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Co+Ga liquid system: enthalpy of formation
ELSF.ViER
6urnal
0i Alloys
and Compounds
217 ( 1997) 240-216
liquid
alloys wrrcsponding
lo the reaction:
Abstract The molar enthalpy
of formalion
of [Co+Gal
,,,,,, , with I~.,, = crl(cr + b)
uCo ,,,,, , A I&a ,,,,, , -3 Co,&, has heen measured with a fully
auromawd
high lemperature
calorimerer.
fracrwn range 0 < .s(.,, < 0.71. The integral molar enthalpy of liwmalion &H”,,,
= (Xc (, I( I - .v(.,, )I -44.069
The enthalpies partial
are negative
molar enrhalpie\
-
with
IOh.
Is,.,, + I4X.hl.r~.,,
a minimum
of cobalt and gallium
The
enrhalpy =
of
l’ormalion
- 34 kJ mol
’wilh
of
the
T/K
< 11594 K and the molar
system (in kilojoules
per mole) ih given by
- 23.MY.r:.,,)
= -
’and .M”,,,(Ga
[Co+Gal
xc.,, = 0.55).
range 1524<
IS.9 kJ mot
’at xc,,= 0.45.independent
of the temperature.
Limiting
were also evaluated:
Ah”,,(Co liquid in x liquid Ga) = - 44 kJ mol
(d,,,_H”,,,
A,,,,,H”,,,
in the lemperilture
of the liquid [Co+Ga]
This
liquid
liquid in x liquid Co) = - 26 kJ mol
system
is less exothermic
result is in agreement
with
than
’
those of
the difference
the neighbowing
between
the equilibrium
alloy
[Ni+Ca]
phase diagram.
These resultsexhibit a discrepancywith the valuespredictedby usingthe Miedema model. Moreover, for several (tnnsition metal+ In or Ga) hinary liquid alloys. the trend of the Fermi enrhalpy function vs. molar fraction has been given. K~wwrd.~:
ICo+Cal
ry\tem:
Liquid alloy: Eahalpy of f
calorimewy: Fermi emhnlpy
1. Introduction
1. I. Equilibriwn
Experimental investigations performed on several (transition metal (Ni. Pd. Pt. Rh, Ir) + sp metal (Al, Ga, In)) liquid binary alloys have shown high negative heats of formation [l-3]. With the cobalt metal. the enthalpies of formation of liquid [Co+lnl alloys are endothermic over the entire molar fraction range. being in agreement with the existence of a liquid miscibility gap 141. On the
The Co+Ga equilibrium phase diagram compiled by Elliott 151 then redrawn by Massalski 161 comes from results essentially published by Kiister and Horn 171 and Schubert and coworkers 18) (Fig. I). This phase diagram exhibits two definite compounds (CoGa and CoGa,,) melting peritectically at 12072 IO “C and 838? IO “C respectively. In the solid state the main features of this
contrary. the enthalpy of formation of the [Co+ AI] liquid system is negative. No data concerning the excess functions of the (Co+Gal liquid system being available, calorimetric determinations of the enthalpy of formation (A,,,H”,, =f&,,)) have been undertaken. Thus. the calorimetric results obtained with the [Co+ Gal syitem and reported in this paper, are a part of the systematic study of the thermodynamic properties of liquid binary alloys constituted by an element (sp metal) of the column I3 (Al, Ga. In) and a transition metal (T.M.) from column(s) 8 to II (Co, Ni, Rh, Pd, Ir, Pt).
system are: (i) the wide range of homogeneity of the CoGa compound (with CsCI-structure BZ-type); (ii) the quasistoichiometric composition of the CoGa, phase. More recently, Feschotte and Eggimann [9] from DTA and X-ray measurements studied the phase diagram (Fig. 2). The main differences between the results of Schubert and coworkers 181 are the peritectic temperature of the C&a_, compound (855 “C instead of 838 “C) and the shape of the solidus line in the CoGa region. The large solid solubility of gallium in cobalt (xol = 0.19 at 1200°C) was confirmed.
oY2c11319/97/$17.00 0 I997 ElsevierScience S.A. All righls rewrved PI/ SO425-8388(96)02588-I
pkasc dicrgrum
241
In 197.5. et high temperature. Katayama et al. [ l3] measured the activities of gallium in solid ]Co+Ga] alloys by potrntiometry with a solid electrolyte. Using the same technique. in 1987. Mikula et al. 1121 obtained the activity of gallium in the fi-CoGa pbass (with as electrolyte Zro, stabilized with 7.5 wt.% CaO) in the temperature range 1073 to 1273 K). At II73 K the values of activity of gallium obtained by Katayama et al.. on the one hand, and by Mikula et al.. on the other hand, are in good agreement. From these data Mikula derived the partial and integtal molar enthalpies of formation (in the solid state) and proposed for the enthalpy of formation a value in (LH” lWl.lll,d .x.,1<,= - 49.4 k.l mot ’ at xc,, = 0.5) reasonable agreement with other reported values.
