Kinetics of solid state reactions Co2+, Cu2+ and Zn2+ basic carbonates with some aliphatic acids

Article abstract of DOI:10.1023/A:1010174828300

The kinetic description and mechanism of the solid-state reactions between metal basic carbonate (M = Co²⁺, Cu²⁺ and Zn²⁺) and aliphatic carboxylic acids (oxalic, tartaric, succinic and citric acids) were studied using non

Full text of DOI:10.1023/A:1010174828300

Journal of Thermal Analysis and Calorimetry, Vol. 63 (2001) 609–616
2+
2+
KINETICS OF SOLID STATE REACTIONS Co , Cu
2+
AND Zn BASIC CARBONATES WITH SOME
ALIPHATIC ACIDS
*
M. A. Moustafa, Z. A. Omran, W. A. A. Bayoumy and M. A. Mousa
Chemistry Department, Faculty of Science, Benha University, Benha, Egypt
(
Received July 23, 2000)
Abstract
The kinetic description and mechanism of the solid-state reactions between metal basic carbonate
2
M=Co , Cu and Zn ) and aliphatic carboxylic acids (oxalic, tartaric, succinic and citric acids)
+
2+
2+
(
were studied using non-isothermal analysis (TG, DTA) and capillary techniques. The reactions were
found to proceed in all cases (except citric acid) by one mole of metal carbonate and two moles of
metal carbonate and two moles of organic acid. The kinetic analyses of non-isothermal data were
best described by each of the dimensional phase boundary R
2
and two-dimensional diffusion con-
trolled reactions D . While the capillary technique showed that the initial reaction occurs at the phase
2
boundary of the reactants and kinetically of the reacting controlled by diffusion mechanism in which
the diffusion species through the product layers are the organic acids.
Keywords: composition effect, kinetic of solid, organic acid diffusion
Introduction
The theories of the rate processes of heterogeneous reaction have been the subject of
various studies. There is a considerable diversity of mechanisms by which solids re-
act and there are several factors, which may control, determine, influence or modify
the rate limiting process [1]. The chemical transformations of solid organic com-
pounds play an important role in explaining the rate of solid-state reactions and the
change occurring in physical properties of organic compounds in terms of chemical
process and crystal structure.
In the present study, we used the isothermal data obtained from TG, DTA (ther-
mal analysis) and capillary techniques for investigating the kinetics of solid-state re-
2
+
2+
actions between basic metal carbonates (Co , Cu and Zn ) and organic acids (ox-
2+
alic, tartaric, succinic, and citric acids) using TG, DTA, thermal analysis and capil-
*
Author to whom all correspondence should be addressed.
1
418–2874/2001/ $ 5.00
Akadémiai Kiadó, Budapest
©
2001 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

6
10
MOUSTAFA et al.: BASIC CARBONATES WITH SOME ALIPHATIC ACIDS
lary techniques. It allows us to study the effect of varying each of chemical composi-
tion and crystal structure on the kinetics of the reaction.
Experimental
Materials and methods
Basic cobalt, copper and zinc carbonates supplied by BDH Chemical Ltd. Company,
as well as oxalic, tartaric, succinic and citric acids of analytical grade were used in
this work.
The products of the investigated reactions were first synthesized in a solution
state. This is done by the drop-wise addition of alcoholic solution of organic acid to a
suspended solution of the metal carbonate with well stirring till the end of the reac-
tion (no more effervescence was observed). The resultant solution was concentrated
and allowed to stand in ice bath for one hour. The precipitated salt was filtered off,
dried in air and analysed.
To investigate the stoichiometric ratio of the reactions, the products were also
synthesized in the solid state by mixing metal carbonates with the organic acids in a
molar ratio similar to that obtained in solution state. The mixtures were finely divided
in agate mortar, and then kept in a thermostat (below the eutectic and melting points
of organic acid) for 24 h.
Kinetic studies
Capillary technique
Kinetics of solid-state reactions in capillary tubes were studied by the technique de-
veloped by Rastogi et al. [2]. Pyrex glass capillaries were used for this purpose. One
end of the capillary was sealed and half of it was filled with organic acid (particle size
–
2
1
00 mesh cm ) with the help of a glass rod. The remaining half of the tube was filled
with basic carbonate of the same particle size. After that, the other end of the capillary
was sealed. The capillary tube was then kept in a thermostat at temperatures of 353,
3
63 and 373 K. The fluctuation in the temperature was not more than ±1.0 K. The re-
action between the solid materials was indicated by observing the change in the col-
our at the interface of the reactants. The rate of the reaction was followed by measur-
ing the thickness of the coloured product layer as a function of time with the help of a
travelling microscope. The coloured products were separated manually by breaking
the reaction tube and the amounts of metal content were analyzed volumetrically by
titration using EDTA solution [3].
Elemental analysis (C and H) for the samples prepared in both solution and
solid-state phases was carried out using Carlo Erba (Model 11.06) instrument.
J. Therm. Anal. Cal., 63, 2001

