2854
J. Phys. Chem. 1995, 99, 2854-2856
Standard Enthalpies of Formation of Ni3V, Ni3Hf, PdsHf, and Pt3Sc and Systematics of AHoffor Ni3Me (Me = La, Hf, Ta), Pd3Me (Me G La, Hf, Ta), and Pt3Me (Me Sc, Ti, V or Y, Zr, Nb) Alloys? Qiti Guo and 0. J. Kleppa" The James Franck Institute, The University of Chicago, 5640 S Ellis Avenue, Chicago, Illinois 60637 Received: May 12, 1994; In Final Form: August 3, 1994@
The standard enthalpies of formation of Ni3V, NbHf, PdsHf, and Pt3Sc have been determined by direct synthesis calorimetry at 1477 f 2 K. The following values of AHOf (H/g atom) are reported: Ni3V, -(21.7 f 1.0); NiaHf, -(47.8 f 1.4); Pd3Hf, -(88.6 f 1.8); Pt3Sc, -(94.6 f 2.0). The results are compared with data available in the literature for Pd3Hf and with predicted values from the model of Miedema et al. A comparison is made to show the systematic variation of the standard enthalpy of formation for A3B type alloys from group to group in the periodic table.
Introduction During the past decade this laboratory has pursued systematic studies of the thermochemistry of the binary intermetallic compounds formed between early transition metals and late transition metals. Our investigations started with the compounds formed between group IV and group Vm transition metals. With a Calvet-type twin calorimeter, which has a maximum operating temperature of about 1100 "C and using a new calorimetric technique, solute-solvent drop calorimetry, Dr. Letitia Topor and the senior author of this paper successfully determined the standard enthalpies of formation of 18 equiatomic compounds of Ti, Zr, and Hf with group VI11 elements. The results are summarized in ref 1. When these results were published, the enthalpies of formation of some of these compounds had also been determined by Gachon et al., who used a completely different technique, high-temperature direct synthesis calorimetry.* We found that in most cases the agreement between the two entirely independent sets of data was good to excellent. This encouraged us to adopt the less cumbersome and less timeconsuming direct-synthesis approach when we extended our investigations to the intermetallic compounds formed between group I11 and group VI11 transition Very recently, our study was further extended to the intermetallic compounds formed between group V elements (V, Nb, Ta) and group VI11 elements8 These measurements were all carried out using a new high-temperature reaction calorimeter which is maintained continuously near 1473 K.9 As stated in our recent article,8 one of our principal interests in carrying out these investigations is to explore the variation of the standard enthalpy of formation for characteristic alloys from group to group in the periodic table. In fact, a comparison was made for this purpose between the values of AH"f for Pt3Me type alloys (Me = Y, Zr, Nb).* It was shown that the magnitude of the enthalpy of formation for these alloys increases somewhat from Pt3Y to Pt3Zr, and then decreases drastically to Pt3Nb. We were interested in finding out if a similar variation exists for Pt3Me (Me = Sc, Ti, V), for Pd3Me (Me = La, Hf, + Qiti Guo, Professor, is with the Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou Province 550002, The People's Republic of China. 0. J. Kleppa, Emeritus F'rofessor, is with the James Franck Institute, University of Chicago, Chicago, IL 60637. This paper was presented at the IUPAC 13th Conference on Chemical Thermodynamics, July 17-22, 1994, Clermont-Ferrand, France. Abstract published in Advance ACS Abstracts, February 1, 1995. @
Ta) as well as for Ni3Me (Me = La, Hf, Ta). However, because the standard enthalpies of formation of some compounds in these series were not available, we could not answer this question. In the present communication, we determined the standard enthalpies of formation of Ni3V, NisHf, PdsHf, and Pt3Sc. This enables us to establish the variation of AIPf for the three abovementioned series of alloys. We were also interested in the Ni3Me (Me = Sc, Ti, V) alloys. However, we cannot complete the comparison for this series, because the compound Ni3Sc does not exist.
