Preparation and magnetic characterization of Fe

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their novel magnetic and catalytic features. Taghvaei et al. [27] reported the analysis of the magnetic losses in iron- based soft magnetic composites with MgO ...

B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

Burçak Ebin, Çig˘dem Toparlı, Sebahattin Gürmen

2013 Carl Hanser Verlag, Munich, Germany

www.ijmr.de

Not for use in internet or intranet sites. Not for electronic distribution.

Metallurgical & Materials Engineering Department, Istanbul Technical University, Istanbul, Turkey

Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles by means of hydrogen reduction assisted ultrasonic spray pyrolysis (USP-HR) Fe/metal oxide nanocomposite particles were produced by means of hydrogen reduction assisted ultrasonic spray pyrolysis. Fe/Fe0.761Mg0.239O and Fe/MgO nanocomposite particles were obtained at 600 and 800 8C, respectively. The thermodynamics of the formation reactions were investigated. Increasing the reaction temperature allowed efficient reduction of the precursor to metallic iron that induces the formation of pure MgO phase. The crystallite sizes of the Fe in the composite structures slightly increased, and also the crystallite sizes of the oxides decreased with elevating temperature. The nanocomposite particles exhibited spherical morphology and their particle sizes were slightly different. All of the samples showed ferromagnetic characteristics and the results indicate that the amount of metal and metal oxide phases most affected the saturation magnetizations of the composite particles which were lower than pure iron. Keywords: Metal/metal oxide composites; Nanocomposite particles; Ultrasonic spray pyrolysis; Magnetic properties

1. Introduction Magnetic particles have been attracting considerable scientific attention because of their numerous potential applications. They can be used in the biomedical field for drug delivery, magnetic resonance imaging (MRI), magnetic separation, cancer diagnosis and treatments [1 – 5]. Furthermore, such particles have been applied to electronic/engineering fields ranging from ferrofluid technology, information storage to magnetic sorbents for environmental engineering [6 – 11]. The magnetic behavior of materials can be modified by changing not only their particle or crystallite size, which cause the quantum size effects and the large surface area, but also particle composition, morphology and advance composite design [12 – 19]. Nanocomposite design enhances magnetic and other physico-chemical properties of materials [20 – 22]. Thus, various studies have focused on the production of iron/ oxide nanocomposite particles to obtain advanced functional materials [23 – 26]. Among them, Fe/MgO composite particles have drawn increasing interest and researchers Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

have attempted various methods to produce them due to their novel magnetic and catalytic features. Taghvaei et al. [27] reported the analysis of the magnetic losses in ironbased soft magnetic composites with MgO insulation. They obtained composite samples by coating MgO on the commercial iron powders by means of the sol-gel method. Rakmak et al. [28] synthesized Fe/MgO nano-crystal catalysts for removal of hydrogen sulfide in a biogas that showed marked catalytic properties. The composite particles were prepared via two major steps including synthesis of MgO nano-crystals supporting media and impregnation of Fe3+ catalysts on the MgO nano-crystal surface. Spretz et al. [29] worked on the Fe/MgO ratio in the composite prepared by impregnation of MgO powders via iron hydroxide precipitation and calcination of the precipitate for the catalytic combustion of methane. They determined that the prepared samples partly contained MgFe2O4 structure. Additionally, Martinez-Boubeta et al. [30] fabricated Fe particles covered by a uniform MgO epitaxial shell using vapor condensation. Their results proved that Fe/MgO nanocomposite particles are useful as contrast agents for MRI and have potential application for cancer therapy and drug delivery systems. Nakayama et al. [31] presented ferromagnetic Fe/MgO nanocomposites obtained by means of hydrogen reduction of ball milled iron salt and MgO powders. Choa et al. [32] synthesized Fe/MgO composite particles via a two step process that contained preparation of Fe-oxide/MgO powders using ultrasonic spray pyrolysis (USP), and followed by reduction of powders to Fe/MgO under hydrogen atmosphere at temperatures between 600 to 1 000 8C. They stated that magnetic properties depend on the particle size, which is affected by process temperature. All these Fe/MgO composite particle preparation processes consisted of two consecutive methods or used commercial powder of one of ingredients in the composite structure. Therefore, the production of Fe/MgO nanocomposite particles in a simple and single step process is a significant field to have an opportunity focusing on physicochemical properties. The direct fabrication of Fe/MgO particles via hydrogen reduction assisted ultrasonic spray pyrolysis (USP-HR) has not been studied yet. The USP technique is a versatile process that paves the way for the production of spherical and non-agglomerated nano/micro size powders. This method has various advantages such as 483

