Characterization and thermal behavior of PrMO3 (M = Co or Ni) ceramic materials obtained from gelatin

Article abstract of DOI:10.1016/j.materresbull.2012.04.078

Metal oxides with perovskite-type structure have attracted considerable interest in recent years due to their magnetic and electrical properties, as well as their catalytic activity. In this study, oxides with PrNiO₃ and PrCoO₃ composition were prepared by using gelatin powder as a precursor agent for its use as a catalyst. The powders obtained were calcined at 700°C and 900°C and characterized using the X-ray diffraction, thermal analysis (thermogravimetry and differential thermal analysis), infrared spectroscopy, temperature programed reduction and scanning electron microscopy techniques. Thermogravimetric data using the non-isothermal kinetic models of Flynn and Wall and Model-free Kinetics were used to determine the activation energy to study the decomposition kinetics of the ligand groups with system's metallic ions that takes part in the synthesis of PrMO₃ (M = Ni or Co).

Full text of DOI:10.1016/j.materresbull.2012.04.078

Materials Research Bulletin 47 (2012) 2605–2609
Contents lists available at SciVerse ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Characterization and thermal behavior of PrMO (M = Co or Ni) ceramic materials
3
obtained from gelatin
a,
a
b
a
a
a
a
F.M. Aquino *, D.M.A. Melo , P.M. Pimentel , R.M. Braga , M.A.F. Melo , A.E. Martinelli , A.F. Costa
a
Federal University of Rio Grande of Norte, Laboratory of Catalysis and Refining – NUPRAR, Av. Senador Salgado Filho, 3000, CEP 59078-970, Natal-RN, Brazil
b
´
Universidade Federal Rural do Semi-Arido, Campus Angicos, CEP 59515-000, Angicos-RN, Brazil
A R T I C L E I N F O
A B S T R A C T
Article history:
Metal oxides with perovskite-type structure have attracted considerable interest in recent years due to
their magnetic and electrical properties, as well as their catalytic activity. In this study, oxides with
Received 3 August 2011
Received in revised form 13 April 2012
Accepted 18 April 2012
Available online 25 April 2012
3 3
PrNiO and PrCoO composition were prepared by using gelatin powder as a precursor agent for its use as
a catalyst. The powders obtained were calcined at 700 8C and 900 8C and characterized using the X-ray
diffraction, thermal analysis (thermogravimetry and differential thermal analysis), infrared spectrosco-
py, temperature programed reduction and scanning electron microscopy techniques. Thermogravimetric
data using the non-isothermal kinetic models of Flynn and Wall and ‘‘Model-free Kinetics’’ were used to
determine the activation energy to study the decomposition kinetics of the ligand groups with system’s
Keywords:
Ceramic materials
Perovskites
Gelatin
metallic ions that takes part in the synthesis of PrMO
3
(M = Ni or Co).
ß 2012 Elsevier Ltd. All rights reserved.
1
. Introduction
is connected to metal ions in the system, using the kinetic models
of Flynn and Wall and ‘‘Model free Kinetics’’, in order to establish
the apparent activation energy as a parameter to characterize and
optimize the synthesis conditions for the applicability of the
material.
3
Rare earth cobalt and nickel oxides, PrMO (M = Co or Ni), have
been extensively studied due to their interesting electrical and
magnetic properties. The PrMO family, in particular Co or Ni,
3
provides an interesting window for studying the evolution of the
electronic characteristics of the oxides that display metallic
conductivity [1–3].
In general, these properties are potentially influenced by the
synthesis method, the calcination conditions (temperature, time,
and atmosphere) and substitutions of the A and/or B sites. There
are several methods for obtaining ceramic oxides with perovskite-
One goal of this work was to synthesize compounds without
using high oxygen pressure and long time of calcination. One of the
advantages of this method was produce powders with large
amount of porous, with the future goal of their application in
catalysis. The method is also a quick and easy route which use low-
cost precursor, the gelatin. The disadvantages is the appearance of
other phases, but probably disappear if we had increased the
calcination time, which would not be interesting, since such
materials would be further tested as catalysts and the long time of
calcination result in a material with lesser superficial area and
fewer porous.
type structures. Recent studies make use of gelatin as
a
polymerization agent and this process appears as a new alternative
for obtaining materials with high efficiency and low cost [4].
