ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2023 30 search for lighter weight automobiles with greater fuel economy. Although SmCo5 magnets had been discovered in the 1960s, all permanent magnet researchers hoped to discover a lower cost permanent magnet composed of the more abundant, less expensive rare earth elements Nd and Pr in combination with Fe. In 1982, Croat discovered the ternary intermetallic phase Nd2Fe14B while investigating the effect of various glass-forming elements like silicon, carbon, and boron on the properties of rapidly solidified NdFe and PrFe alloys. This intermetallic phase is the basis of all families of NdFeB permanent magnets currently being produced. The rapidly solidified material became the basis for a new family of magnetically isotropic bonded permanent magnets. Although the magnetic strength of these bonded magnets is lower than that of a sintered magnet, thin-walled bonded ring magnets with high thermal stability can be rapidly produced. These magnets have found wide application in small motors for a range of industrial, consumer electronic, and computer peripheral applications. Such thin- walled ring magnets are almost impossible to produce by sintering. Croat’s method was later developed into a hot-deformed process in which nanocrystalline magnetic powder made via the rapid solidification process is hot-deformed in a mold. This led to the development of a family of hot-deformed neodymium magnets that possess an equivalent strength to that of a sintered magnet. Notably, the process is capable of producing thinwalled, axially oriented ring magnets that are now used in high-end servo and stepper motors. MAKING MAGNETS: SINTERING In 1975, Masato Sagawa was working on research to reinforce the mechanical strength of the samarium- cobalt magnet. In this research, he questioned why magnets made of iron, which is abundantly available and has a high magnetic moment, does not exhibit a high coercivity. Meanwhile, he learned that the development of rare earth and iron (R-Fe) magnets had been difficult due to the small interatomic distances between the iron atoms. With this knowledge, he developed a hypothesis that adding elements with a small atomic radius between the iron atoms would expand the iron’s interatomic distance. He then started making alloys of various compositions by putting different minerals into an arc furnace. He chose elements with small atomic diameters, such as carbon and boron, as additives to the R-Fe alloy, and tested various rare earth elements including samarium and neodymium. In 1978, he eventually found that the combination of neodymium, iron, and boron produced the greatest coercivity. Sagawa’s detailed study then extended from various compositions to different manufacturing conditions, including different particle sizes of alloy powders and thermal applications. As a result, he established his own sintering process, in which the magnetic powder is compressed in a mold for shaping and then sintered to form bonds between the particles to reinforce the mechanical strength. Sintered neodymium magnets showed a maximum energy product of 320 kJ/m3 (the maximum energy of the samarium-cobalt magnet at that time was 240 kJ/m3). Mass production of the magnet began just three years from the time Sagawa applied for the patent in August 1982. This permanent magnet was originally MAGNETS THROUGH THE MILLENNIA The first permanent magnet was found in naturally occurring mineral deposits in Magnesia, Greece, around 600 BCE. In 1917, an artificial permanent magnet was developed by Dr. Kotaro Honda followed by other types of artificial magnets. At the same time, research on a magnet that combined cobalt and a rare earth also progressed. In 1969, Dutch scientist K.H.J. Buschow and his colleagues established a compression molding process to manufacture magnets, and this process enabled the commercialization of samarium- cobalt permanent magnets. However, both samarium and cobalt are rare earth elements, primarily produced in Africa and subject to fluctuations in cost and availability. In order to secure stable mass production of industrial magnets, a high-performance magnet made of abundant and affordable materials is a necessity. NdFeB magnets are helping to meet this need. Croat Sagawa THE HONDA FOUNDATION The Honda Foundation was established in December 1977 with a donation from Soichiro Honda, founder of Honda Motor Co. Ltd., and his brother Benjiro. The foundation focuses on activities that help develop and disseminate ecotechnology, which aims to contribute to the development of both scientific technology and mankind by harmonizing the human and natural environments. One of these initiatives is the Honda Prize, an international award that acknowledges significant achievements in ecotechnology. In addition, the foundation supports international symposia and colloquia to search for resolutions to today’s grand challenges, while the Honda Y-E-S programs are designed to develop the next generation of engineers and scientists. The foundation aims to contribute to “the creation of a truly humane civilization” through these activities.
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