2. Experimental
CO
20
CO
60
GO
prucedure
The determination of the enthalpy of formation of the ICo+Gal system at 1524
at%Ga
thermostated sample charger 1151. The sensing device (an Eyraud-Petit-type thermopile) is constituted of I6 thermocouples (PI+ 6 wt.%Rh-Pt + 30 wt.9 Rh). The experimental and reference crucibles (located along tbe same vertical axis in the experimental chamber) are surrounded by the junctions of thermocouples. Tbe experimental cell employed was an alumina tube closed at the lower end
By solution calorimetric method (with Br-HBr mixture as solvent) Predel and Vogelbein ] IO] have determined the enthalpy of formation of the [Co+Ga] solid alloy (seven mole fractions ber~~een 0.25 < .rcc,< 0.69 htve been investigated) The enthalpy of formation exhibits large values (with a maximum of about negative -44.5 kJ mol-’ with xc,, = 0.25). In 1982, Henig et al. [I II measured calorimetrically. at
(external diameter: I2 mm: total height: 470 mm). The lower p: 4 . this tube was machined to lit the themtopile dimension. The alloying process was performed in a thinwalled horon nitride crucible of about 5Omm height and 6.5 mm inside diameter. this crucible fitted tightly in the alumina tube. The long alumina crucible extending from the hot part of the furnace to the cold region of the calorimeter makes it possible to: (i) keep a purified
II00 K. the enthalpy of formation of the ]Co+Ga] solid system in the molar fraction range 0.25 < .rc#,< O.%. From these results they deduced: (i) the limiting partial molar enthalpy of solution of solid Co (f.c.c.) in Ga (liq). -50.2 kJ mol.‘; (ii) the molar enthalpy of formation of the solid CoGa alloy (referred to Co,,,,,, and Ga ,,qu,d) with
atmosphere (argon) during the measurements: (ii) prevent any contact of the metal vapours with the thermocouples. A constant argon tlow is also maintained in the expetimental chamber (outside of the crucible) and in the furnace. Before entering the calorimeter. high purity argon was passed over a t&based catalyst held at 420 K and over a
a minimum at .roiil= 0.529 with -36.86 kJ mol. ‘: (iii) the maximum of the enthalpy of formation of the /3-CoGa phase (-35.5 kJ mol-‘). In 1987, Mikula et al. ]I21 published a comparison between the results of the enthalpy of formation of this solid phase proposed by Henig et rd. [I I]. Katayama et al. [ 131, Predel and Vogelbein ]lO] and themselves. The Predel and Vogelbein values are the most negative and exhibit a minimum. It must be noticed that Miedema and coworkers [ 141 have predicted a value in good agreement (-31 kJ mol-‘).
titanium sponge Iheated to II20 K. The cobalt (99999wt.%) wire was rinsed with pure acetone and cut into small pieces. The gallium (99.999 wt.%) rod was melted under a dilute solution of hydrochloric acid (5%) in warm water, divided into small droplets, and dried after rinsing with cold distilled water. The calorimetric measurements were performed by a series of direct additions of cobalt to the liquid bath formed by gallium and the alloy. The calorimeter was calibrated from additions of aalumina at the end of each series of measurements.
CO
20
at Fig. 2. The Cn+Gs
equilibrium
so
co
each alloying process was calculated and the variation of the enthalpy of mixing vs. the molar fraction was deduced. Entbalpy contents of the added metal (cobalt) were taken from Hultgren et al. [16]. a-alumina crystals and enthalpy contents were obtained from NIST [ 171. The experimental temperature is known to +3 K. and the integral enthalpy of formation was determined to 3% with an accuracy of about 0.2% on the molar fraction.
Go
%Ga
phase diqnm
A digital microvoltmeter and a microcomputer allow the e.m.f. data from the thermopile to be detected and stored at regular time periods. With software, the heat involved in
60
from Feschotte and Eggimann 191.
1537 K with 0
< 0.754 and 0
< 0.537
1672K with 0
3. Resultsand discussion
1688 K with 0 < xc0 < 0.533
Calorimetric measurements have been performed at: 1694 K with 0
< 0.535
1524 K with 0 < xc0 < 0.596 I536 K with 0 < xc0 < 0.646
From these results the enthalpies of mixing corm sponding to the reaction
T/K=
1524
xlcol 0.064 “.I22
," = 3')7.;2
T/K=
A.“... H”.. - 2.831
.I(
IS36
cm
,n = 4oY.XI
T/K=1537
m=4122
LH”..
X(CO) 0.053 0.103
4,J"n. -2.467 -4.816
O.ISI 0.193
-5.988 -8.774
- I.XO -6.69
- 5.832
