Stages of thermal decomposition of sodium oxo-salts of sulphur

Article abstract of DOI:10.1007/s10973-008-9195-8

Thermal behaviour of sodium oxo-salts of sulphur: Na₂SO ₄, Na₂S₂O₇, Na₂S ₂O₆, Na₂SO₃, Na₂S ₂O₅, Na₂S<

Full text of DOI:10.1007/s10973-008-9195-8

Journal of Thermal Analysis and Calorimetry, Vol. 96 (2009) 1, 147–154
STAGES OF THERMAL DECOMPOSITION OF SODIUM OXO-SALTS
OF SULPHUR
*
Beata Jaszczak-Figiel and Z. Gontarz
Warsaw University of Technology, Department of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland
Thermal behaviour of sodium oxo-salts of sulphur: Na2SO4, Na2S2O7, Na2S2O6, Na2SO3, Na2S2O5, Na2S2O4, Na2S2O3, Na2S3O6 and
of sulphides Na2S and Na2S2 was studied on heating up to 1000°C. The experiments were performed with anhydrous compounds ob-
tained from commercial products by recrystallisation and dehydration. The stage mechanisms of decomposition of anionic sub-lat-
tices of the salts have been proposed basing on the Górski’s morphological classification of simple species. The thermal stability
and the stage decomposition mechanisms were correlated with the structure and the potential chemical properties of the salt anions.
The thermal decomposition processes were studied by means of thermal analysis, and the decomposition products were identified
by means of X-ray phase analysis.
Keywords: elementary transformations, Górski’s morphological classification, sodium oxo-salts, thermal decomposition mechanism
Introduction
Investigations on thermal decomposition of chemical
compounds are usually reported in the form of single,
individual studies. In the present paper we are going
to show, basing on the example of sulphur oxo-salts, a
complex approach to the problem of thermal decom-
position of chemical compounds and their interpreta-
tion at the molecular level.
As a start point we shall use the atomic core-
based definition of chemical elements, proposed by
Górski, and the classification of simple species devel-
oped on that basis by the same author [1]. According
to that conception all the simple species of sulphur
(both oxy-anions and neutral molecules) can be lo-
cated in a system obtained by filling the valence states
of sulphur cores by electrons and oxide anions.
In such a system a simple species can be de-
scribed by of a set of three numbers:
Fig. 1 Tabular version of classification of sulphur simple spe-
• number of free electrons in the valence states of
sulphur pertaining to one sulphur core in the simple
species (ev),
cies and potential possibilities of the species as guided
reactants
The positions of the simple species shown in
Fig. 1 correspond to definite chemical properties, and
thus also to a definite reactivity, which for mono-
centric species is represented by a set of arrows.
The arrows show potential products of transformation
of a given species transformed according to elemen-
tary processes resulting from the uniform definition
of acids, bases, oxidizers and reducers [1]. Elemen-
tary reactions of individual species consist in either
loss or acceptance of electrons in red–ox processes or
• number of electric charges brought by the oxide an-
ions into the sphere of sulphur core and calculated
per one core (ez),
• a number of sulphur cores in the simple species (n).
The three numbers enable to create a three-di-
mensional system of simple species, which for inte-
gral values of ev and ez can be represented in tabular
form as a set of simple species of sulphur projected on
the ev–ez plane as shown in Fig. 1.
*
Author for correspondence: zyggon@ch.pw.edu.pl
1388–6150/$20.00
© 2009 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands

JASZCZAK-FIGIEL, GONTARZ
Table 1 Elementary half-reactions in transformations of mono-centric sulphur species
Species
SO24–
Properties
Elementary half-reactions
oxbas
bas
SO42– +8Æ®S2–+4O2–
SO24– ®SO03+O2–
or
SO24– ®S2–+4O0
SO3
ac
SO03+O2–®SO24–
2SO03+ 2Æ®S2O26–
SO3+2Æ®SO02+O2–
ox
or
or
SO03+ 2Æ®SO23–
SO03®SO02+O0
oxbas
SO23–
oxbas
redac
bas
SO32– + 6Æ®S2–+ 3O2–
SO32– +O2–®SO24– +2Æ
SO23– ®SO02+O2–
or
or
SO23– ®S2–+3O0
SO32– +1/2O2®SO24–
red
SO23– ®SO3+2?
