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Porous manganese-based magnetocaloric material for magnetic refrigeration at room temperature
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192 www.elsevier.com/locate/jmmm
Porous manganese-based magnetocaloric material for magnetic refrigeration at room temperature J.A. Lozanoa,, M.P. Kostowa, E. Bru¨ckb, J.C. de Limaa, A.T. Prataa, P.A.P. Wendhausena a
Mechanical Engineering Department, Federal University of Santa Catarina, Florianopolis 88040-900, SC, Brazil Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
b
Available online 21 February 2008
Abstract The powder metallurgy technique has been exploited as a means to prepare porous magnetocaloric materials. The alloy Mn1.1Fe0.9P0.46As0.54 was previously synthesized by mechanical alloying followed by a solid-state reaction for crystallization and homogenization. Subsequently, the alloy was comminuted and sintered at 1298 K. The obtained sintered product is aimed to be tested in a magnetic regenerator of a prototype machine. r 2008 Elsevier B.V. All rights reserved. PACS: 75.30.Sg Keywords: Magnetocaloric material; Manganese-based compound; Porous material; Magnetic refrigeration
1. Introduction Magnetic refrigeration, based on the magnetocaloric effect (MCE), is showing growing importance as a candidate for replacing conventional vapor-compression refrigeration systems for room-temperature applications [1]. Working near to the magnetic phase transition of magnetic materials, i.e., the Curie temperature, an adiabatic application of a magnetic field reduces the magnetic entropy by ordering the magnetic moments. This results in an increase in the temperature of the magnetic material. Consequently, adiabatic removal of the field reverts the magnetic entropy back to its original state and cools the material [2]. A manganese-based compound, recently discovered by Bru¨ck and Tegus [3], shows a giant MCE and is a great candidate for room-temperature magnetic refrigerant applications. This compound can efficiently operate in low fields of about 2 T that easily can be generated by permanent magnets. Additionally, by varying the composiCorresponding author. Tel.: +55 48 3721 9268x224.
E-mail address: [email protected] (J.A. Lozano). 0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2008.02.044
tion its operation temperature can be easily tuned, in order to produce an active magnetic refrigeration regenerator (AMRR). Some of the most interesting magnetocaloric properties of these compounds are achieved on the Mn1.1Fe0.9P0.46As0.54 alloy, which exhibits a maximum adiabatic temperature change of 3 K for a field change from 0 to 1 T at 288 K and its thermal hysteresis is less than 2 K [4]. For higher temperatures and larger temperature spans, the active magnetic regenerative (AMR) cycle is used [5]. In this cycle, the magnetic material is not only the working material but also a thermal regenerator, and therefore it would be desirable to have it with porous structure. The material in the regenerator, in the form of a porous solid, would have a high surface area of contact with the heat transfer fluid. Hence, an AMRR could be produced using different pieces of porous MCE material arranged according to their transition temperature [6]. A first attempt to study the fabrication of such porous structures is exploited in this work by using conventional powder metallurgy techniques based on sintering of loose powders. These porous structures are widely characterized by mercury injection poresizer and image analysis techniques [7].
ARTICLE IN PRESS e190
J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
2. Materials and methods
Relative Intensity
Amorphous Phase
Polycrystalline Phase
40
20
60
80
2θ (degrees) Fig. 1. X-ray diffraction pattern of Mn1.1Fe0.9P0.46As0.54 compound taken at ambient temperature in zero field.