2013 Carl Hanser Verlag, Munich, Germany

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B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

short production time, narrow particle size distribution, controllable particle size from micrometer to nanometer scales, high purity of the products, and ease of control of the composition and morphology of the powders. USP is based on thermal decomposition or reduction of constant sized aerosol droplets of the precursor solution obtained by means of powerful ultrasound source [33 – 38]. In this research, simple and one step production of Fe/ MgO nanocomposite particles via USP-HR is reported. In addition, dependence of magnetic properties on the process temperature, which directly influences the oxide formation, particle and crystallite sizes, was investigated. A thermodynamic approach for the decomposition and reduction reactions was applied to evaluate the nanocomposite particle formation from metal nitrate salts.

2. Experimental 2.1. Materials The reagents, Mg(NO3)2 · 6H2O (99.9 %, Merck) and Fe(NO3)3 · 9H2O (99.9 %, Merck) were of analytical grade and used without further purification. Stoichiometric amounts of metal salts were dissolved in deionized water and stirred for 15 min to prepare the corresponding solution. The concentrations of iron nitrate and magnesium nitrate salts in the precursor were 0.085 and 0.015 M, respectively. 2.2. Experimental procedure Nanocrystalline Fe/MgO particles were synthesis via USP using aqueous solution of iron and magnesium nitrate under hydrogen (H2) gas flow at temperatures 600 and 800 8C. Table 1 shows the details of the experimental parameters. The experimental set up consists of an ultrasonic spray generator, heating zone and collection chamber. Nitrogen at 0.5 L min–1 flow rate was used to create an inert atmosphere prior to and after the reduction process due to the safety regulations. The aerosol droplets of the corresponding solution were generated by a high frequency ultrasonic atomizer (Gapusol, 9001, 2.5 MHz). The mist was then carried into a preheated zone by H2 gas flow. H2 was used without mixing any inert gas in the experiments as a carrier/reducing agent at 0.5 L min–1 gas flow rate. Reduction/decomposition reactions of metal salts took place in the quartz reactor (0.25 m heated zone, and 0.02 m diameter) in the electrically heated furnace (Nabertherm, Germany) at 600 and 800 8C. Reaction products were collected in traps connected to the outlet of the quartz reactor. The residence time was calculated as 9.42 s by assuming that the rate of droplets and the carried gas are equal. However, the real residence time can be obtained by correcting for gas flow rate due to thermally generated gas expansion. The real residence

times taking into account the gas expansion for 600 and 800 8C were 3.20 and 2.60 s, respectively. This short reaction time is sufficient for the reduction/decomposition of droplets to metal/metal oxide particles in H2 atmosphere. The thermodynamics of the composite particle formation by hydrogen reduction/decomposition of metal nitrates were investigated using HSC software. X-ray diffraction (XRD) patterns were recorded on a Philips-1700 X-ray diffractometer with Cu-Ka radiation to determine the phase and crystal structure of the particles. The crystallite sizes were calculated using the Scherrer formula on the XRD data [37 – 39]. The chemical compositions of particles were analyzed with an energy dispersive spectroscopy (EDS) instrument. The size and morphology of the particles were investigated in a field emission scanning electron microscope (FE-SEM, JEOL JSM 700F). Particle size and size distribution were determined from SEM images using Leica Image Manager. All the clearly observed particles on the SEM images were taken into account in these analyses. The theoretical particle size was calculated using the necessary formulations given in our previous study [37] and the report of Choa et al. [32]. The magnetic properties of samples were measured with an AD Magnetometer. The magnetic hysteresis loop measurements were carried at room temperature with an applied magnetic field up to 20 000 Oe.