Experimental and Starting Materials The determinations were all carried out at 1477 f 2 K in a single-unit differential microcalorimeter which has been described in detail earlierS9 All experiments were conducted in an inert atmosphere of argon gas. This gas was purified by passing it through a silica tube full of titanium grains maintained at about 900 "C to eliminate possible traces of oxygen and nitrogen. The actual synthesis reactions were carried out in BN crucibles. Calibration of the calorimeter was achieved by dropping five or six pieces of 2 mm diameter high-purity copper wire of known mass from room temperature into the calorimeter at 1477 f 2 K. The enthalpy of pure copper at this temperature, 46 596 Jlmol, was taken from Hultgren et a1.I0 The calibrations were reproducible within f l % . The calibrations establish a calibration factor,fc, (in counts/ J), which converts the integral of the area under the reaction curve, which is expressed in total counts, into joules. We have known for a long time that this factor decreases regularly from calibration to calibration, due mainly to the diffusion of Rh from the Pt-Rh alloy into the pure Pt at the junctions of the thermopile. For this reason the calibrations are repeated with 2 or 3 week intervals. Each time, when a new calibration factor was generated, it was used for all measurements until the next calibration. We have concluded that this way of using fcU introduces small errors into our measurements. Because this factor decreases from day to day, the later a measurement is carried out, the larger the error will be. To reduce the errors from this source to a minimum, we will from now on use interpolated values offc,, for all of our measurements. If & ( I ) is the standard deviation of the first calibration and 83(2) is the standard deviation of the second calibration, the uncertainty of
0022-3654/95/2099-2854!§09.00/0 0 1995 American Chemical Society
J. Phys. Chem., Vol. 99, No. 9, 1995 2855
Standard Enthalpies of Formation
+ a,(,,
2 our interpolated fcU is calculated from 8 3 = d83(l12 . Figure 1 shows the actual values offcu for our new calorimeter measured four times within a period of 59 days. We started to operate this calorimeter late in August of 1993, and all the new data reported in this paper were obtained using it. The readers will find in Table 1 how much this change in the way of using fcU will influence our reported standard enthalpies of formation. The metallic purities of the metals used in this study ranged from 99.5% for V, 99.6% for Hf, 99.9% for Ni, Sc, and Pt to 99.95% for Pd. The particle sizes were -200 mesh for Pd and Pt, -325 mesh for Hf, V, and Ni. Hf has large affinity for oxygen. The -325 mesh Hf powder was packed under Ar by the manufacturer. This powder was examined by X-ray diffraction. The X-ray diffraction pattern obtained was in a perfect agreement with the corresponding ASTM standard, and we could not positively identify any amount of HfOz in this Hf powder. The calorimetric samples were prepared by mixing two powders that were accurately weighed according to the appropriate stoichiometry; the mixtures were then pressed into 4 mm diameter pellets. The nickel powder used for the preparation of the Ni3V and Ni3Hf samples was reduced in pure hydrogen at about 600 "C for 1 h and was passed through a 325 mesh sieve just before the pellets were made. Sc was purchased as a small ingot and stored in a vacuum desiccator. Fine filings of Sc were prepared just before we prepared the pellets of Pt3Sc. All the metals were purchased from Johnson Matthey, AESAR Group, except for Pt, which was obtained from Engelhard as platinum black. The platinum black was fired in air overnight at about 700 "C. This promoted growth in the grain size of Pt; at the same time the color changed from black to light gray. After this treatment the platinum powder was passed through a 200 mesh sieve.
Experimental Results The standard enthalpy of formation of the compound A3B (where, A Ni, Pd, or Pt; B = Sc, Hf, or V) was obtained from the difference between two sets of determinations. In the first set the following reaction took place in the calorimeter:
3A (s, 298 K)
+ B (s, 298 K) = A3B (s, 1477 K)
(1)
The products of reaction 1 were reused in a subsequent set of measurements to determine the corresponding heat contents: A3B (s, 298 K) = A3B (s, 1477 K)
(2)
+ B (s, 298 K) = A3B (s, 298 K)
X
Y
kV
Time in Days Figure 1. Variation of calibration factor, feu, with time for our new
calorimeter. listed two sets of results in Table 1. The set with the subscript "uncorr" indicates use of a single value of feu, while the set with the subscript "corr" indicates use of interpolated values of feu. We have also marked how many days after the calibration each measurement was carried out. Obviously, the later the measurement, the larger the correction. After the measurements all the alloy samples were examined first by visual inspection and then by powder X-ray diffraction and by scanning electron microscopy (SEM). The results of these examinations are listed in Table 2. As can be seen from this table, all the four alloys were melted during direct synthesis in our calorimeter. This had undoubtedly promoted the completion of the direct synthesis reactions. From this table it also will be seen that there is no ASTM standard for the compound Pd3Hf. However, the X-ray diffraction pattems for Ni3Hf and Pt3Sc are in perfect agreement with the corresponding ASTM pattems. The X-ray diffraction pattern for Ni3V was taken after the sample was annealed at about 900 "C overnight. It is known that Ni3V becomes disordered above 1045 "C,I1while our direct synthesis was conducted at 1477 K (1204 "C). The X-ray pattern of our annealed Ni3V matched very well the ASTM standard but showed fewer reflections than the ASTM pattern and some of the reflections were rather broad. Hence, our sample was not a perfectly ordered phase. It is, of course, also not a fully disordered phase. SEM examinations indicated that all the four compounds were single phase. It is evident that our direct synthesis was successful for all the four compounds. Hence the reported values of the standard enthalpy of formation should be considered very reliable.
