Thermal decomposition of cadmium formate in inert and oxidative atmosphere

Article abstract of DOI:10.1016/j.tca.2008.09.003

Thermal decomposition of cadmium formate, Cd(HCOO)₂, was studied in dynamic helium and air atmosphere by means of simultaneous TGA, DTA and MS analysis. It was found that the cadmium formate decomposes at about 210 °C to metallic cadmium and cadmium carbonate which next decomposes with formation of cadmium oxide. In helium cadmium melts, evaporates and the reaction residue consists of CdO and a small amount of elementary carbon formed in result of pyrolysis of formate groups. In air cadmium oxidizes and the final solid product of decomposition is CdO. The gaseous products of cadmium formate decomposition are: carbon dioxide, water, carbon monoxide, formaldehyde, methyl alcohol and methyl formate.

Full text of DOI:10.1016/j.tca.2008.09.003

Thermochimica Acta 479 (2008) 12–16
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Thermochimica Acta
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Thermal decomposition of cadmium formate in inert and oxidative atmosphere
Barbara Małecka∗, Agnieszka Ła˛cz
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2008
Received in revised form 3 September 2008
Accepted 6 September 2008
Available online 12 September 2008
Thermal decomposition of cadmium formate, Cd(HCOO)2, was studied in dynamic helium and air atmo-
sphere by means of simultaneous TGA, DTA and MS analysis. It was found that the cadmium formate
decomposes at about 210 ◦C to metallic cadmium and cadmium carbonate which next decomposes with
formation of cadmium oxide. In helium cadmium melts, evaporates and the reaction residue consists of
CdO and a small amount of elementary carbon formed in result of pyrolysis of formate groups. In air
cadmium oxidizes and the final solid product of decomposition is CdO. The gaseous products of cadmium
formate decomposition are: carbon dioxide, water, carbon monoxide, formaldehyde, methyl alcohol and
methyl formate.
Keywords:
Cadmium formate
Thermal decomposition
TG
© 2008 Elsevier B.V. All rights reserved.
DTA
Mass spectrometric analysis
1. Introduction
uct CO2 was reported and little amounts of CO, methyl alcohol and
methyl formate.
Cadmium and its compounds find a wide spectrum of techno-
logical applications in industry and analysis as catalysts, colorants,
elements of sensors and storage batteries (nickel–cadmium or
silver–cadmium), stabilizers, materials for semiconductors and
transparent conductive oxide films [1–9]. Authors of the present
paper in recent years made an effort to study thermal decompo-
sition of the series of cadmium carboxylates and dicarboxylates
(cadmium malonate, acetate and succinate) to reveal the individ-
ual role of the cation and the anions in this reaction [10–12]. This
work concerns the decomposition of cadmium formate in inert and
oxidative atmosphere.
Thermal decomposition of cadmium formate was studied on the
occasion of research on the hydrated mixed Cu–Cd formats [15] and
Sr–Cd formats [16] in oxidative atmosphere. As solid intermediate
products anhydrous formates were reported. For decomposition of
CdSr(HCOO)4 the final product was mixture of CdO and SrCO3 and
decomposition of Cu0.47Cd0.53(HCOO)2 lead to mixture of CdO and
CuO.
The goal of this work is to find out the routes of decomposition
of cadmium formate as well as solid and gaseous products of this
reaction.
The anhydrous cadmium formate has a monoclinic, polymer
structure with seven-coordinated Cd atoms with the distorted
square-pyramidal geometry. Each cadmium atom is combined
with seven oxygen atoms belonging to five different formic lig-
ands [13]. It means that in the cadmium formate structure there
are bridging and chelating Cd–O bonds with length in the range
2.259(4)–2.599(7) Å.
The reaction of thermal decomposition of Cd(HCOO)2 was not
investigated very often earlier. In paper [14] which was devoted to
the decomposition in inert atmosphere of series of metal formates
the metallic cadmium and cadmium carbonate were indicated as
products of Cd(HCOO)2 decomposition. As a main gaseous prod-
2. Experimental
2.1. Material
Cadmium formate was synthesized by dissolving cadmium car-
bonate in a hot, 15% aqueous solution of formic acid. According to
high volatility of formic acid 10% excess of this reactant was used.
All reactants were analytically pure and delivered by P.O.Ch. Gli-
wice S.A. The received solution was filtered off and left for a period
of 4–5 weeks for the crystallisation process. The crystals formed
were washed with distilled water, filtered using Büchner’s funnel
to remove the remaining formic acid and then dried at 130 ◦C in a
dryer to receive an anhydrous compound. After grinding in an agate
mortar, the fraction of 10–100 ␮m grain size was separated for fur-
ther investigations. The sample was kept in a desiccator over CaO
during the whole process of investigations.
∗
Corresponding author.
E-mail address: bmalecka@agh.edu.pl (B. Małecka).
0040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2008.09.003