A preliminary thermogravimetric analysis is sufficient for
verifying the temperature at which these oxides are stabilized
and the thermal behavior of the material studied. Thermogravi-
metric analysis (TGA) is one of the most commonly used
technologies to study a variety of primary reactions of decompo-
sition of solids and estimate the kinetics parameters of these
processes [5].
2. Experimental
2.1. Synthesis of oxide powders
A modified Pechini method was used to synthesize the PrNiO
3
Thus, a study was conducted on the thermal degradation of
organic matter, derived from the gelatin used as a organic
3
and PrCoO . Perovskites were synthesized by using gelatin as a
precursor organic and metallic nitrates as starting reagent [5].
Initially, nickel nitrate or cobalt nitrate (Aldrich Chem, 99.9%) was
added to a beaker containing deionized water under constant
stirring between 60 8C and 70 8C for 5 min. Praseodymium (III)
nitrate hexahydrate was added and the system was homogenized
for another 5 min. Gelatin was then added to the solution at 70 8C
3 3
precursor in the synthesis of PrNiO and PrCoO powders, which
*
Corresponding author. Tel.: +55 84 3211 9241.
E-mail address: flavyma@hotmail.com (F.M. Aquino).
0025-5408/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2012.04.078

2
606
F.M. Aquino et al. / Materials Research Bulletin 47 (2012) 2605–2609
and stirred for 40 min. Next, the temperature was increased to
0 8C for 1 h, resulting in a resin. After being heat-treated at 350 8C
for 2 h, the primary composite oxides were calcined at 700 8C and
00 8C for 4 h.
9
9
2.2. Materials characterization
The obtained ceramic powders were characterized by various
techniques. Infrared absorption spectroscopy (IR) was carried out
using KBr pellets. A Shimadzu IR Prestige-21 instrument was used
ꢀ
1
to scan the range of 4500–400 cm . X-ray diffraction was
˚
performed using Cu Ka radiation (l = 0.15418 A) in a Shimadzu
XRD-6000, the diffraction angles (2u) were scanned in a range
varying between 108 and 908 with a step 0.028 and identification of
the compounds were performed by comparison with data from
JCPDS – International Center of Diffraction Data. Temperature
programed reduction (TPR) was performed in Micromeritics
AUTOCHEM II equipment. The powder with an average weight
Fig. 1. Curve Arrhenius.
3. Results and discussion
3 3
The thermogravimetric curves (TG) of the PrCoO and PrNiO
ꢀ1
of 20 mg was heated at a rate of 50 mL min , temperature 308 to
000 8C, under a gas flow of 10% H /Ar. The scanning electron
1
2
microscopy images were obtained using Philips XL – 30 ESEM
equipment, with a power supply of 20 kV. The thermal analysis (TG
and DTA) used for the experiments were carried out simulta-
neously using Shimadzu 60H equipment. Because the Flynn and
Wall and ‘‘Model-free Kinetics’’ models require at least three
dynamic curves with different heating rates, the following were
powders, are represented in Fig. 2. Also in Fig. 2c was observed that
the decomposition of the gelatin and the precursor powders occurs
in three distinct steps. The first step, which corresponds to a
reduction of 12.2%, is associated to humidity (hydration water).
The second, around 44.4%, can be attributed to the elimination of
amino acid fragments, usually proline, which is thermodynami-
cally susceptible to thermal degradation in oxidant atmosphere.
The last step, with mass loss of around 41.4%, may be associated to
glycine degradation [10]. Decomposition occurs at higher tem-
peratures for precursor powders, owing to the glycine interaction
by means of the carboxylate groups and amine with the metal ions
forming the coordination groups, thereby providing more stability
to the structure and avoiding the oxidation of a large amount of
glycine.
ꢀ
1
used: 10, 20 and 30 8C min
00 8C. The mass of the powder was approximately 1 mg, the
powder support was alumina, and the carrier gas was synthetic air
between room temperature and
7
ꢀ1
with a flow of 50 mL min
.3. Kinetic methods
The ASTM E1641 standard determination of kinetic parameters
.
2
via thermogravimetry is based on methods proposed by Flynn and
Wall [6] and ‘‘Model-free Kinetics’’ [7–9] that are models based on
the isoconversion principle, which states that a constant conver-
sion (a) of the reaction rate is only a function of temperature, and
allow determination of the kinetic parameters of a reaction, as
activation energy, by thermal analysis. In the typical experiments
The differential thermal analysis curves of the precursor
powders (Fig. 3) show a sharp exothermal peak in the 300–
450 8C range. This peak can be attributed to the decomposition
processes of the organic groups and the rupture of bonds between
the metal ions and carboxyl groups of the organic template [10].