or
2SO23– ®S2O26– +2Æ
SO2
ac
SO02+O2–®SO23–
ox
2SO02+ 2Æ®S2O24–
SO02+ 4Æ®S0+2O2–
SO02+O2–®SO03+ 2Æ
or
or
or
SO02+ Æ®SO2–
SO02®S0+2O0
SO02+O0®SO03
oxbas
redac
S2–
redac
red
S2–+4O2–®SO24– + 8Æ
2S2–®S22– +2Æ
or
S2–+4O0®SO24–
S22–
red
S22– ®2Sn+2Æ
redac
ox
S22– +3O2–®S2O23– +6Æ
S22– +2Æ®2S2–
or
S22– +3O0®S2O23–
in loss or acceptance of oxide anions O2– participating
in the ac–bas processes.
dium metal, or as acids, on forming ion pairs in the
gas products. Hence all salts containing this cationic
counterion should form, as far as thermal stability and
sequence of thermal dissociation stages are con-
cerned, a consistent reaction series resulting from the
properties of the species formed in the decomposition
and products of steadily increasing stability.
There exists also a specific type of elementary
reactions, which is a combination of the two pro-
cesses. Such reactions proceed with either acceptance
or loss of oxygen atoms and thus they are equivalent
to either a loss of 2Â and acceptance of O2– or a loss of
O2– and acceptance of 2Â . Hence these reactions may
be considered as coupled redac or oxbas reactions.
The list of elementary half-reactions in transforma-
tions of mono-centric species of sulphur, as resulting
from their positions in the classification system, is
shown in Table 1.
Experimental
The tests were performed with the use of salts of the
following origin: Na2SO4 (a.p., POCh), Na2S2O7 ob-
tained by thermal decomposition of Na2S2O8 (a.p.,
POCh) at 220°C, Na2S2O6 obtained by dehydration of
Na2S2O6·2H2O (a.p., POCh) at 150°C, Na2SO3 (a.p.,
POCh), Na2S2O5 (a.p., POCh), Na2S2O4 (a.p., POCh),
Na2S2O3 obtained by dehydration of Na2S2O3·5H2O
(a.p., POCh) at 150°C, Na2S·9H2O (a.p., POCh),
Na2S2·2H2O obtained by synthesis from Na2S·9H2O
(a.p., POCh)and S (a.p., POCh), Na2S3O6 obtained by
synthesis from Na2S2O3 and H2O2 (a.p., POCh), then
twice recrystallized and dried at 70°C.
Overall transformations of the anionic sub-lat-
tices of the salts under study may be regarded as a
sum of the series of elementary processes passed on
the starting salt anions and on the intermediate spe-
cies formed.
Sodium salts of the anions were used in the ex-
periments because of the specific properties of the
Na+ cations. The large cationic radius (102 pm) [2],
small charge, and low electron binding energy cause
that during the decomposition of the salts the cations
do not participate in the decomposition of the anionic
sub-lattices neither as acid-base reactants nor as oxi-
dants. Only at temperatures exceeding 1000°C, hence
about the decomposition temperatures of Na2SO4 and
Na2S, sodium cations can participate in such pro-
cesses as oxidizers, on passing to the gas phase as so-
The thermal stability of the compounds was de-
termined by means of complex thermal analysis using
the OD 202 Derivatograph, system Paulik–Paulik–
Erdey under the following conditions: DTA 1/5,
DTG 1/10 and TG 100. The samples weighing several
hundred mg were heated (in alumina crucibles) with a
148
J. Therm. Anal. Cal., 96, 2009

THERMAL DECOMPOSITION OF SODIUM OXO-SALTS OF SULPHUR
rate of 10°C min–1 in the stream of O2-free nitrogen
(flow rate 50 cm3 min–1). Solid products of thermal
dissociation were identified by means of X-ray phase
analysis using a Siemens HZG4 apparatus.
