Microestructural and Magnetic Characterization of BaFe12O19
Microestructural and Magnetic Characterization of BaFe12O19 J. A. Cortés1*; J H. Marín2; M. A. Ramírez1 1
Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá, Guaratinguetá, SP, Brasil. 2 Universidad Nacional de Colombia, Facultad de Ciencias Sede Medellín, Medellín, Ant, Colombia.
The BaFe12O19 has high potential to be used as permanent magnets, as well as being the most widely used material for this kind of applications due to its low cost and high Curie temperature. In this work ceramics bulk of BaFe12O19 were conformed with cylindrical geometry, with 15 mm of diameter and 5 mm of thickness. The samples were conformation with uniaxial pressure of 4500 psi, from milled powder of 4, 6 and 8 hours and calcined at a temperature of 750° C to obtain the desired phase. The samples were sintered for periods of 24 hours at a temperature of 1100° C. Measures of density were realized, which show an upcoming density of 80% of the theoretical density. XRD analysis was made, which show the phase formation, however the different peaks were found with a discrepancy of 0.09 degrees respect to the characteristic peaks of barium ferrite found in literature, this is probably due to the stress in the structure. The magnetic response of the powder was obtained with the technique VSM a coercivity force close to the (3,8 kOe) and the remanence in the range of (14,93 to 37,00 emu/g) where the sample was not more retentive which scored higher milling time.
Keywords: ferrites, magnetic properties, solid state reaction. Introduction The ferrites of Barium are important ceramics utilized in the electroceramic industry, especially in magnetic storage systems [1], because of your high magnetic density, low cost of fabrication and high temperature of Curie. The BaFe12O19 can be obtained by different methods of processing; however the most utilized method is solid state reaction. This work seeks to determine the influence of the milling, the sinterization time and the importance of the porosity in the magnetic properties. Experimental part Barium ferrites (BaFe12O19) were made, starting from barium carbonate (BaCO3) and iron oxide (Fe2O3) with a purity of 99.9%. These precursors were mixed in a planetary mill with steel balls for period of 8 hours, and then placed in an oven with rate of 5°C/min up to temperature of 750°C. This temperature the phase barium ferrite was obtained [2]. The powder calcined was subject to a grinding process at times 4, 6 and 8 hours in a planetary mill with agate spheres due to its hardness in mosh’s scale. After milling, ceramic bodies were formed with a diameter of 15mm and thickness of 5mm by applying uniaxial pressure of 4500 psi, then placed in a oven at 1100° C for 24 hours to sinterization process. The samples were characterized by X-ray Diffraction (DRX), Scan Electron Microscopy (SEM) and Vibrating Sample Magnetometry (VSM). Results and discussion As shown in Figure 1 (a) was possible to obtain the phase of barium ferrite for all three samples. The Figure 1 (b) shows that the samples have a high grade of porosity, which can cause a displacement of the peaks in the DRX, also proved that the sample of barium ferrite that was milled for 6 hours was the one who show the higher density. To determine the grade of porosity, the density of the sample was measured by Archimedes method. The figure 2 (a) shows high grain growth and intragranular porosity, not as
high as presented in Figure 2 (b) which have a higher porosity. The magnetic characterization showed a saturation of 60 emu/g, higher than the ferrite that exhibit more porosity, which was 25.78 emu / g. 4
6
8
34,4
600
79,2
300
Density 32,8
Porosity
77,6
% Density
78,4
% Porosity
Intensity
33,6
4 Horas 6 Horas 8 Horas
32,0 76,8
0 31,2 76,0
20
40
60
80
4
Degree
6
8
Time milling (Hours)
Figure. 1 – (a) DRX of barium ferrites milled at times of 4, 6 and 8 hours. (b) Percentage of density and porosity for different barium ferrite pressed at 4500 psi, varying the time milling.
(emu/g)
(a)
60
30
(b) -10000
0 0
10000
(Oe)
-30
-60
Figure. 2 – (a) SEM for the sample with milling time of 6 hours (b) SEM for the sample with milling time of 8 hours
6 Hours 8 Hours
Figure.3- Magnetic hysteresis curves of barium ferrites with milling times of 6 and 8 hours.
Conclusions
The solid state reaction appears to be the simplest and most economical method to produce this type of ceramics, even though not obtain a full dense ceramic (90% of theoretical density). BaFe12O19 with higher porosity could be decreasing its remanence property, which would be a problem in terms of applications. The increase in the milling time is not influencing the formation of barium ferrite phase, however is causing a drop in density, creating a porous ceramic as shown in the results of the SEM, which apparently is doing fall the remaining property of the ferrite. Therefore for ferrites with good remanence not very large milling times are required. References [1]. R. R. Corrêa1, C. W. Pachoal, W. A. Rocha. Characterization of barium hexaferrite prepared by a ceramic synthesis method, Departamento de Física, Universidade Federal do Maranhão,Campus Bacanga, S. Luís, MA [2]. R. Valenzuela,. Magnetic ceramics. Nueva York. Cambridge University Press. 1994. 312p. Acknowledgement: Capes.
