Materials Sciences and Applications, 2011, 2, 416-420
doi:10.4236/msa.2011.25054 Published Online May 2011 (http://www.SciRP.org/journal/msa)
Copyright © 2011 SciRes. MSA
Combustion and Ball Milled Synthesis of Rare
Earth Nano-Sized Ceria Powder
Ranjan Sen, Siddhartha Das, Karabi Das
Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, India.
Email: ranjansen2001@gmail.com
Received March 29th, 2011; revised April 2nd, 2011; accepted April 10th, 2011.
ABSTRACT
This paper reports a study on nanocrystalline ceria powd er prepared by high energy ball-milling and combu stion syn-
thesis methods. The combustion synthesis was carried out using ceric ammonium nitrate as oxidizer and citric acid,
glycine or citric acid plus glycin e as fuel. The minimum crystallite size of ceria powder is obtained by combustion syn -
thesis of ceric ammonium nitrate and citric acid. The ceria powder produced by combustion synthesis of ceric ammo-
nium nitrate and citric acid and glycine has less agglomeration of particles than other techniques.
Keywords: Ceramics, Ball Milling, Combustion Synthesis, Nano-Sized Ceria, X-Ray Diffraction
1. Introduction
Now day’s different routes such as mechanical alloying,
combustion synthesis, plasma forming, explosive form-
ing, electro deposition and sol-gel process are used for
producing nano-sized ceramics or metals. Among them,
high energy ball milling and combustion synthesis are
the most useful techniques for producing nano-sized ce-
ramics and ceramic-composites. The ball milling tech-
nique is more environmentally safe than the method of
chemical synthesis, producing far less chemical waste [1].
A number of nanostructured metal oxides and their solid
solutions such as Fe2O3-SnO2 [2], ZrO2-Fe2O3 [3], TiO2-
Fe2O3 [4], TiO2-WO3 [5], Pb(Zr0.52Ti0.48)O3 [6], SrTiO3
[7], SiC, Si3N4 and quartz (SiO2) powders [8] have been
prepared by using high-energy ball milling method.
Moore et al. [9] reported that compared with convention-
al ceramic processing, the most obvious advantages of
combustion synthesis are primarily the generation of a
high reaction temperature which can volatilize low boil-
ing point impurities and therefore, result in higher purity
products, the short exothermic reaction times result in
low operating and processing costs, the high thermal
gradients and rapid cooling rates can give rise to new
non-equilibrium or metastable phases and inorganic ma-
terials can be synthesized and consolidated into a final
product in one step by utilizing the chemical energy of
the reactants. In our present study nano-sized ceria pow-
der has been synthesized by different techniques includ-
ing high energy ball milling technique and combustion
synthesis. In the ball milling technique the nano-sized
ceria particles have been produced after 10 h milling of
as-received ceria powders. Combustion synthesis has
been carried out by using 1) ceric ammonium nitrate
(CAN) ((NH4)2Ce(NO3)6) and glycine (NH2CH2COOH)
2) CAN and citric acid (C6H8O7) and 3) CAN, glycine
(NH2- CH2COOH) and citric acid, this process is also
called mixed fuel technique.
The nano-sized ceria powders produced by different
routes have been characterized by the X-ray diffraction
(XRD), field emission scanning electron microscopy
(FESEM) and high resolution transmission electron mi-
croscopy (HRTEM).
2. Experimental Procedure
2.1. Synthesis of Ceria Powders by High Energy
Ball Milling Technique
High energy ball milling (HEBM) of ceria powder (Alfa
Aecer, 99.5%) is carried out using cemented tungsten
carbide milling media with toluene as the process control
agent. The mill is operated at a speed of 300 rpm and the
ball to powder ratio is 10: 1. The 10h ball milled powder
is washed with distilled water and then with ethyl alcohol
followed by drying.