In cases where greater amounts of the decompo-
sition products were needed the decomposition was
carried out in a tubular furnace, in a stream of nitro-
gen, at specified temperatures determined from the
data of thermal analysis.
Results and discussion
The highest thermal stability, among the sodium salts
of sulphur oxy-acids, was obtained for Na2SO4, which
did not decompose over the whole temperature region
studied. It underwent a reversible polymorphic trans-
formation at 255°C and melted without decomposi-
tion at 920°C. According to literature data sodium
sulphate(VI) passes to the gas phase with thermal dis-
sociation above 1200°C, and the gas products contain
Na(g), SO2(g) and O2(g) [3]. The decomposition mecha-
nism of pure Na2SO4 leading to Na2O, SO2 and O2 as
the end products, proposed by Lee [4] is of lesser
probability.
Fig. 2 TG, DTG, DTA curves of Na2S2O7
Na2S appeared to be thermally stable up to 920°C.
Thermal analysis curves of Na2S·9H2O do not reveal
any effect besides to the ones due to dehydration of the
hydrous sulphide occurring below 200°C. According
to literature data sodium sulphide melts at 1177°C, and
a phase transition is observed at 1000°C [5].
A lesser thermal stability was for Na2SO3 which
is decomposed without change of mass, with an exo-
thermic effect with maximum at 660°C, to give a mix-
ture of solid products Na2SO4 and Na2S, conforming
to the balance equation:
Fig. 3 TG, DTG, DTA curves of Na2S2O5
A small exothermic effect due to the dispropor-
tionation of sulphate(IV) formed is observed at
740°C. According to Erdey [9] the decomposition of
that compound in air atmosphere proceeds with a
maximum on DTA curve at 170°C. Sulphate(IV) is
oxidized to sulphate(VI) and the disproportionation
effect is invisible. The theoretical loss of mass is
33.68%, and the one calculated from our experimen-
tal data is 30.07%.
4Na2SO3®3Na2SO4+Na2S
(1)
Na2S2O7 (Fig. 2) melts at 405°C, and its decom-
position proceeds in a wide temperature range from
380 to 900°C, according to the balance equation:
Na2S2O7®SO03+Na2SO4
(2)
Thermal dissociation of Na2S2O6 (Fig. 4) pro-
ceeds at temperatures above 250°C, with a maximum
on DTA curve at 280°C, according to equation:
Some endothermic effects were also observed at
temperatures above 600°C. According to literature
data Na2S2O7 decomposes in the temperature range
380–790°C [6], and melting point of that compound
is 402°C [7, 8]. Theoretically calculated loss of mass
is 36.0%, and the value obtained in our experiments is
36.21%.
Na2S2O6®SO2+Na2SO4
(4)
and the thermal analysis curves are identical with the
ones obtained formerly by Zsakó et al. [10]. Theoreti-
cal loss of mass is 31.07%, and the one calculated
from our experiments is 31.34%.
The decomposition of Na2S2O5 (Fig. 3) proceeds
at temperatures above 140°C, with a maximum on
DTA curve observed at 200°C, conforming to equa-
tion:
Na2S2O4 decomposes above 130°C, with a
strong exothermic effect and a maximum on DTA
curve at 180°C (Fig. 5). The decomposition proceeds
with a theoretical mass loss 18.39%, due to liberation
Na2S2O5®Na2SO3+SO2
(3)
J. Therm. Anal. Cal., 96, 2009
149

JASZCZAK-FIGIEL, GONTARZ
Fig. 6 TG, DTG, DTA curves of Na2S2O3
Fig. 4 TG, DTG, DTA curves of Na2S2O6
data and equal to 13.33% deviates considerably from
the theoretically calculated one, perhaps due to the
complicated decomposition mechanism of Na2S2O4.
Figure 6 shows the results of thermal analysis of
sodium thiosulphate. The effect observed on the DTA
curve at 320°C corresponds to the melting process.