0.02 11.79°C 4.275J/g
0.00 Heat Flow (w/g)
Polycrystalline samples of the alloy Mn1.1Fe0.9P0.46As0.54 were synthesized by a solid-state reaction. A prior mechanical alloying with the appropriate proportions of the starting materials in a high-energy ball mill was carried out in order to obtain homogeneous samples [3]. After this process, an amorphous phase was obtained. The powders were compacted into pellets wrapt in molybdenum foils and sealed in quartz tubes under an argon atmosphere. These tubes were placed on a furnace and heated to a top temperature of 1273 K for 1 h, followed by an homogenization process at 923 K for 50 h [8]. X-ray diffraction was performed on the amorphous and polycrystalline sample in a PHILIPS X’PERT X-ray diffractometer. And a specific heat measurement in a DSC DuPont 2100, with zero field, was carried out for the MCE sample with temperature increasing from 275 to 320 K, in order to determine the temperature and the heat of the transformation on this MCE material. Following a loose powder sintering technique in an alumina matrix [7], a porous magnetocaloric structure was generated. Synthesized compounds were hand-milled and sieved to obtain MCE particles in the ranges 75–90 mm and 90–125 mm. Sintering process was carried out in a controlled atmosphere furnace with an argon atmosphere at 100 Pa and low temperature hydrogen cleanings. Loose Mn1.1Fe0.9P0.46As0.54 powder contained in an alumina matrix was heated to a top temperature of 1298 K for 30 min and then it was homogenized at 923 K for 15 h. High-pressure mercury porosimetry and image analysis characterization techniques were employed to evaluate porosity and pore size distribution of the sintered MCE material [9]. Additionally, the percolation diameter and the total surface area of the sintered material were determined through a poresizer test using a Micromeritics poresizer 9320. As well, two-dimensional image analysis technique is used to describe the form, size and organization of the structure phases in a material [7]. Using optical microphotographs images, the porosity and the pore size distribution were determine using a computer software named IMAGO developed by LMPT/UFSC and ESSS [10].
-0.02 -0.04 -0.06 -0.08 -0.10 14.06°C
-0.12 0
10 20 Temperature (°C)
30
40
50
CSC v4.08 Oupont 2100
Fig. 2. Specific heat measurement in zero field.
3. Results and discussion An X-ray diffraction pattern for the Mn1.1Fe0.9 P0.46As0.54 sample is shown in Fig. 1. This pattern shows that the compound crystallizes in the hexagonal Fe2P type structure [1]. A temperature-dependence measurement on the specific heat of the sintered sample is shown in Fig. 2. From this measurement, one can observe a 287 K Curie temperature and a 4.275 J/g heat of transformation of this MCE material.
Fig. 3. Scanning electron microscopy image of the sintered sample.
Obtained sintered sample shows a porous structure as the scanning electron microscopy (SEM) image demonstrated in Fig. 3.
ARTICLE IN PRESS J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
6 5
0.08 Frequency (%)
Cumulate Volume (mL/g)
0.1
0.06 Intrusion Extrusion
0.04
0.02
0 1000
e191
4 3 2 1 0
100
10
1 0.1 Pore Size (um)
0.01
0.001
Fig. 4. Pore size distribution curve.
Fig. 5. Color and binary microphotograph of the MCE sample.
Porosity of the sample was calculated through a mercury volume intrusion into the porous corresponding to a 46.76% and a bulk density of 4.907 g/mL of the porous material. Fig. 4 shows the pore size distribution curve obtained by injection of mercury on the sample. The percolating diameter is defined as the pore diameter in which the material is permeable for mercury. In a porous material corresponds to the maximum derivate of the cumulative volume versus pore size curve. Therefore, the percolating diameter for a MCE sample sintered at 1298 K corresponded to 10.56 mm. As known, the smaller pores contain the higher specific area, given to the porous material a total surface area of 6.708 m2/g. This surface area represents the contact area that the refrigerant, liquid or gas, will have with the MCE material in order to extract energy from it. A microphotograph of a MCE sample sintered at 1298 K obtained by optical microscopy is shown in Fig. 5 as a binary image for software calculations. The porosity and
0
10
20
30 40 Diameter (um)
50
60
Fig. 6. Pore diameter distribution obtained by image analysis.
the pore diameter distribution of this image were calculated using the software IMAGO. Through the software, the porosity was calculated to be 40.58%. A pore diameter distribution obtained by image analysis is shown in Fig. 6. The pore diameter varies from 3.3 to 56.6 mm, and the most frequent pore size is 14.6 with a D50 of about 16.5 mm for the sintered sample. It is important to control the pore size on a porous regenerator structure. Since the higher the pore size, the lower pressure charge to pass the refrigerant fluid through it. However, the smaller the pore size, the higher surface area of contact with the refrigerant. Therefore, an optimal pore size should be determined for a porous MCE material. In addition, it is essential for pores to be interconnected, since they will determine the permeability of the material, hence, the pressure charge on the refrigerant fluid.
