Thermodynamic properties of silicate glasses and melts: II. System SrO-SiO2

Article abstract of DOI:10.1134/S1070363206120073

High-temperature mass spectrometry was used to determine the Gibbs energies, activities, and chemical potentials of SrO and SiO₂ in glasses and melts of the SrO-SiO₂ system in the temperature range 1840-1970 K. Negative deviations fr

Full text of DOI:10.1134/S1070363206120073

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 12, pp. 1878 1884.
Pleiades Publishing, Inc., 2006.
Original Russian Text S.I. Lopatin, S.M. Shugurov, V.L. Stolyarova, N.G. Tyurnina, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 12,
pp. 1966 1973.
Thermodynamic Properties of Silicate Glasses and Melts:
II.1 System SrO SiO2
S. I. Lopatina, S. M. Shugurova, V. L. Stolyarovaa, and N. G. Tyurninab
a St. Petersburg State University,
Universitetskii pr. 26, St. Petersburg, 198504 Russia
b Grebenshchikov Institute of Silicate Chemistry,
Russian Academy of Sciences, St. Petersburg, Russia
Received May 18, 2006
Abstract High-temperature mass spectrometry was used to determine the Gibbs energies, activities, and
chemical potentials of SrO and SiO2 in glasses and melts of the SrO SiO2 system in the temperature range
1840 1970 K. Negative deviations from the ideal behavior were revealed in the system. The standard enthal-
pies of formation and atomization of gaseous SrSiO2 and SrSiO3 were determined.
DOI: 10.1134/S1070363206120073
The information on vaporization and thermodyna-
mic properties of glasses and melts of the SrO SiO2
system is important for modeling physicochemical
properties of multicomponent silicate glasses contain-
ing strontium oxide, aiming at preparing materials
with preset properties. Among such materials are
special-purpose multicomponent liquating glasses
[2, 3], boron- and lead-free glazes [3, 4], and boro-
silicate glasses for radioactive waste disposal [5 7].
of the vapor we observed Sr+, SrO+, SrMoO4+,
SrMoO+3, MoO3+, and MoO+2 ions in a 1:0.01:0.062:
0.013:0.005:0.012 ratio. The origin of these ions in
the mass spectra of the vapor over SrO has been con-
sidered in detail in [10]. To deduce equations for the
dependence of the partial pressures of SrO and Sr over
individual strontium oxide on temperature, we plotted
the ion currents of SrO+ and Sr+ in the mass spectra
of the vapor over SrO against reciprocal temperature
in the range 1744 1983 K and measured the partial
pressures of strontium oxide and atomic strontium by
the method of comparison of ion currents, using gold
as pressure standard [11]. The temperature depen-
dences of the partial pressures of SrO and Sr (Pa) can
be described by Eqs. (1) and (2), respectively.
Phase equilibria in the SrO SiO2 system are fairly
well understood [8] and presented in Fig. 1. Glasses
in the given system are formed in the range 1.4
19.9 mol% SrO [2].
The aim of the present work was to study the com-
position of vapor over glasses and melts of the SrO
SiO2 system, as well as the thermodynamic properties
of the components of this system by means of high-
temperature mass spectrometry.
logp(SrO) = (28121 830)/T + (12.48 0.17), (1)
logp(Sr) = (2195 654)/T + (11.6 0.08).
(2)
Vaporization of SrO. When heated in neutral
conditions, SrO vaporizes with almost complete dis-
sociation into atomic strontium and oxygen, and a
small part of SrO sublimes without decomposition [9].
Vaporization of SiO2. Vaporization of individual
silicon dioxide has been studied in sufficient detail
[12]. In the range 1807 1976, the partial pressure of
silicon monoxide is described by Eq. (3).
Strontium oxide was obtained by fairly long heat-
ing of strontium carbonate in a vacuum at 1400 K.
Therewith, vacuum worsened due to dissociation of
the salt and evolution of CO2. As the sample was
further heated in a molybdenum chamber (weakly
reducing conditions) at 1983 K, in the mass spectra
logp(SiO, Pa) = (24676 552)/™ + (13.07 0.01). (3)
Vaporization and thermodynamic properties of
the components of the SrO SiO2 system. As seen
from the phase diagram of the SrO SiO2 system [8]
(Fig. 1), in the range 1840 1970 K, there are both
heterogeneous regions and a homogeneous melt
region, and the condensed phase contains three com-
1
For communication I, see [1].