This is followed by a start of decomposition of
Na2S2O3 at 380°C, manifested by a strong exothermic
effect. The decomposition may be presented by the
following balance equation:
4Na2S2O3® 3Na2SO4+Na2S5
(6)
Literature data concerning the decomposition of
thiosulphate take notice of an endothermic effect at
330°C as being due to melting of the compound, and
an exothermic effect at 470°C due to the decomposi-
tion [9]. Na2S2 does not decompose up to 920°C. Af-
ter the end of dehydration at 250°C, Na2S2 melts at
470°C (literature data: 469.5°C [12], 475°C [13],
482° [14], 478°C [15]).
Fig. 5 TG, DTG, DTA curves of Na2S2O4
of SO2. The solid products were found to contain
Na2SO3 and Na2S2O3. The decomposition proceeds
conforming to the following reaction:
Na2S3O6 was stable up to temperature 200°C. It
decomposes in two stages with maxima on the DTA
curve at 250 and 320°C (Fig. 7), conforming to the
equation:
2Na2S2O4® SO2+Na2S2O3+Na2SO3
(5)
Higher temperatures reveal some effects con-
nected with transformations of the decomposition
products: an endothermic effect at 310°C due to the
melting of thiosulphate produced and another one
above 450°C connected with its decomposition. The
results of former studies [11] suggest that both the de-
composition temperature and the mechanism of de-
composition are connected with layer thickness of the
compound. In cases where the sample was spread in a
thin layer in the crucible two exothermic effects at
215 and 250°C, respectively, were observed, and for a
thick layer the decomposition proceeded at 205°C.
The loss in mass as calculated from the experimental
Na2S3O6® SO2+S+Na2SO4
(7)
Thermoanalytical curves obtained for that com-
pound are identical with those obtained previously
[11]. Theoretical loss of mass is 40.03%, and that ob-
tained in our experiments was calculated as 39.16%.
While comparing the temperature regions of de-
composition of sodium salts of sulphur anions pre-
sented in Fig. 8a it is possible to relate their stability
with the structure of the anions. The stability of the
compounds depends on the stability of sulphur spe-
cies and this, in turn, on the binding energy of S–O
bonds in species with single central core or of S–S
150
J. Therm. Anal. Cal., 96, 2009

THERMAL DECOMPOSITION OF SODIUM OXO-SALTS OF SULPHUR
Fig. 8b Interrelation between S–S bond length and thermal
stability of two-core sulphur species
ity is observed in the SO2– , and a lesser one in SO2– .
4
3
In bicentric anions having the S–S bond the least sta-
bility is observed in the S O2– anion with the longest
2
4
S–S bond, and the highest stability in S O2– anion
2
3
with the shortest S-S bond. Among bicentric sulphur
species the highest stability was found in S O2– anion
Fig. 7 TG, DTG, DTA curves of Na2S3O6
2
7
having an oxide bridge. All the sulphur oxy-anions,
both the charged species and oxide molecules, are in-
terconnected through elementary reactions that con-
sist on transfer of either electrons of oxide ligands.
Hence there is a question, whether thermal transfor-
mations of anionic sub-lattices in sodium salts can be
built from the elementary reactions that link the an-
ions cited with the species of end products of the de-
composition?
As can be seen in Fig. 8a the highest stability is
observed in the series of species with monocoric co-
ordination centre disposed in the line ez+ev=8,
namely: SO24– , SO2– , S2– and the oxide species: SO3
3
and SO2. The species of Na2SO4 and Na2S that have
the anions with symmetrically equilibrated fields of
sulphur cores (in SO24– the sulphur core has a purely
ligand environment, and in S2– the environment is
purely electronic) when heated above 920°C, pass to
the gas phase thus becoming an equilibrium state of
various species unstable in the solid phase [3, 4]. SO2
molecules and S atoms are also stable at temperatures
above 1000°C.