Universidade Estadual Paulista, Faculdade de Engenharia de Guaratinguetá, Guaratinguetá, SP, Brasil. 2 Universidad Nacional de Colombia, Facultad de Ciencias Sede Medellín, Medellín, Ant, Colombia.
The BaFe12O19 has high potential to be used as permanent magnets, as well as being the most widely used material for this kind of applications due to its low cost and high Curie temperature. In this work ceramics bulk of BaFe12O19 were conformed with cylindrical geometry, with 15 mm of diameter and 5 mm of thickness. The samples were conformation with uniaxial pressure of 4500 psi, from milled powder of 4, 6 and 8 hours and calcined at a temperature of 750° C to obtain the desired phase. The samples were sintered for periods of 24 hours at a temperature of 1100° C. Measures of density were realized, which show an upcoming density of 80% of the theoretical density. XRD analysis was made, which show the phase formation, however the different peaks were found with a discrepancy of 0.09 degrees respect to the characteristic peaks of barium ferrite found in literature, this is probably due to the stress in the structure. The magnetic response of the powder was obtained with the technique VSM a coercivity force close to the (3,8 kOe) and the remanence in the range of (14,93 to 37,00 emu/g) where the sample was not more retentive which scored higher milling time.
Keywords: ferrites, magnetic properties, solid state reaction. Introduction The ferrites of Barium are important ceramics utilized in the electroceramic industry, especially in magnetic storage systems [1], because of your high magnetic density, low cost of fabrication and high temperature of Curie. The BaFe12O19 can be obtained by different methods of processing; however the most utilized method is solid state reaction. This work seeks to determine the influence of the milling, the sinterization time and the importance of the porosity in the magnetic properties. Experimental part Barium ferrites (BaFe12O19) were made, starting from barium carbonate (BaCO3) and iron oxide (Fe2O3) with a purity of 99.9%. These precursors were mixed in a planetary mill with steel balls for period of 8 hours, and then placed in an oven with rate of 5°C/min up to temperature of 750°C. This temperature the phase barium ferrite was obtained [2]. The powder calcined was subject to a grinding process at times 4, 6 and 8 hours in a planetary mill with agate spheres due to its hardness in mosh’s scale. After milling, ceramic bodies were formed with a diameter of 15mm and thickness of 5mm by applying uniaxial pressure of 4500 psi, then placed in a oven at 1100° C for 24 hours to sinterization process. The samples were characterized by X-ray Diffraction (DRX), Scan Electron Microscopy (SEM) and Vibrating Sample Magnetometry (VSM). Results and discussion As shown in Figure 1 (a) was possible to obtain the phase of barium ferrite for all three samples. The Figure 1 (b) shows that the samples have a high grade of porosity, which can cause a displacement of the peaks in the DRX, also proved that the sample of barium ferrite that was milled for 6 hours was the one who show the higher density. To determine the grade of porosity, the density of the sample was measured by Archimedes method. The figure 2 (a) shows high grain growth and intragranular porosity, not as
high as presented in Figure 2 (b) which have a higher porosity. The magnetic characterization showed a saturation of 60 emu/g, higher than the ferrite that exhibit more porosity, which was 25.78 emu / g. 4
6
8
34,4
600
79,2
300
Density 32,8
Porosity
77,6
% Density
78,4
% Porosity
Intensity
33,6
4 Horas 6 Horas 8 Horas
32,0 76,8
0 31,2 76,0
20
40
60
80
4
Degree
6
8
Time milling (Hours)
Figure. 1 – (a) DRX of barium ferrites milled at times of 4, 6 and 8 hours. (b) Percentage of density and porosity for different barium ferrite pressed at 4500 psi, varying the time milling.
(emu/g)
(a)
60
30
(b) -10000
0 0
10000
(Oe)
-30
-60
Figure. 2 – (a) SEM for the sample with milling time of 6 hours (b) SEM for the sample with milling time of 8 hours
6 Hours 8 Hours
Figure.3- Magnetic hysteresis curves of barium ferrites with milling times of 6 and 8 hours.
Conclusions
The solid state reaction appears to be the simplest and most economical method to produce this type of ceramics, even though not obtain a full dense ceramic (90% of theoretical density). BaFe12O19 with higher porosity could be decreasing its remanence property, which would be a problem in terms of applications. The increase in the milling time is not influencing the formation of barium ferrite phase, however is causing a drop in density, creating a porous ceramic as shown in the results of the SEM, which apparently is doing fall the remaining property of the ferrite. Therefore for ferrites with good remanence not very large milling times are required. References [1]. R. R. Corrêa1, C. W. Pachoal, W. A. Rocha. Characterization of barium hexaferrite prepared by a ceramic synthesis method, Departamento de Física, Universidade Federal do Maranhão,Campus Bacanga, S. Luís, MA [2]. R. Valenzuela,. Magnetic ceramics. Nueva York. Cambridge University Press. 1994. 312p. Acknowledgement: Capes.