1878

THERMODYNAMIC PROPERTIES OF SILICATE GLASSES AND MELTS: II.
1879
Sr2SiO4
+ liquid
2325
T, C
Sr2SiO4
+ liquid
Liquid
2400
2400
2170
Sr2SiO4
SrO
2200
2000
1800
1600
2200
2000
1800
1600
+ Sr3SiO3
+ liquid
2080
2150
Sr2SiO4
+ liquid
Two
liquids
Sr3SiO5
Sr2SiO4
SrSiO3
+
+ liquid
Crystallobalit
1545
Tridimit
+ liquid
+ liquid
Sr2SiO4
+ SrSiO3
1400
1400
1200
SrSiO3
SrSiO3 + Tridymite
1200
SrO
0
10 20 30 40 50 60 70 80 90 100
SiO2
SiO2 mol%
Fig. 1. Phase diagram of the SrO SiO system [8].
2
pounds: SrO SiO2 (1:1), 2SrO SiO2 (2:1), and
3SrO SiO2 (3:1).
MoO2 and MoO3, as well as strontium molybdates
SrMoO3 and SrMoO4 [10].
The activities of SrO and SiO2 in glasses and melts
of the SrO SiO2 system were determined by means
of differential mass spectrometry, using Eqs. (4) and
(5), respectively.
We studied the composition of the vapor over the
SrO SiO2 system in the composition range 10
90 mol% SrO and determined the activities of its
components. The mass spectra of the vapor over
samples with varied contents of the SrO SiO2 system
components in the range 1840 1970 K contained
SiO+, Sr+, SrO+, MoO2+, MoO3+, SrMoO4+, and
SrMoO+3 ions. The intensity ratio of these ion currents
depended both on the temperature and on the com-
position of the condensed phase of the system. To
determine the molecular composition of the vapor
over the samples, we measured the appearance ener-
gies of ions in the vapor mass spectra by the method
of vanishing current, using gold as standard [11]. The
appearance energy of SrMoO+3 was not measured
because of the low intensity of this ion current. The
SiO+, SrO+, Sr+, MoO2+, MoO3+, and SrMoO+4 ions are
molecular, because the ionization efficiency curves
have no inflections, and the appearance energies
coincide, within error, with the ionization energies of
the corresponding molecules [10, 13].
0
0
+
+
,
aSrO = pSrO/pSrO = ISrO /ISrO
(4)
aSiO = pSiO /pS0iO = (pSiO pO)/(pS0iO p0O)
2
2
2
0
= (ISiO IO )/(ISiO I0O ).
(5)
+
+
+
+
Here pi, Ii, p0i , and Ii0 are the partial pressures of
molecular forms and the intensities of ion currents in
the mass spectra of the vapor over the sample and
individual oxides SrO or SiO2, respectively. For
standards in the determination of component activities
we used individual strontium oxide and silicon di-
oxide placed in the reference chamber. Dissociation
of silicon dioxide into gaseous monoxide and oxygen
and reaction of samples with chamber material are
similar to those described in [1, 10, 12]. The O+ or
O+2 ion current intensities proportional to the partial
pressures of atomic and molecular oxygen in the
vapor over the samples and standard were not measu-
red because of the high background near m/z 16 and
32. In view of the fact that the partial pressures of
molybdenum oxides and atomic oxygen are related to
each other by Eq. (6), the partial pressure of atomic
oxygen in Eq. (6) was replaced by Eq. (7), using
Eq. (8).
The mass spectra of the vapor over glasses and
melts of the SrO SiO2 system, the dependences of ion
currents on temperature and vaporization time, as well
as the appearance energies of identified ions provide
evidence to show that heating of the samples at 1840
1970 K results in vaporization of SiO, SrO, Sr, and
oxygen. Reaction of the sample with the material of
the chamber produces gaseous molybdenum oxides
MoO3(gas) = MoO2(gas) + O(gas),
(6)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 12 2006

1880
LOPATIN et al.
