Purpose: Analysis of microstructure and magnetic properties of BaFe12O19 powder obtained by milling and annealing of Fe2O3 and BaCO3 precursors.
Design/methodology/approach: The mixture of iron oxide (Fe2O3) and barium carbonate (BaCO3) powders was used to obtain BaFe12O19 powder by using high-energy ball milling and heat treatment processes. The X-ray diffraction methods were used for qualitative, quantitative phase analyses and for crystallite size and lattice distortion determination. The thermal properties of the studied powders were analyzed using the differential thermal analysis (DTA). The magnetic properties of examined powder material were studied by resonance vibrating sample magnetometer (R-VSM). The size of powder particles was determined by a laser particle analyzer.
Findings: The milling process of iron oxide and barium carbonate mixture causes decrease of the crystallite size of involved phases. The X-ray diffraction investigations of Fe2O3 and BaCO3 mixture milled for 50 hours and annealed at 850, 900, 950 and 1000°C enabled the identification of hard magnetic BaFe12O19 phase and also small amount of Fe2O3 phase. The magnetic properties of studied powders are dependent on temperature of their annealing. The sample annealed at 1000°C has the best hard magnetic properties from all studied samples. The content changes of hard magnetic phase (BaFe12O19) with the increase of annealing temperature results in the improvement of hard magnetic properties.
Practical implications: The BaFe12O19 powder can be suitable component to produce sintered hard magnetic materials.
Originality/value: The study results of BaFe12O19 powders confirm the utility of applied investigation methods in the microstructure and magnetic properties analysis of powder materials.
Keywords: X-ray phase analysis; R-VSM; High-energy ball milling; Bariu

Babilas, R.

Dercz, Grzegorz

Nowosielski, R.

Pająk, Lucjan

Skowroński, W.

