Motors and Drives


Fig. 1. It is estimated that hybrid electric cars such as the Toyota Prius contain around 30 kg of rare-earth elements in the motors and other components.


4 Applications ranging from servo motors for industrial automation, through to electric and hybrid vehicles, are often reliant on rare- earth magnets. Jon Severn investigates why the price of these magnets has risen so much and reviews some developments that could help to alleviate the problem.


4 Les applications, depuis les servomoteurs pour l’automatisation industrielle aux véhicules électriques et hybrides, dépendent souvent des aimants de terres rares. Jon Severn enquête sur l’origine d’une telle augmentation du prix de ces aimants et passe en revue certains développements qui pourraient aider à réduire ce problème


4 Anwendungen wie Servomotoren für die Industrieautomatisierung bis hin zu Motoren für Elektro- und Hybridfahrzeuge sind oft auf Seltene-Erde-Magneten angewiesen. Jon Severn untersucht, warum der Preis für diese Magneten so stark gestiegen ist und stellte Entwicklungen vor, mit denen das Problem entschärft werden könnte.


High-performance motors dispense with expensive rare-earth magnets


R


are-earth magnets are typically two to three times stronger than ferrite or ceramic permanent magnets. In electric motors, the use of rare-earth magnets enables greater performance


to be obtained from a smaller, lighter motor. Clearly this has its attractions for electric vehicles, where a lighter, more efficient motor reduces the amount of stored energy that has to be transported in the form of petrol, hydrogen or batteries; according to Rare Earth Metals Inc, the Toyota Prius hybrid electric car contains 30kg of rare-earth elements, used in the motors, metal hydride batteries, glass, catalysts and electronics (Fig. 1). For industrial applications, the benefits of rare-earth magnets typically relate to the higher performance available from a motor of the same size, or lighter motors for equipment that is in motion. Another related application for rare- earth magnets is in the generators installed in wind turbines, where the long-term efficiency gains make it worth installing higher-cost, higher-performance generators. The term ‘rare-earth magnet’ is somewhat


misleading, as the magnet is actually an alloy containing relatively small amounts of the rare- earth elements. For example, neodymium magnets, which are the most commonly used type of


rare-earth magnet in motors, are made from an alloy of neodymium, iron and boron (Nd2


Fe14 ) magnets - are not as rare as the term B).


Furthermore, the rare-earth elements - neodymium in this case, or samarium in samarium-cobalt (SmCo5


suggests: samarium is the fortieth most abundant element in the Earth’s crust, making it more common than tin, whereas neodymium is almost as abundant as copper. However, rare-earth elements are seldom found in concentrated and economically exploitable forms, hence they are referred to as ‘rare’. Today’s main difficulty with rare-earth elements


is that China controls approximately 95 per cent of the world’s supply. Before it attained this dominant position, China cut its prices, making mines elsewhere in the world uneconomic. As these mines closed, China’s dominance increased. Having cornered the market, China has been able to reduce export quotas and force prices to surge (and manufacturers to relocate to China). While it is true that the current high prices are making it economic for some mines in other countries to reopen, China is likely to retain its strong position for the foreseeable future. At the end of 2011 some rare-earth metal prices started to fall, but prices will most probably remain volatile and largely controlled by China.


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