Table 1. Intensities of SiO+, SrO+, MoO3+, and MoO+2 ion currents in the mass spectra of the vapor over the SrO SiO2
system and SrO and SiO2 standards, and the activities of SrO and SiO2, determined by Eqs. (7), (10), (4), and (9), at 1840,
1920, and 1970 K
I, over sample
I, over standards SiO2 and SrO
MoO+3 MoO+2 SrO+
aSiO
aSrO
2
xSrO
wt%
,
T,
K
SiO+
MoO3+ MoO2+ SrO+ SiO+
(7)
(10)
(4)
(9)
10.0 1840 205
1920 720
1970 1534
20.0 1840 185
1920 575
1970 1742
30.0 1840 200
1920 628
1970 707
40.0 1840 325
1920 1125
29
126
241.8
42
138
360
16.2
44.5
39
14
51
102
2.2
8.2
21
17.5
85.5
195
25
84
240
11.1
39
48
11.5
43.5
105
2.7
10.5
27
1.5
5.0
13.2
1.8
1.6
200
705
0.6 1517
200
590
1.5 1800
27
123
252
45
156
372
16
81
201
27
90
255
25.5 3.9
34.5 10.7
75.9 25.0
10.4 3.6
72.5 8.9
193
11.5 3.9
59
129
12.6 3.2 3.2 10
44.8 9.7 7.5 10
1.0
0.99
1.0
0.93
0.92
1.0
0.85
0.66
0.53
0.71
0.60
0.48
0.18
0.22
0.16
2
11.8
5.1 10
2
2
0.4
9.5
23.4
4.2 10
6.4 10
5.1 10
5.6 10
8.4 10
5.6 10
7.8 10
9.2 10
4.0 10
5.7 10
7.8 10
9.4 10
8.2 10
0.10
2
2
2
0.75
0.55
0.38
0.22
1.6 10
4.0 10
7. 9 10
0.16
2
2
2
2
2
2
2
2
2
2
2
0.2
0.6
2.1
0.2
217.5 40.2
723
994
345
51.8
82.8
16.7
96.6
224
18.4
83
162
18.4
69
0.7 1641
1970 2615
50.0 1840 123
1920 335
2.4
0.3
4539
342
0.5 1194
1.6 2573
932
914
2.4 2301
0.4 560
26.2
8.7
20.5
1970 651
2
2
2
60.0 1840
60
1.1
3.5
9.6
1.3
0.5
0.9
0.3
0.8
1920 150
1970 310
2
2
218.5 172.5 22.7 7.7 10
9.7 10
3.9 10
0.30
3
3
3
66.7 1840
1.2
51
150
260
39
99
230
2.6 1.2 10
5.4 1.3 10
17.0 1.9 10
2.3
5.8 2.4 10
18.3 2.9 10
2.5
6.0 1.6 10
19.0 1.8 10
2.4
0.15
0.13
0.11
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1920
1970
8.5
25.5
0.7 1371
1.8 2705
2.3
3.9
0.53
75.0 1840
1920
4
4
1.8
4.8
0.3
0.8
0.9
5.8 1630
180
390
120
290
1970
2.8 18.3 3514
2.5
0.8
80.0 1840
1920
4
4
0.7
2.5
0.4
0.9
6.0 1560
146
365
98
268
1970
2.7 19.0 3398
90.0 1840
1920
2.4
5.7
5.7
4
1970
2.1
0.6
2.5 18.6 3720
420
310
18.6 1.0 10
and SiO2 at 1970 K were additionally calculated by
the Belton Fruechan (9) [14] and Gibbs Duhem equa-
tions (10), respectively.
+
+
I
/I
MoO2 MO3
0
,
+
aSiO = ISiO+/I
SiO+
(7)
(8)
0
2
0
+
I
/I
MoO2 MO3
xSrO=xSrO
p0 = KepMoO /pMOO
.
3
IS+iO
SiO2
x
xSrO
2
,
ln SrO(xSrO) = xSiO d ln
ln
(9)
IS+r
2
xSrO
=
1
Here Ke is the equilibrium constant of reaction (6).
ln
SrO
In further research the activities of SiO2 in glasses
and melts of the SrO SiO2 systems were determined
by measuring the intensities of the SiO+, MoO2+, and
MoO+3 ion currents in the mass spectra of the vapor
over samples and individual silicon dioxide.