Discussion
From eqs 1 and 2 we have 3A (s, 298 K)
Calibration Factor Variation
(3)
and the standard enthalpy of formation, AH"f is given by AH"XA3B) = AH( 1) - AH(2) where AH(1) and AH(2) are the enthalpy changes per gram atom for eqs 1 and 2, respectively. Table 1 summarizes the experimental results obtained for NisV, Ni3Hf, PdsHf, and Pt3Sc. The reported values of AH( 1) and AH(2) are averages of five-to-six individual determinations with standard deviations 81 and 82,respectively. If the standard deviation for the calibration is 8 3 , the overall uncertainty in the reported standard enthalpy of formation is calculated from 8 = J.To show the difference between using a single value of fc,, and using the interpolated values, we have
Figure 2 shows plots of our experimental results for the standard enthalpies of formation of NhV, Ni3Hf, PdsHf, and Pt3Sc. All values are given in kJ/g atom. The earlier calorimetric result for Pd3Hf by Gachon et a1.I2 is also included in Figure 2. The predicted values of the standard enthalpies of formation for all the considered and related alloys were obtained from the model developed by Miedema et al.I33l4and are also shown in Figure 2. From this figure we see that the model gives slightly less exothermic values than observed in all cases except for Ni?Hf, for which the predicted value, -48 kJ/g atom, is in excellent agreement with our experimental result, -47.8 kJ/g atom. Figure 2 also shows that the earlier value of the enthalpy of formation for Pd3Hf reported by Gachon et al., -100.1 kJ/g atom,12 is much more exothemic than our value, -88.6 kJ/g atom. Figure 3 shows the systematic variation of AHOf for Ni3Me (Me La, Hf, Ta), Pd3Me (Me = La, Hf, Ta), and for Pt3Me
2856 J. Phys. Chem., Vol. 99, No. 9, 1995
Guo and Kleppa
TABLE 1: Observed Heats of Reaction, Average Heat Contents at 1477 K, and Calculated Standard Enthalpies of Formation, in kJlg Atom* compound Ni3V Ni3Hf Pd3Hf Pt3Sc
AH( 1)uncon
H01471 - H'298 = AH(2)uncon
20.64 0.48(6)C9! -13.33 & 0.71(5)(3) -56.37 f 1.00(6)(7' -61.24 f 1.68(5)'"
41.94 f 0.53(6)(1°' 34.13 f 0.77(6)(4J 3 1.11 f 0.78(5)(8! 32.59 f 0.98(5)@)
*
AHof,uncon -21.3 -47.5 -87.5 -93.8
f 0.9 & 1.4 f 1.8 f 2.0
AH(1)con
H01477 - H0298 = AH(2)corr
20.96 f 0.49 -13.40 f 0.71 -57.04 f 1.01 -61.70 f 1.69
42.64 f 0.54 34.37 i0.78 31.53 f 0.79 32.88 ic 0.99
Awf.con -21.7 -47.8 -88.6 -94.6
f 1.0 f 1.4 i 1.8 f 2.0
Numbers in parentheses immediately after the measured data indicate the numbers of experiments averaged. Numbers in superscript parentheses indicate the numbers of days after a calibration the measurements actually were carried out. AH(1) and AH(2) for Ni3V, Ni3Hf, and Pd3Hf were determined between the zeroth day calibration and the 17th day calibration, while AH(1) and AH(2) for Pt3Sc were measured between the 17th day calibration and the 36th day calibration.
TABLE 2: Summars of Visual Inspection, X-ray Diffraction, and Scanning Electron Microscopy (SEM) Examination Results compound
visual inspection
X-ray diffraction
SEM examination
Ni3V
sample melted during direct synthesis
single phase
Ni3Hf Pd3Hf Pt3Sc
sample melted during direct synthesis sample melted during direct synthesis sample melted during direct synthesis
Ni3V (with less reflections than ASTM and some are broad) Ni3Hf No ASTM file Pt3Sc
-40
.ao
- -0-.Calculated
from
Present Work
Hf
0.2
0,4
06 XN,
Ni
0.8
single phase single phase single phase
AHof for R3Zr given by S e l h a o ~ i ;(7) ' ~ AWf for Ni3La given by Shilov et a1.;I6 and (8) AHof for Ni3Ti cited from Hultgren et al.I7 As can be seen from Figure 3, the magnitude of the enthalpy of formation for all Ni3Me, PdsMe, and Pt3Me type alloys increases somewhat from the compounds in which Me group 111 elements to the compounds in which Me = group IV elements. While there is virtually no change from Pt3Sc to Pt3Ti, there is a drastic decrease to the compounds in which Me = group V elements. We expect to observe similar trends for other alloys between groups 111, IV, and V elements, on one hand, and group VI11 elements on the other.