2.2. Synthesis of Ceria Powders by Combustion
Synthesis Techniques
Nano-sized ceria single crystals are synthesized by the
Combustion and Ball Milled Synthesis of Rare Earth Nano-Sized Ceria Powder
Copyright © 2011 SciRes. MSA
417
combustion of aqueous solutions containing metal nitrate
and fuel. Three different fuels i.e., glycine, citric acid or
glycine and citric acid have been used in the present study.
Assuming complete combustion, the theoretical equa-
tion for the formation of ceria with different fuels can be
written as follows:
(NH4)2Ce(NO3)6 (aq) + (8/3)NH2CH2COOH (aq)
CeO2 (s) + (16/3)CO2 (g) + (32/3)H2O (g) + (16/3)N2 (g)
(1)
(NH4)2Ce(NO3)6 (aq) + (4/3)C6H8O7 (aq) CeO2(s) + 8
CO2 (g) + (28/3)H2O (g) + 4N2 (g) (2)
(NH4)2Ce(NO3)6 (aq) + (4/3)NH2CH2COOH (aq) + (2/3)
C6H8O7 (aq) CeO2 (s) + (20/3)CO2 (g) + 10H2O (g) +
(14/3)N2 (g) (3)
In this experiment the aqueous solution is prepared by
disolving the proper amount of CAN (lobachemie, >99.5%)
and fuel (Merck, >99.7%) in distilled water. The solution
is stirred using magnetic stirrer for 2h. The resulting
stirred solution is evaporated in small portions (~200 ml,
producing 5 g powder) in a tall beaker (approximately 20
cm tall) on an electrical heater at 225˚C, during which it
boils, foams and undergoes smoldering (flameless) com-
bustion to produce the corresponding oxides. After com-
pletion of reaction it is observed that the powders are
well contained within the beaker. However enough care
is taken to ensure that the batches are sufficiently small
to avoid an unmanageable reaction, both for safety rea-
sons and also to ensure a homogeneous reaction. The
resulting fine powders are calcined at 500˚C for 2 hrs in
muffle furnace.
2.3. XRD
All the X-ray diffraction (XRD) experiments are carried
out in a XRD machine (Phillips), using 40 kV voltage, 30
mA current, 0.2 mm receiving slit, scintillation counter
detector and Cu Kα radiation. But no monochromator is
attached with this system.
2.4. Microstructural Characterization
The powders have been examined using a field emission
scanning electron microscopy FESEM (ZEISS) operating
at 5.0 kV attached with an energy dispersive X-ray spec-
trometer (EDS).
A high resolution transmission electron microscope
(HRTEM) (JEOL 2010F) operating at 200 kV is used to
find the crystallite size of the ceria powder. The ceria
powder is dispersed in acetone and the solution is kept in
an ultrasonic vibrator for 1 hour. The solution is then
allowed to settle down for 2 min and a drop of the solu-
tion is taken from the top layer and dropped on a carbon
coated grid followed by drying at room temperature.
3. Results and Discussion
Figure 1 shows the XRD patterns of the ceria powder
produced by 10 h ball milling and combustion synthesis.
The broadening of peaks in the XRD patterns is due to
three factors, i.e., instrumental error, lattice strain and
nano-sized crystallite. In order to determine the crystal-
lite size, the instrumental line broadening of the meas-
ured profiles is corrected using a Si (111) single crystal
(PW3132/62) disc (32 mm diameter and 2 mm thick) as
the standard sample. The structural broadening only due
to crystallite size and lattice strain (B(struct)) is obtained
using the following equation:

22
obs std
struct
BBB (1)
where, Bstd and Bobs are full width at half-maximum of
any particular reflection from the standard sample (sili-
con disc) and the sample, respectively.
The analysis has been done by Williamson-Hall me-
thod [10]. In this method it is assumed that both size and
strain broadened profiles are Lorentzian. Based on this
assumption, a mathematical relation is established between
the integral breadth (
), volume weighted average crys-
tallite size (Dv) and the lattice strain (
) as follows.
cos 12sin
2
v
D






(2)
The plot of cos



versus 2sin



gives the va-
lue of the lattice strains from the slope and crystallite size
Figure 1. XRD patterns of (a) ceria powders produced by 10
h ball milling, (b) CAN + citric acid, (c) CAN + glycine and
(d) CAN + citric acid + glycine.