3. Results and discussion XRD patterns of the resultant particles are given in Fig. 1. The peaks for the sample produced at 600 8C were indexed with Fe and Fe0.761Mg0.239O. The observed peak at 458 belongs to (110) diffraction of body centered cubic structured Fe with the lattice parameter a = 2.867 Å (Space Group: Im-3 m) which is consistent with the reported data (JCPDS Card No: 01-087-0721). Also, the other peaks at 36, 42, 61 and 738 represent the (111), (200), (220) and (311) diffractions of cubic Fe0.761Mg0.239O with the lattice parameter

Fig. 1. XRD analysis of the particles produced at (a) 600 8C and (b) 800 8C.

Table 1. Experimental parameters.

484

No

Fe(NO3)3 · 9H2O Concentration (M)

Mg(NO3)2 · 6H2O Concentration (M)

Frequency (MHz)

Temperature (8C)

H2 Flow Rate (L · min–1)

1 2

0.085 0.085

0.015 0.015

2.5 2.5

600 800

0.5 0.5

Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

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B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

a = 4.305 Å (Space Group: Fm-3 m). The chemical formula of the Fe0.761Mg0.239O compound given in reported data (JCPDS Card No: 01-077-2369) is (MgO)0.239 · (FeO)0.761. This oxide compound is the product of insufficient reduction of iron nitrate at 600 8C due to the short residence time in the heated zone. Figure 1b shows that increasing the reaction temperature causes the termination of the iron reduction reaction. The main peak indicates iron structure and the small peak at 438 refers to (200) diffraction of cubic MgO with lattice parameter a = 4.223 Å (Space Group: F23, JCPDS Card No: 01-074-1225). The XRD results show that Fe/Fe0.761Mg0.239O composite particles were produced at 600 8C, whereas Fe/MgO composite particles were obtained by elevating the reaction temperature to 800 8C under constant H2 flow. Crystallite sizes of the different phases were calculated with the Scherrer equation using (110) peaks for Fe, (200) peak for Fe0.761Mg0.239O and (200) peak for MgO crystallites. Instrumental broadening was taken into account to obtain accurate crystallite sizes in the calculation. The crystallite sizes of the Fe and Fe0.761Mg0.239O in the particles obtained at 600 8C were determined as 40 and 34 nm, respectively. Moreover, Fe/MgO composite particles prepared at 800 8C were composed of 46 nm Fe and 24 nm MgO crystallites. Based on the XRD results, some of the possible reaction equations during the reduction/decomposition of metal nitrates to metal/metal oxide composite particles were assumed to be Eqs. (1 – 4). The Gibb’s free energies (DGo) of the reactions were computed using HSC software for the temperature range of 100 – 1 000 8C and are shown in Fig. 2. DGo values of the Eq. (1) and Eq. (3) are nearly equal to each other and negative, indicating both of the reactions are spontaneous. In addition, magnesium nitrate decomposes to MgO at 600 and 800 8C depends on DGo values of the Eq. (2). During the particle formation, iron nitrate reduced to Fe and FeO by hydrogen reduction at 600 8C. However, transformation of FeO to Fe is impossible as the reaction depends on DGo values of Eq. (4) in short residence time. Thus, FeO reacted with MgO to generate (MgO)0.239 · (FeO)0.761 compound at 600 8C and Fe/ Fe0.761Mg0.239O composite particles formed. Elevating the reaction temperature to 800 8C increased the possibility of metallic iron formation against FeO due to increasing par-

tial pressure of gases in the reaction. Therefore, Fe/MgO composite particles were produced directly with USP at 800 8C. Fe(NO3)3 + 3H2(g) ? Fe + 3H2O(g) + 3NO2(g)

