Powder Metallurgy Progress, Vol.11 (2011), No 3-4
201
SYNTHESIS AND CHARACTERIZATION OF IRON OXIDE
POWDERS
M.N. Batin, V. Popescu
Abstract
Iron oxide powders (α-Fe2O3) were obtained via a chemical process. A
homogenous mixture prepared from iron (II) chloride tetrahydrate and
urea of analytical purity and water was heated at 90°C for a few hours in
order to obtain the precursor powders. The obtained precipitates were
filtered, washed and dried at room temperature, finally forming the
precursor powders. Then the powders were heated in an oven at different
temperatures. It was observed that the thermal treatment plays an
important role in the size and the structure of the final product. The iron
oxide powders were characterized by X-Ray Diffraction and UV-VIS
spectroscopy. We also determined the grain size from XRD analysis.
Keywords: iron oxide, hematite α-Fe2O3, thermal treatment, XRD
INTRODUCTION
Iron oxide particles with controlled size and shape have attracted great attention in
the last years. Because of their unique properties, the iron oxides are used in a wide range
of applications as gas sensors [1, 2], catalysts [3] or pigments [4]. Due to their notable
properties such biocompatibility and magnetism, iron oxides (α-Fe2O3,γ- Fe2O3 and Fe3O4)
are used in biomedicine as Magnetic Resonance Imaging contrast agents, vectors for drug
delivery or agents for hyperthermia therapy [5,6]. Iron oxides are also used as a material for
magnetic storage media [7] and in lithium-ion batteries [8,9].
Among the iron oxides, hematite (α-Fe2O3) is the most common iron oxide in
nature. α-Fe2O3 is an n-type semiconductor, having a small band gap (2.1 eV) [10] and is
the most stable iron oxide under ambient conditions. Because of its small bang gap,
hematite can absorb about 40% of the sunlight [11] which is an important advantage for its
use in solar energy conversion.
In the last years many efforts have been focused on the obtaining methods of iron
oxides. At present, iron oxide particles are synthesized by different methods such as the
sonochemical route [12], coprecipitation [11], solid state chemical reaction [13],
hydrothermal methods [10, 14], wood template [15], sol-gel [16] and mechanical methods
[17,18].
In this work, we obtained iron oxide particles from homogenous precipitation of
FeCl2·4H2O in the presence of NH2CONH2. The aim of this paper is to study the effect of
the concentration of reactants, precipitation time, and thermal treatment on the formed iron
oxide.
Medina-Natalia Batin, Violeta Popescu, Technical University of Cluj Napoca, Faculty of Materials and
Environmental Engineering, Department of Chemistry, Cluj Napoca, Romania
Powder Metallurgy Progress, Vol.11 (2011), No 3-4
202
MATERIALS AND METHODS
The starting chemicals used were iron (II) chloride tetrahydrate (FeCl2)
and urea (NH2CONH2). Distilled water was used as solvent. All the reactants were
analytically pure and used without further purification.
Precursor powders were synthesized by homogenous precipitation of iron (II)
chloride in an aqueous solution that contained urea.
A fresh aqueous solution of FeCl2·H2O was prepared and mixed with an aqueous
solution of NH2CONH2. Experimental conditions for the preparation of precipitates are
given in Table 1. The experiments were performed in a thermostatic bath (Raypa Trade) at
90 °C. After a proper heating time, the solutions were filtered; the precipitates were washed
several times with distilled water and then dried at room temperature.
α-Fe2O3 powders were obtained by thermal treatment of precursor powders
prepared by the mentioned method, in an oven in presence of air for 4 hours at different
temperatures.
Tab.1. Experimental conditions for sample preparation.
Sample
S1
S2
S3
S4
FeCl2
[M]
1
1
0.9
0.9
NH2CONH2
[M]
1
1
0.7
0.7
Precipitation
time [hours]
2
3
2
3
Temperature of thermal
treatment [ºC]
500
500
400
400
X-ray diffraction patterns of samples were carried out on a Shimadzu XRD 6000
diffractometer with Cu Kα radiation, wavelength of 1.5405 Å. Scans were recorded in the
2θ ranging from 10° to 60°, with a scan rate of 2°/min. Optical properties of the samples
were studied using a Perkin Elmer Lambda 35 spectrophotometer.
RESULTS AND DISCUSSION
The crystal structure and the phase composition of samples were identified by Xray diffraction powder. X-ray diffraction patterns of precursor powders obtained at different
precipitation times are presented in Fig.1. The diffraction peaks of the precursor powders
can be indexed to the tetragonal FeO(OH) - akaganeite (PDF Number 34-1266).
We observed that the precipitation time of the reactants concentration has not
influenced the phase composition or the structure of the formed powders. For all samples
(S1, S2, S3, S4) the XRD analysis confirmed the formation of FeO(OH) phase.
Presence of diffraction peaks in XRD spectra of the treated samples at 2θ = 24.1°,
33.1°, 35.6°, 40.8°, 49.4°, 54.0°, 57.5° (57.4° for sample S4T) were in good agreement with
the corresponding (012), (104), (110), (113), (024), (116) and (018) ((122) for S4)
diffraction planes of hematite α-Fe2O3 (PDF Number 33-0664). It can be observed from
XRD patterns of the treated samples (Fig.2) that after the thermal treatment the sample S4T
represents low crystallinity from among the rest of the samples.
Powder Metallurgy Progress, Vol.11 (2011), No 3-4
203
Fig.1. Diffraction patterns of the precursor powders.
Figure 2. presents the diffraction patterns for the treated samples (S1T and S2T
treated at 500 °C, S3T and S4T treated at 400 °C).
Fig.2. XRD patterns of treated samples - α-Fe2O3.
