Effect of metal oxide additives on the thermal decomposition kinetics of potassium metaperiodate

Article abstract of DOI:10.1007/s10973-009-0411-y

The effect of additives (CuO, MnO₂ and TiO₂) on the thermal decomposition kinetics of potassium metaperiodate (KIO₄) to potassium iodate (KIO₃) has been studied in air by thermogravimetry under isothermal conditions. Irrespective of whether p- or n-type, the metal oxides show only a little or no influence on the rate of the decomposition except for the small decrease when the oxide concentration is as high as 10 wt%. The rate law for the decomposition of KIO₄ (Prout-Tompkins model) remained unaffected by the additives.

Full text of DOI:10.1007/s10973-009-0411-y

J Therm Anal Calorim (2010) 100:177–181
DOI 10.1007/s10973-009-0411-y
Effect of metal oxide additives on the thermal decomposition
kinetics of potassium metaperiodate
K. Muraleedharan Æ M. P. Kannan Æ
T. Gangadevi
Received: 9 April 2009 / Accepted: 5 August 2009 / Published online: 29 August 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract The effect of additives (CuO, MnO2 and TiO2)
on the thermal decomposition kinetics of potassium me-
taperiodate (KIO4) to potassium iodate (KIO3) has been
studied in air by thermogravimetry under isothermal con-
ditions. Irrespective of whether p- or n-type, the metal
oxides show only a little or no influence on the rate of the
decomposition except for the small decrease when the
oxide concentration is as high as 10 wt%. The rate law for
the decomposition of KIO4 (Prout–Tompkins model)
remained unaffected by the additives.
defect concentrations either by doping or by prior
mechanical and/or thermal treatments of the lattice and
thereby throw some light on the topochemistry and the
decomposition mechanism of solids.
We have reported the effects of pre-treatments on the
thermal reactivity of several high-energy solids such as
halates and perhalates [7–13] that throw light on the
mechanism of their decomposition. Thermal decomposi-
tion of halates and perhalates, which occupy an important
place in modern solid-state chemistry, is extremely sensi-
tive to the presence of impurities, additives, etc., and more
data of this kind are desirable.
Keywords Isothermal decomposition kinetics Á
KIO4 Á Metal oxide additives—CuO, MnO2 and TiO2
According to thermoanalytical studies, KIO4 decom-
poses in two steps [14, 15]. At about 570 K, KIO4
decomposes with heat evolution to potassium iodate
(KIO3) and oxygen. The decomposition of KIO3 to KI
takes place in the range 780–800 K. In the thermal
decomposition of KIO4 it has not been proved possible to
identify the six valent iodine compound, K2IO4, analogous
to the compounds, M2IO4, formed in the decomposition of
lithium and sodium periodates. We have studied the effects
of several pre-treatments on the kinetics and mechanism of
the thermal decomposition of KIO4. We observed that
KIO4 decomposes via Prout–Tompkins mechanism. Our
earlier investigations [9, 12] showed that the isothermal
decomposition of KIO4 follows Prout–Tompkins kinetics
at all temperatures studied and we proposed that the
probable rate determining step in the thermal decomposi-
tion of KIO4 is the transfer of an electron from the perio-
date anion to the potassium cation rather than the rupture of
I–O bond or the diffusion of cations/anions.
Introduction
Solid state reactions are generally complex since they are
very sensitive to the history of the solid. A number of
factors associated with mechanical, chemical and radiation
treatments are found to influence the reactivity of solids.
Reactivity of solids is greatly modified by pre-treatments
and the nature of influence of the pre-treatments provides
valuable information on the elementary steps and thereby
on the mechanism and control of solid-state reactions
[1, 2]. Thermogravimetric analysis (TG) has been used to
obtain thermal stability parameters of solids [3–6]. The
broad objectives of the present investigation are to study
the importance of imperfections on the decomposition
kinetics of potassium periodate (KIO4), by altering the
In continuation of our investigations on the thermal
behaviour of periodates of alkali metals [8, 9, 12, 13] in
this paper we report the effect of metal oxide, such as
cupric oxide (CuO), manganese oxide (MnO2) and titanium
K. Muraleedharan (&) Á M. P. Kannan Á T. Gangadevi
Solid State Chemistry Laboratory, Department of Chemistry,
University of Calicut, Calicut, Kerala 673 635, India
e-mail: kmuralika@gmail.com
123