0.043 0.,4X
0.177
- 8.084
0.236
- IO.15
0.232 02x1
- IO.576 - 12.172
KWY 0.370
- 13.00 - 14.47
0.324
- 13.3113
O.JZ1
- IS.flo
0.363
- Il.227
0.46h
0.39x O.J.70 0.159
- l4.XO3 - IS.136 - 15.2X8
O.SW o.s-10 0.57
I
- IS.hX IS.23 14.87
o.JXh 0.51 I
0.53s
- lS.?YX - IS.191 - 1-1.97.l
O.SYX 0.6.?3 0.616
- IA.20 - 13.63 13.M
0.557
- 14.7oh
0.57x 0.5%
- 11.3Xh - l-w33
T/K = I610
,n = 377.15
r,Co, u, = Jh7.27
O.Mh 0.137 0.102
A ,.,..V.. ~3.lSY ~7.1OS -9.X67
-3.x53
0.257
- II.XZY
0.149
-7.329
o..wx
- 13.287
0.212
- 10.34x
0.3.53
- I-t.ZhS
r,Cu, 0.074
0.270
- I?.Xfxl
0.397
- IS.Oh.5
".I40
-7.12
0.321
- I.LSXX
0 -1.77
- 15.3hh
0.2US
- IO.2.5
0.3hS O.JM
- 15.76') - 16.12X
0.477
- lS.Nh
0.26.5 0.317
-12.66 -14.4,
0.43X
- 16.266
T/K = I616
,I, 7 103.0x
0.470 O.SOO
- Ih.?JO
0.527
-l6.OYl
UC01 0.07’)
LH”,,, - 3.YY
O.SSl
- IS.701
0.177
- X.7Y
0.574
- IS.293
o.su1
-I&X7? - IJ.396
0.2hl 0.336 0.-101
- l?.S? - IS.05 - IS.70
0.631 0.647
- 13.8X') - 13.362
0.560 o.soX OSJY
-1h.11 - 15.X? - 15.11)
,,I = 3OiM.l
o.sn.5
- Ia6
O.hlh
- 13.YY
T/K=
IW
A,.,,.H”,,,
.X(cw 0.07x
- 16.21X
TIK = 1672 -
IS.77
-
0.2.36
-I I.532
0.276
- 12.859
0.312 0.345 0.376 0.W WM o.JS6 II.?135
-13.889 -14.678 - 152.34 -15.610 -15.851 - 15.979 - IS.959
0.512
- 15.813
0.5.36 0.558 0.579 0.59x
- IS.579 - 15.269 - 14.557 -13901
T/K=
1623
m = 301.97 L.ff", - 3.77
0.363
- 1s.s
0.404 0.441
- 16.16 - 16.4s
0.476
- 16.45
OS08
-16.40
a.537
-IS.06
T/K = 1623
,I = _alOSl
rccw 0.145
%,,H", -6.88
0.26O 0.3S3 0.426
- II.79 - 14.70 -15.93 -16.06 - 15.49 - 14.81
.tiCO) 0.091 0.174
LH",U -4.30 -x.05
0.643
- 13.27
0.66Y O.hY4
- 12.JY -11.49
0.24s 0.323 O.Joo
- 11.10 - 13.72 - 15.s.l
0.717
- IO.68
0.4X6 OS38 0.581
,n = wJ.oh
0.617 0.647
- 14.02 - 13.05
T/K = 168X
MI= 150.17
.r(co) 0.123
LFs, -5.x7
0.673 0.696
- 12.26 - Il.57
0.717
- 10.83
X(CO)
LJ”..
0.234 0.322 0.401
-10.90 - 14.03 - IS.76
0.736 0.7S.l
-10.04 -9.30
0.2s4 0.418 0.533
-II.oo - IS.25 - IS.53
T,K=
16x2
T/K=1694
m=3SO.l?
.tiCO) 0.171
4nu.H'. -8.05
0.328
-13.80
0.448
-15.64
a AhOrn
0
o
0
’
.
0 .
0
~co,,,&, , + hGa, ,,,, , -P Co,Ga,
~,,,,, , with .I-(.,,= (I/((( + h)
have been calculated and listed in Table I. Given the temperature range scanned and the very high trmprraturr of the measurements. the scatter is low. Thus. no temperature dependence of the enthalpies of formation of the liquid alloys has hrrn remarked within the limits 01 experimental error. Taking into ~ccoum the liquid alloy d:~t:r.the 6 =,f(.r,-,,) function (C=_!I ,,,,, H”,,,/x ,.,,(I -x,.,,) (Fig. 3) then the A ,,,,,HO,,, =./Lr,.,,) function has been calculated by the leas1 squares method (in kilojoules per mole): A,,,,,H”,,, = (.V’,.,,)(I
- .v(.,,)I-44.069- I Oh.7 I.+,,
+ I48.6ls;.,, - 33.x59X;.,,
1
The smoothed values of the [-function. integral molar enthalpy and partial molar enthalpy are listed in Table 2 (Fig. 3). The experimental data obtained at 1524. 1536 and
o.nn
o.ui1 0.10 0.20
4.7’) ‘MS
.
ah%l(GaP 0 0 p
1517 K. on the one hand, and at 1602. 1610 and I616 K. o!i the other hand. are reported in Fig. 5 and Fig. 6 respectrvely. The extremum of the A ,,,,, Ho,,, =,fC.r,-,,) function is located at about - IS.9 kJ mol ’ with .I-(.,,= 0 4.5 and the limiting partial enthalpies of Ga in pure liquid cobalt and of liquid cobalt in pure liquid gallium were also Ak”,,,(Co liquid in x liquid Ga) = evaluated: Ah”,,(Ga liquid in x liquid Co) = 44 kJ mol ’ and 26kJmol ‘. These data are different from those obtained using the same calorimetric method for the neighbour system [Ni+ Gal. For this system the corresponding, data are: and Ah”,,,(Ni liquid in r liquid Ga) = - 82 kJ mol AV,,,(Ga liquid in Y. liquid Co) = - I08 kJ mol ’ and the extremum of the enthalpy of mixing is located at about -34 kJ mol ’with .vN, = 0.55. This difference is in agreement with the two equilibrium phase diagrams and the relative stabiliry of the intermetallic compounds: the system Ni-Ga exhibits several definite compounds (seven). one of them with a congruent melting point (NiGa with a
--MO7 -Sl.4, -4.4,
0.00 _
- 4.07 -532x - SY.hh
- ?.OY
-h3.3S
0.30
13.3
- 3Y.47
0.40 0.41
15.4x -~IS.XX
- 3.14 - 22.47
~704 - I0.W
- h4.SO -6417
0.W
- IS.XI
- 17.1s
- IJ.JX
- 63.3
0.5s 0.6n 0.70
-- IS.29 - IJ.3-l -- II.37 7.4s
- 1x9 -x.3.5 - 2.7s - 032
- IX.X3 -2.X3.3 -31.47 --x5.1.5
-61.77 - SY.7.5 s4. -ih.S.l
- 3.34
- 0.97
- 24.66 26.03
-37.13 - 26.03
