Thermal and electrical properties of manganese (II) oxalate dihydrate and cadmium (II) oxalate monohydrate

Article abstract of DOI:10.1016/s0040-6031(98)00608-x

The thermal decomposition of MnC₂O₄·2H₂O and CdC₂O₄·H₂O have been studied by two probe direct current electrical conductivity measurements under the atmospheres of static air, dynamic dry n

Full text of DOI:10.1016/s0040-6031(98)00608-x

Thermochimica Acta 326 (1999) 187±192
Thermal and electrical properties of manganese (II) oxalate dihydrate
and cadmium (II) oxalate monohydrate
*
A.K. Nikumbh , A.E. Athare, S.K. Pardeshi
Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007, India
Received 4 May 1998; received in revised form 14 September 1998; accepted 22 October 1998
Abstract
The thermal decomposition of MnC
2
O
4
Á2H
2
O and CdC
2
O
4
ÁH
2
O have been studied by two probe direct current electrical
conductivity measurements under the atmospheres of static air, dynamic dry nitrogen and dynamic air. The products at each
decomposition stage have been characterized by infrared spectroscopy and X-ray powder diffraction. The electrical
conductivity measurements were found to give additional information on the solid-state reaction as compared to that obtained
from conventional thermal analytical techniques (such as TG and DTA). # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Electrical conductivity; Electrochemical analysis; Thermal decomposition; Oxalates; Solid-state reaction
1
. Introduction
and CdC O ÁH O by using direct current electrical
2
4
2
conductivity measurement has not been investigated
yet. This paper deals with a systematic change of
electrical properties as well as that of ambient atmos-
pheres on thermal decomposition of the
MnC O Á2H O and CdC O ÁH O. This study has been
The thermal decomposition of metal oxalate com-
plexes have been studied by numerous workers. The
decomposition of oxalate complexes is usually com-
plicated and occurs in a series of steps. The most
obvious change is caused by the environment when the
actual product is different due to the in¯uence of the
surrounding as atmosphere. The different oxide pro-
ducts were obtained in case of manganese (II) oxalate
dihydrate (MnC O Á2H O); the exact nature of the
2
4
2
2
4
2
supplemented with X-ray powder diffraction and
infrared spectroscopy.
2. Experimental
2
4
2
product depending on experimental conditions is an
example that may be cited in literature [1±7]. The
decomposition of cadmium (II)oxalate (CdC O ÁH O)
MnC O Á2H O and CdC O ÁH O were prepared
2
4
2
2
4
2
using the methods described in literature [9,10]. Ele-
mental and the thermal analyses con®rms the presence
of water of hydration; and the polymeric octahedral
structure have been assigned by infrared spectra [11]
for these compounds.
2
4
2
in air or an inert atmosphere leads to the formation of
CdO has also been reported in literature [7,8]. How-
ever, the thermal decomposition of MnC O Á2H O
2
4
2
The procedure used for measurements of direct
current electrical conductivity, infrared spectroscopy
*
Corresponding author. Tel.: +91-1457719; fax: +91-0212-
3
0
53899; e-mail: aknik@unipune.in
040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 4 0 - 6 0 3 1 ( 9 8 ) 0 0 6 0 8 - X