MOUSTAFA et al.: BASIC CARBONATES WITH SOME ALIPHATIC ACIDS
611
Thermal analysis technique
The kinetics of the thermal reaction for the mixed solids were investigated using
DTA and non-isothermal TG techniques by using thermal analyser (Shimadzu, model
DT-30). Experiments were carried out in air atmosphere at a constant heating rate of
–
1
1
0 K min and using α-Al O as a reference material. DTA and TG curves were re-
2
3
corded in the temperature range between room temperature and the decomposition
temperature of the investigated acids. Thermal changes of the solid reaction based on
the mass loss obtained during the course of the reaction are used for calculating the
kinetic parameters.
Infrared spectra
IR spectra for the samples obtained in each of solution and solid phases were scanned
using Beckman Infrared 4220 double beam spectrophotometer and KBr disc tech-
nique.
Magnetic measurements
The molar magnetic susceptibility χ of the products formed in both solution and
solid phase was determined at room temperature using Gouy’s method [4].
m
Results and discussion
The elemental analysis results for the samples obtained in liquid and solid phases, Ta-
ble 1, show that the reaction proceeds by one mole of basic metal carbonates and two
moles of organic acids (except in case of citric acid). The ratio between the different
2
+
2+
carbonates and the citric acid was found to be 1:1, 1.5:1 and 1.5:1 for Cu -, Co - and
2
Zn -carbonate, respectively, Table 1. This may be attributed to that the citric acid
+
contains one carboxylic group more than that of other acids. The χ -values obtained
m
in each of liquid and solid phases are almost equal, Table 1. This supports our results
that the products formed in both phases are identical. The IR spectra of the products
obtained from the reactions in both liquid and solid phases were found to be identical
–
1
where strong absorption bands at 1630–1550 and 1410–1380 cm due to asymmetric
and symmetric carboxylate stretching vibrations, respectively were observed indicat-
ing the formation of metal–carboxylate bonds [5]. New bands appearing in the spec-
–
1
tra of the products in range 600–300 cm are taken as a good assignment for the
metal–oxygen bond vibrations.
The reaction between the basic metal carbonate and the organic acid in solid
phase occurs in manner in which the organic acid surface is tending to react with the
carbonate anion to form carbonic acid followed by the immersion of metal cation into
the carboxylate anion to form complex or salt of acid. So by thermal analysis tech-
niques it is possible to follow the degree of conversion (α) in the reaction by means of
TG and DTA measurements [6]. Hence by using several established mathematical re-
action models [7], the mechanism and the kinetic parameters of the reaction can be
J. Therm. Anal. Cal., 63, 2001

Table 1 Analytical data for the products of the reactions in solid and liquid phases
*
χ
–3
Reactants
C/%
H/%
Metal/%
M
⋅1 0
Products
1
3.21
13.11)
2.16
(2.18)
32.43
(32.24)
4.0
(4.1)
CoCO
CuCO
3
⋅C o(OH)
⋅C u(OH)
2
2
+oxalic acid
+oxalic acid
CoC
2
O
O
4
⋅2 H
⋅1 /2H
⋅2 H
2
O
(
(
(
(
(
(
(
(
(
(
(
(
14.99
14.95)
39.82
(39.56)
8.3
(8.0)
3
–
CuC
2
4
2
O
13.43
13.31)
1.96
(1.66)
36.21
(36.24)
2.1
(1.9)
ZnCO
3
⋅⋅ n(ΟΗ)
2
+oxalic acid
ZnC
2
O
4
2
O
23.18
23.19)
1.82
(1.93)
28.05
(28.50)
2.0
(1.9)
CoCO
3
⋅C o(OH)
⋅C u(OH)
2
+tartaric acid
+tartaric acid
CoC
4
4
Η
4
4
Ο
6
18.34
18.08)
3.81
(3.77)
23.32
(23.92)
0.9
(0.8)
CuCO
3
2
CuC
Η
Ο
6
⋅3 H
⋅H
2
O
21.37
20.57)
2.46
(2.59)
28.54
(28.25)
0.9
(0.9)
ZnCO
CoCO
CuCO
3
⋅⋅ n(ΟΗ)
2
+tartaric acid
ZnC
4
Η
4
Ο
6
2
O
27.36
27.43)
2.34
(2.29)
33.92
(33.71)
2.0
(1.7)
3
3
⋅C o(ΟΗ)
2
+succinic acid
+succinic acid
CoC
4
4
Η
4
4
Ο
4
26.33
26.74)
2.17
(2.23)
35.06
(35.38)
1.4
(1.1)
⋅C u(ΟΗ)
2
CuC
Η
Ο
4
26.12
26.47)
2.16
(2.21)
35.74
(36.04)
2.8
(3.0)
ZnCO
3
⋅⋅ n(ΟΗ)
2
+succinic acid
ZnC
4
Η
4
Ο
4
24.45
25.96)
1.76
(1.80)
29.94
(31.87)
4.0
(4.4)
CoCO
3
⋅C o(ΟΗ)
2
+citric acid
+citric acid
Co
3
2
(C
6
Η
7 8 2
Ο )
20.42
20.51)
2.20
(2.28)
32.81
(36.18)
3.4
(3.0)
CuCO
3
⋅C u(ΟΗ)
2
Cu
6 8 9
C Η Ο
26.11
25.08)
2.87
(2.74)
33.99
(34.16)
5.9
(6.1)
ZnCO
3
⋅Z n(ΟΗ)
2
+citric acid
3 6 8 8 2
Zn (C Η Ο )
*
–
χM is the molar magnetic susceptibility; Results of liquid phases are in pharentheses

