High-Energy Rare-Earth Magnets
High-Energy Rare-Earth Magnets
Rare-earth metals feature unpaired electrons in their atomic structures, creating high magnetic moments and enabling them to store vast amounts of energy within magnets.
Permanent magnets made from rare earth elements are integral parts of climate economy products such as electric vehicles and wind turbines, such as Neodymium and Samarium-Cobalt magnets being among the most frequently found types.
1. Samarium-Cobalt
Samarium-cobalt (SmCo) magnets are stronger than neodymium magnets and work over a wider temperature range with excellent coercivity. Samarium-cobalt magnets were among the first high-energy rare-earth magnets commercially available and tripled the maximum energy product of any previously available rare earth magnets.
SmCo magnets are made by pressing special samarium powder into die-formed shapes or by compression bonding, producing components with close tolerances without needing post-processing steps such as machine grinding. As this material can be quite fragile, special care must be taken when handling it to avoid cracks and chips.
These magnets are typically coated in nickel-cobalt alloy for corrosion resistance and found in computer disc drives, sensors, traveling wave tubes and linear actuators. On occasion, however, some discolorations that appears as oxidation is visible; these are most often iron impurities and do not cause any reduction of magnetic performance.
SmCo magnets can generally be divided into two main groups based on their samarium-to-cobalt ratio: Series 1-5 magnets contain one samarium atom for every five cobalt atoms; while more recently developed SmCo2-17 types boast higher iron contents and slightly reduced energy products.
2. Neodymium-FeB
Neodymium magnets are permanent magnets composed of an alloy composed of neodymium, iron and boron that is known to be one of the strongest magnetic materials available today. Neodymium magnets have wide ranging commercial, industrial and technical uses and applications across industries and commercial settings.
Neodymium stands out among rare earth elements as having the strongest magnetic properties and is therefore used for various consumer, industrial and professional applications.
Neodymium magnets may be popular, yet these powerful devices must be handled carefully to avoid injuries and property damage. Prolonged exposure can result in chemical burns or other painful injuries as well as damage to electronic equipment.
Neodymium magnets should always be kept out of liquid environments as this can compromise their magnetic properties and lead to corrosion in humid conditions, especially if left uncoated. All magnets should be coated with an anticorrosion layer in order to minimize or avoid corrosion altogether.
3. NdFeB Magnets
Neodymium-iron-boron magnets boast the highest tensile strength and smallest footprint among rare earth permanent magnets. Their small size enables them to produce greater magnetic energy per volume than samarium-cobalt and ferrite magnets, but require higher temperatures in order for their magnetic properties to fully develop. Unfortunately, neodymium-iron-boron magnets are prone to oxidation more readily than their peers and should be protected from air and moisture contact.
NdFeB magnets are in high demand for use in electronic devices, electric vehicles and wind turbines due to their use in smaller electric vehicle motors; more magnets can also be fit into each motor thanks to their smaller size, while their higher energy-to-weight ratio enables stronger magnetic fields than with comparable volumes of samarium cobalt or alnico magnets.
Production of NdFeB involves crushing and milling raw materials into fine powders, roasting to convert metals to oxides, selective leaching with acids such as HCl or HNO3 to remove iron, precipitating rare earths as oxalate salts, then calcining to recover rare earth oxides for use as starting products for the manufacturing process. This environmentally friendly method produces only minimal volumes of waste streams, water waste streams, and oxalic acid as waste streams and emissions.
4. NdFeC
Neodymium iron boron, or NdFeB magnets are among the strongest magnetic materials currently available. Available in various shapes, sizes and grades - they are commonly used in applications that require high performance magnets - including loudspeakers, computer hard disk drives, fishing reel brakes etc.
As NdFeB magnets require many rare earth elements for their strength, especially samarium and cobalt, they consume significant quantities. Because of this fact, it is crucial that ways be found for recycling these rare-earth magnets.
Researchers have successfully implemented a new method for recycling magnets through leaching with hydrochloric and sulfuric acids. This allows researchers to remove neodymium and iron without demagnetization; additionally, this process makes possible skipping grinding milling or oxidative roasting processes altogether.
Scientists' work marks an important step forward towards replacing rare-earth permanent magnets. Researchers discovered that tetrataenite, an "extreme magnet" formed over millions of years in meteorites, can be artificially synthesized using common elements like phosphorus. This may accelerate development of powerful magnets used for wind turbines, electric vehicles and missiles.
5. NdFeC Magnets
Neodymium-iron-boron magnets are one of the strongest permanent magnets available today and come in an extensive variety of shapes and sizes for various industrial, technical and commercial uses. Their application areas range from high magnetic remanence or coercivity applications, through higher energy products than ferrite or alnico magnets to applications requiring high magnetic remanence or coercivity values and greater coercivity values than their counterparts such as ferrite or alnico magnets. Neodymium iron boron magnets contain rare earth elements such as Neodymium Praseodymium Dysprosium making them critical raw materials (CRM).
NdFeB powder combined with binder can be combined in injection molding, extrusion, calendering or compression bonding processes to produce bonded magnets without losing coercivity significantly. To do this, researchers investigated selective leaching of rare earths using inorganic acid HCl for selective leaching from both non-roasted and roasted NdFeB magnets under identical leaching processes; results indicate that more acid was required to dissolve oxides on roasted magnets than non-roasted ones.
These results will enable researchers to tailor the chemical composition and hot deformation conditions of NdFeC magnets that consume less HREE than their neodymium-iron-boron counterparts, and therefore can be employed more energy-efficient elevators, wind turbines, electric bicycles and hybrid automobiles.