(10)
ln
=
(xSrO/xSiO )dln
.
SrO
SiO2
2
0
SrO
ln
The activities of SrO and SiO2 in glasses and melts
of the SrO SiO2 system, obtained at 1840, 1920, and
1970 K, are listed in Table 1, and the plots of the
components activities against the concentration of SrO
at 1920 and 1970 K are presented in Fig. 2. In the
In the melts of the SrO SiO2 systems containing
from 20 to 66.7 mol% of SrO, the activities of SrO
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 12 2006

THERMODYNAMIC PROPERTIES OF SILICATE GLASSES AND MELTS: II.
samples with low SrO or SiO2 contents, the com-
1881
ai
ponent activities were determined only at those
temperatures at which the SiO+, MoO3+, MoO2+, and
SrO+ ion current intensities were higher than the
sensitivity of the mass spectrometer.
ai
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
1.0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2
The component activities of the melt of the SrO
SiO2 system, determined at 1970 K by the method of
comparison of ion currents and by Belron Fruechan
fairly fit each other.
To determine the component activities of melts by
3
Eqs. (9) and (10), one should extrapolate the x(SiO2) =
0.1
0.0
f[ln(I+SiO/I+Sr) ln(xSiO /xSrO)] and xSrO/xSiO = fln
4
SiO2
plots to zero –(SiO2)2 and xSrO/xSiO valu2es, respec-
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
2
mol fraction of SrO
tively, which brings additional errors in the resulting
values. The errors in the activities determined by the
method of comparison of ion currents are 5 10% for
SrO and 8 15% for SiO2. Since the activities of SrO
and SiO2, determined by Eqs. (9) and (10), were
calculated for a narrow concentration range, the ther-
modynamic properties of the SrO SiO2 system were
considered using values calculated by Eqs. (4) and (7).
Fig. 2. Plot of component activities (a ) vs. SrO con-
centration in the condensed phase of the SrO SiO
system at 1920 and 1970 K. (1) SiO , 1970 K; (2) SiO ,
1920 K; (3) SrO, 1970 K; and (4) SrO, 1920 K.
i
2
2
2
The position of these minimum agrees well with the
results in [16], obtained in determining the enthalpy
of formation of in the SrO SiO2 system from 1 mol
of the oxides at 298 K.
The chemical potentials ( i), excess chemical
E
potentials ( ), Gibbs energies ( G), and excess
Gibbs energies ( Gð) of the components in glasses
and melts of the SrO SiO2 system were calculated by
Eqs. (11) (14).
When comparing the thermodynamic parameters
determined in glasses and melts of the SrO SiO2 and
BaO SiO2 systems [1], one can note that the degree of
the negative deviation of the melts of these two
systems from the ideal behavior depends on the acid
base properties of the modifier oxide. Comparison of
the Gibbs energies of mixing in the SrO SiO2 and
BaO SiO2 systems shows that the deviation depends
on the type of the modifier cation and the polymeriza-
tion degree of silicate anions and becomes more
negative in going from the first system to the second.
G = xi
,
(11)
(12)
(13)
(14)
i
= RTlnai,
i
E
Gð
=
xi
,
i
E
i
= RTln .
i
The resulting values are listed in Table 2, and the
ð
Since the vapors over the barium silicate [1, 17]
and calcium silicate systems [18] were shown to
contain gaseous silicates, whereas that over the SrO
B2O3 SiO2 system, SrSiO molecules [19], we made
an attempt to find strontium silicates in the vapor over
the SrO SiO2 system, too. Vaporization was per-
formed from a single tungsten chamber, since, as
mentioned above, using a molybdenum chamber we
found in the vapor over the strontium silicate system
molybdenum oxides MoO2 and MoO3 and in the
vapor mass spectrum, MoO+2 and MoO3+ ions at the
same m/z values as the SrSiO+2 and SrSiO3+ ions,
respectively.
plots of
,
,
G, and Gð against the composi-
tion of the icondensed phase of the SrO SiO2 system
are shown in Figs. 3 and 4.