0.x0 0.90
I.no
-
0.00
0.00
-
I3
245
temperature of fusion of ahout 1493 K [YJ. On the contrary. the [Co+GaJ system has only two compounds (CoGa and CoGa, ) with incongruent melting points. Only Miedrma and coworkers II11 have proposed thermodynamic information concerning hinary alloy\ including a transition metal. They have found: for the Co-Ga
system:
A/t”,,,(Co liquid in x liquid Ga) = - 39 kJ mol ’ and Ah”,,,(Ga liquid in x liquid Co) = - 5 I kJ mol ‘. The extremum of the enthalpy of mixing is located at ahout - II kJ mol ’ with sc,, = 0.5: for the Ni-Ga
system:
Ak’,,,(Ni liquid in = liquid Ga) = - 53 kJ mol A/t”,,,(Ga liquid in x liquid Co) = - hY kJ mol
xvw
0.5
’
and
‘_ The
ex-
90
tremum
of
- I5 kJ mol
the
rnthalpy
of
mixing
is
located
at
about
’with
.r(.,, = 0.5. The comparison between calorimetric and predicted results leads us to the following remarks: (i) the discrepancy between experimental and predicted values is somewhat large: (ii) the small difference between the prcdictcd values of the enthalpy of formation of liquid alloys (- I I and - IS kJ mol ’ at .V = 0.5) corresponds to a similar rffcct when an atom of cobalt is replaced by an atom of nickel. This fact is contradicted by the experimental results (-15.9 kJ mol ’ and -34 kJmol ’ for [Co+ Gal and INi +Gal systems respectively). To descri’bc the energy transfer connected with the bonding process. a new formalism has been introduced: the Femti cnthalpy F,, 1IS]. This function is d&ted as follows: F,, = J/r,,, - /I, r\,,J - /I’,,,. where h ,“,. It,,,, and molar partial enthalpies of the ‘t”, “I are the respective B-metal and of the transition metal (TM) taken at the particular concentration of the alloy and the limiting partial molar enthalpy of B-metal at infinite dilution (all data are referred to the liquid state). The trend of the variation of thr F,, vs. molar fraction curve (Fig. 7) gives an indication of the transfer of electrons; the Co- and Ni-based alloys F,, curves are not as signilicant as those obtained with Pd and h-based alloys. Nevertheless. the break point followed by a tint part at the Co-rich side indicate a sharing of 2.5 electrons with Co. In the solid phase (electronic phase &Cl structure). a transfer of electrons from aluminium and gallium to cobalt has been indicated by Feschotte and Eggimann 191.
4. Conclusion T
Fig. 6. The A ,,,,.H”,,, =pr,.,,) I602 K (0).
curve. Exprimcnul
I610 K t+) and 1616 K
(0).
rrsullr obtained at
With a very high temperature (fully automated) calorimeter. the enthalpy of formation of the [Co+Ga]
system
liquid
I6 kJ
mol
exothrrmic. system. from
This
gallium
has
’with
been
_x(.~,= 0.15).
measured
but less exothermic result
(A,.,,,H”,,,
The enthalpy
corresponds
than those of the INi to
transfer
=
-
of formation
of
is
+Gaj
electrons
171 W. KG\trr and E. Horn. Z. Me r,,,, kd.. ,.P (1952) 33.1. IX1 P. Esalingrr and K. Schuben. 2. McfuNkd.. 48 (19.57) 176. K. Schubert. H.L. Lukah. H.G. Mrissnrr and S. Elhan. Z. M~fucrlllid..SO lY.59) x34. IYI I? Febchow and P. Eggimann. 1. &.r,+Qmsnou Me,,. 6.3 1979) 15.
,
t IlY7.5) (
I I01 B. Predel and W. Vo@ein. 7/wrmo&n. Artu. 1.7 133. I E.-T. Henig. H.L. Lukar and C. Petzow. Z. Mrrrrrll~d.. z7 1982) 87. lIZI A. Mikula. W. Schuster. Y.A. Cheng and ET. Henig. Z. Mrrdlkd..
to cobalt.
[I I
7x llYX7l
References
[I31
172.
I. Katayama. N. Kemori and Z. Koruka. 7irrn.r. Jpu. hr.
Mer.. 16
(1975) 423. 1I I I). El Allom. E. Hayer. M. Game-Exard
and J.P. Brw
,Mcr,rl/.
,
Trsr,n. H. 2.3 1992) 39. (?I I>. El Allam. E. Hayrr. M. C&me-beard and J P. Brw Mcwll. Tnsn. 8. 26 , IY9.5) 7hl. 13, P. A,,re.. M. Gaunu-Fxxd. E. Ha>er and J.P. Bnl,. 1. d,,r>,-r CW~I/‘J.. L!!/ , lYY5, 1.83. 141 J.P. Bru\. M. Game-Escard. D. El Allam and R. Haddad. J. Alkyr (‘““IpI.. tn par.
II41 F.R. de Bwr. R. Boom. W.C.M. Marrenr. A.R. Miuduma and A.K. Tmmiriwt Mead Ahw. NonhNicsen. Cokrsion irt Merrr/.s Holland. Amsterdam. 19X8. Hayer. F. Gehringrr. K.L. Komarrk. M. Guna-Exxrd Brw Z. Mrru//!s/.. 80 1989) ,X6.
[I.51 E.
II61R. Huhgrm.
and J.P.
,
P.D. Desa’i, D.T. Hawkins. M. Glewr. K.K. Kelley and D.D. Wagman, Srkrwrl wlwr of Tl~rn,s~~~~~nrr,li~hprrrir~.~ oJ the Ncwwo. ASM. Metals Park. OH. 1973.
l I71 NIST. National Institute ol’ Standards and Technology. US Drpanmrnt of Commerce. Washingmn. DC 2034. USA. 118) E. Hayer. M. Game-Escerd and J.P. Bror. m prrperation.