Combustion and Ball Milled Synthesis of Rare Earth Nano-Sized Ceria Powder
Copyright © 2011 SciRes. MSA
418
from the ordinate intercept.
The average crystallite size and lattice strain of ceria
powder produced by different routes are calculated from
the x-ray diffractograms and represented in Figure 2. It
is observed that for ball milled ceria the crystallite size
(42 nm) and lattice strain (13.35 × 104) are larger than
the crystallite size and lattice strain of ceria produced by
the other routes. But minimum crystallite size (17 nm)
and lattice strain (2.58 × 104) are observed for ceria
powder produced by combustion synthesis of solution
containing CAN and citric acid. There is not any signifi-
cant change in crystallite size and lattice strain of ceria
powder produced by combustion synthesis of either CAN
and glycine or CAN, glycine and citric acid.
The
surface
morphology
of
the
ceria powders pro-
duced by different synthesis routes is
studied
using FE-
Figure 2. The crystallite size and lattice strain of ceria pow-
ders produced by different routes.
(a) (b)
(c) (d)
Figure 3. FESEM micrograph of ceria powder prepared by a) 10 h ball milling and combustion synthesis containing; b) CAN
and citric acid, c) CAN and glycine and d) CAN, citric acid and glycine.
Combustion and Ball Milled Synthesis of Rare Earth Nano-Sized Ceria Powder
Copyright © 2011 SciRes. MSA
419
SEM.
Figure 3 shows the FESEM micrograph of ceria
powder prepared by ball milling and combustion synthe-
sis routes. From Figure 3 it is clear that the ceria powder
produced by combustion synthesis has large number of
porosity, but ball milled ceria powder is free from porosi-
ty. The ceria powder produced by mixed fuel process has
larger size of porosity (micro meter) compared to the
same produced by using citric acid or glycine as fuel.
Figure 4
shows
the
HRTEM
results of
ceria powder
prepared by ball milling and combustion synthesis.
The
nanocrystalline nature
of the ceria powder is further con-
firmed by this HRTEM
examination.
From Figure 4 it is
observed that the
size
distribution
of
the ceria
powder
particles produced by 1) ball milling technique
varies
from 30 to 50
nm, and combustion synthesis containing
2) CAN and citric acid varies from 10 to 20 nm, 3)
CAN and glycine varies from 28 to 38 nm and (d) CAN,
citric acid and glycine varies from 25 to 35 nm. Ceria
powder produced from combustion synthesis contain-
ing CAN and citric acid has lower particle size than the
ceria powder produced by other routes. But on the con-
trary ceria powder produced from combustion synthesis
(a) (b)
(c) (d)
Figure 4. HRTEM
micrograph of
ceria powder prepared by a) 10h ball milling, and combustion synthesis containing b)
CAN and citric acid, c) CAN and glycine and d) CAN, citric acid and glycine.
Combustion and Ball Milled Synthesis of Rare Earth Nano-Sized Ceria Powder
Copyright © 2011 SciRes. MSA
420
containing CAN and citric acid and glycine has less
agglomeration of particles than other techniques.
4. Conclusions
The nanosized ceria powder can be produced by
high energy ball milling and combustion synthesis
techniques.
From XRD it is found that the crystallite size (42
nm) and lattice strain (13.35 × 104) of ball milled
ceria are larger than the crystallite size and lattice
strain of ceria produced by the combustion synthe-
sis technique. Minimum crystallite size (17 nm)
and lattice strain (2.58 × 104) are observed for ce-
ria powder produced by combustion synthesis of
CAN and citric acid.
TEM analysis shows that the particles of ceria
powder are uniformly distributed or less agglome-
rated in the mixed fuel process.
FESEM study reveals that the ceria powder pro-
duced by combustion synthesis has large number of
porosity, but ball milled ceria powder is free from
porosity.
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