i
The activities of SrO and SiO2, determined in the
present work, are in a good agreement with the phase
diagram of the system [8]. In the melt region, a ne-
gative deviation from ideality is observed, implying
that the system components actively interact with each
other to form new chemical bonds and, a result, new
chemical compounds. The formation of the silicate
melt from strontium oxide and silicon dioxide in-
volves strong chemical interaction with cleavage of
two bridging Si O Si bonds and formation on their
place of two terminal oxygen atoms. The plots of G
and Gð on the composition of the condensed phase
show a minimum at the strontium silicate composition,
whose presence derives from the fact that all bridging
atoms and free oxygens convert into nonbridging [15].
In the mass spectra of the vapor over the starting
composition (66.7 mol% SrO 33.3 mol% SiO2) in
the temperature range 2180 2340 K we detected Sr+,
SrO+, SiO+, SiO2+, WO2+, WO+3, SrWO4+, SrWO+3,
SrSiO+, SrSiO2+, and SrSiO+3 ions. Comparison of the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 12 2006

1882
LOPATIN et al.
Table 2. Chemical and excess chemical potentials of SrO and SiO2, and Gibbs energies and excess Gibbs energies in the
SrO SiO2 system at 1840, 1920, and 1970 K, obtained in the present work
1
E
1
, kJmol
i, kJmol
Content of SrO,
mole fraction
T, K
G, kJ
GE, kJ
SrO
SiO2
SrO
SiO2
0.10
0.20
0.30
0.40
0.50
0.60
0.67
0.75
0.80
0.90
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
1840
1920
1970
0
0.16
0
1.11
1.33
0
2.49
6.63
1.61
1.52
1.73
2.30
2.23
3.65
2.97
0.94
4.56
2.58
0
48.70
11.03
4.87
0.45
50.60
45.00
45.53
46.01
40.60
44.09
40.72
39.08
49.24
45.73
41.78
36.17
39.92
37.71
29.02
32.57
36.15
0
0
0
0
0
0
0
0
0
24.91
18.66
27.11
26.79
20.85
30.08
26.10
24.07
38.64
34.66
30.43
28.36
31.77
29.35
22.90
26.18
29.59
4.40
4.59
4.71
3.41
3.56
3.65
1.61
1.69
1.73
11.19
9.00
3.20
0.81
6.05
8.70
9.44
10.49
10.44
11.82
27.13
23.88
24.55
32.47
29.75
28.40
43.69
46.70
47.70
15.40
18.45
19.45
20.78
21.18
22.84
37.74
34.95
35.89
42.76
40.49
39.43
53.40
56.83
58.09
10.40
5.24
8.15
12.02
26.23
24.17
30.02
52.66
41.35
41.99
102.88
106.08
102.63
3.65
15.63
13.11
18.66
38.64
26.72
26.98
85.92
88.38
84.47
133.05
133.41
110.92
110.71
33.26
33.35
24.29
24.14
139.52
141.23
113.83
114.87
27.90
28.25
19.92
20.05
150.85
113.14
15.09
9.76
measured appearance energies of the ions with those
reported in [1, 10, 13] showed that the vapor contains
strontium, silicon, and tungsten oxides, atomic stron-
tium, oxygen, as well as strontium tungstates and
silicates. The partial pressures of the molecular forms
of the vapor were determined by the method of com-
parison of ion currents with gold as pressure standard
[11]. The ionization cross sections of the molecular
forms were calculated by the additivity method with
use of atomic cross sections [20].
SrO + SiO = SrSiO2,
SrO + SiO2 = SrSiO3,
(15)
(16)
ln Ke(T)
rH0(T) = R
(1/T)
(17)
(18)
,
rH0(0) = T[
0(T)
RlnKe(T)].
r
Here rH0(0), rH0(™), and
0(™) are the
r
changes of the reaction enthalpy and reduced Gibbs
energy at the temperatures 0 and ™, respectively;
R, gas constant; and Ke, equilibrium reaction constant.
To determine the standard enthalpies of formation
of gaseous strontium silicates, we measured the
equilibrium constants of gas-phase reactions (15) and
(16) and calculates the enthalpies of these reactions by
Eqs. (17) and (18).