The crystallization of the PrCoO
complete at 700 8C, with the formation of species with PrCoO
perovskite-type structure at a higher proportion and a number of
Co spinel phase peaks. The results illustrated in Fig. 5 show the
diffractograms of the PrNiO powder, with complete crystallization
of PrNiO structure at 700 8C and isolated oxides such as Pr 11 and
NiO. According to the Escote et al. [11], PrNiO
3
powder, revealed in Fig. 4, is
is necessary to obtain least at three different heating rates (
b
) and
3
plotting ln (
a
) against 1/T giving straights lines with slopes ꢀE /R.
a
The Flynn and Wall kinetic model is an iterative method that uses
linear regression to determine the slope and ‘‘Model-free Kinetics’’
is an integral method which allows to evaluate both simple and
complex reactions. These methods were used to evaluate which
one best fits to determine the apparent activation energy for
decomposition gelatin bound to metal ions of the system as a
parameter for characterizing and optimizing the conditions of
synthesis and applicability of these materials. These models were
used to determine the apparent activation energy (Eq. (1)) and
3 4
O
3
3
6
O
3
monophasic
conversion (
a) as a function of temperature.
ꢀ
ꢁ
b
RA
gð
E
R
a
1
ln
¼ ln
ꢀ
(1)
2
T
E
a
a
Þ
a
T
a
a
Fig. 1 illustrates obtaining the activation energy and pre-
exponential factor from the Arrhenius curve (linear regression). As
the equation of the line y = a + a x we have, by linear regression
fits the best straight line y = a + a x. Thus it have:
0
1
0
1
ꢀ
ꢁ
RA
gð
ꢀE
a
a
o
¼ ln
ea
1
¼
(2)
E
a
a
Þ
R
From Eq. (2) it possible obtain E = ꢀRꢁa
1
.
a
Fig. 2. Thermogravimetric curves of powders (a) PrCoO
3
, (b) PrNiO
3
and (c) gelatin.

F.M. Aquino et al. / Materials Research Bulletin 47 (2012) 2605–2609
2607
Table 1
Effect of calcination temperature (Tcal) on crystallinity, crystallite size (DDRX) and
microdeformations.
Temperature (8C)
Crystallite size (nm)
Crystallinity (%)
PrCoO
PrCoO
3
3
700
900
44
83
93
96
PrNiO
PrNiO
3
700
900
48
52
66
84
3
3 3
Fig. 3. Differential thermal analysis curves of powders (a) PrCoO and (b) PrNiO .
powders are obtained only from sol–gel methods and high-
temperature–high-pressure thermal treatment. Such character-
istics suggest that only prolonged thermal treatments under
oxygen pressures are capable of eliminating the secondary oxide
phases in these materials.
Considering that the phases become crystalline at 700 8C,
crystallinity and mean crystallite size were determined. The latter
was calculated using the Deybe–Scherrer equation [12,13] (Table
1). According to that, peak width is inversely proportional to mean
crystallite size. As expected, crystallinity increased with an
increase in calcination temperature, since higher temperatures
Fig. 5. X-ray diffraction pattern of PrNiO
3
for the powder calcined at 700 8C/
ꢀ
1
5 8C min
.
(greater thermal energy) accelerate the accommodation of atoms
in the crystalline structure. Higher temperatures also promote
greater crystallite growth.
The PrCoO
3
perovskite was reduced in two steps and these two
reduction peaks are related to changes in perovskite structure
[15,16]. At around 360 8C it is reduced from Co to Co and
3
+
2+
The absorption spectra in the infrared region for the PrNiO
PrCoO powders treated at 900 8C, respectively are shown in Fig. 6.
