Thermodynamic stability of RuTe2 solid by vapor pressure study

Article abstract of DOI:10.1016/S0925-8388(02)01119-2

The vaporization behavior of the intermetallic compound RuTe₂(s) was studied in the temperature range of 831-1148 K by the Knudsen effusion technique. As a prerequisite to the study, the nature of the vaporization equilibrium was first obtained. Phase analysis of the partially evaporated sample of RuTe₂(s) from thermogravimetric experiment carried out in inert environment showed the TG residue to be a biphasic mixture of Ru(s) and RuTe₂(s). This result together with the available thermodynamic information of Te vapor revealed that the compound incongruently volatilize as RuTe₂(s)=Ru(s)+Te₂(g). The equilibrium vapor pressure of Te₂(g) derived from the measurement at the different temperatures could be expressed as ln(p/Pa)(±0.33) = -33231.2/T+33.67 (831 ≤ T/K ≤ 1148). The result of this study is discussed in the light of the reported data on the intermetallic compound.

Full text of DOI:10.1016/S0925-8388(02)01119-2

Journal of Alloys and Compounds 352 (2003) 140–142
L
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Thermodynamic stability of RuTe solid by vapor pressure study
2
a
a
a
a
b
a
a ,
*
M. Ali Basu , A.N. Shirsat , R. Mishra , A.S. Kerkar , S.C. Kumar , S.R. Bharadwaj , D. Das
a
Applied Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
b
Analytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
Received 11 March 2002; accepted 6 July 2002
Abstract
The vaporization behavior of the intermetallic compound RuTe (s) was studied in the temperature range of 831–1148 K by the
2
Knudsen effusion technique. As a prerequisite to the study, the nature of the vaporization equilibrium was first obtained. Phase analysis of
the partially evaporated sample of RuTe (s) from thermogravimetric experiment carried out in inert environment showed the TG residue
2
to be a biphasic mixture of Ru(s) and RuTe (s). This result together with the available thermodynamic information of Te vapor revealed
2
that the compound incongruently volatilize as RuTe (s)5Ru(s)1Te (g). The equilibrium vapor pressure of Te (g) derived from the
2
2
2
measurement at the different temperatures could be expressed as ln( p/Pa)(60.33) 5 2 33231.2/T 1 33.67 (831 # T/K # 1148). The
result of this study is discussed in the light of the reported data on the intermetallic compound.

2002 Elsevier Science B.V. All rights reserved.
Keywords: Ruthenium telluride; Vapour pressure measurement; Knudsen effusion method; Thermodynamic properties
2
1
1
. Introduction
2108.8 kJ mol by Mills [3]. Therefore, it was decided
to reinvestigate the vaporization behavior of this com-
pound to obtain more reliable thermodynamic data. Mea-
surement of vapor pressure of tellurium over the biphasic
Among the various fission products generated during the
operation of reactor with UO fuel, palladium, rhodium,
2
ruthenium and tellurium are the group of intermetallic
forming elements [1]. Tellurium being significantly vola-
tile has a tendency of migrating to lower temperature zone
of the fuel pin. This eventually leads to its accumulation at
the fuel-clad boundary and thereby to initiate processes
like stress corrosion cracking of the clad [1], which is
detrimental to the long-term integrity and stability of the
fuel-clad assembly. Tellurium migration is largely depen-
dent on the thermodynamic stability of its intermetallic
phases with the other metallic fission products. In this
context the thermodynamic stability data of ruthenium
telluride is significant. The only available data for
ruthenium telluride is that from tensimetric study of
tellurium vapor over the biphasic mixture of the inter-
metallic phase with ruthenium by Svendsen [2]. The
mixture of RuTe and Ru was carried out in the tempera-
ture range of 831–1148 K by using the Knudsen effusion
with forward collection technique.
2
2. Experimental
The compound RuTe2 was prepared by taking
ruthenium and tellurium powders (Aldrich, purity.99.9%)
in stoichiometric proportions and sealing the mixture under
vacuum. The sealed ampoule was heated for 5 h at 900 8C.
The intermetallic compound with chemically assayed
composition RuTe2.014 was characterized by XRD and
thermogravimetric analysis prior to the evaporation study.
Thermogravimetric analysis showed observable mass loss
above 850 K. The total mass loss from a given amount of
the sample corroborated to stoichiometry of the compound
prepared. XRD analysis of the partially evaporated sample
from TG showed that the residue was the biphasic mixture
enthalpy of formation of RuTe (s) derived from their
2
investigation which covers the composition range of
RuTe1.96 to RuTe2.00 in the temperature interval of 1276–
1
423 K differs by about 30 kJ from the estimated value of
of Ru(s) and RuTe (s). The XRD pattern showed lines of
2
both p- and m-RuTe (s) due to incomplete transformation
of the p-phase that is the stable form of the telluride at the
high temperature [4]. The XRD and TG data together with
*
Corresponding author. Tel.: 191-225-505-151; fax: 191-225-519-
13.
E-mail address: dasd@apsara.barc.ernet.in (D. Das).
2
6
0
925-8388/02/$ – see front matter
 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0925-8388(02)01119-2