To determine the standard enthalpy of formation
of SrSiO(gas), we made an attempt to measure the
equilibrium constants of gas-phase reactions (19)
and (20).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 12 2006

THERMODYNAMIC PROPERTIES OF SILICATE GLASSES AND MELTS: II.
1883
2SrSiO2 = SrSiO + SrSiO3,
Sr + SiO = SrSiO.
(19)
(20)
dard enthalpies of atomization of salts and the enthal-
pies of atomization of anion-forming oxides [24],
represented by Eq. (21). The coefficients k and b of
Eq. (21) were 1.028 0.017 and 896.2 26.8, res-
pectively.
The intensity of the SrSiO+ ion current continuously
decreased. The partial pressure of SrSiO did not react
adequately to varied temperature and to either in-
creased or decreased partial pressures of Sr, SiO,
SrSiO2, and SrSiO3. For this reason, we failed to
measure the enthalpies of reactions (19) and (20), and
the mechanism of appearance of the SrSiO species
remained unknown.
atH0(MmXOn, gas, 298)
= k atH0(XOn 1, gas, 298) + b.
(21)
The high regression coefficient (0.998) and the
standard deviation of 70.3 provide evidence for the
validity of our obtained standard enthalpies of forma-
tion and atomization of gaseous SrSiO2 and SrSiO3.
The thermodynamic functions of gaseous oxides,
required for calculation of the enthalpies of reactions
(15) and (16) were taken from [21], and those of
SrSiO3 and SrSiO2(gas) were calculated by means of
statistical thermodynamics in the rigid rotator har-
monic oscillator approximation. For the SrSiO2 and
SrSiO3 molecules we accepted cyclic structures of
C2v symmetry, analogous to the molecular structures
of barium silicates [1, 17]. The interatomic distances
and normal mode frequencies for the SiO2 and SiO3
were taken equal to those in BaSiO2 and BaSiO3
EXPERIMENTAL
The work was performed by high-temperature mass
spectrometry on an MS-1301 mass spectrometer at an
ionizing energy of 25 V. The block of double molyb-
denum one-temperature effusion chambers was heated
by electronic bombardment. The temperature was
measured with an EOP-66 optical pyrometer with an
accuracy of
5
in the range 1600 2300 K. The
[1, 17]: r(Si O) 1.63
for both molecules, r(Si=O)
instrument was preliminarily calibrated by CaF2 vapor
pressure [21, 31].
1.55 , and OSiO angle 101 for SrSiO3 and 104 for
SrSiO2. The normal mode frequencies for SrSiO21were
taken to be 922, 874, 478, 120, 75, and 65 cm and
for SrSiO3, 1237, 924, 849, 490, 421, 411, 120, 75,
The SrO SiO2 system was synthesized using stron-
tium carbonate of special purity grade and silicon di-
oxide of pure grade as starting materials. Glasses and
ceramic samples of the system were synthesized in a
platinum crucible in a silit oven at 1473 2063 K for
2 h. The load was ground in an agate mortar for 2 h.
Ceramic samples were calcined in two stages in
platinum crucibles in air in a silit oven at temperatures
lower the solidus point. The quality of the synthesized
samples was controlled by X-ray phase and chemical
analyses.
1
and 65 cm . The thermodynamic functions of
gaseous SrSiO2 and SrSiO3 were calculated with Sr O
interatomic distances and normal mode frequencies
equal to those in strontium tantalates and niobates
[22, 23].
The enthalpies of reactions involving gaseous
SrSiO2 and SrSiO3, calculated by Eqs. (17) and (18)
and reduced to the standard temperature 298 K, were
366 48 and 36 5 for reaction (15) and 505 56
1
and 505 5 kJ mol for reaction (16), respectively.
ACKNOWLEDGMENTS
By combining the weighted average enthalpies of re-
actions (15) and (16), reduced to 298 K, with the
heats of formation of gaseous SrO, SiO, and SiO2 [21]
we could calculate the standard enthalpies and ato-
mization of gaseous strontium silicates: 474 18 and
1583 20 for SrSiO2; and 841 20 and 2199
The work was financially supported by the Russian
Foundation for Basic Research (project no. 05-03-
08029-ofi_p).
1
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