Fig. 8a Temperature ranges of decomposition of sulphur ox-
ides and sodium salts
A lower stability is observed in SO23– anions in
Na2SO3. This compound decomposes at 720°C in a
complex disproportionation accompanied by a strong
exothermic effect. The products obtained in the de-
composition of sodium sulphate(IV) are the more sta-
ble, formerly discussed compounds, containing more
stable species SO42– and S2– (reaction 1). The complex
disproportionation consists in a cascade reaction of
oxygen transfer effected within the line ez+ev=8, in
which a part of SO23– anions play the role of redac re-
actants transformed then into SO24– anions, and the
other part are oxbas reactants being transformed into
S2–, as shown in Fig. 9 (equations in Table 1). Hence
the decomposition consists in a transfer of oxygen at-
and S–O–S bonds in species with two or more central
atoms of sulphur. The energies of these bonds are in
correlation with their length. Among the mono-core
species under consideration the shortest S–O bond is
observed in the SO24– anion (147 pm [16] as compared
with 151 pm [17] in SO23– ). The shortest S–O bonds in
the oxides are 141 pm in SO3 [18] and 143 pm in SO2
[19]. The S2O27– anion in Na2S2O7 with 163 pm S–O
bond length [20] is the sole species with an S–O–S
oxide bridge. Other bi-coric sulphur species contain
only S–S bonds with the lengths of: 214 pm in S2O62–
[21], 222 pm in S2O25– [22], 239 pm in S2O24– [23],
200 pm in S2O23– [24] and 213 pm in S22– [12]. As re-
sults from Fig. 8b a correlation exists between their
bond lengths and thermal stability. The highest stabil-
oms betweenSO2– anions. The anions, while acting as
3
J. Therm. Anal. Cal., 96, 2009
151

JASZCZAK-FIGIEL, GONTARZ
S2O62– ®2SO–3
S O2– ®SO–3 +SO–2
2
5
S O2– ®2SO–
2
2
4
S O2– ®2SO– +S–
2
3
3
The formation of free radicals in the primary de-
composition can be traced by means of the EPR tech-
nique. Literature data show that formation of radicals
was found in the decomposition of Na2S2O6 (SO– )
3
[25], Na2S2O5 (only SO– radicals were found) [26],
2
and Na2S2O4 (SO– ) [26], and no radicals were de-
2
tected in the decomposition of thiosulphate. None of
the radicals formed was stable. They undergo succes-
sive reactions proceeding with a transfer of electrons
and oxide anions owing to the differences in ac–bas
properties of the species resulted after the transfer of
electrons. In the case of S2O62– anion (Fig. 10) the de-
composition proceeds through the following succes-
sive stages:
Fig. 9 Schemes of thermal decomposition of S2O27– in
Na2S2O7, SO23– in Na2SO3 and S2O52– in Na2S2O5
S2O62– ®2SO–
(I)
(IIa)
(IIb)
the oxbas reactants must pass, successively, though
SO2– and SO2–, two unstable sulphur oxy-anions hav-
3
2
2SO–3 ®SO0+SO2–
ing still stronger oxbas properties (analogous changes
in the oxbas properties are observed in the series of
chlorine oxy-anions occupying the places along the
line ez+ev=8, namely: ClO– , ClO– , ClO– and ClO–).
3
3
SO30+SO2– ®SO2– +SO2
3
4
4
3
2
among which the stages IIa (electron transfer) and IIb
(transfer of oxide ligand) can proceed simultaneously
to give the final products:
Hence the decomposition leads to obtaining of sul-
phur species with purely electron and ligand environ-
ment, the most stable in the system. Despite of the in-
crease of basic properties the unstable species SO22–
and SO2– do no react with Na+ cations.