Characteristic bands can be observed between 600 and 500 cm
3
and
2
+
0
3
between 510 and 572 8C from Co to Co . Fig. 7b shows the
reduction peaks for the PrCoO powder calcined at 700 8C. They
occur at approximately 380 8C relative to the reduction of Co to
ꢀ1
3
3+
in relation to coordination of the cobalt or nickel cation with the
carboxylic groups of the gelatin. Spinel structure formation relative
2
+
2+
0
Co and at 514.1 8C relative to the reduction of Co to Co . The
to the cobalt oxide (Co
the compound PrCoO
attributions in the FTIR spectrum with frequency
3
O
4
) observed in the X-ray diffractograms for
third peak is in lesser proportion, relative to the reduction of the
3
. Spinel-type oxides can be seen with two
ꢀ1
v
1
of 665 cm
compound was
observed bands assigned to ester that is located about 1620 and
ꢀ1
and v of 580 cm [14]. However, to the PrNiO
2 3
ꢀ1
1
520 cm , the first peak is assigned to M (C 55 O), while the second
is assigned to M (COO–).
Fig. 4. X-ray diffraction pattern of PrCoO
3
for the powder calcined at 700 8C/
Fig. 6. Absorption spectra in the IR region for the PrNiO
calcined at 900 8C/4 h.
3 3
and PrCoO powders
ꢀ
1
5
8C min
.

2
608
F.M. Aquino et al. / Materials Research Bulletin 47 (2012) 2605–2609
2
+
0
(
Ni ! Ni ) [17]. The last peak can be attributed to reduction of
the segregated NiO phase (Eq. (3)), corroborating previously
presented X-ray diffraction results [18].
0
NiO þ H
2
! Ni þ H
2
O
(3)
The micrographs in Fig. 8 show the PrCoO
3
and PrNiO
3
powders
calcined at temperatures of (a and c) 700 8C and (b and d) 900 8C,
respectively. Fig. 8a and b shows that particles of PrCoO are round
3
with good crystallinity, uniform distribution and little particle
agglomeration. Moreover, with an increase in temperature from
700 8C to 900 8C, there is better system organization. The PrNiO
3
powder (Fig. 8c and d) exhibits morphology with considerable
porosity and the formation of agglomerated nanometric particles.
The gelatin provides the system with a large amount of organic
matter, which is then removed during calcinations, favoring the
appearance of pores in the material, especially in the nickel
powder.
The second and third stages of mass loss obtained from the
thermogravimetric curves, above 300 8C, are generally associated
to the decomposition processes of organic groups and the breaking
of bonds between the metal ions and the carboxyl groups of the
gelatin. In these stages were determined the activation energy
values involved in process through Flynn and Wall and ‘‘Model-
free Kinetics’’ methods. It is observed in Tables 2 and 3 that the
3 3
Fig. 7. Profile of temperature programed reduction for (a) PrCoO and (b) PrNiO
values are approximate, with values of linear correlation coeffi-
ꢀ
1
calcined at 700 8C/5 8C min
.
2
cient near to PrNiO
3
(R = 0.97 for the model of Flynn and Wall and
2
3
R = 0.99 for Model-free Kinetics) and PrCoO with values of linear
2
spinel phase at 572.6 8C. ThePrNiO
3
peaks of H
2
consumption at
correlation coefficient near (R = 0.91 for the model of Flynn and
Wall and R = 0.98 for Model-free Kinetics), suggesting that both
2
3
65 8C, 453 8C and 597 8C are also illustrated in Fig. 7a. The first TPR
3+
2+
peak corresponds to the first nickel reduction (Ni ! Ni ), while
methods are suitable for the determination of activation energy.
However, comparing the activation energy for the compounds and
the second peak corresponds to the reduction to metallic nickel
3 3 3 3
Fig. 8. Electron micrograph of (a) PrCoO 700 8C; (b) PrCoO 900 8C; (c) PrNiO 700 8C and (d) PrNiO 900 8C.

F.M. Aquino et al. / Materials Research Bulletin 47 (2012) 2605–2609
2609
Table 2
The powders were nanometric and porous. The infrared spectros-
copy results obtained reveal characteristic bands between 600 and
Activation energies for the 5.0–90.0% conversions for the PrCoO
by the Flynn and Wall and ‘‘Model-free Kinetics’’ methods.
3
powders obtained
Flynn and Wall,
ꢀ1
5
00 cm relative to coordination of the cobalt or nickel cation
with the carboxyl groups of the gelatin, for the materials at 700 and
00 8C. Scanning electron microscopy shows that the PrCoO
Conversion (%)
Model-free Kinetics,
(kJ/mol)
E
a
a
E (kJ/mol)
9
3
5
107
116
126
136
138
130
92
125
131
130
121
111
103
97
material exhibits round particles, good crystallinity, uniform
distribution and no particle agglomeration. For the two powders
studied, the activation energy values obtained for the second
degradation region with both methods showed a similar behav-
ioral trend, and the values of Pearson correlation coefficients
suggest that the studied methods are adequate for determining the
kinetic parameter related to decomposition energy, i.e., the
interaction of organic matter ligand groups with metallic ions of
the system.