1
88
A.K. Nikumbh et al. / Thermochimica Acta 326 (1999) 187±192
and X-ray powder diffraction were similar to those
reported earlier [12,13].
gives an endothermic peak at 1308C corresponding to
dehydration of MnC O Á2H O; a broad exothermic
2
4
2
peak at 2708C corresponding to the oxidative decom-
position of MnC O . The TG curve showed a con-
tinuous weight loss from 2308C until ®nal
2
4
3
3
3
. Results and discussion
.1. Static air atmosphere
.1.1. MnC O Á2H O
recrystallization to Mn O . Due to the broadness of
3
4
the exothermic peak in the DTA curve and to the
continuous weight loss in the TG curve, the various
meta-stable intermediates formed during this oxida-
tive decomposition step could not be determined in
detail. However, the direct current electrical conduc-
tivity, represented in Fig. 1(a), gave complete infor-
mation on the intermediates by showing different
region of conductivity.
2
4
2
The temperature variation of the electrical conduc-
tivity, ꢀ, (Fig. 1(a)) did not show initial decrease in
0
conductivity (Region B ) up to 958C. Then there was a
constant conductivity between 958 and 2268C (Region
B). The ꢀ value started to increase from 2268 to 3128C
0
(
Region C), followed by a decrease and then sharp
At B in Fig. 1(a) there was no observable change in
increase in ꢀ up to 3508C (Region D). Later, ꢀ
remained almost constant in the temperature range
X-ray diffraction pattern and infrared spectrum. This
indicates the desorption of physically adsorbed water
molecules on the upper surface of the particles. In the
temperature range corresponding to Region B, the
3
50±4008C (Region E).
A comparison of thermal analysis (TG and DTA)
6±8] with conductivity analysis in static air of
[
infrared spectrum revealed no H O peak, while the
2
MnC O Á2H O shows that the conductivity analysis
X-ray powder diffraction pattern generally showed
polycrystallinity with a decrease in inter-planar
spacings [14]. The elemental analysis agreed with
the formula MnC O .
2
4
2
gives a much more detailed view of the decomposition
process. TG shows a continuous mass loss around
1
00±1508C with a plateau up to 2208C [6±8]. DTA
2
4
�
1
Fig. 1. Plot of log ꢀ vs. T for (a) MnC
2
O
4
Á2H
2
O and (b) CdC
2
O
4
ÁH O. ꢀ, during decomposition; X, cooling cycle.
2

A.K. Nikumbh et al. / Thermochimica Acta 326 (1999) 187±192
189
In the temperature range corresponding to Region C
in Fig. 1(a), the infrared spectra showed wide
changes. When MnC O Á2H O was heated isother-
metal±oxygen stretching frequencies due to presence
of CdO [15]. The X-ray diffraction pattern of this
isothermally heated sample showed the structure to be
polycrystalline in nature, the peaks corresponding to
both CdC O and CdO were observed. The infrared
2
4
2
mally at 2908C, the infrared spectrum showed a
decrease in the intensities of the coordinated oxalate
2
4
�
1
bands, and bands occurred at 604 cm
4
(m) and
75 cm (m) for the M±O stretching frequencies
due to the presence of the manganese oxide formed
15]. The X-ray diffraction pattern indicate that this
spectrum and X-ray diffraction pattern for the sample
decomposed isothermally at 5008C (Region D)
showed mainly CdO. The sample was brown and
had an electrical conductivity value of about
�
1
[
�
5
� 1
� 1
sample was polycrystallite in nature; peaks corre-
sponding to both MnO and MnC O were observed.
10
ꢀ
It is well known that [6,7] the temperature and the
cm [18].
2
4
Although a tendency for a sharp increase in ꢀ was
observed at 3318C (Region D), the characteristic high
mechanism of the decomposition of oxalate was
altered by the surrounding atmosphere. Hence, it is
important to compare the data obtained under the
atmosphere with the data obtained under different
atmospheres.
�
5
� 1 � 1
cm ) could not be
ꢀ
value of Mn O (ꢁ10
ꢀ
3
4
obtained under dynamic conditions. However, the X-
ray diffraction studies con®rmed mainly to Mn O and
3
4
traces of MnO were formed at this temperature. The
infrared spectrum of the parent sample heated at
3.2. Dynamic dry nitrogen atmosphere
3
408C showed no bands due to coordinated carboxy-
late, but strong bands of Mn±O stretching frequencies
were observed. A sample in Region E in Fig. 1(a) was
predominantly Mn O ; the X-ray diffraction pattern
3.2.1. MnC O Á2H O
2
4
2
�
1
Region B in the plot of log ꢀ against T shown in
Fig. 2(a), can be related to dehydration of
MnC O Á2H O. Isothermal heating of the parent com-
3
4
con®rmed the formation of this phase. The sample
thus obtained at 4008C shows a change in ꢀ as the
temperature is changed. (see cooling and heating cycle
in Fig. 1(a)). This behaviour is characteristic of
Mn O and it has tetragonally deformed spinel
2
4
2
pound at 2258C showed its polycrystalline nature as
revealed by its X-ray diffraction pattern, and the
elemental analysis ®tted well to the formula MnC O4
[14].
2
3
4
[
16,17].
The conductivity plot (Fig. 2(a)) showed a decrease
and then steep increase in ꢀ at 316±4058C (Region C)
and then remained constant above this temperature
(Region D). The infrared spectrum and X-ray diffrac-
tion pattern of the isothermally heated parent com-
pound in Region C showed that MnO was present
together with some MnC O . Similarly, the infrared
spectrum and X-ray diffraction pattern for the sample
decomposed isothermally at 4508C showed mainly
MnO; the sample was greyish green. No line which
could be assigned to metallic manganese was detected
in our work. The sample thus obtained at 4508C shows
a variation in ꢀ with temperature. This behaviour is a
characteristic of the non-stoichiometry present in
MnO [16,17].
3
.1.2. CdC O ÁH O
2
4
2
In comparison of thermal analysis (TG and DTA)
7,8] with the conductivity analysis (plot for log ꢀ
[
�
1
against T ) of CdC O ÁH O in static air atmosphere
2
4
2
(Fig. 1(b)) showed the different intermediate phases
which occurred during the decomposition. The Region
2
4
0
B and B corresponds to dehydration of CdC O ÁH O
2
4
2
under this atmosphere. The isothermally heated sam-
ple under this atmosphere at 2608C, showed no H±OH
band in infrared spectrum and the X-ray diffraction
pattern showed broad peaks with a decrease in inter-
planar spacing. The elemental analysis also agreed
well with the anhydrous oxalate (CdC O ) formation.
2
4
The value of ꢀ steadily increased from 3528 to 4408C
Region C) and the infrared spectrum of isothermally
heated CdC O ÁH O sample at 3908C showed a
(
3.2.2. CdC O ÁH O
2
0
4
2
� 1
Region B and B in the plot of log ꢀ against T
(Fig. 2(b)), correspond to the dehydration of
2
4
2
decrease in intensity of coordinated carboxylate
�
1
bands, in addition bands at 605 cm
(m),
� 1
(s) and 462 cm (m) observed for
CdC O ÁH O. The isothermally heated parent sample
2
4
2
�
1
4
87 cm
at 2408C under dynamic nitrogen atmosphere was

