0.45Fe0.55 Al0.48Fe0.52 Al0.51Fe0.49 Al0.32Fe0.68 Al0.33Fe0.67 Al0.34Fe0.66 Al0.45Fe0.55
23.15 25.81 25.63 27.8 29.8 32.03 35.5 34.03 34.78 35 36.14 23.6 24.4 22.7 36.6
Al0.5Fe0.5
24.4
Al0.5Fe0.5 Al0.25Fe0.75
32.2 19.3
[25] 2002 Gonzales
[2] 1961 Radcliffe
Method and remarks
Ref.
1140e1600 Vapor pressure and [5] 2003 Knudsen’s effusion Bencze mass spectrometer method. Reference state: Fe(s, fcc) and Al(l).
1180e1508 1100 Calphad Method Reference state: Al-fcc, Fe-bcc. 0 Ab initio density functional theory (DFT). Reference state :Al-fcc, Fe-bcc.
[6] 2006 Bencze [18] 1981 Ansara quoted in [9] [24] 2006 Maugis
S** e Structural characterization was performed. a R. E. Watson e quoted in Ref. [9].
1173 Isopiestic method. Reference state: Al-fcc, Fe-bcc.
0 Ab initio density functional theory (DFT). Reference state: Al-bcc, Fe-bcc, spin unpolarized calculations. Reference state: Al-bcc, Fe-bcc, spin polarized calculations. Reference state: Al-fcc, Fe-fcc, spin unpolarized calculations. Reference state: Al-fcc, Fe-fcc, spin polarized calculations. 298 Direct reaction calorimetry. Reference state Al-fcc, Fe-bcc.
[1] 1964 Eldrich
[23] 2005 Lechermann
samples for Al2Fe and Al5Fe2 phases, respectively (Tables 5 and 6). The determined values of formation enthalpy were 27.8 kJ/mol of atoms for the Al2Fe intermetallic phase and 30.5 kJ/mol of atoms for the Al5Fe2 one. The set of experimental data of the formation enthalpy of AleFe solid alloys obtained with different calorimetric techniques, recalculated using the EMF data, results of partial pressure measurements and calculated using different models are shown in Table 7 and Fig. 6. This comparison shows that the differences between these data reach even about 20 kJ/mol of atoms especially in the concentration region from 0.4 up to 0.8 mole fraction of Al. The data obtained for the Al2Fe phase using the calorimetric technique [11,12] are very close to the value measured in this study and the results obtained from the EMF and partial pressure measurements [1,2] are by 4e7 kJ/mol of atoms lower than these measured by the calorimetric method in Ref. [11,12], this study. The formation enthalpy of the Al66Fe34 phase calculated based on the Miedema model [26] is by about 2 kJ/mol of atoms less exothermic, while the enthalpy reported in [19e21] is more exothermic in comparison to the data measured in this study. The value of formation enthalpy of Al5Fe2 phase observed in this work is almost the average value of the data given in Ref. [1,2,11,12] and the observed differences oscillate around 2.5 kJ/mol of atoms and it is only 0.5 kJ/mol of atoms lower than the value measured in this work. The formation enthalpy of Al3Fe phase obtained from Miedema model [26] and ab-initio calculations [23] are much more endothermic than these derived experimentally and differ by about 10e20 kJ/mol of atoms. 5. Conclusions
[14] 1963 Ferro
The results of the X-ray structural and scanning analysis showed that the preparation procedure of Al2Fe and Al5Fe2 intermetallic phases proved to be correct. The measured values of formation enthalpies of Al2Fe and Al5Fe2 phases are in reasonable agreement with the data from earlier
W. Ga˛ sior et al. / Intermetallics 24 (2012) 99e105
calorimetric studies. The observed deviations oscillate around 2.5 kJ/mol of atoms. The formation enthalpies obtained by Calphad method for the Al5Fe2 phase are almost identical and for the Al2Fe by 2 kJ/mol of atoms more exothermic in comparison with the values measured in this work. The formation enthalpy of Al2Fe phase calculated with the Miedema model is by 2.7 kJ/mol atoms less exothermic in comparison with the value obtained in this study. The formation enthalpy of AleFe alloys calculated from the data obtained by the electromotive force and vapor pressure methods are in most cases more exothermic than these obtained with the calorimetric technique. The formation enthalpy of Al3Fe intermetallic phase calculated from the Miedema model and ab-initio calculations are much more endothermic in comparison with the experimental data. The AleFe system due to its high complexity is still a serious challenge as far as the experiment and modeling of the phase equilibria. Acknowledgments This study was carried out in the frame of the European Project “COST Action 535: Thermodynamics of Alloyed AluminideseTHALU”. Financial support from Polish Ministry of Science and Informatics of project Nr 62/E-88/SPB/COST/T-08/DWM 122/2004-2007 is gratefully acknowledged. References [1] [2] [3] [4] [5]
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