6urnal
0i Alloys
and Compounds
217 ( 1997) 240-216
liquid
alloys wrrcsponding
lo the reaction:
Abstract The molar enthalpy
of formalion
of [Co+Gal
,,,,,, , with I~.,, = crl(cr + b)
uCo ,,,,, , A I&a ,,,,, , -3 Co,&, has heen measured with a fully
auromawd
high lemperature
calorimerer.
fracrwn range 0 < .s(.,, < 0.71. The integral molar enthalpy of liwmalion &H”,,,
= (Xc (, I( I - .v(.,, )I -44.069
The enthalpies partial
are negative
molar enrhalpie\
-
with
IOh.
Is,.,, + I4X.hl.r~.,,
a minimum
of cobalt and gallium
The
enrhalpy =
of
l’ormalion
- 34 kJ mol
’wilh
of
the
T/K
< 11594 K and the molar
system (in kilojoules
per mole) ih given by
- 23.MY.r:.,,)
= -
’and .M”,,,(Ga
[Co+Gal
xc.,, = 0.55).
range 1524<
IS.9 kJ mot
’at xc,,= 0.45.independent
of the temperature.
Limiting
were also evaluated:
Ah”,,(Co liquid in x liquid Ga) = - 44 kJ mol
(d,,,_H”,,,
A,,,,,H”,,,
in the lemperilture
of the liquid [Co+Ga]
This
liquid
liquid in x liquid Co) = - 26 kJ mol
system
is less exothermic
result is in agreement
with
than
’
those of
the difference
the neighbowing
between
the equilibrium
alloy
[Ni+Ca]
phase diagram.
These resultsexhibit a discrepancywith the valuespredictedby usingthe Miedema model. Moreover, for several (tnnsition metal+ In or Ga) hinary liquid alloys. the trend of the Fermi enrhalpy function vs. molar fraction has been given. K~wwrd.~:
ICo+Cal
ry\tem:
Liquid alloy: Eahalpy of f
calorimewy: Fermi emhnlpy
1. Introduction
1. I. Equilibriwn
Experimental investigations performed on several (transition metal (Ni. Pd. Pt. Rh, Ir) + sp metal (Al, Ga, In)) liquid binary alloys have shown high negative heats of formation [l-3]. With the cobalt metal. the enthalpies of formation of liquid [Co+lnl alloys are endothermic over the entire molar fraction range. being in agreement with the existence of a liquid miscibility gap 141. On the
The Co+Ga equilibrium phase diagram compiled by Elliott 151 then redrawn by Massalski 161 comes from results essentially published by Kiister and Horn 171 and Schubert and coworkers 18) (Fig. I). This phase diagram exhibits two definite compounds (CoGa and CoGa,,) melting peritectically at 12072 IO “C and 838? IO “C respectively. In the solid state the main features of this
contrary. the enthalpy of formation of the [Co+ AI] liquid system is negative. No data concerning the excess functions of the (Co+Gal liquid system being available, calorimetric determinations of the enthalpy of formation (A,,,H”,, =f&,,)) have been undertaken. Thus. the calorimetric results obtained with the [Co+ Gal syitem and reported in this paper, are a part of the systematic study of the thermodynamic properties of liquid binary alloys constituted by an element (sp metal) of the column I3 (Al, Ga. In) and a transition metal (T.M.) from column(s) 8 to II (Co, Ni, Rh, Pd, Ir, Pt).
system are: (i) the wide range of homogeneity of the CoGa compound (with CsCI-structure BZ-type); (ii) the quasistoichiometric composition of the CoGa, phase. More recently, Feschotte and Eggimann [9] from DTA and X-ray measurements studied the phase diagram (Fig. 2). The main differences between the results of Schubert and coworkers 181 are the peritectic temperature of the C&a_, compound (855 “C instead of 838 “C) and the shape of the solidus line in the CoGa region. The large solid solubility of gallium in cobalt (xol = 0.19 at 1200°C) was confirmed.
oY2c11319/97/$17.00 0 I997 ElsevierScience S.A. All righls rewrved PI/ SO425-8388(96)02588-I
pkasc dicrgrum
241
In 197.5. et high temperature. Katayama et al. [ l3] measured the activities of gallium in solid ]Co+Ga] alloys by potrntiometry with a solid electrolyte. Using the same technique. in 1987. Mikula et al. 1121 obtained the activity of gallium in the fi-CoGa pbass (with as electrolyte Zro, stabilized with 7.5 wt.% CaO) in the temperature range 1073 to 1273 K). At II73 K the values of activity of gallium obtained by Katayama et al.. on the one hand, and by Mikula et al.. on the other hand, are in good agreement. From these data Mikula derived the partial and integtal molar enthalpies of formation (in the solid state) and proposed for the enthalpy of formation a value in (LH” lWl.lll,d .x.,1<,= - 49.4 k.l mot ’ at xc,, = 0.5) reasonable agreement with other reported values.