MOUSTAFA et al.: BASIC CARBONATES WITH SOME ALIPHATIC ACIDS
613
deduced (α, T, and t) from the data obtained from DTA and TG curves. This was done
using different kinetic models, Table 2, and by applying the regression analysis
method to get the best fit for the experimental results.
Table 2 Kinetic model equations used in this work [7]
Reaction model
Symbol
g(α)
1–(1–α)
1–(1–α)
f(α)
2(1–α)
3(1–α)
1/2α
1
1
/2
/3
1/2
2/3
Two-dimensional phase boundary
Three-dimensional phase boundary
One-dimensional diffusion
Two-dimensional diffusion
Three-dimensional diffusion
Four-dimensional diffusion
Random nucleation
R
2
3
R
2
D
1
D
2
D
3
D
4
A
2
A
3
A
4
α
(α+(1–α)ln(1–α)
–l/ln(1–α)
1
/3 2
2/3
1/3
[1–(1–α) ]
3(1–α) /2[1–(1–α)
–1/3
2/3
(1–2/3α)–(1–α)
3/2[(1–α) –1]
1
1
1
/2
/3
/4
1/2
[–ln(1–α)]
[–ln(1–α)]
[–ln(1–α)]
2(1–α)[–ln(1–α)]
3(1–α)[–ln(1–α)]
4(1–α)[–ln(1–α)]
(1–α)
2/3
3/4
Random nucleation
Random nucleation
First order kinetics
F
F
F
1
–ln(1–α)
1/(1–α)
2
Second order kinetics
Third order kinetics
2
(1–α)
2
3
3
[1/(1–α)]
(1–α)
Prout–Tompkins
B
1
ln[α/(1–α)]
lnα
α(1–α)
Exponential law
E
1
α
The kinetics were studied from the non-isothermal data using a single heating
rate. Three kinetic analysis methods were done here. Integral method is only applied
on data obtained from TG curves [8] while the differential method is applied on those
obtained from both TG and DTA curves [9]. The results obtained from the use of the
three kinetic analysis methods can differentiate between reaction mechanisms more
practically than those found by applying only one method.
The results of the different kinetic models showed that these reactions are best
described by either two-dimensional phase boundary controlled reaction mechanism
R or by two-dimensional diffusion function D . The kinetic data for the R -mecha-
2
2
2
nism are summarized in Table 3. It is noteworthy that the accuracy of kinetic results
obtained is variable, depending on the composition of reactants and the calculation
methods used. For the most reactions investigated it was noticed that the correlation
coefficient values obtained using differential method are more closer to unity than
those obtained by means of the integral method [10]. Generally, it was found that the
reaction mechanism is not varied with changing the chemical composition of the in-
vestigated reactant.
The reaction investigated can be considered as an acid-base reaction type. The
difference in reactivity and kinetic parameters may be due to the difference in the pro-
ton transfer capabilities of the organic acids to react with the carbonate anion when
the reactants are present in contact with each other. Inspection of the whole kinetic
J. Therm. Anal. Cal., 63, 2001