1
90
A.K. Nikumbh et al. / Thermochimica Acta 326 (1999) 187±192
�
1
Fig. 2. Plot of log ꢀ vs. T for (a) MnC
2
O
4
Á2H
2
O and (b) CdC
2
O
4
ÁH O: ꢀ, during decomposition X, cooling cycle.
2
found to be less crystalline as shown from the X-ray
diffraction pattern, while the infrared spectrum
showed no H±OH band. The elemental analysis
agreed well with the anhydrous compound (CdC O ).
Further, the conductivity plot showed a steady
increase in values of ꢀ in the temperature range
Further, this plot revealed a de®nite regions of con-
ductivity corresponding to the various intermediates
formed. The isothermal decomposition study under
this atmosphere demonstrated that the intermediates
were similar to those obtained under the static air
atmosphere (see Fig. 1(a)).
2
4
2
50±3808C (Region C). The infrared spectrum and
X-ray diffraction pattern for sample heated isother-
mally at 3608C showed that CdO was present in this
stage together with some CdC O . A steep increase in
3.3.2. CdC O ÁH O
2
4
2
�
1
Region B in the plot of log ꢀ against T (Fig. 3(b))
corresponds to the dehydration of CdC O ÁH O. There
2
4
2
4
2
ꢀ
has been observed in Region D corresponding to
was a steady increase in the value of ꢀ between 3408
and 4108C (Region C), then there was a steep increase
in values of ꢀ in the temperature range 410±5108C
(Region D). The infrared and the X-ray diffraction for
the sample decomposed isothermally at 3808 and
CdO formed as the ®nal product. X-ray diffraction
analysis has con®rmed the formation of this phase.
Although the decomposition behaviour was mostly
the same in static air and dynamic dry nitrogen atmos-
pheres some critical differences were observed. These
differences could be clari®ed when the study was
carried out under dynamic air atmosphere.
5008C showed CdO along with anhydrous CdC O4
2
and pure CdO, respectively.
The gaseous products obtained by the thermal
decomposition of MnC O Á2H O or CdC O ÁH O
2
4
2
2
4
2
3
3
.3. Dynamic air atmosphere
under dynamic (pure and dry) nitrogen atmosphere
were analysed by qualitative gas detection method.
Carbon dioxide was detected by precipitation as cal-
cium carbonate from a solution of calcium hydroxide,
while carbon monoxide was detected by reduction of
.3.1. MnC O Á2H O
2
4
2
�
1
The plot of log ꢀ against T (Fig. 3(a)) showed
0
Region B and B, indicating dehydration steps.