B. Małecka, A. Ła˛cz / Thermochimica Acta 479 (2008) 12–16
13
2.2. Methods
Thermogravimetry (TG) and differential thermal analysis (DTA)
were carried out on SDT 2960 TA INSTRUMENTS apparatus. The
samples of mass around 10 mg were placed in the standard plat-
inum crucibles and heated at rates between 2 ◦C min−1, 5 ◦C min−1
and 10 ◦C min−1. All presented results were obtained at heat-
ing rate: 5 ◦C min−1. The measurements were carried out under
dynamic conditions (the flow of 100 cm3 min−1) in helium (purity
99.999%) and synthetic air atmospheres (<15 ppm H2O).
The volatile products of decomposition were analysed using the
quadrupole mass spectrometer BALZERS QMD 300 THERMOSTAR
operated with an electron impact ionizer (70 eV). The mass spec-
trometer was connected on-line with SDT apparatus by the quartz
capillary heated up to 200 ◦C. The measurements were performed
in a scan mode for m/z (where m is mass of the molecule and z is
a charge of the molecule in electron charge units) range from 10 to
114, which is the atomic weight of cadmium isotope 114 Cd.
The amounts of carbon and hydrogen in the prepared reactant
were measured using combustion analysis. Cadmium content was
determined using atomic absorption spectroscopy. The phase com-
position of the initial sample, samples decomposed to some extent
and solid residue was carried out using Phillips X-ray diffractome-
ter using CuK␣ radiation. IR spectroscopy of the reactants was
performed on BIO-RAD FTS60V spectrometer using the KBr pel-
let technique. The residue was also analysed by JMS-5400 (JEOL)
scanning electron microscope.
Fig. 2. TG and DTA curves of Cd(HCOO)2 decomposition in helium (5 ◦C min−1).
mass loss to the end of the process is about 75% at the heating rate
2 ◦C min−1 to 85% at the heating rate 10 ◦C min−1 and is much higher
than theoretical weight loss equal to 36.57% when assuming CdO
as the final product or 44.47% when assuming Cd as the final prod-
uct of decomposition. This means that the mass loss is connected
with the evolution of the volatile products which have to arise not
only from decomposition of formate groups but also have to contain
cadmium.
The results of XRD analysis of the sample taken from 285 ◦C pre-
sented in Fig. 3 show that in the 1st stage Cd, CdCO3 and CdO form.
The presence of CdCO3 in this sample was additionally confirmed
by IR spectroscopy but the IR spectrum was distorted by cadmium
oxide and traces of elementary carbon. This stage of reaction is con-
nected with the mass loss about 37% and strong single endothermic
effect on the DTA curve.
After the 2nd stage of decomposition in the sample Cd and CdO
was found. In this stage two overlapping endothermic peaks on
the DTA curve are seen: one corresponding to decomposition of
CdCO3 and the second, very sharp peak at 321 ◦C, corresponding to
cadmium melting [18]. The mass loss is about 4.0%.
The partial pressure of cadmium increases from about 14 Pa at
321 ◦C to 9 kPa at 600 ◦C (calculated on the basis of thermodynamic
data from [19]) which means that cadmium evaporates and the
3rd stage of mass loss on the TG curve is connected with this pro-
cess. The residue at 600 ◦C was CdO (Fig. 3). EDS analysis of the
residue revealed also the traces of carbon (Fig. 4). Elementary car-
3. Results and discussion
The chemical composition of the initial sample was determined
as: 55.6% Cd (55.53%), 11.6% C (11.87), 0.9% H (1.00%) and agreed
well with theoretical expectation for an anhydrous cadmium
formate (in brackets). The chemical analysis was supplemented
with X-ray diffraction analysis and infrared spectroscopy. The
X-ray pattern for the powder received differs from data in ASTM
card ICDD 32-1357 for Cd(HCOO)2 (Fig. 1), but this card is described
as “doubtful” in database. IR spectrum of initial sample hav-
ing signals at 2958 cm−1
,
2920 cm−1
1572 cm−1
,
2865 cm−1
1405 cm−1
,
2747 cm−1
1380 cm−1
,
,
2715 cm−1
,
,
1603 cm−1
1064 cm−1
,
,
,
1358 cm−1
,
and 764 cm−1 corresponds with the
results published earlier [17].
3.1. Decomposition in helium
The thermal decomposition of Cd(HCOO)2 in helium starts
approximately at about 210 ◦C (DTG onset). On the TG curve three
steps are seen (Fig. 2) in the temperature ranges: 210–300 ◦C (1st
stage), 300–340 ◦C (2nd stage) and 340–600 ◦C (3rd stage). The total
Fig. 3. XRD patterns of samples of partially decomposed Cd(HCOO)2 taken from
different temperatures (helium).
Fig. 1. XRD pattern of synthesized Cd(HCOO)2 and spectrum of Cd(HCOO)2 form
ASTM card ICDD 32-1357.