Table 3 Kinetic parameters for solid–solid reactions between organic acids and basic carbonates investigated using R
ferential and integral methods on TG as well as DDTA method
2
-model by applying dif-
Cobalt carbonate
Copper carbonate
Zinc carbonate
Organic
acid
Kinetic method
E
a
/
–1
E
a
/
–1
E
a
/
–1
–
1
A/s
r
–1
A/s
r
–1
A/s
r
kJ mol
44.4
50.3
19.0
56.0
48.8
49.9
24.2
67.3
46.0
48.0
23.1
62.4
kJ mol
36.1
41.2
9.8
kJ mol
51.5
59.2
28.1
59.6
51.9
59.2
38.5
68.2
53.5
50.5
31.2
65.1
1
.1
.2
.5
.8
.7
.4
.3
.6
.9
.5
.6
.6
1.4
1.0
oxalic
tartaric
succinic
citric
10
10
10
10
10
10
10
10
10
10
10
10
0.9990
0.9993
0.9991
0.9989
0.9986
0.9990
0.9990
0.9989
–
10
10
10
10
10
10
10
10
10
10
10
10
0.9994
0.9989
0.9994
0.9989
0.9990
0.9987
0.9991
0.9982
–
10
10
10
10
10
10
10
10
10
10
10
10
0.9997
0.9996
0.9994
0.9993
0.9991
0.9990
0.9990
0.9990
–
TG-differential
method
1
3
0
1
1
3
0
1
1
3
0
1.5
3.8
0.9
1.8
1.5
3.4
0.9
1.6
1.8
3.7
0.8
1.0
3.3
0.8
1.6
1.2
3.1
0.6
1.9
1.5
3.4
0.7
49.2
44.1
45.5
18.5
58.0
38.8
46.2
12.1
52.0
TG-integral method
DDTA method
oxalic
tartaric
succinic
citric
oxalic
tartaric
succinic
citric
–
–
–
–
–
–
–
–
–

MOUSTAFA et al.: BASIC CARBONATES WITH SOME ALIPHATIC ACIDS
615
data present knows that there is no correlation between the activation energy (E ) and
pK of the organic acid. This may be due to the differences in the nature and the crys-
a
a
tal structure for each of the organic acids and the basic carbonates.
On the basis of E values, Table 3, the reactivity order for the organic acids to-
wards the carbonates investigated was found to increase in the order:
a
Succinic>oxalic>tartaric>citric
The reactions investigated may be considered as anion exchange reaction in
which the weakly acidic groups are anion exchange reactions where the weakly
2
+
acidic groups (carbonate and hydroxyl) on M are replaced by more favourable
carboxylate anion. These reactions occur by proton transfer from the organic acid,
which combines with carbonate and hydroxyl ions to liberate carbon dioxide and wa-
ter as gaseous products. The reactivity of metal carbonates increases with decreasing
2
Fig. 1 Relation between square of thickness ε vs. time (t) for the reactions between
each of a – CoCO
3
⋅C o(OH)
2
and (1, 2) – oxalic and (3, 4) – succinic acids;
b – CuCO ⋅C u(OH)
3
2
and (1, 2) – succinic and (3, 4) – oxalic acids
J. Therm. Anal. Cal., 63, 2001

6
16
MOUSTAFA et al.: BASIC CARBONATES WITH SOME ALIPHATIC ACIDS
the ionic radius of cations indicating that the diffusion of the cations may participate
in increasing the order of the reactivity of the reaction. So the rate of the reaction may
be controlled by the phase boundary and two-dimensional diffusion mechanism. The
activation energy values (E ) for the formation of the carboxylate are significantly
lower than the heats of sublimation of the organic acids [11]. This can eliminate the
a
significance contribution of vapour phase produced from the reactions (H O and
CO ).
2
2
The kinetics of the investigated solid reactions have been also determined by the
capillary technique at 353, 363, 373 K under isothermal conditions. The thickness of
the coloured product layer was measured as a function of time. The data obtained
were compared with the various solid-state reaction models [12]. The kinetic data
were found to be best described by the parabolic equation:
2
ε = kt + c
(1)
where c and k are constants.
2
Typical plots of ε vs. t are given in Fig. 1. The parabolic nature of Eq. (1) indi-
cates that the rate of the reactions investigated is controlled by diffusion mechanism
reaction. The direction of the movement of coloured boundary formed at the surface
of reactions indicates that the diffusing species through the product layer is the or-
ganic acid. The metal basic carbonates have a polymeric network in their crystals [13]
and the binding forces are very strong covalent bonds through the crystals [1]. The
diffusion of carbonates will thus require the breaking of many covalent bonds, where-
as the organic acids investigated are held together by weak inter- or intramolecular
hydrogen bonds and their diffusion requires very small amount of energy which is
available at the temperatures at which these reactions have been studied.
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2
3
4
5
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