4. Conclusions The resulting sintered samples show that magnetocaloric porous structures can be obtained by sintering loose powder. Moreover, the Mn1.1Fe0.9P0.46As0.54 synthesis was well controlled since similar Curie temperatures (287 K) and a similar X-ray diffraction patterns were obtained. Using the established sintering parameters for this material, a porous structure with sufficient mechanical resistance and an optimal porosity of 46% was attained by this method. However, the achieved pore size will require a high pressure for a refrigerant fluid. Therefore, it is recommended to sinter larger MCE powder particles in order to establish a higher porosity as well as higher permeability values. On the other hand, smaller pore size of the MCE cell represents a higher surface contact area, which might increase heat transfer with the refrigerant fluid. In this case a less dense fluid, like humid helium, would be suggested.
ARTICLE IN PRESS e192
J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
Acknowledgments The authors are grateful to Professor Celso Fernandes and Rafael Ferreira for helpful discussions. Also, the authors thank FINEP for financial support. References [1] O. Tegus, E. Bruck, K. Buschow, F. Boer, Nature 415 (6868) (2002) 150. [2] M. Richard, A. Rowe, R. Chahine, J. Appl. Phys. 95 (4) (2004) 2146. [3] E. Bru¨ck, O. Tegusi, F.R. de Boer, US Patent No. 7,069,729 (filed July 2006).
[4] O. Tegus, Novel materials for magnetic refrigeration, Ph. D. Thesis, University of Amsterdam, 2003. [5] J.A. Barclay, Proceedings of 2nd Conference of Refrigeration for Cryogenic Sensor and Electronic Systems, 1982. [6] J.A. Barclay, W.A. Steyert Jr., US Patent No. 4,332,135 (filed June 1982). [7] E. Reimbrecht, M. Fredel, E. Bazzo, F. Pereira, Mater. Res. 2 (3) (1999) 225. [8] E. Bru¨ck, Magnetocaloric Refrigeration at Ambient Temperature, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Elsevier, Amsterdam, 2007, pp. 235–292. [9] E. Reimbrecht, E. Bazzo, C. Binder, J. Muzart, Mater. Res. 6 (4) (2003) 481. [10] /http://www.imagosystem.com.br/S.
Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192 www.elsevier.com/locate/jmmm
Porous manganese-based magnetocaloric material for magnetic refrigeration at room temperature J.A. Lozanoa,, M.P. Kostowa, E. Bru¨ckb, J.C. de Limaa, A.T. Prataa, P.A.P. Wendhausena a
Mechanical Engineering Department, Federal University of Santa Catarina, Florianopolis 88040-900, SC, Brazil Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
b
Available online 21 February 2008
Abstract The powder metallurgy technique has been exploited as a means to prepare porous magnetocaloric materials. The alloy Mn1.1Fe0.9P0.46As0.54 was previously synthesized by mechanical alloying followed by a solid-state reaction for crystallization and homogenization. Subsequently, the alloy was comminuted and sintered at 1298 K. The obtained sintered product is aimed to be tested in a magnetic regenerator of a prototype machine. r 2008 Elsevier B.V. All rights reserved. PACS: 75.30.Sg Keywords: Magnetocaloric material; Manganese-based compound; Porous material; Magnetic refrigeration
1. Introduction Magnetic refrigeration, based on the magnetocaloric effect (MCE), is showing growing importance as a candidate for replacing conventional vapor-compression refrigeration systems for room-temperature applications [1]. Working near to the magnetic phase transition of magnetic materials, i.e., the Curie temperature, an adiabatic application of a magnetic field reduces the magnetic entropy by ordering the magnetic moments. This results in an increase in the temperature of the magnetic material. Consequently, adiabatic removal of the field reverts the magnetic entropy back to its original state and cools the material [2]. A manganese-based compound, recently discovered by Bru¨ck and Tegus [3], shows a giant MCE and is a great candidate for room-temperature magnetic refrigerant applications. This compound can efficiently operate in low fields of about 2 T that easily can be generated by permanent magnets. Additionally, by varying the composiCorresponding author. Tel.: +55 48 3721 9268x224.