14
B. Małecka, A. Ła˛cz / Thermochimica Acta 479 (2008) 12–16
Fig. 4. EDS analysis of the residue of Cd(HCOO)2 decomposition in helium.
bon is produced in result of pyrolysis of formate groups. The mass
loss in the 3rd stage is about 40% for the measurement carried out
at 5 ◦C min−1 and presented in Fig. 3, but reaches about 44% dur-
ing measurement at 10 ◦C min−1. This difference can be explained
taking into consideration that at the 3rd stage cadmium is partly
oxidized by the traces of oxygen present in helium. The longer
time of the experiment at the low heating rate makes the oxidizing
advances and leads to the lower mass loss.
The mass spectrum of the gas produced by the decomposing
cadmium formate in the 1st stage of decomposition contained
the following m/z signals: 12, 15, 16, 17, 18, 28, 29, 30, 31, 32,
44 and 60. The analysis of this spectrum showed that in this
stage the following gas products evolve: carbon dioxide, water,
carbon monoxide, formaldehyde (HCOH), methyl alcohol (CH3OH)
and methyl formate (HCOOCH3). Table 1 contains mass spectra of
gaseous products of decomposition taken from NIST database [20].
Fig. 5 shows intensities of detected m/z signals characteristic of the
identified gases. From the comparison of the surface area of m/z sig-
nals it can be deduced that the main gaseous product of Cd(HCOO)2
thermal decomposition is CO2.
Fig. 5. Mass spectrometric signals of chosen m/z recorded during decomposition of
Cd(HCOO)2 in helium.
•
2nd stage:
CdCO3 → CdO + CO2↑
•
3rd stage:
The only gas evolved during the second stage was CO2. No evo-
lution of gas was observed for the third stage of decomposition.
Taking into consideration the results of the analysis of solid
and gaseous products of reaction in helium it can be stated that
decomposition proceeds as follows:
Cdliquid → Cdvapour
↑
Calculations carried out on the basis of the mass change in the
second stage of decomposition as well as the weight of the residue
indicated that the value of x for the 1st stage of reaction can be
estimated as 0.2–0.3.
•
1st stage:
Cd(HCOO)2 → xCdCO3 + (1 − x)Cd
3.2. Decomposition in air
+ (CO2, CO, H2O, HCOH, CH3OH, HCOOCH3) ↑
The thermal decomposition of cadmium formate in air proceeds
by two separate stages (Fig. 6). Average total mass loss of 36.6% in
the whole reaction stays in a good agreement with theoretical value
36.57% assuming CdO as the final product of decomposition. The
first stage, with the mass loss of 32% within the temperature range
210–290 ◦C, is accompanied by very strong exothermic effect. XRD
pattern of the sample taken from 290 ◦C reveals signals for CdO
and CdCO3 (Fig. 7). The second stage (290–365 ◦C) is described by
endothermic effect on the DTA curve and the mass lost about 7.3% in
relation to mass from 290 ◦C. The XRD pattern for sample at 400 ◦C
(Fig. 7) reveals only the signals of CdO.
Table 1
Mass spectra of the gaseous products of Cd(HCOO)2 decomposition [20]
Compound
Mass spectrum m/z (intensity)
CO2
H2O
CO
HCOH
CH3OH
HCOOCH3
44(100), 28(9,8), 16(9,6), 12(8,7), 22(1,0)
18(100) 17(21,0) 16(1,0)
28(100) 12(4,7) 16(2,0)
29(100) 30(58,0) 28(24,0) 15(2,0) 12(1,0)
31(100) 32(75,0) 29(44,0) 15(12,0) 30(6,4) 28(4,5)
31(100) 32(46,0) 29(45,0) 60(38,0) 15(19,0) 30(6,0) 28(4,8) 44(1,0)
Only signals with intensity >1% were given.