S O2– ®SO2– +SO2
2
6
4
In the case of S O2– the decomposition leads to
2
5
Thermal stability of the salts containing
bicentric sulphur species (disposed along the line
ez+ev=7) is smaller than that observed in the former
group of salts, although also in this group the highest
stability is observed in salts having the anions with
purely ligand (S2O72– ) or purely electron (S22– ) envi-
ronment of both atomic cores and with both ligand
and electron environment at individual sulphur cores
in S2O23– . The salt with S2O27– anions was the most sta-
ble among the oxy-salts in this group. The decompo-
sition of that salt following its melting consists in rup-
ture of the oxide bridge (Fig. 9) hence in an ac–bas
disproportionation due to volatility of SO03:
formation of SO2 and SO2– . The asymmetrical struc-
3
S O2– ®SO03+SO24–
2
7
The stability of the other oxy-salts containing
bicentric anions with S–S bonds is diverse according
to the strength of the S–S bonds, which are the weak-
est in each of those anions. The simplest way of de-
composition of the S–S bonds consists in the
homolytic rupture leading to formation of
monocentric radical species:
Fig. 10 Schemes of thermal decomposition of S2O26– in
Na2S2O6 and S2O23– in Na2S2O3
152
J. Therm. Anal. Cal., 96, 2009

THERMAL DECOMPOSITION OF SODIUM OXO-SALTS OF SULPHUR
ture of S2O25– and the presence of SO2– radicals [26]
of S2O62– , by transfer of electrons and oxide ligands,
thus leading to formation of SO23– and SO. The unsta-
ble SO disproportionates into SO2 and S, and the lat-
ter reacts with SO2– anions to produce S O2– anions.
detected in the decomposition suggest that the first
stage of decomposition of S2O25– anions consists in
formation of the radicals:
3
2
3
The salt of the S O2– anion, which is the most
S O2– ®SO– +SO–
2
2
3
2
5
3
stable among the bicoric sulphur salts (Fig. 10), de-
composes to SO2– and S2– (4S and S2–). At the decom-
4
5
and electron transfer takes place in the successive
stage (Fig. 9):
position temperature the S O2– anion dissociates:
2
3
S O2– ®S+SO2–
SO–3 +SO– ®SO2– +SO2
2
3
3
2
3
and then theSO2– anion disproportionates toSO2– and
S2– with simultaneous binding of sulphur by S2– to
3
4
A single stage heterolytic decomposition, lead-
ing directly to formation of the end products, should
also not be excluded:
form S2– :
5
4SO2– +4S®3SO2– +S2–
S2O25– ®SO2– +SO2
3
4
5
3
Thermal dissociation of sodium trithionate, con-
taining a complex S O2– anion and representing a se-
The decomposition of anions in Na2S2O4 may be
presented as a scheme the following elementary trans-
formations (Fig. 11):
3
6
ries of salts having thionate anions, proceeds in con-
formity with the following equation:
2S2O24– ®4SO–
2
Na2S3O6®SO2+S+Na2SO4
4SO– ®2SO2+2SO2–
2
2
Thermal decomposition of multicentric species
such as S O2– proceeds in a way analogous to the
2SO0+2SO2– ®2SO2– +2SO
3
6
2
2
3
thermal decomposition of Na2S2O6. The mechanism
of that reaction may be interpreted as follows:
2SO®S+SO2
S3O62– ®S O– +SO–
3
(I)
(IIa)
(IIb)
(III)
SO2– +S®S O2–
2
3
3
2
3
S2O3– +SO– ®S O2– +SO3
2S O2– ®S O2– +SO2+SO2–
3
2
3
2
4
2
3
3
S O2– +SO3®S2O2+SO2–
The process depends on the properties of the spe-
cies formed successively in the course of the decom-
position. The SO–2 radicals, formed in the rupture of
the S–S bond, react with one another, like in the case
2
3
4
S2O2®SO2+S
SS3O62– ®SO2+S+SO2–
4
Conclusions
The morphological classification of sulphur oxy-
compounds, which joins their structures and their
transformations into a coherent system that enables to
divide the real, often complex transfosrmations of an-
ionic sublattices of the salts, by making use of the reg-
ularity of variation of chemical properties observed in
the system, into a sequence of elementary transforma-
tions consisting in transfer of electrons or oxide lig-
ands between simple species in the systems of decom-
posing anionic sublattices of the salts. In the decom-
position of sodium oxosalts of sulphur the role of Na+
cations is limited principally to stabilisation of the an-
ionic sublattices. The oxidizing and acidic properties
of these salts are too weak to enable them to partici-
pate as reagents in transformation of the species in de-
composition. The presented scheme of decomposition
of anionic sublattices of sodium oxosalts may serve a
Fig. 11 Scheme of thermal decomposition of S2O24– in
Na2S2O4
J. Therm. Anal. Cal., 96, 2009
153