Journal of Achievements of Materials and Manufacturing Engineering

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Microstructure and magnetic properties of BaFe12O19 powder  Author: R. Nowosielski, R. Babilas, Grzegorz Dercz, Lucjan Pająk, W. Skowroński  Citation style: Nowosielski R., Babilas R., Dercz Grzegorz, Pająk Lucjan, Skowroński W. (2008). Microstructure and magnetic properties of BaFe12O19 powder. "Journal of Achievements in Materials and Manufacturing Engineering" (Vol. 27, iss. 1 (2008), s. 51-54). © Copyright by International OCSCO World Press. All rights reserved. 2008VOLUME 27ISSUE 1March2008Short paper 51of Achievements in Materialsand Manufacturing EngineeringMicrostructure and magnetic properties of BaFe12O19 powderR. Nowosielski a, R. Babilas a,*, G. Dercz b, L. Pająk b, W. Skowroński c a Division of Nanocrystalline and Functional Materials and Sustainable Pro-ecological Technologies, Institute of Engineering Materials and Biomaterials, Silesian University of Technology, ul. Konarskiego 18a, 44-100 Gliwice, Polandb Institute of Materials Science, University of Silesia, ul. Bankowa 12, 40-007 Katowice, Polandc Department of Electronics, AGH University of Science and Technology, ul. Mickiewicza 30, 30-059 Kraków, Poland*  Corresponding author: E-mail address: rafal.babilas@polsl.plReceived 04.01.2008; published in revised form 01.03.2008Methodology of researchAbstrActPurpose: Analysis of microstructure and magnetic properties of BaFe12O19 powder obtained by milling and annealing of Fe2O3 and BaCO3 precursors.Design/methodology/approach: The mixture of iron oxide (Fe2O3) and barium carbonate (BaCO3) powders was used to obtain BaFe12O19 powder by using high-energy ball milling and heat treatment processes. The X-ray diffraction methods were used for qualitative, quantitative phase analyses and for crystallite size and lattice distortion determination. The thermal properties of the studied powders were analyzed using the differential thermal analysis (DTA). The magnetic properties of examined powder material were studied by resonance vibrating sample magnetometer (R-VSM). The size of powder particles was determined by a laser particle analyzer.Findings: The milling process of iron oxide and barium carbonate mixture causes decrease of the crystallite size of involved phases. The X-ray diffraction investigations of Fe2O3 and BaCO3 mixture milled for 50 hours and annealed at 850, 900, 950 and 1000°C enabled the identification of hard magnetic BaFe12O19 phase and also small amount of Fe2O3 phase. The magnetic properties of studied powders are dependent on temperature of their annealing. The sample annealed at 1000°C has the best hard magnetic properties from all studied samples. The content changes of hard magnetic phase (BaFe12O19) with the increase of annealing temperature results in the improvement of hard magnetic properties.Practical implications: The BaFe12O19 powder can be suitable component to produce sintered hard magnetic materials.Originality/value: The study results of BaFe12O19 powders confirm the utility of applied investigation methods in the microstructure and magnetic properties analysis of powder materials.Keywords: X-ray phase analysis; R-VSM; High-energy ball milling; Barium ferrite1. Introduction Barium ferrites are well known hard magnetic materials, which are based on iron oxides. They are also called as ferrite magnets and could not be easily replaced by any other magnets [1-4]. Barium ferrites are scientifically and technologically attractive, because of their relatively high Curie temperature, high coercive force and high magnetic anisotropy field, as well as their excellent chemical stability and corrosion resistivity [5,6]. Ferrites are still widely used although they have less magnetic strength than rare earth magnets [7]. Due to these properties, .		IntroductionShort paper52Journal of Achievements in Materials and Manufacturing EngineeringR. Nowosielski, R. Babilas, G. Dercz, L. Pająk, W. SkowrońskiVolume 27 Issue 1 March 2008many methods of synthesis have been developed to obtain a low production cost of powder particles of barium ferrite [8]. Barium ferrites are usually produced by the conventional mixed oxide ceramic method, which involves the calcination of  a mixture of BaCO3 and Fe2O3 at 1200°C. More recently, they have been fabricated by milling and heat treatment process [9-11]. The aim of this paper is the microstructure analysis and magnetic properties characterization of BaFe12O19 powder obtained by milling and heat treatment of Fe2O3 and BaCO3precursors.2. Material and research methodology The BaFe12O19 powders were obtained from the mixture of iron oxide Fe2O3 (99% purity) and barium carbonate BaCO3(99% purity) powders (1.1BaCO3 + 6Fe2O3) by using high-energy ball milling and heat treatment processes.  