University of Delaware ENERGY INSTITUTE SYMPOSIUM March 17, 2008 Newark, DE Novel Materials for High Energy and Power Density George C. Hadjipanayis and John Q. Xiao, University of Delaware, U.S.A. hadji@udel.edu jqx@udel.edu
Magnets for Energy-Related Applications Energy Generation Permanent Magnets Soft Magnets Energy Storage Supercapacitors Novel Materials with High Energy & Power Density George Hadjipanayis John Xiao Energy Efficient Magnetocaloric Materials Refrigerants 10000 TMR = 258.4% High Efficiency Electronic Devices Spintronics* R (Ohm) 8000 6000 4000 2000-200 -100 0 100 200 Magnetic Field (Oe)
Energy Stored by a Permanent Magnet: Energy Product BH For a given airgap, V m proportional to BH is inversely
Modern Permanent Magnets A high performance permanent magnet must have: a high remanence to produce a large magnetic induction a high H c (H c M r /2) to avoid easy demagnetization a high T C to resist thermal demagnetization. Modern high-performance magnets are based on Fe- or Co-rich rareearth alloys: Sm-Co, Nd-Fe-B Fe and Co provide the high magnetization and high Curie temperature Rare earth metals, such as Sm, Nd, Pr, provide the high anisotropy and coercivity. 1952 1735 1985
Progress in Permanent Magnets In the last 100 years, the strength of the magnets [(BH) max and H c ] increased by a factor of 100.
Applications of Permanent Magnets In a typical modern car permanent magnets are used in more than 30 places!
Energy-Efficient Efficient Automotive Applications Electric Power Steering Motor Hybrid Electric Vehicle Motor Y. Matsuura. J. Magn. Magn. Mater. 303 (2006).
More Efficient Rotors for Electric Motors Surface Permanent Magnet Interior Permanent Magnet High-performance Nd-Fe-B sintered magnets are playing an increasingly important role in automobile and electric appliances driven by the issues of energy saving and efficiency. In an air-conditioner compressor motor Inserted permanent magnet rotor has better efficiency than a surface mounted rotor. Y. Matsuura. J. Magn. Magn. Mater. 303 (2006).
Energy-Saving Bearings and Suspensions Magnetic bearings operate without friction, require no lubricants, wear-free and virtually maintenance-free. Research Centre Jülich Waukesha Bearings Turbomolecular pump with permanent magnetic bearings
Magnetic Levitation Train Magnetic levitation systems based on permanent magnets (like "Inductrack", the electrodynamic permanent magnet system) are the most energy efficient and fail safe. Such systems, however, are still under development.
Wind Turbines Permanent magnets can replace the excitation winding of synchronous machines and eliminate the need for a mechanical gearbox, coupling the wind turbine to the generator (to adopt a varying wind speed and the constant grid frequency). This 2.5 MW wind turbine from General Electric employs a permanent magnet generator, enabling higher efficiency at low wind speeds. GE product brochure
Wind Turbines This futuristic design also incorporates the magnetic levitation of vertical blades. The first "MagLev" wind turbine is allegedly now been built in China.
Energy Storage Systems The energy storage flywheel system proposed by K. Murakami et al. [Cryogenics 47 (2007) 272] employs both permanent magnet and superconducting magnetic bearings. The superconducting magnetic bearing (SMB) suppresses the vibrations of the flywheel rotor, whereas the permanent magnet bearing controls the rotor position. Permanent magnet bearing
MRI Logging Magnetic Resonance Imaging Logging uses large permanent magnets to create a strong static magnetic polarizing field inside the formation. The signal amplitude from the precessing hydrogen nuclei is a measure of the total hydrogen content, or porosity, of the formation.
New-Generation Magnets: Hard/Soft Nanocomposites Magnetic exchange coupling allows us to combine the magnetic hardness of rareearth compounds with the high magnetization of soft magnetic materials. The predicted (BH) max of the hard-soft composites exceeds 100 MGOe (59 MGOe is the present record for sintered Nd-Fe-B). Because the exchange interaction has very short range, the composite material must be of a nanoscale.
Historical Development of Nanostructured Nd-Fe Fe-B B Magnets 100 (BH)max (MGOe) 80 60 40 20 Our Challenge 0 Single Phase Isotropic Decoupled M r /M s = 0.5 (BH) max = 12 MGOe Single Phase Isotropic Exchange -Coupled M r /M s > 0.5 (BH) max = 20 MGOe Nanocomposites Isotropic Coupled M r /M s > 0.5 (BH) max > 20 MGOe Nanocomposites Anisotropic Coupled M r /M s > 0.5 (BH) max ~ 100 MGOe Hard phase Soft phase Magnetization
Our Current Efforts in Anisotropic Nanocomposites Obtain isotropic nanocomposites and induce texture by hot plastic deformation (die-upseting) c - axes c - axes These efforts are supported by DoE
Our Current Efforts in Anisotropic Nanocomposites Use anisotropic hard magnetic particles as a substrate when synthesize Fe nanoparticles chemically (e.g., by FeCl 2 + NaBH 4 + H 2 O Fe(B) + NaCl + H 2 + H 2 O): the resulting core/shell elements can be consolidated into anisotropic hard-soft nanocomposites. These efforts are supported by DoE
High-Temperature Permanent Magnets Temperature stability is a critical issue for any permanent magnet. Some applications set especially challenging requirements for the temperature stability. Ion Engine in NASA s Deep Space I Concept of an Aircraft Integrated Power Unit Magnetic Bearings (T op 425 o C) Magnet Rings (T op = 350-550 o C)
Temperature Stability of Different Permanent Magnets 50 (BH) max (MGOe) 45 40 35 30 25 20 Nd-Fe-B Sm-Co 15 100 200 300 400 500 600 Maximum Operating Temp. ( o C)
Control of the Temperature Stability In the so-called 2:17 Sm-Co magnets, a sophisticated thermal processing develops cellular nanostructure, which pins the magnetic domain walls. By controlling the dimensions and chemistry of the cellular nanostructure we can widely vary temperature stability of the magnets. 30 H cj (koe) 25 20 15 10 5 0 New magnet A New magnet B Commercial magnet 300 400 500 600 700 800 Temperature (K) UD/EEC work supported by AFOSR
Magnetic Refrigeration Magnetic refrigeration is based on the magnetocaloric effect (MCE), a magnetothermodynamic phenomenon in which a reversible change in temperature of magnetic materials occurs with the magnetization/demagnetization of MCE materials. An applied magnetic field orients the spins and heats up the material. Removal of field leads to spin randomization and material cools down. Cycling the material through the hot and cold states and venting the heat the system can generate an overall cooling effect Magnetic-refrigeration cycle E.Brück. J. Phys. D: Appl. Phys. 38 (2005) R381.
Advantages of Magnetic Refrigeration Magnetic refrigeration is energy-efficient efficient. The conventional vapor-compression technology is very mature, but it has the maximum efficiency of only 40% a theoretical Carnot cycle. Magnetic refrigeration already showed an efficiency of up to 60% (with gadolinium). Magnetic refrigeration is environmentally friendly. It eliminates ozone depleting gases (CFCs), reduces the need for global warming greenhouse effect gases (HCFC sand HFCs) and other hazardous chemicals like NH 3. A prototype built by The Astronautics Corporation of America
New Materials for Magnetic Refrigeration Adiabatic temperature change T ad temperature magnetic refrigeration: for some magnetocaloric materials for room a Curie temperature; b crystallographic transition temperature. We have applied for DoE support of development of new magnetocaloric materials.