2. Experimental
CO
20
CO
60
GO
prucedure
The determination of the enthalpy of formation of the ICo+Gal system at 1524
at%Ga
thermostated sample charger 1151. The sensing device (an Eyraud-Petit-type thermopile) is constituted of I6 thermocouples (PI+ 6 wt.%Rh-Pt + 30 wt.9 Rh). The experimental and reference crucibles (located along tbe same vertical axis in the experimental chamber) are surrounded by the junctions of thermocouples. Tbe experimental cell employed was an alumina tube closed at the lower end
By solution calorimetric method (with Br-HBr mixture as solvent) Predel and Vogelbein ] IO] have determined the enthalpy of formation of the [Co+Ga] solid alloy (seven mole fractions ber~~een 0.25 < .rcc,< 0.69 htve been investigated) The enthalpy of formation exhibits large values (with a maximum of about negative -44.5 kJ mol-’ with xc,, = 0.25). In 1982, Henig et al. [I II measured calorimetrically. at
(external diameter: I2 mm: total height: 470 mm). The lower p: 4 . this tube was machined to lit the themtopile dimension. The alloying process was performed in a thinwalled horon nitride crucible of about 5Omm height and 6.5 mm inside diameter. this crucible fitted tightly in the alumina tube. The long alumina crucible extending from the hot part of the furnace to the cold region of the calorimeter makes it possible to: (i) keep a purified
II00 K. the enthalpy of formation of the ]Co+Ga] solid system in the molar fraction range 0.25 < .rc#,< O.%. From these results they deduced: (i) the limiting partial molar enthalpy of solution of solid Co (f.c.c.) in Ga (liq). -50.2 kJ mol.‘; (ii) the molar enthalpy of formation of the solid CoGa alloy (referred to Co,,,,,, and Ga ,,qu,d) with
atmosphere (argon) during the measurements: (ii) prevent any contact of the metal vapours with the thermocouples. A constant argon tlow is also maintained in the expetimental chamber (outside of the crucible) and in the furnace. Before entering the calorimeter. high purity argon was passed over a t&based catalyst held at 420 K and over a
a minimum at .roiil= 0.529 with -36.86 kJ mol. ‘: (iii) the maximum of the enthalpy of formation of the /3-CoGa phase (-35.5 kJ mol-‘). In 1987, Mikula et al. ]I21 published a comparison between the results of the enthalpy of formation of this solid phase proposed by Henig et rd. [I I]. Katayama et al. [ 131, Predel and Vogelbein ]lO] and themselves. The Predel and Vogelbein values are the most negative and exhibit a minimum. It must be noticed that Miedema and coworkers [ 141 have predicted a value in good agreement (-31 kJ mol-‘).
titanium sponge Iheated to II20 K. The cobalt (99999wt.%) wire was rinsed with pure acetone and cut into small pieces. The gallium (99.999 wt.%) rod was melted under a dilute solution of hydrochloric acid (5%) in warm water, divided into small droplets, and dried after rinsing with cold distilled water. The calorimetric measurements were performed by a series of direct additions of cobalt to the liquid bath formed by gallium and the alloy. The calorimeter was calibrated from additions of aalumina at the end of each series of measurements.
CO
20
at Fig. 2. The Cn+Gs
equilibrium
so
co
each alloying process was calculated and the variation of the enthalpy of mixing vs. the molar fraction was deduced. Entbalpy contents of the added metal (cobalt) were taken from Hultgren et al. [16]. a-alumina crystals and enthalpy contents were obtained from NIST [ 171. The experimental temperature is known to +3 K. and the integral enthalpy of formation was determined to 3% with an accuracy of about 0.2% on the molar fraction.
Go
%Ga
phase diqnm
A digital microvoltmeter and a microcomputer allow the e.m.f. data from the thermopile to be detected and stored at regular time periods. With software, the heat involved in
60
from Feschotte and Eggimann 191.
1537 K with 0
< 0.754 and 0
< 0.537
1672K with 0
3. Resultsand discussion
1688 K with 0 < xc0 < 0.533
Calorimetric measurements have been performed at: 1694 K with 0
< 0.535
1524 K with 0 < xc0 < 0.596 I536 K with 0 < xc0 < 0.646
From these results the enthalpies of mixing corm sponding to the reaction
T/K=
1524
xlcol 0.064 “.I22
," = 3')7.;2
T/K=
A.“... H”.. - 2.831
.I(
IS36
cm
,n = 4oY.XI
T/K=1537
m=4122
LH”..
X(CO) 0.053 0.103
4,J"n. -2.467 -4.816
O.ISI 0.193
-5.988 -8.774
- I.XO -6.69
- 5.832