A.K. Nikumbh et al. / Thermochimica Acta 326 (1999) 187±192
191
�
1
Fig. 3. Plot of log ꢀ vs. T for (a) MnC
2
O
4
Á2H
2
O and (b) CdC
2
O
4
ÁH
2
O.
ꢂ
3
12� 400 C
iodine pentoxide into iodine. These gases were also
con®rmed by gas liquid chromatography (not shown).
These chromatograms showed the presence of polar
gases (namely CO , H etc. . .). The gases were col-
lected at ca. 3508C.
The different paths followed by the decomposition
2
MnO ‡ MnC2O4
ThetransformationofMnC O toMnOwasthe®nalstep
!
Mn3O4 ‡ 2CO " (3)
2
4
detected in a dynamic dry nitrogen atmosphere, while
CdC O transformed to CdO under static air, dynamic
dry nitrogen and dynamic air atmospheres:
2
2
2
4
ꢂ
4
0� 330 C
of MnC O Á2H O and CdC O ÁH O in different atmo-
2
4
2
2
4
2
CdC2O4 Á H2O
!
CdC2O4 ‡ H2O "
(4)
spheres showed complete dehydration, as was seen
from conductivity measurements and the infrared
spectrum. A transformation of MnC O to MnO was
ꢂ
330� 410 C
2
CdC2O4
!
CdC2O4 ‡ CdO ‡ CO " ‡CO2 "
(5)
10� 520 C
2
4
also detected in static and dynamic air atmospheres. A
separate phase of MnO could not be obtained; this
compound always occurred with MnC O . Thus, the
ꢂ
4
CdC2O4 ‡ CdO
!
2CdO ‡ CO " ‡CO2 "
6)
2
4
(
transformation of MnO and MnC O seems to be an
2
4
equilibriumreaction.ThismixtureofMnOandMnC O
2
4
is then transformed to Mn O which is the ®nal product
3
4. Conclusions
4
obtainedinstaticairanddynamicair.Thesereactionsare
presented as follows:
The present study revealed the following ®ndings
on the solid-state dehydration and decomposition of
ꢂ
4
0� 226 C
MnC O Á2H O and CdC O ÁH O.
MnC O Á 2H O
!
MnC O ‡ 2H O " (1)
2
4
2
2
4
2
2
4
2
2
4
2
ꢂ
(a) The oxidative decomposition behaviours of
MnC O Á2H O and CdC O ÁH O were better
2
26� 312 C
MnC2O4
!
MnO ‡ CO " ‡CO2 "
(2)
2
4
2
2
4
2

1
92
A.K. Nikumbh et al. / Thermochimica Acta 326 (1999) 187±192
[
[
6] E.D. Macklen, J. Inorg. Nucl. Chem. 30 (1968) 2689.
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electrical conductivity measurements which
showed different regions of conductivity for the
intermediates formed.
(
[
8] C. Duval, Inorganic Thermogravimetric Analysis, Elsevier,
Amsterdam, 1953, p. 531.
(
b) The final product of decomposition in static air
and dynamic air was found to be Mn O for
[9] D. Dollimore, D. Nicholson, J. Chem. Soc. A (1962) 960.
10] R. David, Bull. Soc. Chim. Fr. (1960) 719.
[
[
3
4
11] J.R. Allan, N.D. Baird, A.L. Kassyk, J. Therm. Anal. 16
MnC O Á2H O. However, the final decomposition
2
4
2
(
1979) 79.
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CdO for CdC O ÁH O.
[
[
12] K.S. Rane, A.K. Nikumbh, A.J. Mukhedkar, J. Mater. Sci. 16
(1981) 2387.
2
4
2
13] A.K. Nikumbh, A.E. Athare, V.B. Raut, Thermochim. Acta
1
86 (1991) 217.
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