M. Ali Basu et al. / Journal of Alloys and Compounds 352 (2003) 140–142
141
the available thermodynamic information of Te vapor [5]
revealed that the compound incongruently volatilize pre-
dominantly as:
d the orifice-to-collimator distance. The vapor pressure
expression for Te (g) in the Knudsen cell obtained by
2
equating the rate of the observed effusion with that
obtainable from the kinetic theory of gas is given by:
RuTe (s) 5 Ru(s) 1 Te (g)
(1)
2
2
2
2
d
2
1
/ 2
p
s
Te2
d
5 (1/A)
s
wTe /t
d
fsr 1 d
/r
g
f
2pRT/MTe2
g
(3)
Under the volatilization equilibrium, the vapor pressure of
Te (g) remains constant at any temperature. This result
was considered while carrying out the vapor pressure
analysis from Knudsen effusion technique.
2
where A is the orifice area, R is the gas constant, and T the
temperature of the Knudsen cell monitored during vapor
collection. The vapor pressures of Te (g) over Ru(s)1
2
For the effusion run, about 1 g of the sample was taken
in a quartz cup inside a Knudsen cell having a knife-edged
orifice with the diameter of 0.0010 m. The cell typically
made of inconel or molybdenum was thoroughly degassed
at high temperature beforehand. The Knudsen cell loaded
with the sample was immediately mounted inside an all
quartz vacuum system and heated by a tungsten furnace.
Temperature measurement was done using Pt/Pt–13% Rh
thermocouple. Temperature stability within the cell could
be maintained within 62 K. The forward collection
arrangement of effusate was identical to that given in Ref.
RuTe (s) at different temperatures were calculated from
2
the experimentally determined parameters involved in the
right hand side of Eq. (3) and are presented in Table 1.
The tabulated pressures above the temperature of 1026 K
are those after correction for the deviation from Knudsen
flow [7] due to high value of pTe2 at high temperatures.
The correction involves the use of the collision diameter sc
of Te (g) which was taken to be 670 pm. This value of s
2
c
for the molecule Te (g) could be arrived from its
2
Leonard–Jones potential parameter s by linear interpola-
tion of s versus s for the known cases. The maximum
c
[6]. In the above experiment the vertical separation be-
correction results in about 38% reduction in the pressure
value observed at the highest temperature, i.e. 1148 K. The
logarithm of the corrected pressures are plotted as a
function of the reciprocal of the temperatures as shown in
Fig. 1. The linear least square fit of ln pTe2 versus 1/T
could be represented as:
tween cell orifice and collimator defining the collection
geometry was typically 0.07 m while the collimator
diameter was 0.022 m.
Several effusion runs were carried out to monitor the
rates of collection of Te on the targets at different
temperatures within the range of 831–1148 K. The collec-
tion period was controlled by interposing a shutter between
the collimator and the vapor source. Frequent monitoring
of the cell temperature was done and found to be constant
during vapor collection on the target made of tantalum.
After the experiment phase analysis of the residue in the
cup was done by XRD to confirm the existence of the
ln( p/Pa)(60.33) 5 2 33231.2/T
1
33.67 (831 # T/K # 1148)
(4)
Table 1
Vaporization data and the third law enthalpy change for the reaction
RuTe (s)5Ru(s)1Te (g)
2
2
biphasic mixture of Ru(s) and RuTe (s). The tellurium
2
a
content on the targets was analyzed by bringing the Te-
deposit into solution of 5% nitric acid and making up the
volume to 10 ml in each case and then, by using ICPAES
technique with proper standard. Some of the ICPAES
results were cross checked by XRF analysis of Te prior to
the dissolution of the deposit.
Temp
Time
(s)
Mass loss (kg)
w(Te)310
Pressure
(Pa)
Third law
DH8298.15 (kJ mol
9
21
(
K)
)
831
5760
3660
3240
1860
1200
960
1080
600
2400
840
840
600
1200
600
450
0.6
0.5
2.0
6.2
7.5
0.002
0.003
0.025
0.080
0.145
0.574
0.518
1.894
2.746
3.126
3.126
6.424
6.360
9.116
20.371
29.371
55.146
66.686
122.732
278.3
282.3
279.9
276.1
278.8
273.5
274.3
285.5
280.6
280.5
280.8
280.9
281.5
278.6
278.0
275.4
276.4
274.9
276.7
8
8
9
9
9
9
52
93
09
34
53
53
23.6
24.0
47.2
268
108
107
164
319
243
440
630
827
1060
1390
1
1
1
014
026
030
3
. Results and discussion
The effusion results were analyzed on the basis of
vaporization equilibrium expressed in Eq. (1) that involves
1031
1
1
1
055
057
058
1085
087
1115
116
1148
Te (g) as the predominant vapor species. The rate of
2
effusion of Te (g) from the orifice was obtained from the
2
observed tellurium content on a target collected over time t
and the geometry of the forward collection as given by:
1
450
300
300
210
1
2
2
2
dE/dt 5
s
wTe /td s1/MTe2
d
fsr 1 d
d
/r
g
(2)
2
1
D H8
(Third Law)5278.664.0 kJ mol .
r
298
where, wTe is the amount of tellurium, M
is the
21
Te2
D H8
298
(Second Law)5283.267.0 kJ mol .
2
2
2
r
a
molecular weight of the Te species and (r 1 d )/r is the
2
Pressures corresponding to temperatures greater than 1026 K have
been corrected for deviation from Knudsen flow.
geometric factor, with r as the radius of the collimator and