Fig. 1. X-ray diffraction patterns of as-prepared Fe2O3 and BaCO3mixture and after 50 hours of milling process Ball milling process was carried out in a vibratory mill  (SPEX 8000 CertiPrep Mixer/Mill) for 50 hours under argon atmosphere. The weight ratio of balls to milled material was 5:1. After milling process the powders were annealed in the electric chamber furnace (Thermolyne 6020C) at 850, 900, 950 and  1000°C in the air under atmosphere pressure for 1 hour. Phase analysis was carried out using the X-Pert Philips diffractometer equipped with curved graphite monochromator on diffracted beam and a tube provided with copper anode. The  X-ray diffraction patterns were recorded by “step-scanning” method in 2ș range from 20° to 140° and 0.05° step. The Rietveld analysis was performed applying DBWS-9807 program that is an update version for Rietveld refinement with PC and mainframe computers. The pseudo-Voigt function was used in the describing of diffraction line profiles at Rietveld refinement. The phase abundance was determined using the relation proposed by Hill and Howard [12-14]. The crystallite sizes and lattice distortions for Fe2O3 and BaCO3 phases were estimated using Williamson-Hall method [15].  The thermal properties of the tested powder were determined by the Mettler thermoanalyser using the differential thermal analysis (DTA) at a heating rate of 15 K/min under an argon atmosphere.The magnetic hysteresis loops of obtained powder material were measured by the Resonance Vibrating Sample Magnetometer (R-VSM). The idea of R-VSM is based on the Faraday induction law and the original Foner solution.The diameter sizes of examined powder particles were determined using Fritsch Particle Sizer “Analysette 22” in measuring range from 0.1 µm to 1180 µm. 3. Results and discussion The diffraction patterns of Fe2O3 and BaCO3 mixture (Fig.1) shows the broadening of diffraction lines for milled samples. These effects indicate that ball milling causes decrease of the crystallite size of tested phases and involved to homogenization of the milled mixture. As the result of milling process the crystallite size (D) of Fe2O3 and BaCO3 phases diminishes to 15 nm and  35 nm, respectively of the milling time up to 50 hours. Fig. 2. DTA pattern of Fe2O3 and BaCO3 mixture after 50 hours of milling process After 50 hours milling process the lattice distortions (<'a/a>)are 0.12% and 0.042% for Fe2O3 and BaCO3, respectively.  The differential thermal analysis showed exothermic reaction peaks at 433°C and at 1033°C (Fig. 2). The first peak probably corresponds to formation of the barium hexaferrite phase. The hysteresis loop of Fe2O3 and BaCO3 mixture after milling is shown in Figure 3. The hard magnetic properties of examined mixture are very low, because of lack of hard magnetic phase. Fig. 3. Hysteresis loop of Fe2O3 and BaCO3 mixture after 50 hours of milling process Fig. 4. X-ray diffraction patterns of Fe2O3 and BaCO3 mixture after 50 hours of milling and annealing at 850, 900, 950 and 1000°C The X-ray diffraction investigations of Fe2O3 and BaCO3mixture milled for 50 hours and annealed at 850, 900, 950 and 1000°C enabled the identification of hard magnetic BaFe12O19phase (Fig. 4). Moreover, the X-ray analysis revealed also the presence of Fe2O3 phase in studied materials. The effect of annealing process on content of BaFe12O19 and Fe2O3 phases for different temperatures is presented in Figure 5 and 6. The annealing process causes increase of content of hard magnetic phase (BaFe12O19) obtained after heat treatment and decrease of Fe2O3 phase. After annealing at 1000°C the contents of BaFe12O19 and Fe2O3 phases are equal to 98.4 and 1.6 wt.%. Fig. 5. Contents of BaFe12O19 phase after 50 hours of milling  and annealing at 850, 900, 950 and 1000°C Fig. 6. Contents of Fe2O3 phase after 50 hours of milling  and annealing at 850, 900, 950 and 1000°C The effect of annealing temperature on magnetic properties of Fe2O3 and BaCO3 mixture is presented in Figure 7. Table 1 contains chosen magnetic properties measured in the field 800 kA/m. The magnetic properties of studied powders are dependent on temperature of their annealing. For example, the sample annealed at 1000°C has the best hard magnetic properties from all studied samples. The remanence (Br) of that material has a value of 0.116 T, the saturation magnetization (Bs) is 0.189 T and coercive force (HC) for sample annealed at 1000°C is 266 kA/m.  The high values of remanence, saturation magnetization and coercivity are certainly associated with the microstructure and phase composition of investigated powders after annealing process. The content increase of hard magnetic phase (BaFe12O19)with the increase of annealing temperature results in improvement of hard magnetic properties.  2.		Material	and	research	methodology.		