JASZCZAK-FIGIEL, GONTARZ
13 D.-G. Oei, Inorg. Chem., 12 (1973) 435.
basis for analysis of the effect of other cationic
counterions, having stronger acidic, oxidizing or re-
ducing properties, as well as of the effect of other re-
actants on modification of transformations of anionic
sublattices in the salts.
14 E. Rosen and R. Tegman, Acta Chem. Scand.,
25 (1971) 3329.
15 E. Rosen and R. Tegman, Acta Scripta., 2 (1972) 221.
16 S. E. Rasmussen, J. E. Jorgensen and B. Lundtoft, J. Appl.
Crystallogr., 29 (1996) 42.
17 L. O. Larsson and P. Kierkegaard, Acta Chem. Scand.,
23 (1969) 2253.
References
18 R. Westrik and C. H. MacGillavry, Acta Cryst.,
7 (1954) 764.
1 A. Górski, Pol. J. Chem., 75 (2001) 159.
2 D. Shannon and C. T. Prewitt, Acta Cryst.,
B25 (1969) 925.
19 B. Post, R. S. Schwartz and I. Fankuchen, Acta Cryst.,
5 (1952) 372.
20 K. St¯hl, T. Balic-Zunic, F. de Silva, K. M. Eriksen,
R. W. Berg and R. Fehrmann, J. Solid State Chem.,
178 (2005) 1697.
3 J. C. Halle and K. H. Stern, J. Phys. Chem.,
84 (1980) 1699.
4 S. W. Lee, K. S. Hong, R. A. Condrate, R. P. Hapanowicz
and R. F. Speyer, J. Mater. Sci., 27 (1992) 4961.
5 K. Wakamura, Phys. Rev. B: Condens. Matter,
59 (1999) 3560.
21 E. de Matos Gomes, J. Ortega, J. Extebarria, F. J. Zuniga
and T. Breczewski, J. Phys.: Condensed Matter,
8 (1996) 2063.
22 K. L. Carter, T. A. Siddiquee, K. L. Murphy and
D. W. Bennett, Acta Cryst., B60 (2004) 155.
23 J. D. Dunitz, Acta Cryst., 9 (1956) 579.
24 S. T. Teng, H. Fuess and J. W. Bats, Acta Cryst.,
40 (1984) 1785.
6 M. M. Barbooti and F. Jasim, Thermochim. Acta,
16 (1976) 402.
7 G. Hatem, M. Gaune-Escard, S. B. Rasmussen and
R. Fehrmann, J. Phys. Chem. B, 103 (1999) 1027.
8 G. Hatem, F. Abdoun, M. Gaune-Escard, K. M. Eriksen
and R. Fehrmann, Thermochim. Acta, 319 (1998) 33.
9 L. Erdey, J. Simon, S. Gál and G. Liptay, Talanta,
13 (1966) 67.
25 G. S. Murthy, R. L. Eager and K. J. McCallum, Can. J.
Chem., 49 (1971) 3733.
26 E. G. Janzen, J. Phys. Chem., 76 (1972) 157.
10 J. Zsakó, E. Brand-Petrik and G. Liptay, J. Thermal Anal.,
12 (1977) 421.
Received: April 21, 2008
Accepted: May 6, 2008
11 K. Goodheat, I. K. O’Neill and D. F. Wardleworth,
J. Appl. Chem. Biotechnol., 24 (1974) 71.
12 P. Böttcher, J. Getzchmann and R. Keller, Z. Anorg. Allg.
Chem., 619 (1993) 476.
DOI: 10.1007/s10973-008-9195-8
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J. Therm. Anal. Cal., 96, 2009