Crystallite size of the treated samples was estimated using the William-Hall [19]
method which is given in equation (1):
β cosθ 1
sin θ
(1)
= + 4ε
λ
λ
D
where : β – is the full width at half maximum of the broadened diffraction line on the 2θ
radius, D - the crystallite size, λ - the wavelenght of the X-radiation, ε - the lattice strain in
percentage.
Powder Metallurgy Progress, Vol.11 (2011), No 3-4
204
One can see that the crystallite size of hematite (α-Fe2O3) has been influenced by
the thermal treatment. The powders treated at 500°C (S1T, S2T) presented an increased
grain size dimension from powders treated at 400°C (S3T,S4T). The sample S4T obtained
by precipitation at 3 hours exhibits a very small grain size dimension in comparison with
the sample S2T obtained at the same precipitation time but at a lower concentration of
reactants. The crystallite size of the hematite samples are presented in Table 2.
Tab.2. Crystallite size of the α-Fe2O3 powders.
S1T
S2T
S3T
S4T
Crystallite size (nm)
109
153
80
32
Lattice strain, ε
0.0010
0.0008
0.0014
0.0037
Optical investigation of the α-Fe2O3 powders was performed using a Perkin Elmer
Lambda 35 spectrophotometer. The optical absorption spectrums were recorded over
wavelengths ranged from 350-900 nm. In Fig.3 are presented the optical absorption spectra
of hematite samples visibly.
Fig.3. Absorption spectres of α-Fe2O3 powders: S1T (T = 500°C), S2T (T =500°C), S3T
(T = 400°C), S4T (T = 500°C).
It can be seen that for all samples there is an absorption decrease with an increase
of wavelength. We observed that α-Fe2O3 powders obtained at 500°C show a narrow
maximum absorption, while the α-Fe2O3 powders obtained at 400°C show a large
maximum absorption. We can conclude that thermal treatment influenced the optical
absorption of the powders. However, the maximum absorption visibly ranged between 560
-572 nm for all samples, results which are in good agreement with the literature data [20].
Powder Metallurgy Progress, Vol.11 (2011), No 3-4
205
CONCLUSIONS
Iron oxide particles were obtained by chemical precipitation. The thermal
treatment of the powders leads to a phase conversion from FeO(OH) to α-Fe2O3. We
observed that the powders treated at 400°C presented smaller grain size than the powders
treated at 500°C. Also the absorption peaks were influenced by the thermal treatment, the
samples treated at higher temperature showed a narrow absorption maximum.
Acknowledgments
This paper was developed within the Project "Doctoral studies in engineering
science for the development society based on knowledge - SIDOC"; Contract POSDRU
/88/1.5/S/60078.
REFERENCES
[1] Patil, D., Patil, V., Patil, P.: Sensors and Actuators B, vol. 152, 2011, p. 299
[2] Zhang, F., Yang, H., Xie, X., Li, L., Zhang, L., Yu, J., Zha, H., Liu B.: Sensors and
Actuators B, vol. 141, 2009, p. 381
[3] Liu, X., Liu, J., Chang, Z., Sun, X., Li, Y.: Catalysis Communications, vol. 12, 2011, p.
530
[4] Pailhé, N., Wattiaux, A., Gaudon, M., Demourgues, A.: Journal of Solid State Cemistry,
vol. 181, 2008, p. 2697
[5] Dias, A., Hussain, A., Marcos, A., Roque, A.: Biotechnology Advances, vol. 29, 2011, p.
142
[6] Mahmoudi, M., Sant, S., Wang, B., Laurent, S., Sen, T.: Advanced Drug Delivery
Reviews, vol. 63, 2011, p. 24
[7] Srivastava, A., Ojha, A., Chaubey, S., Singh, J., Sharma, P.: Journal of Alloys and
Compounds, vol. 500, 2010, p. 206
[8] Tartaj, P., Amarilla, JM.: Journal of Power Sources, vol. 196, 2011, p. 2164
[9] Hassan, MF., Rahman, MM., Guo, ZP., Chen, ZX., Liu, HK.: Electrochimica Acta, vol.
55, 2010, p. 5006
[10] Penga, D., Beysena, S., Li, Q., Suna, Y., Yanga, L.: Particuology, vol. 8, 2010, p. 386
[11] Boumaza, S., Boudjemaa, A., Omeiri, S., Bouarab, R., Bouguelia, A., Trari, M.: Solar
Energy, vol. 84, 2010, p. 715
[12] Amir, HR., Vaezib, MR., Shokuhfarc, A., Rajabalic, Z.: Particuology, vol. 9, 2011, p. 95
[13] Karami, H.: J Clust Sci, vol. 21, 2010, p. 11
[14] Liang, HF., Wang, ZC.: Materials Letters, vol. 64, 2010, p. 2410
[15] Ding, J., Fan, T., Zhanga, D., Saito, K., Guoa, Q.: Solid State Communications, vol. 151,
2011, p. 802
[16] Teja, AS., Koh, PY.: Progress in Crystal Growth and Characterization of Materials, vol.
55, 2009, p. 22
[17] Arbain, R., Othman, M., Palaniandy, S.: Minerals Engineering, vol. 24, 2011, p. 1
[18] Roy, D., Deb, P., Basumallick, A., Basu, B.: J Opt, vol. 39, 2010, no.2, p. 102
[19] Xu, SY., Zhang, JC., Zhong, MJ., Chen, HD., Zhang, Z.,. M., He, ZM.: Journal of
Shanghai University, vol. 9, 2005, no. 6., p. 550
[20] Chiriă, M, Grozescu, I.: Chem. Bull., Politehnica Univ, vol. 54, 2009, no. 68