178
K. Muraleedharan et al.
dioxide (TiO2), additives on the isothermal decomposition
kinetics of KIO4 to KIO3 at 570 K. CuO is a black solid
having molar mass of 79.545 with an ionic structure. It
melts above 1474 K with some loss of oxygen. CuO has
application as a p-type semiconductor, because it has a
narrow band gap of 1.2 eV [16]. MnO2 is a blackish brown
solid having molar mass of 86.937. It is stable up to its
melting point, 808 K, above which it decomposes. It is
used extensively as an oxidizing agent in organic synthesis.
The effectiveness of the reagent depends on the method of
preparation, a problem that is typical for other heteroge-
neous reagents where surface area, among other variables,
is significant [17]. MnO2 is also used as a catalyst in the
laboratory preparation of oxygen from potassium chlorate,
a classical experiment of elementary chemistry classes.
Manganese dioxide also catalyses the decomposition of
hydrogen peroxide to oxygen and water. TiO2 is a white
solid having a molar mass of 79.870. It melts at 2143 K
and boils at 3245 K. Titanium dioxide is the most widely
used white pigment because of its brightness and very high
refractive index (g = 2.4). It is also used as a semi-con-
ductor [18].
as a function of time (t) at 570 K for initially mixed metal
oxide samples of KIO4 at different concentrations.
Results and discussion
The a–t curves for the decomposition of pure KIO4 and the
results of its thermal decomposition kinetics were reported
earlier [12]. Similar curves were obtained for all metal
oxide mixed samples of KIO4. The a–t data were fitted to
various solid state kinetic equations available in the liter-
ature (Table 1) using the method of weighted least squares
as described earlier [9]. In all cases the Prout–Tompkins
equation [21], ln[a/(1 - a)] = kt, which is the simplest
case of an autocatalytic reaction [22], gave the best fits for
all metal oxide mixed samples studied. Additives did not
change the basic shape (sigmoid) of the a–t plots and the
decomposition proceeded through the same way as that of
pure KIO4 (Figs. 1, 2, 3).
The values of rate constant (k) for the thermal decom-
position of pure and metal oxide mixed samples of KIO4
are given in Table 2. Surprisingly the metal oxides show a
little or no influence on the rate of decomposition except
the small decrease of rate when the oxide concentration is
as high as 10 wt%. We note that none of these metal oxides
alters the reaction model (Prout–Tompkins) of the
decomposition process.
Experimental
All the chemicals used were of AnalaR grade reagents of E
Merck. Pure sample of KIO4 was prepared by the method
described earlier [12]. Mixtures of KIO4 with oxides such
as CuO, MnO2 and TiO2 were prepared with oxide con-
centrations 0.5, 1, 2, 5 and 10 wt%. The particle size of
both the components was fixed in the range 90–106 l. The
thermogravimetric measurements in static air were carried
out on a manual thermobalance fabricated in this laboratory
[9, 12], the upgraded version of that used by Hooley [19].
The major problem [20] of the isothermal experiment is
that a sample requires some time to reach the experimental
temperature. During this period of non-isothermal heating,
the sample undergoes some transformations that are likely
to affect the results of the following kinetic analysis. The
situation is especially aggravated by the fact that under
isothermal conditions, a typical solid-state process has its
maximum reaction rate at the beginning of the transfor-
mation. So we fabricated a thermobalance particularly for
isothermal studies, in which loading of the sample is pos-
sible at anytime after attaining the desired constant tem-
perature. This will avoid the effect of pre-heating, usually
observed in common TG instruments. The operational
characteristics of the thermobalance are: accuracy; balance:
Philips and Taylor [23] studied the kinetics of thermal
decomposition of KIO4 to KIO3 in vacuum by measuring
the pressure of oxygen evolved as a function of time and
they observed a four-stage process. The last two stages,
which contribute more than 99.9% of the decomposition,
were best represented by the Prout–Tompkins and the
Table 1 Different reaction models used to describe the reaction
kinetics
S1. no.
Reaction model
Function/g(a)
1
Power law
a1/4
2
Power law
a1/3
3
Power law
a1/2
4
Power law
a3/2
5
One-dimensional diffusion
Mampel (first order)
Avrami–Erofeev
Avrami–Erofeev
Avrami–Erofeev
Three-dimensional diffusion
Contracting sphere
Contracting cylinder
Second order
a2
6
-ln(1 - a)
[-ln(1 - a)]1/4
[-ln(1 - a)]1/3
[-ln(1 - a)]1/2
[1 - (1 - a)1/3]2
1 - (1 - a)1/3
1 - (1 - a)1/2
(1 - a)-1 - 1
ln[a/(1 - a)]
7
8
9
10
11
12
13
14
1 9 10-5 g, temperature:
0.5 K, sample mass:
5 9 10-2 g, particle size: 90–106 l and crucible: plati-
num. The fraction of solid decomposed (a) was measured
Prout–Tompkins
123