(1)

Mg(NO3)2 + H2(g) ?MgO + H2O(g) + 2NO2(g)

(2)

Fe(NO3)3 + 2H2(g) ? FeO + 2H2O(g) + 3NO2(g)

(3)

FeO + H2(g) ? Fe + H2O(g)

(4)

The compositions of the products prepared via USP method were further studied using EDS. Fe, Mg and O are clearly shown in Fig. 3, indicating complex compositions of the products. Any impurities which could possibly contaminate from the waste product of the reduction/decomposition reactions, such as N were not detected. The stoichiometric atomic ratio of Fe to Mg in the precursor is 5.67 : 1. EDS analysis indicated that the atomic Fe : Mg ratios of the particles produced at 600 and 800 8C were 5.29 : 1 and 5.12 : 1, respectively. Using the elemental contents and chemical formula of Fe0.761Mg0.239O compound, the amounts of metal/metal oxide were calculated. Thus, Fe/Fe0.761Mg0.239O composite particles contained 67 mol.% metal phase and 33 mol.% oxide phase. Also, Fe/MgO composite particles were composed of 84 mol.% Fe and 16 mol.% MgO. Theoretical elemental contents of the particles are close to experimental values. This clearly indicates that USP is a suitable method for the preparation of particles with complex composition. Backscattered electron SEM images of the samples are shown in Fig. 4. Heavy elements, which have high atomic number, backscatter electrons more strongly than light elements, which have low atomic number, and thus appear brighter in the backscattering SEM images. Distinctly

(a)

(b) Fig. 2. Thermodynamic investigation of the composite particle formation.

Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

Fig. 3. EDS analysis of the particles obtained at (a) 600 8C and (b) 800 8C.

485

(a)

(b)

Fig. 4. Backscattered electron SEM images of the particles prepared at (a) 600 8C and (b) 800 8C.

2013 Carl Hanser Verlag, Munich, Germany

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Not for use in internet or intranet sites. Not for electronic distribution.

B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

(a)

(b)

(c)

(d)

Fig. 5. SEM images of the particles prepared at (a) 600 8C, (b) 600 8C, (c) 800 8C, and (d) 800 8C.

486

Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

bright and dark regions in the images were not observed and the shades of the particles were similar, indicating that Fe and Mg are distributed homogeneously in the particle structure. Figure 5 shows SEM images of nanocrystalline Fe/ Fe0.761Mg0.239O and Fe/MgO composite particles. It is clear that both samples produced at 600 8C and 800 8C have spherical morphology. The size of Fe/Fe0.761Mg0.239O composite particles ranged between 180 and 350 nm. Particle sizes of Fe/MgO composite particles ranged between 145 and 370 nm. The average particle sizes and theoretical calculated size of the samples are given Table 2. The theoretical size calculation assumed full densification of particles. The obtained average particle sizes were mildly coarser than the theoretical which means those particles probably include porosity in their structure. The standard deviation results showed that particles obtained at 600 8C reaction temperature had slightly narrower particle size distribution than particles prepared at 800 8C. Both metallic and metal oxide particle formation in USP include nucleation of primary particles of nanosize, and their aggregation resulting in submicron secondary particles [37, 38, 40]. In this research, metal and metal oxide phases nucleated and formed crystallites, and then submicron composite particles were obtained by aggregation of those crystallites/primary particles. Thus, we suppose that metal and metal oxide phases in the composite particles are present as mixed crystallites/ particles. Magnetic hysteresis loops of the samples are shown in Fig. 6, which reveals the ferromagnetic behavior. The saTable 2. Average particle sizes, theoretical calculated sizes and standard deviation of the particle sizes. Temperature (600 8C)

Temperature (800 8C)

Theoretical calculated size

Average particles size (nm)

