J. Am. Ceram. Soc., 91 [1] 337–341 (2008)
DOI: 10.1111/j.1551-2916.2007.02145.x
r 2007 The American Ceramic Society
ournal
J
Application of Non-Arrhenius Method for Analyzing the
Decomposition Kinetics of SrCO3 and BaCO3
Saikat Maitraw and Narayan Bandyopadhyay
Goverment College of Engineering and Ceramic Technology, Kolkata-700010, India
Jayita Pal
Meghnand Saha Institute of Technology, Kolkata-700107, India
The nonisothermal kinetics of thermal decomposition of SrCO3
and BaCO3 was studied by thermo-gravimetry following non-
Arrhenius integral approach of Harcourt and Esson. Variation
of activation energy of these two carbonates with fraction de-
composition was compared and the average activation energy in
the decomposition range was computed.
lished for individual decomposition of the two carbonates under
both isothermal and nonisothermal conditions.
Arvanitidis et al.4 studied the kinetics of the decomposition of
SrCO3 in argon to SrO and CO2 were studied in the temperature
range 1000–1350 K. The thermal decomposition was followed
simultaneously by thermo-gravimetric analysis (TGA) and
differential thermal analysis (DTA) during linear heating. By
using a nonisothermal method, the complete rate expression was
determined from a relatively small number of experimental runs.
The recommended rate expression for the SrCO3 decomposition
is da/dt 5 B exp (ꢀE/RT)(1ꢀa)[p] where a is the ratio between
the actual weight change and the theoretical final weight change,
da/dt is the time derivative of a, B is a rate constant in s-0, E is
the activation energy in J/mol, R is the gas constant in
J ꢁ (Kꢁ mol)ꢀ1, T is the temperature in kelvin, and n is a factor
depending on the geometry of the particles. The activation
energy, E, for the decomposition of SrCO3 was evaluated to
be 210 kJ/mol. Curves of calculated a versus temperature agree
well with the experimental results.
I. Introduction
HE SrCO3 and BaCO3 have been widely used as the starting
materials for the synthesis of ferroelectric titanate ceramics
T
by solid-state reactions. The decomposition behavior of these
carbonates is of significant importance for controlling the nature
and the rate of formation of the final products. Many works
have been reported on the decomposition behavior of these two
carbonates.
Hancock and Sharp1 described a method of comparing the
kinetics of isothermal solid-state reactions based on the classical
equation for analysis of nucleation and growth process and ap-
plied it to the decomposition of kaolinite, brucite, and BaCO3.
In this method, plots of ln ln(1ꢀa) vs ln(time), where a is the
fraction reacted, were used to distinguish reaction mechanisms.
For the decomposition of BaCO3, linear plots with slopes, which
change either gradually or dramatically with temperature, were
noted. The decomposition in N2 takes place by a phase bound-
ary mechanism from 10161 to 10351C and by a diffusion mech-
anism from 9611 to 10351C.
Maitra et al.5 developed a new method using a Turbo-C-
based computer program to evaluate the integral of the kinetic
equation for analyzing the kinetics of thermal decomposition of
MgCO3, CaCO3, SrCO3, and BaCO3. It was observed that
the decomposition reaction of MgCO3 and CaCO3 followed
two-dimensional diffusion-controlled kinetics and the decom-
position reaction of SrCO3 and BaCO3 followed a Ginstling–
Brounshtein model-based diffusion-controlled kinetics.
Maitra et al.6 further used genetic algorithm to determine the
kinetic model of magnesite and limestone from DTA data.
It was observed that both the reactions mostly followed the
Avrami-Erofeev kinetics model.
All kinetic studies envisage one of two methods; namely,
differential and integral. The integral approach of kinetic study
is more convenient, reliable, and accurate than the differen-
tial method (Tang et al.7). But the evaluation of the integral
function of the rate equation, g(a), in nonisothermal kinetics
Criado et al.2 studied the influence of thermal treatment on
the structure and thermal stability of alkaline earth carbonates.
They proposed a mechanism that when the lattice energy in-
creases, slipping of the lattice planes becomes more difficult and
the fracture of the particles would be favored with regards to the
plastic deformation of the crystal. The model accounts for the
changes in the activation energy and the enthalpy of the alkaline
earth carbonates as a function of grinding.
Koga and Tanaka3 studied the kinetics of the thermal decom-
positions of CaCO3, SrCO3, and BaCO3 into their oxides by the-
rmo-gravimetry at constant and linearly increasing temperatures.
The kinetics of the isothermal decompositions of calcium and
of a heterogeneous reaction is difficult, as the Arrhenius integral
R
T eꢀE=RT dT does not have an analytical solution.
0
In the present investigation therefore a non-Arrhenius ap-
proach was followed, avoiding the solution of the Arrhenius in-
tegral to investigate the decomposition kinetics of alkaline earth
carbonates.
strontium carbonates were described by the law Rn 51ꢀ(1ꢀa)1/n
,
where n5 1.8 and 1.2, respectively. The kinetics of the noniso-
thermal decompositions of the two carbonates, analyzed by the
Ozawa and Coats-Redfern methods, was in keeping with the iso-
thermal kinetics. A ‘‘true’’ kinetic compensation law was estab-
II. Experimental Procedure
SrCO3 and BaCO3 of G.R. grade supplied by E. Merck
(Mumbai, India) were used in the present investigation. These
carbonates were first heated to 2001C in an atmosphere of car-
bon dioxide (CO2) to make them moisture free. The samples
were cooled to room temperature and allowed to stand overnight
under a (CO2) atmosphere. TG measurements of the samples
were carried out with a thermo-balance at four different heating
S. Mukherjee—contributing editor
Manuscript No. 23161. Received May 2, 2007; approved September 7, 2007.
wAuthor to whom correspondence should be addressed. e-mail: maitrasaikat@
rediffmail.com
337