Effect of metal oxide additives on the thermal decomposition kinetics of potassium metaperiodate
179
1.0
Table 2 Values of rate constant (k) for the thermal decomposition of
pure and CuO, TiO2 and MnO2 mixed samples of KIO4 at 570 K
0.5 wt%
1 wt%
2 wt%
5 wt%
10 wt%
Oxide
Concentration/wt%
k 9 103/s-1
0.8
0.6
0.4
0.2
0.0
Nil
0
4.5308
4.5311
4.5245
4.4895
4.0818
3.8459
4.5156
4.5702
4.5520
4.1719
3.8824
4.5426
4.5603
4.5650
4.1405
3.8468
CuO
0.5
1.0
2.0
5.0
10.0
0.5
1.0
2.0
5.0
10.0
0.5
1.0
2.0
5.0
10.0
TiO2
20
25
30
Time/min
35
40
Fig. 1 a–t Curves for the thermal decomposition of CuO mixed KIO4
at 570 K
MnO2
1.0
0.5 wt%
1 wt%
2 wt%
0.8
5 wt%
10 wt%
0.6
0.4
0.2
0.0
the above value, they proposed that the rupture of I–O bond
determines the rate of the decomposition of KIO4 to KIO3.
Our earlier investigations [8, 12] showed that the isother-
mal decomposition of KIO4 follows Prout–Tompkins
kinetics with an E value of 209 kJ mol-1. On the light of
the results we proposed that the probable step in the ther-
mal decomposition of KIO4 is the transfer of an electron
from the periodate anion to the potassium cation rather than
the rupture of I–O bond or the diffusion of cations/anions.
Very few studies were reported in the literature on the
thermal decomposition of KIO4 in the presence of different
additives. Solymosi [24] found that the preliminary mixing
of the solid product, KIO3 with KIO4 caused practically no
change in the course of the reaction. In both cases the
decomposition was found to be autocatalytic, and the rate
maximum appeared at about 50% conversion, independent
of the temperature. However, substantial increase in the
rate was caused by KI and NiO [24] without any essential
change in the activation energy values. Furuichi et al. [25]
from DTA experiments in static air, found no effect on
the decomposition of KIO4 by the addition of a-Al2O3 or
a-Fe2O3 to KIO4. The same authors from scanning electron
microscopic (SEM) and X-ray studies [26] reported con-
siderable differences in the decomposition behaviour of
pure KIO4 and KIO4 mechanically mixed with a-Fe2O3.
Rudolf and Freeman [27] found that the p-type oxides
(Cr2O3, MnO2, CuO and NiO) effectively catalyse the
decomposition of KClO4. They explained the significance
of the p-character of the oxides by the promotion of the
electron-transfer process. MnO2 exerts a large catalytic
effect on the decomposition of ammonium perchlorate at
20
25
30
35
40
Time/min
Fig. 2 a–t Curves for the thermal decomposition of MnO2 mixed
KIO4 at 570 K
1.0
0.5 wt%
1 wt%
2 wt%
0.8
0.6
0.4
0.2
0.0
5 wt%
10 wt%
20
25
30
Time/min
35
40
Fig. 3 a–t Curves for the thermal decomposition of TiO2 mixed
KIO4 at 570 K
contracting cube equations, respectively with an E value of
191 kJ mol-1 for both stages. As the heat of the decom-
position process (DH = -208 kJ mol-1) is almost equal to
123

180
K. Muraleedharan et al.
508 K [28]. While the decomposition of pure ammonium
perchlorate is immeasurably slow below 473 K, in the
presence of CuO it already begins at 453 K after an
induction period of about 10–15 h. TiO2 was found to be
practically inactive in the decomposition of both ortho-
rhombic and cubic ammonium perchlorate.
of KIO4 so that the oxides lack electron acceptor property
with respect to KIO4. Thus the electrons may flow from the
oxide to KIO4, which affects the electron transfer reaction
adversely. The possibility of chemisorptions of the
decomposition product, O2, on the semiconductor surface
can also lead to an inhibition of the decomposition process.
In this study we have examined the effect of mixing
KIO4 with metal oxides such as CuO and MnO2 (p-type
semiconductors) and TiO2 (n-type semiconductor). In both
CuO and MnO2, the current carriers are holes and have a
narrow band gap [16, 17]. On the other hand TiO2 is an
electronic semi-conductor in which the current carriers are
free electrons [18]. None of these oxides influenced the
decomposition of KIO4 (at 570 K) up to a concentration of
2 wt%, above which these oxides desensitized the
decomposition rather than catalyzing it. The extent of
desensitization has gone up to ca. 15% when the oxide
concentration is 10 wt%. The rate law of the decomposi-
tion remained unaffected by the additives, which implies
that Prout–Tompkins model is still valid.
Conclusions
The behaviour of mechanical mixtures of KIO4 with n- and
p-type semiconducting oxides suggests that the electron
work functions of these oxides might be smaller than that
of KIO4 so that they lack electron acceptor property with
respect to KIO4 and thus fail to favour electron transfer
process. More studies are, however, necessary to draw any
correlation between electron work functions of the oxides
and their effect on decomposition rate.
The influence of a heterophase additive in reactions
involving charge transfer may be connected with the
electrical properties of the additives. When a metal is
placed in contact with a semiconductor a flow of electrons
takes place across the boundary as long as there exists a
difference between the free energies of the electrons in the
two substances. In a similar fashion, when a solid (e.g.
KIO4) is placed in contact with a semiconducting additive
(e.g. CuO) a contact potential difference arises at the
interface between the solid and the additive. This contact
potential depends on the work functions of electron from
the solid and the additive, and may cause either an increase
or decrease in the number of electrons in the contact layer.
Semiconducting oxides for which the electron work func-
tions are greater than that of the solid accept electrons from
the contact layer and thus catalyse electron-transfer process
occurring in the solid, where as additives with smaller
electron work functions decelerate the electron transfer
process. For instance, the thermolysis of KMnO4, where
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