E-mail address: [email protected] (J.A. Lozano). 0304-8853/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2008.02.044
tion its operation temperature can be easily tuned, in order to produce an active magnetic refrigeration regenerator (AMRR). Some of the most interesting magnetocaloric properties of these compounds are achieved on the Mn1.1Fe0.9P0.46As0.54 alloy, which exhibits a maximum adiabatic temperature change of 3 K for a field change from 0 to 1 T at 288 K and its thermal hysteresis is less than 2 K [4]. For higher temperatures and larger temperature spans, the active magnetic regenerative (AMR) cycle is used [5]. In this cycle, the magnetic material is not only the working material but also a thermal regenerator, and therefore it would be desirable to have it with porous structure. The material in the regenerator, in the form of a porous solid, would have a high surface area of contact with the heat transfer fluid. Hence, an AMRR could be produced using different pieces of porous MCE material arranged according to their transition temperature [6]. A first attempt to study the fabrication of such porous structures is exploited in this work by using conventional powder metallurgy techniques based on sintering of loose powders. These porous structures are widely characterized by mercury injection poresizer and image analysis techniques [7].
ARTICLE IN PRESS e190
J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
2. Materials and methods
Relative Intensity
Amorphous Phase
Polycrystalline Phase
40
20
60
80
2θ (degrees) Fig. 1. X-ray diffraction pattern of Mn1.1Fe0.9P0.46As0.54 compound taken at ambient temperature in zero field.
0.02 11.79°C 4.275J/g
0.00 Heat Flow (w/g)
Polycrystalline samples of the alloy Mn1.1Fe0.9P0.46As0.54 were synthesized by a solid-state reaction. A prior mechanical alloying with the appropriate proportions of the starting materials in a high-energy ball mill was carried out in order to obtain homogeneous samples [3]. After this process, an amorphous phase was obtained. The powders were compacted into pellets wrapt in molybdenum foils and sealed in quartz tubes under an argon atmosphere. These tubes were placed on a furnace and heated to a top temperature of 1273 K for 1 h, followed by an homogenization process at 923 K for 50 h [8]. X-ray diffraction was performed on the amorphous and polycrystalline sample in a PHILIPS X’PERT X-ray diffractometer. And a specific heat measurement in a DSC DuPont 2100, with zero field, was carried out for the MCE sample with temperature increasing from 275 to 320 K, in order to determine the temperature and the heat of the transformation on this MCE material. Following a loose powder sintering technique in an alumina matrix [7], a porous magnetocaloric structure was generated. Synthesized compounds were hand-milled and sieved to obtain MCE particles in the ranges 75–90 mm and 90–125 mm. Sintering process was carried out in a controlled atmosphere furnace with an argon atmosphere at 100 Pa and low temperature hydrogen cleanings. Loose Mn1.1Fe0.9P0.46As0.54 powder contained in an alumina matrix was heated to a top temperature of 1298 K for 30 min and then it was homogenized at 923 K for 15 h. High-pressure mercury porosimetry and image analysis characterization techniques were employed to evaluate porosity and pore size distribution of the sintered MCE material [9]. Additionally, the percolation diameter and the total surface area of the sintered material were determined through a poresizer test using a Micromeritics poresizer 9320. As well, two-dimensional image analysis technique is used to describe the form, size and organization of the structure phases in a material [7]. Using optical microphotographs images, the porosity and the pore size distribution were determine using a computer software named IMAGO developed by LMPT/UFSC and ESSS [10].
-0.02 -0.04 -0.06 -0.08 -0.10 14.06°C
-0.12 0
10 20 Temperature (°C)
30
40
50
CSC v4.08 Oupont 2100
Fig. 2. Specific heat measurement in zero field.
3. Results and discussion An X-ray diffraction pattern for the Mn1.1Fe0.9 P0.46As0.54 sample is shown in Fig. 1. This pattern shows that the compound crystallizes in the hexagonal Fe2P type structure [1]. A temperature-dependence measurement on the specific heat of the sintered sample is shown in Fig. 2. From this measurement, one can observe a 287 K Curie temperature and a 4.275 J/g heat of transformation of this MCE material.
Fig. 3. Scanning electron microscopy image of the sintered sample.
Obtained sintered sample shows a porous structure as the scanning electron microscopy (SEM) image demonstrated in Fig. 3.
ARTICLE IN PRESS J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
6 5
0.08 Frequency (%)
Cumulate Volume (mL/g)
0.1
0.06 Intrusion Extrusion
0.04
0.02
0 1000
e191
4 3 2 1 0
100
10
1 0.1 Pore Size (um)
0.01
0.001
Fig. 4. Pore size distribution curve.