273.79

257.48

202.5

Standard deviation

78.68

112.59



2013 Carl Hanser Verlag, Munich, Germany

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B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

turation magnetization (Ms) and coercivity (Hc) values for nanocrystalline Fe/Fe0.761Mg0.239O composite particles were 35.56 emu · g–1 and 156 Oe, respectively. The Ms value of Fe/MgO composite particles dramatically increased to 106.2 emu · g–1 and the Hc value slightly reduced to 132 Oe. The magnetization values of the samples are smaller than bulk iron which is 218 emu · g–1 [41] and some reported data of various iron nanostructures produced using different methods, such as 213 emu · g–1 [42], 167.2 emu · g–1 [43], 174.9 emu · g–1 [44] and 147 emu · g–1 [45]. The existence of antiferromagnetic materials in the composite particles reduced the saturation magnetization of the particles. The reason for the low saturation magnetization of Fe/ Fe0.761Mg0.239O composite particles is the relatively small fraction of Fe (ferromagnetic) and high amount of complex oxide (antiferromagnetic) in the particle structure. Further, composite particles obtained at 800 8C were composed of mainly Fe and little antiferromagnetic MgO. Thus, Fe/ MgO composite particles have higher saturation magnetization than Fe/Fe0.761Mg0.239O structure.

4. Conclusion Fe/MgO nanocomposite particles were successfully produced using hydrogen assisted ultrasonic spray pyrolysis (USP-HR) with iron nitrate and magnesium nitrate solution as a precursor. It was observed that while Fe/Fe0.761Mg0.239O composite particles were prepared at 600 8C, reduction of iron nitrate salt in the precursor to metallic iron became more effective by elevating the reaction temperature to 800 8C and Fe/MgO particles were obtained. The crystallite size of the iron in the composite structure grew slightly by elevating the temperature. In addition, the oxide crystallite size decreased due to a combination of reduced molecular amount and homogeneous distribution in the composite. The particle sizes of both samples were similar, but a narrower particle size distribution was obtained at 600 8C. Magnetic characterization of the particles showed that samples had ferromagnetic properties and lower saturation magnetization than bulk iron. The main cause of the reduced value of saturation magnetization was antiferromagnetic oxide phase in the composites. The magnetic properties of Fe/MgO composite particles can be manipulated by control of metal and metal oxide phase contents. Authors thank to Prof. Dr. Hakan Kockar and Dr. Oznur Karaagac (Balikesir University, Physics Department) for magnetic measurements. References

Fig. 6. Magnetic hysteresis loops of the particles obtained at (a) 600 8C and (b) 800 8C.

Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

[1] Y.H. Xu, J. Bai, J .P. Wang: J. Magn. Magn. Mater. 311 (2007) 131. DOI:10.1016/j.jmmm.2006.11.173 [2] M. Shinkai: J. Biosci. Bioeng. 94 (2002) 606. PMid:16233357; DOI:10.1016/S1389-1723(02)80202-X [3] J.H. Yua, D.W. Lee, B.K. Kim, T. Jang: J. Magn. Magn. Mater. 304 (2006) e16. DOI:10.1016/j.jmmm.2006.02.027 [4] S. Laurent, S. Dutz, U.O. Häfeli, M. Mahmoudi: Adv. Colloid Interfac. 166 (2011) 8. [5] J. Dobson: Drug Develop. Res. 67 (2006) 55. DOI:10.1002/ddr.20067 [6] J. Wang, M. Yao, G. Xu, P. Cui, J. Zhao: Mater. Chem. Phys. 113 (2009) 6. DOI:10.1016/j.matchemphys.2008.07.031 [7] R.H. Kodama: J. Magn. Magn. Mater. 200 (1999) 359. DOI:10.1016/S0304-8853(99)00347-9 [8] Y.M. Zheng, S.F. Lim, J.P. Chen: J. Colloid. Interf. Sci. 338 (2009) 22. PMid:19643427; DOI:10.1016/j.jcis.2009.06.021

487

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B. Ebin et al.: Preparation and magnetic characterization of Fe/metal oxide nanocomposite particles