0.043 0.,4X
0.177
- 8.084
0.236
- IO.15
0.232 02x1
- IO.576 - 12.172
KWY 0.370
- 13.00 - 14.47
0.324
- 13.3113
O.JZ1
- IS.flo
0.363
- Il.227
0.46h
0.39x O.J.70 0.159
- l4.XO3 - IS.136 - 15.2X8
O.SW o.s-10 0.57
I
- IS.hX IS.23 14.87
o.JXh 0.51 I
0.53s
- lS.?YX - IS.191 - 1-1.97.l
O.SYX 0.6.?3 0.616
- IA.20 - 13.63 13.M
0.557
- 14.7oh
0.57x 0.5%
- 11.3Xh - l-w33
T/K = I610
,n = 377.15
r,Co, u, = Jh7.27
O.Mh 0.137 0.102
A ,.,..V.. ~3.lSY ~7.1OS -9.X67
-3.x53
0.257
- II.XZY
0.149
-7.329
o..wx
- 13.287
0.212
- 10.34x
0.3.53
- I-t.ZhS
r,Cu, 0.074
0.270
- I?.Xfxl
0.397
- IS.Oh.5
".I40
-7.12
0.321
- I.LSXX
0 -1.77
- 15.3hh
0.2US
- IO.2.5
0.3hS O.JM
- 15.76') - 16.12X
0.477
- lS.Nh
0.26.5 0.317
-12.66 -14.4,
0.43X
- 16.266
T/K = I616
,I, 7 103.0x
0.470 O.SOO
- Ih.?JO
0.527
-l6.OYl
UC01 0.07’)
LH”,,, - 3.YY
O.SSl
- IS.701
0.177
- X.7Y
0.574
- IS.293
o.su1
-I&X7? - IJ.396
0.2hl 0.336 0.-101
- l?.S? - IS.05 - IS.70
0.631 0.647
- 13.8X') - 13.362
0.560 o.soX OSJY
-1h.11 - 15.X? - 15.11)
,,I = 3OiM.l
o.sn.5
- Ia6
O.hlh
- 13.YY
T/K=
IW
A,.,,.H”,,,
.X(cw 0.07x
- 16.21X
TIK = 1672 -
IS.77
-
0.2.36
-I I.532
0.276
- 12.859
0.312 0.345 0.376 0.W WM o.JS6 II.?135
-13.889 -14.678 - 152.34 -15.610 -15.851 - 15.979 - IS.959
0.512
- 15.813
0.5.36 0.558 0.579 0.59x
- IS.579 - 15.269 - 14.557 -13901
T/K=
1623
m = 301.97 L.ff", - 3.77
0.363
- 1s.s
0.404 0.441
- 16.16 - 16.4s
0.476
- 16.45
OS08
-16.40
a.537
-IS.06
T/K = 1623
,I = _alOSl
rccw 0.145
%,,H", -6.88
0.26O 0.3S3 0.426
- II.79 - 14.70 -15.93 -16.06 - 15.49 - 14.81
.tiCO) 0.091 0.174
LH",U -4.30 -x.05
0.643
- 13.27
0.66Y O.hY4
- 12.JY -11.49
0.24s 0.323 O.Joo
- 11.10 - 13.72 - 15.s.l
0.717
- IO.68
0.4X6 OS38 0.581
,n = wJ.oh
0.617 0.647
- 14.02 - 13.05
T/K = 168X
MI= 150.17
.r(co) 0.123
LFs, -5.x7
0.673 0.696
- 12.26 - Il.57
0.717
- 10.83
X(CO)
LJ”..
0.234 0.322 0.401
-10.90 - 14.03 - IS.76
0.736 0.7S.l
-10.04 -9.30
0.2s4 0.418 0.533
-II.oo - IS.25 - IS.53
T,K=
16x2
T/K=1694
m=3SO.l?
.tiCO) 0.171
4nu.H'. -8.05
0.328
-13.80
0.448
-15.64
a AhOrn
0
o
0
’
.
0 .
0
~co,,,&, , + hGa, ,,,, , -P Co,Ga,
~,,,,, , with .I-(.,,= (I/((( + h)
have been calculated and listed in Table I. Given the temperature range scanned and the very high trmprraturr of the measurements. the scatter is low. Thus. no temperature dependence of the enthalpies of formation of the liquid alloys has hrrn remarked within the limits 01 experimental error. Taking into ~ccoum the liquid alloy d:~t:r.the 6 =,f(.r,-,,) function (C=_!I ,,,,, H”,,,/x ,.,,(I -x,.,,) (Fig. 3) then the A ,,,,,HO,,, =./Lr,.,,) function has been calculated by the leas1 squares method (in kilojoules per mole): A,,,,,H”,,, = (.V’,.,,)(I
- .v(.,,)I-44.069- I Oh.7 I.+,,
+ I48.6ls;.,, - 33.x59X;.,,
1
The smoothed values of the [-function. integral molar enthalpy and partial molar enthalpy are listed in Table 2 (Fig. 3). The experimental data obtained at 1524. 1536 and
o.nn
o.ui1 0.10 0.20
4.7’) ‘MS
.
ah%l(GaP 0 0 p
1517 K. on the one hand, and at 1602. 1610 and I616 K. o!i the other hand. are reported in Fig. 5 and Fig. 6 respectrvely. The extremum of the A ,,,,, Ho,,, =,fC.r,-,,) function is located at about - IS.9 kJ mol ’ with .I-(.,,= 0 4.5 and the limiting partial enthalpies of Ga in pure liquid cobalt and of liquid cobalt in pure liquid gallium were also Ak”,,,(Co liquid in x liquid Ga) = evaluated: Ah”,,(Ga liquid in x liquid Co) = 44 kJ mol ’ and 26kJmol ‘. These data are different from those obtained using the same calorimetric method for the neighbour system [Ni+ Gal. For this system the corresponding, data are: and Ah”,,,(Ni liquid in r liquid Ga) = - 82 kJ mol AV,,,(Ga liquid in Y. liquid Co) = - I08 kJ mol ’ and the extremum of the enthalpy of mixing is located at about -34 kJ mol ’with .vN, = 0.55. This difference is in agreement with the two equilibrium phase diagrams and the relative stabiliry of the intermetallic compounds: the system Ni-Ga exhibits several definite compounds (seven). one of them with a congruent melting point (NiGa with a
--MO7 -Sl.4, -4.4,
0.00 _
- 4.07 -532x - SY.hh
- ?.OY
-h3.3S
0.30
13.3
- 3Y.47
0.40 0.41
15.4x -~IS.XX
- 3.14 - 22.47
~704 - I0.W
- h4.SO -6417
0.W
- IS.XI
- 17.1s
- IJ.JX
- 63.3
0.5s 0.6n 0.70
-- IS.29 - IJ.3-l -- II.37 7.4s
- 1x9 -x.3.5 - 2.7s - 032
- IX.X3 -2.X3.3 -31.47 --x5.1.5
-61.77 - SY.7.5 s4. -ih.S.l
- 3.34
- 0.97
- 24.66 26.03
-37.13 - 26.03