Fig. 5. Color and binary microphotograph of the MCE sample.
Porosity of the sample was calculated through a mercury volume intrusion into the porous corresponding to a 46.76% and a bulk density of 4.907 g/mL of the porous material. Fig. 4 shows the pore size distribution curve obtained by injection of mercury on the sample. The percolating diameter is defined as the pore diameter in which the material is permeable for mercury. In a porous material corresponds to the maximum derivate of the cumulative volume versus pore size curve. Therefore, the percolating diameter for a MCE sample sintered at 1298 K corresponded to 10.56 mm. As known, the smaller pores contain the higher specific area, given to the porous material a total surface area of 6.708 m2/g. This surface area represents the contact area that the refrigerant, liquid or gas, will have with the MCE material in order to extract energy from it. A microphotograph of a MCE sample sintered at 1298 K obtained by optical microscopy is shown in Fig. 5 as a binary image for software calculations. The porosity and
0
10
20
30 40 Diameter (um)
50
60
Fig. 6. Pore diameter distribution obtained by image analysis.
the pore diameter distribution of this image were calculated using the software IMAGO. Through the software, the porosity was calculated to be 40.58%. A pore diameter distribution obtained by image analysis is shown in Fig. 6. The pore diameter varies from 3.3 to 56.6 mm, and the most frequent pore size is 14.6 with a D50 of about 16.5 mm for the sintered sample. It is important to control the pore size on a porous regenerator structure. Since the higher the pore size, the lower pressure charge to pass the refrigerant fluid through it. However, the smaller the pore size, the higher surface area of contact with the refrigerant. Therefore, an optimal pore size should be determined for a porous MCE material. In addition, it is essential for pores to be interconnected, since they will determine the permeability of the material, hence, the pressure charge on the refrigerant fluid.
4. Conclusions The resulting sintered samples show that magnetocaloric porous structures can be obtained by sintering loose powder. Moreover, the Mn1.1Fe0.9P0.46As0.54 synthesis was well controlled since similar Curie temperatures (287 K) and a similar X-ray diffraction patterns were obtained. Using the established sintering parameters for this material, a porous structure with sufficient mechanical resistance and an optimal porosity of 46% was attained by this method. However, the achieved pore size will require a high pressure for a refrigerant fluid. Therefore, it is recommended to sinter larger MCE powder particles in order to establish a higher porosity as well as higher permeability values. On the other hand, smaller pore size of the MCE cell represents a higher surface contact area, which might increase heat transfer with the refrigerant fluid. In this case a less dense fluid, like humid helium, would be suggested.
ARTICLE IN PRESS e192
J.A. Lozano et al. / Journal of Magnetism and Magnetic Materials 320 (2008) e189–e192
Acknowledgments The authors are grateful to Professor Celso Fernandes and Rafael Ferreira for helpful discussions. Also, the authors thank FINEP for financial support. References [1] O. Tegus, E. Bruck, K. Buschow, F. Boer, Nature 415 (6868) (2002) 150. [2] M. Richard, A. Rowe, R. Chahine, J. Appl. Phys. 95 (4) (2004) 2146. [3] E. Bru¨ck, O. Tegusi, F.R. de Boer, US Patent No. 7,069,729 (filed July 2006).
[4] O. Tegus, Novel materials for magnetic refrigeration, Ph. D. Thesis, University of Amsterdam, 2003. [5] J.A. Barclay, Proceedings of 2nd Conference of Refrigeration for Cryogenic Sensor and Electronic Systems, 1982. [6] J.A. Barclay, W.A. Steyert Jr., US Patent No. 4,332,135 (filed June 1982). [7] E. Reimbrecht, M. Fredel, E. Bazzo, F. Pereira, Mater. Res. 2 (3) (1999) 225. [8] E. Bru¨ck, Magnetocaloric Refrigeration at Ambient Temperature, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Elsevier, Amsterdam, 2007, pp. 235–292. [9] E. Reimbrecht, E. Bazzo, C. Binder, J. Muzart, Mater. Res. 6 (4) (2003) 481. [10] /http://www.imagosystem.com.br/S.