Acknowledgment. This work has been supported by NSF under Grants CHEM-9014789 and CHEM-9313885 and has also benefited from the general facilities of the University of Chicago Material Research Laboratory (MRL). We like to extend our thanks to Dr. A. M. Davis for his kind help in SEM and energy dispersive X-ray analyses. References and Notes
- 1 80
m 01
\ 7
Y
I
I
I
I
- - 0 - - Ni,(La,Hf,Ta) - - N - - Ni3(Sc,Ti,V) . -140 - - 0 - - Pd,(La,Hf.Ta) . - - A - - Ptl(Sc,T!,V) . -120 I - - 0 - - Pt,(Y.Zr.Nb) - 1 0 0 - & _ _ _ _ _ # - ----- - - 0, 0 - - - - - - - -.r - -'Q-80 -160
+d
O
-
'
'
Q,
. -..
Sc Y La T i Z r Hf V Nb T a Figure 3. Variation of standard enthalpies of formation for Ni3Me
La, Hf, Ta), Pd3Me (Me La, Hf, Ta), Pt3Me (Me = Sc, Ti, = Y, Zr, Nb). The comparison for Ni3Me (Me = Sc, Ti, V) is not complete because Ni3Sc does not exist. (Me
V) and for Pt3Me (Me
(Me Sc, Ti, V) type alloys. Our previous comparison for Pt3Me (Me = Y, Zr, Nb)8 is also included in this figure. However, because the compound Ni3Sc does not exist, we cannot have a complete comparison for Ni3Me (Me = Sc, Ti, V). The data used for drawing Figure 3 include the following: (1) the four new values of AHof reported in this paper for N t V , Ni3Hf, Pd3Hf, and Pt3Sc; (2) AW'f data for Ni3Ta, PdsTa, Pt3V, and Pt3Nb given by Guo and Kleppa;8 (3) AZPf for Pt3Ti given by Gachon et a1.;I2 (4) AHof for Pd3La given by Selhaoui and Kleppa$ (5) AHof for Pt3Y given by Selhaoui and K l e ~ p a (6) ;~
Topor, L.; Kleppa, 0. J. J. Less-Common Metals 1989, 155, 61Gachon, J. C.; Charles, J.; Hertz, J. Calphad 1985, 9, 29-34. Selhaoui, N.; Kleppa, 0. J. J. Chim. Phys. 1993, 90, 435-443. Selhaoui, N.; Kleppa, 0. J. J. Alloys Compounds 1993,191, 145Selhaoui, N.; Kleppa, 0. J. J. Alloys Compounds 1993,191, 155Selhaoui, N.; Kleppa, 0. J. Z. Metallk. 1993, 84, 744-747. Guo, Q.; Kleppa, 0. J. Metall. Trans. 1994, 25B, 73-77. Guo, Q.; Kleppa, 0. J. J . Alloys Compounds 1994, 205, 63-67, Kleppa, 0. J.; Topor, L. Thermochim. Acta 1989, 139, 291-297. Hultgren, R.: Desai, P. D.: Hawkins, D. T.: Gleiser. M.: Kellev. K. K.;'Wagman, D. D. Selected Values of Thermodynamic Properties hf the Elements, ASM: Metals Park, OH, 1973. (11) Massalski, T. B.; Okamoto, H.; Subramanian, P. R.; Kacprzak, L. Binary Alloy Phase Diagrams, 2nd ed.; ASM: Material Park, OH, 1990; Vol. 3, p 2881. (12) Gachon, J. C.; Selhaoui, N.; Aba, B.; Hertz, J. J. Phase Equilib. 1992, 13, 506-511. (13) Niessen, A. K.; de Boer, F. R.; Boom, R.; de Chatel, P. F.; Mattens, W. C. M.; Miedema, A. R. Calphad 1983, 7, 51-70. (14) de Boer, F. R.; Boom, R.; Mattens, W. C. M.; Miedema, A. R.; Niessen, A. K. Cohesion in Metals Transition Metal Alloys; NorthHolland: Amsterdam, 1988. (15) Selhaoui, N. Thesis, University of Nancy, France, 1990. (16) Shilov, A. L.; Padurets, L. N.; Kost, M. E. Russ. J. Phys. Chem. 1983, 57, 338-340. (17) Hultgren, R.; Desai, P. D.; Hawkins, D. T.; Gleiser, M.; Kelley, K. K. Selected Values of Thermodynamic Properties of Binary Alloys; ASM: Metals Park, OH, 1973. JP94 1 156M