results	and	discussion53Methodology of researchMicrostructure and magnetic properties of BaFe12O19 powdermany methods of synthesis have been developed to obtain a low production cost of powder particles of barium ferrite [8]. Barium ferrites are usually produced by the conventional mixed oxide ceramic method, which involves the calcination of  a mixture of BaCO3 and Fe2O3 at 1200°C. More recently, they have been fabricated by milling and heat treatment process [9-11]. The aim of this paper is the microstructure analysis and magnetic properties characterization of BaFe12O19 powder obtained by milling and heat treatment of Fe2O3 and BaCO3precursors.2. Material and research methodology The BaFe12O19 powders were obtained from the mixture of iron oxide Fe2O3 (99% purity) and barium carbonate BaCO3(99% purity) powders (1.1BaCO3 + 6Fe2O3) by using high-energy ball milling and heat treatment processes.  Fig. 1. X-ray diffraction patterns of as-prepared Fe2O3 and BaCO3mixture and after 50 hours of milling process Ball milling process was carried out in a vibratory mill  (SPEX 8000 CertiPrep Mixer/Mill) for 50 hours under argon atmosphere. The weight ratio of balls to milled material was 5:1. After milling process the powders were annealed in the electric chamber furnace (Thermolyne 6020C) at 850, 900, 950 and  1000°C in the air under atmosphere pressure for 1 hour. Phase analysis was carried out using the X-Pert Philips diffractometer equipped with curved graphite monochromator on diffracted beam and a tube provided with copper anode. The  X-ray diffraction patterns were recorded by “step-scanning” method in 2ș range from 20° to 140° and 0.05° step. The Rietveld analysis was performed applying DBWS-9807 program that is an update version for Rietveld refinement with PC and mainframe computers. The pseudo-Voigt function was used in the describing of diffraction line profiles at Rietveld refinement. The phase abundance was determined using the relation proposed by Hill and Howard [12-14]. The crystallite sizes and lattice distortions for Fe2O3 and BaCO3 phases were estimated using Williamson-Hall method [15].  The thermal properties of the tested powder were determined by the Mettler thermoanalyser using the differential thermal analysis (DTA) at a heating rate of 15 K/min under an argon atmosphere.The magnetic hysteresis loops of obtained powder material were measured by the Resonance Vibrating Sample Magnetometer (R-VSM). The idea of R-VSM is based on the Faraday induction law and the original Foner solution.The diameter sizes of examined powder particles were determined using Fritsch Particle Sizer “Analysette 22” in measuring range from 0.1 µm to 1180 µm. 3. Results and discussion The diffraction patterns of Fe2O3 and BaCO3 mixture (Fig.1) shows the broadening of diffraction lines for milled samples. These effects indicate that ball milling causes decrease of the crystallite size of tested phases and involved to homogenization of the milled mixture. As the result of milling process the crystallite size (D) of Fe2O3 and BaCO3 phases diminishes to 15 nm and  35 nm, respectively of the milling time up to 50 hours. Fig. 2. DTA pattern of Fe2O3 and BaCO3 mixture after 50 hours of milling process After 50 hours milling process the lattice distortions (<'a/a>)are 0.12% and 0.042% for Fe2O3 and BaCO3, respectively.  The differential thermal analysis showed exothermic reaction peaks at 433°C and at 1033°C (Fig. 2). The first peak probably corresponds to formation of the barium hexaferrite phase. The hysteresis loop of Fe2O3 and BaCO3 mixture after milling is shown in Figure 3. The hard magnetic properties of examined mixture are very low, because of lack of hard magnetic phase. Fig. 3. Hysteresis loop of Fe2O3 and BaCO3 mixture after 50 hours of milling process Fig. 4. X-ray diffraction patterns of Fe2O3 and BaCO3 mixture after 50 hours of milling and annealing at 850, 900, 950 and 1000°C The X-ray diffraction investigations of Fe2O3 and BaCO3mixture milled for 50 hours and annealed at 850, 900, 950 and 1000°C enabled the identification of hard magnetic BaFe12O19phase (Fig. 4). Moreover, the X-ray analysis revealed also the presence of Fe2O3 phase in studied materials. The effect of annealing process on content of BaFe12O19 and Fe2O3 phases for different temperatures is presented in Figure 5 and 6. The annealing process causes increase of content of hard magnetic phase (BaFe12O19) obtained after heat treatment and decrease of Fe2O3 phase. After annealing at 1000°C the contents of BaFe12O19 and Fe2O3 phases are equal to 98.4 and 1.6 wt.%. Fig. 5. Contents of BaFe12O19 phase after 50 hours of milling  and annealing at 850, 900, 950 and 1000°C Fig. 6. Contents of Fe2O3 phase after 50 hours of milling  and annealing at 850, 900, 950 and 1000°C The effect of annealing temperature on magnetic properties of Fe2O3 and BaCO3 mixture is presented in Figure 7. Table 1 contains chosen magnetic properties measured in the field 800 kA/m. The magnetic properties of studied powders are dependent on temperature of their annealing. For example, the sample annealed at 1000°C has the best hard magnetic properties from all studied samples. The remanence (Br) of that material has a value of 0.116 T, the saturation magnetization (Bs) is 0.189 T and coercive force (HC) for sample annealed at 1000°C is 266 kA/m.  