B. Małecka, A. Ła˛cz / Thermochimica Acta 479 (2008) 12–16
15
Fig. 6. TG and DTA curves of Cd(HCOO)2 decomposition in air (5 ◦C min−1).
The mass spectrum of the gas evolving from the decomposing
cadmium formate in the first stage contained the same m/z signals
as during decomposition in helium: 12, 15, 17, 18, 29, 30, 31 and 44,
except of 60. The intensity of signal m/z = 60 is about 100 times low-
ers than that for m/z = 44. Based on these results as gaseous products
of decomposition in air H2O, CO2 and HCOH, CH3OH, HCOOCH3 can
be stated. The changes in intensity of m/z signals 28 as well as 16
and 32 cannot be measured because they occur compared to high-
level signals corresponding to N2 and O2, respectively, which are
components of air. In consequence these important signals charac-
teristic of HCOH and CH3OH cannot be considered. Some gaseous
products like HCOOCH3 can be oxidized in the secondary reactions
in which a great amount of CO2 and H2O is produced. The lack of
signal m/z = 60 in the spectrum is probably the consequence of low
content of HCOOCH3 in gaseous products (m/z = 60 is the fourth
highest signal in HCOOCH3 spectrum) resulting from its oxidation.
CO2 is the only gaseous product emitted above 290 ◦C in the
second stage of decomposition (Fig. 8).
Fig. 8. Mass spectrometric signals of chosen m/z recorded during decomposition of
Cd(HCOO)2 in air.
•
1st stage:
Cd(HCOO)2 → xCdCO3 + (1 − x)Cd
+ (CO2, H2O, HCOH, CH3OH, HCOOCH3)
Cd + 1/2O2 → CdO
•
2nd stage:
CdCO3 → CdO + CO2
The strong exothermic effect for the first stage of Cd(HCOO)2
decomposition in air, the absence of cadmium in the sample
partially decomposed and lack of endothermic effect with the min-
imum at 321 ◦C suggest that cadmium (the original product of
thermal decomposition of cadmium formate) is oxidized to CdO
by the oxygen from air.
The x value calculated in the same way as it was done for reaction
in helium was found to be 0.2–0.3 which is the same range as for
the decomposition in helium.
In conclusion it was found that cadmium formate thermal
decomposition in air proceeds similarly as in helium:
4. Summary
The temperature of the beginning of decomposition of cadmium
formate which is 210 ◦C is not influenced by the gas atmosphere.
This can be regarded as the argument that the mechanism of reac-
tion is the same in inert and oxidative environment.
The decomposition proceeds in two stages. The first stage leads
to the cadmium and cadmium carbonate as the solid products.
In inert atmosphere cadmium melts and evaporates. The rate of
cadmium evaporation is significantly high when the temperature
exceeds 400 ◦C. In oxygen containing atmosphere cadmium imme-
diately oxidizes to CdO.
The temperature of the second stage is 300 ◦C. In this stage
CdCO3 decomposes to CdO with evolution of CO2 as the only
gaseous product. In result the residue of Cd(HCOO)2 decomposi-
tion is CdO, which is the product of CdCO3 decomposition, and in
air it is additionally formed as the product of cadmium oxidation
being the secondary reaction.
Fig. 7. XRD pattern of partially decomposed Cd(HCOO)2 taken from 290 ◦C and the
final product of decomposition (air).

16
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Authors wish to acknowledge the Polish Ministry of Science and
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No. 11.11.160.110.
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