[9] S.F. Lim, Y.M. Zheng, J.P. Chen: Langmuir. 25 (9) (2009) 4973. PMid:19323493; DOI:10.1021/la802974x [10] F. Macasek, J.D. Navratil, S. Dulanska: Sep. Sci. Technol. 37 (2002) 3673. DOI:10.1081/SS-120014826 [11] Y. He, X. Li, M.T. Swihart: Chem. Mater. 17 (2005) 1017. DOI:10.1021/cm048128t [12] A.K. Gupta, M. Gupta: Biomaterials. 26 (2005) 3995. PMid:15626447; DOI:10.1016/j.biomaterials.2004.10.012 [13] Y. Sahoo, Y. He, M.T. Swihart, S. Wang, H. Luo, E.P. Furlani, P.N. Prasad: J. Appl. Phys. 98 (2005) 054308/1. DOI:10.1063/1.2033145 [14] M. Anhalt: J. Magn. Magn. Mater. 320 (2008) e366. DOI:10.1016/j.jmmm.2008.02.072 [15] S. Pane, E. Gomez, E. Valles: Electrochem. Commun. 9 (2007) 1755. DOI:10.1016/j.elecom.2007.03.034 [16] J.B. Jun, S.Y. Uhm, J.H. Ryu, K.D. Suh: Colloid. Surface. A. 260 (2005) 157. DOI:10.1016/j.colsurfa.2005.03.020 [17] D.S. Xue, Y.L. Huang, Y. Ma, P.H. Zhou, Z.P. Niu, F.S. Li, R. Job, W.R. Fahrner: J. Mater. Sci. Lett. 22 (2003) 1817. DOI:10.1023/B:JMSL.0000005429.24974.e8 [18] D.C. Jiles: Acta Materialia. 51 (2003) 5907. DOI:10.1016/j.actamat.2003.08.011 [19] B. Weidenfeller, M. Anhalt, W. Riehemann: J. Magn. Magn. Mater. 320 (2008) e362. DOI:10.1016/j.jmmm.2008.02.071 [20] S. Neralla, D. Kumar, S. Yarmolenko, J. Sankar: Compos. Part BEng. 35 (2004) 157. DOI:10.1016/j.compositesb.2003.08.005 [21] D.P. Yang, Y.D. Zhang, S. Hui: J. Appl. Phys. 91 (2002) 8198. DOI:10.1063/1.1417995 [22] H. Kondo, T. Sekino, N. Tanaka, T. Nakayama, T. Kusunose, K. Niihara: J. Am. Ceram. Soc. 88 (2005) 1468. DOI:10.1111/j.1551-2916.2005.00243.x [23] X.Q. Shen, M.X. Jing, W.X. Li, D.H. Li: Powder Technol. 160 (2005) 229. DOI:10.1016/j.powtec.2005.08.021 [24] H. Wang, T. Sekino, K. Niihara: Chem. Lett. 34 (2005) 298. DOI:10.1246/cl.2005.1160 [25] Q. Zeng, I. Baker, J.A. Loudis, Y. Liao, P.J. Hoopes, J.B. Weaver: Appl. Phys. Lett. 90 (2009) 233112.1. DOI:10.1063/1.2746064 [26] E. Popovici, F. Dumitrache, I. Morjab, R. Alexandrescu, V. Ciupina, G. Prodan, L. Vekas, D. Bica, O. Marinica: Appl. Surf. Sci. 254 (2007) 1048. DOI:10.1016/j.apsusc.2007.09.022 [27] A.H. Taghvaei, A. Ebrahimi , K. Gheisari, K. Janghorban: J. Magn. Magn. Mater. 322 (2010) 3748. DOI:10.1016/j.jmmm.2009.11.008 [28] N. Rakmak, W. Wiyaratn, C. Bunyakan, J. Chungsiriporn: Chem. Eng. J. 162 (2010) 84. DOI:10.1016/j.cej.2010.05.001 [29] R. Spretz, S.G. Marchetti, M.A. Ulla, E.A. Lombardo: J. Catal. 194 (2000) 167. DOI:10.1006/jcat.2000.2921 [30] C. Martinez-Boubeta, L. Balcells, R. Cristòfol, C. Sanfeliu, E. Rodríguez, R. Weissleder, S. Lope-Piedrafita, K. Simeonidis, M. Angelakeris, F. Sandiumenge, A. Calleja, L. Casas, C. Monty, B. Martinez: Nanomed.-Nanotechnol. 6 (2010) 362. PMid:19800988; DOI:10.1016/j.nano.2009.09.003 [31] T. Nakayama, B.S. Kim, H. Kondo, Y.H. Choa, T. Sekino, M. Nagashima, T. Kusunose, Y. Hayashi, K. Niihara: J. Eur. Ceram. Soc. 24 (2004) 259. DOI:10.1016/S0955-2219(03)00237-1 [32] Y.H. Choa, J.K. Yang, B.H. Kim, Y.K. Jeong, J.S. Lee, T. Nakayam , T. Sekino, K. Niihara: J. Magn. Magn. Mater. 266 (2003) 12 – 19. DOI:10.1016/S0304-8853(03)00450-5 [33] M. Liu, M.L. Zhou, L.H. Zhai, D.M. Liu, X. Gao, W. Liu: Physica C, 386 (2003) 366 – 369. DOI:10.1016/S0921-4534(02)02152-4