1
42
M. Ali Basu et al. / Journal of Alloys and Compounds 352 (2003) 140–142
for RuTe (s) derived from the second law analysis of the
2
2
1
vapor pressure data are 2120.068.0 kJ mol
0.567.0 J K
and
2
1
21
9
mol , respectively. The value of en-
thalpy of formation from the third law analysis works out
2
1
to be 2115.465.0 kJ mol . The value of enthalpy of
formation agrees fairly well with the estimated value
2
1
2
108.8 kJ mol [3], but differs by about 20 kJ from the
21
values of 2141.762.6 kJ mol reported by Cordfunke et
al. [8] which is based on the tensimetric measurements by
Svendsen [2]. The second law entropy of RuTe (s) ob-
2
tained from this study agrees well with the estimated value
2
1
21
of 95.062.5 J mol
K
[8] and also, with that derived
21 21
from the tensimetric study [2], i.e. 89.5 J mol
K .
s d
Fig. 1. ln pTe2 /Pa vs. reciprocal temperature..
Using data of Gibbs energy of formation of Te (g) from
2
Acknowledgements
[8] and the vapor pressure data from Eq. (4), the Gibbs
energy of formation of RuTe (s) can be expressed as:
2
The authors thank Dr J.P. Mittal, Director, Chemistry
and Isotope Group, BARC and Dr N.M. Gupta, Head,
Applied Chemistry Division, BARC for their support and
encouragement during this work. They also acknowledge
the help rendered by Dr H.N. Bajpai of Analytical Chemis-
try Division for the XRF analysis of tellurium.
2
1
D G8 (RuTe , s) (67.0 kJ mol ) 5 2 161.7
f
2
1
0.1T (831 # T/K # 1148)
(5)
The slope and intercept of the vapor pressure (Eq. (4))
yield, respectively, the values of enthalpy and entropy
changes averaged over the working range of temperatures
(
831–1148 K) for the incongruent vaporization represented
21
References
in Eq. (1). These values are (276.366.0) kJ mol and
2
1
21
1
83.866.0 J mol
data obtained from Eq. (4) were treated with the help of
H(T)–H(298.15) values of RuTe (s), Ru(s) and Te (g) to
K , respectively. The thermodynamic
[1] H. Kleykamp, J. Nucl. Mater. 131 (1985) 221.
[2] S.R. Svendsen, J. Chem. Thermodyn. 9 (1977) 789.
2
2
[3] K.C. Mills, Thermodynamic Data For Inorganic Sulphides,
Selenides and Tellurides, Butterworth, London, 1974, 552 pp.
[4] P. Barin, Thermochemical Data of Pure Substances, 3rd Edition,
VCH, Weinheim, 1995.
obtain the second law enthalpy at 298.15 K for the
vaporization reaction (1). The thermal functions for
RuTe (s), Ru(s) and Te (g) were taken from Cordfunke et
al. [8]. The vapor pressure data were directly treated with
the help of free energy functions of the chemical species
involved in the evaporation reaction (1) to yield the third
law enthalpy at 298.15 K. The third law enthalpies are also
presented in Table 1. It can be seen from this Table that
these is no systematic variation of the third law enthalpy
and also there is general agreement between the second
2
2
[
5] S. Bernath, H. Kleykamp, W. Smykatz-Kloss, J. Nucl. Mater. 209
1994) 128.
(
[6] R. Mishra, M. Ali Basu, S.R. Bharadwaj, A.S. Kerkar, D. Das, S.R.
Dharwadkar, J. Alloys Comp. 290 (1999) 97.
[7] J.W. Hastie (Ed.), Characterization of High Temperature Vapors and
Gases, Proceedings of the 10th Material Research Symposium,
NBS, Maryland, 1978, Vol. 1, 1979, p. 14.
[
8] E.H.P. Cordfunke, R.J.M. Konings (Eds.), Thermochemical Data for
Reactor Materials and Fission Products, North Holland, Amsterdam,
1990.
2
1
law (283.267.0 kJ mol ) and third law (278.664.0 kJ
mol ) enthalpies. The values of D H8
2
1
and S8298.15
f
298.15