The high values of remanence, saturation magnetization and coercivity are certainly associated with the microstructure and phase composition of investigated powders after annealing process. The content increase of hard magnetic phase (BaFe12O19)with the increase of annealing temperature results in improvement of hard magnetic properties.  Short paper54 READING DIRECT: www.journalamme.orgJournal of Achievements in Materials and Manufacturing Engineering Volume 27 Issue 1 March 2008Table 1. Magnetic properties of Fe2O3 and BaCO3 mixture after 50 hours of milling and different annealing temperature (field 800 kA/m) Annealingtemperature [oC] Coercive force Hc[kA/m] Remanence,Br[T] Saturationmagnetization, Bs[T] 850 253 0.099 0.164 900 279 0.102 0.168 950 219 0.104 0.172 1000 266 0.116 0.189 Fig. 7. Hysteresis loops of Fe2O3 and BaCO3 mixture after 50 hours of milling and annealing at 850, 900, 950 and 1000°C The diameter arithmetic mean of examined population of Fe2O3 and BaCO3 powders after 50 hours of milling is  7.64(6) µm. Moreover, the size of powders, which are the most probable (mode) is 15.11(7) µm. The representative diameter of examined powders (median) is equal to 4.37(5) µm. 4. Conclusions The investigations performed on the Fe2O3 and BaCO3mixture after milling and heat treatment allowed to formulate the following statements: x high-energy milling of studied composite powder for 50 hours results in the decrease of Fe2O3 and BaCO3 crystallite size to 15 nm and 35 nm, respectively, x the barium ferrite phase appeared to be the main component of milled for 50 hours and annealed at 1000°C sample  (98.4 wt.%), whereas the content of Fe2O3 phase is the much lower (1.6 wt.%), x the magnetic properties of studied powders is dependent on temperature of their annealing, x the best magnetic properties were obtained for powder annealed at temperature of 1000°C, x the diameter arithmetic mean of Fe2O3 and BaCO3 mixture powder  particles after 50 hours of milling is about 8 µm. References [1] J. Qiu, M. Gu, Magnetic nanocomposite thin films of BaFe12O19 and TiO2 prepared by sol-gel method, Applied Surface Science 252 (2005) 888-892. [2] B. ZiĊbowicz, D. Szewieczek, L.A. DobrzaĔski, New possibilities of application of composite materials with soft magnetic properties, Journal of Achievements in Materials and Manufacturing Engineering 20 (2007) 207-210. [3] L.A. DobrzaĔski, M. Drak, B. ZiĊbowicz, Materials with specific magnetic properties, Journal of Achievements in Materials and Manufacturing Engineering 17 (2006) 37-40. [4] M. Drak, L.A. DobrzaĔski, Corrosion of Nd-Fe-B permanent magnets, Journal of Achievements in Materials and Manufacturing Engineering 20 (2007) 239-241. [5] N. Shams, X. Liu, M. Matsumoto, A. Morisako, Manipulation of crystal orientation and microstructure of barium ferrite thin film, Journal of Magnetism and Magnetic Materials 290-291 (2005) 138-140. [6] O. Carp, R. Barjega, E. Segal, M. Brezeanu, Nonconventional methods for obtaining hexaferrites, Thermochimica Acta 318 (1998) 57-62. [7] J. Ding, W.F. Miao, P.G. McCormick, R. Street, High-coercivity ferrite magnets prepared by mechanical alloying, Journal of Alloys and Compounds 281 (1998) 32-36. [8] A. Mali, A. Ataie, Structural characterization of nanocry-stalline BaFe12O19 powders synthesized by sol-gel combustion route, Scripta Materialia 53 (2005) 1065-1075. [9] M.H. Makled, T. Matsui, H. Tsuda, H. Mabuchi, M.K. El-Mansy, Magnetic and dynamic mechanical properties of barium ferrite-natural rubber composites, Journal of Materials Processing Technology 160 (2005) 229-233. [10] J. Konieczny, L.A. DobrzaĔski, A. Przybyá, J.J. Wysáocki, Structure and magnetic properties of powder soft magnetic materials, Journal of Achievements in Materials and Manufacturing Engineering 20 (2007) 139-142. [11] P. Gramatyka, A. Kolano-Burian, R. Kolano, M. Polak, Nanocrystalline iron based powder cores for high frequency applications, Journal of Achievements in Materials and Manufacturing Engineering 18 (2006) 99-102. [12] R. Nowosielski, R. Babilas, G. Dercz, L. Pająk, Micro-structure of composite material with powders of barium ferrite, Journal of Achievements in Materials and Manufacturing Engineering 17 (2006) 117-120. [13] R. Nowosielski, R. Babilas, J. Wrona, Microstructure and magnetic properties of commercial barium ferrite powders, Journal of Achievements in Materials and Manufacturing Engineering 20 (2007) 307-310. [14] R. Nowosielski, R. Babilas, G. Dercz, L. Pająk, J. Wrona, Structure and properties of barium ferrite powders prepared by milling and annealing, Archives of Materials Science and Engineering 28/12 (2007) 735-742. [15] G.K. Williamson, W.H. Hall, X-ray line broadening from filed aluminium and wolfram, Acta Metallurgica 1 (1953) 22-31. .		conclusionsreferences

Microstructure and magnetic properties of BaFe12O19 powder

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Microstructure and magnetic properties of BaFe12O19 powder

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