0.x0 0.90
I.no
-
0.00
0.00
-
I3
245
temperature of fusion of ahout 1493 K [YJ. On the contrary. the [Co+GaJ system has only two compounds (CoGa and CoGa, ) with incongruent melting points. Only Miedrma and coworkers II11 have proposed thermodynamic information concerning hinary alloy\ including a transition metal. They have found: for the Co-Ga
system:
A/t”,,,(Co liquid in x liquid Ga) = - 39 kJ mol ’ and Ah”,,,(Ga liquid in x liquid Co) = - 5 I kJ mol ‘. The extremum of the enthalpy of mixing is located at ahout - II kJ mol ’ with sc,, = 0.5: for the Ni-Ga
system:
Ak’,,,(Ni liquid in = liquid Ga) = - 53 kJ mol A/t”,,,(Ga liquid in x liquid Co) = - hY kJ mol
xvw
0.5
’
and
‘_ The
ex-
90
tremum
of
- I5 kJ mol
the
rnthalpy
of
mixing
is
located
at
about
’with
.r(.,, = 0.5. The comparison between calorimetric and predicted results leads us to the following remarks: (i) the discrepancy between experimental and predicted values is somewhat large: (ii) the small difference between the prcdictcd values of the enthalpy of formation of liquid alloys (- I I and - IS kJ mol ’ at .V = 0.5) corresponds to a similar rffcct when an atom of cobalt is replaced by an atom of nickel. This fact is contradicted by the experimental results (-15.9 kJ mol ’ and -34 kJmol ’ for [Co+ Gal and INi +Gal systems respectively). To descri’bc the energy transfer connected with the bonding process. a new formalism has been introduced: the Femti cnthalpy F,, 1IS]. This function is d&ted as follows: F,, = J/r,,, - /I, r\,,J - /I’,,,. where h ,“,. It,,,, and molar partial enthalpies of the ‘t”, “I are the respective B-metal and of the transition metal (TM) taken at the particular concentration of the alloy and the limiting partial molar enthalpy of B-metal at infinite dilution (all data are referred to the liquid state). The trend of the variation of thr F,, vs. molar fraction curve (Fig. 7) gives an indication of the transfer of electrons; the Co- and Ni-based alloys F,, curves are not as signilicant as those obtained with Pd and h-based alloys. Nevertheless. the break point followed by a tint part at the Co-rich side indicate a sharing of 2.5 electrons with Co. In the solid phase (electronic phase &Cl structure). a transfer of electrons from aluminium and gallium to cobalt has been indicated by Feschotte and Eggimann 191.
4. Conclusion T
Fig. 6. The A ,,,,.H”,,, =pr,.,,) I602 K (0).
curve. Exprimcnul
I610 K t+) and 1616 K
(0).
rrsullr obtained at
With a very high temperature (fully automated) calorimeter. the enthalpy of formation of the [Co+Ga]
system
liquid
I6 kJ
mol
exothrrmic. system. from
This
gallium
has
’with
been
_x(.~,= 0.15).
measured
but less exothermic result
(A,.,,,H”,,,
The enthalpy
corresponds
than those of the INi to
transfer
=
-
of formation
of
is
+Gaj
electrons
171 W. KG\trr and E. Horn. Z. Me r,,,, kd.. ,.P (1952) 33.1. IX1 P. Esalingrr and K. Schuben. 2. McfuNkd.. 48 (19.57) 176. K. Schubert. H.L. Lukah. H.G. Mrissnrr and S. Elhan. Z. M~fucrlllid..SO lY.59) x34. IYI I? Febchow and P. Eggimann. 1. &.r,+Qmsnou Me,,. 6.3 1979) 15.
,
t IlY7.5) (
I I01 B. Predel and W. Vo@ein. 7/wrmo&n. Artu. 1.7 133. I E.-T. Henig. H.L. Lukar and C. Petzow. Z. Mrrrrrll~d.. z7 1982) 87. lIZI A. Mikula. W. Schuster. Y.A. Cheng and ET. Henig. Z. Mrrdlkd..
to cobalt.
[I I
7x llYX7l
References
[I31
172.
I. Katayama. N. Kemori and Z. Koruka. 7irrn.r. Jpu. hr.
Mer.. 16
(1975) 423. 1I I I). El Allom. E. Hayer. M. Game-Exard
and J.P. Brw
,Mcr,rl/.
,
Trsr,n. H. 2.3 1992) 39. (?I I>. El Allam. E. Hayrr. M. C&me-beard and J P. Brw Mcwll. Tnsn. 8. 26 , IY9.5) 7hl. 13, P. A,,re.. M. Gaunu-Fxxd. E. Ha>er and J.P. Bnl,. 1. d,,r>,-r CW~I/‘J.. L!!/ , lYY5, 1.83. 141 J.P. Bru\. M. Game-Escard. D. El Allam and R. Haddad. J. Alkyr (‘““IpI.. tn par.
II41 F.R. de Bwr. R. Boom. W.C.M. Marrenr. A.R. Miuduma and A.K. Tmmiriwt Mead Ahw. NonhNicsen. Cokrsion irt Merrr/.s Holland. Amsterdam. 19X8. Hayer. F. Gehringrr. K.L. Komarrk. M. Guna-Exxrd Brw Z. Mrru//!s/.. 80 1989) ,X6.
[I.51 E.
II61R. Huhgrm.
and J.P.
,
P.D. Desa’i, D.T. Hawkins. M. Glewr. K.K. Kelley and D.D. Wagman, Srkrwrl wlwr of Tl~rn,s~~~~~nrr,li~hprrrir~.~ oJ the Ncwwo. ASM. Metals Park. OH. 1973.
l I71 NIST. National Institute ol’ Standards and Technology. US Drpanmrnt of Commerce. Washingmn. DC 2034. USA. 118) E. Hayer. M. Game-Escerd and J.P. Bror. m prrperation.