1
2
3
4
5
6
7
8
9
0
0
0
0
0
0
0
0
0
92
92
95
89
100
89
Table 3
Acknowledgments
Activation energies for the 5.0–90.0% conversions for the PrNiO
by the Flynn and Wall and ‘‘Model-free Kinetics’’ methods.
3
powders obtained
Flynn and Wall,
The authors thank to CAPES and CNPq, the Post graduate
program in Materials Science and Engineering (PPgCEM) for the
financial support and Laboratory of Catalysis and Refining—
NUPRAR.
Conversion (%)
Model-free Kinetics,
(kJ/mol)
E
a
a
E (kJ/mol)
5
153
156
147
130
115
105
96
146
149
141
125
111
101
93
10
20
30
40
50
60
70
80
90
References
[1] D.B. Rogers, J.M. Honigand, J.B. Goodenough, Mater. Res. Bull. 2 (1967) 223–230.
[2] J.A. Alonso, M.J. Martinez-Lope, I. Rasines, J. Solid State Chem. 120 (1995) 170.
[3] I.V. Nikulina, M.A. Novojilova, A.R. Kaul, A.F. Maiorovab, S.N. Mudretsovab, Mater.
89
86
Res. Bull. 39 (2004) 803–810.
83
81
[4] M. Kakihana, J. Sol–Gel Sci. Technol. 6 (1) (1996) 7–55.
[5] A.O.G. Maia, J. Non-Cryst. Solids 352 (2006) 3729–3733.
[6] F.S. Oliveira, P.M. Pimentel, R.M.P.B. Oliveira, D.M.A. Melo, M.A.F. Melo, Mater.
Lett. 64 (2010) 2700–2703.
77
75
PrCoO
3
and PrNiO
3
, the PrNiO
3
values were slightly higher, which
[7] J.H. Flynn, Polym. Lett. 4 (1966) 323–328.
[
[
8] S. Vyazovkin, C.A. Wight, Thermochim. Acta 340 (1999) 53–68.
9] S. Vyazovkin, N. Sbirrazzuoli, Anal. Chim. Acta 355 (1997) 175–780.
may be due to a higher interaction of the organic matter ligand
groups with the metallic ions of the system. What was
corroborated by the infrared spectra, because it still possesses
carboxyl groups attached to gelatin.
[
10] S. Vyazovkin, D. David Dollimore, J. Chem. Inf. Comput. Sci. 36 (1996) 42–45.
[11] A.S. Menezes, C.M.R. Rem e´ dios, J.M. Sasaki, L.R.D. Silva, J.C. G o´ es, P.M. Jardim,
M.A.R. Miranda, J. Non-Cryst. Solids 353 (2007) 1091–1094.
[
12] M.T. Escote, A.M. Silva, J.R. Matos, R.F. Jardim, J. Solid State Chem. 151 (2000) 298–
3
07.
4
. Conclusions
[13] L.V. Azaroff, Elements of X-Ray Crystallography, McGraw-Hill Book Company,
New York, 1968, 552 pp.
[
14] S.F.C.X. Soares. Development of Perovskite Cells for Use Insolid Oxide Fuel,
Monograph of Chemistry, Department of Chemistry, University of Rio Grande
of Norte, Natal, 2008.
The results obtained demonstrate that gelatin, through its
carboxylate groups and amine, is an efficient template to be used in
the synthesis of ceramic powders, given that it is a chelating and
polymerizing agent of metallic ions. With respect to the calcined
powders the perovskite phase formation was observed in X-ray
diffraction patterns, starting at 700 8C for the two powders studied.
[15] M.P. Pimentel, A.E. Martinelli, D.M.A. Melo, A.M.G. Pedrosa, J.D. Cunha, C.N. Silva,
Mater. Res. 8 (2005) 221–224.
[
[
16] M.A. Pena, J.L.G. Fierro, Chem. Rev. 101 (2001) 1981–2017.
17] R. Lago, J. Catal. 167 (1997) 198–209.
[18] Y. Eurico, M. Tanabe e Elisabete, Qu ı´ m. Nova 32 (5) (2009) 1129–1133.