488

[34] N.K. Kim, S.G. Kim: Powder Technol. 145 (2004) 155. DOI:10.1016/j.powtec.2004.06.012 [35] K. Okuyama, I.W. Lenggoro: Chem. Eng. Sci. 58 (2003) 537. DOI:10.1016/S0009-2509(02)00578-X [36] X. Shi, S. Wang, X. Duan, Q. Zhang: Mater. Chem. Phys. 112 (2008) 1110. DOI:10.1016/j.matchemphys.2008.05.011 [37] B. Ebin, S. Gürmen: Metall 65/4 (2011) 151. [38] S. Gurmen, B. Ebin: J. Alloy. Compd. 492 (2010) 585. DOI:10.1016/j.jallcom.2009.11.186 [39] O.M. Lemine: Superlattice Microst., 45 (2009) 576. DOI:10.1016/j.spmi.2009.02.004 [40] B. Ebin, S. Gurmen: KONA Powder Part. J. 29 (2011) 134. [41] D.L. Huber: Small 1/5 (2005) 482. DOI:10.1002/smll.200500006 [42] Y.C. Han, H.G. Cha, C.W. Kim, Y.H. Kim, Y.S. Kang: J. Phys. Chem. C 111 ( 2007) 6275. DOI:10.1016/j.nbd.2007.07.017 [43] H.G. Cha, Y.H Kim, D.K. Lee, I.C. Jeong, H.W. Kwon, Y.S. Kang: Solid State Phenomena, 1191 (2007) 51. [44] I. Narita, T. Oku, H. Tokoro, K. Suganuma: J. Electron Microsc. 55(3) (2006) 123. PMid:16585048; DOI:10.1093/jmicro/dfl005 [45] H. Cao, G. Huang, S. Xuan, Q. Wu, F. Gu, C. Li: J. Alloy. Compd. 448 (2008) 272. DOI:10.1016/j.jallcom.2006.10.019

(Received April 4, 2012; accepted August 23, 2012; online since November 15, 2012) Bibliography DOI 10.3139/146.110883 Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5; page 483 – 488 # Carl Hanser Verlag GmbH & Co. KG ISSN 1862-5282 Correspondence address Prof. Dr. Sebahattin Gürmen Istanbul Technical University Metallurgical and Materials Eng. Dept. Ayazaga Campus 34469 Sarıyer Istanbul Turkey Tel.: +90 212 285 34 82 Fax: +90 212 285 34 27 E-mail: [email protected]

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Int. J. Mater. Res. (formerly Z. Metallkd.) 104 (2013) 5

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