John J. Croat

From ETHW

Biography[edit source]

The rare earth-iron-boron permanent magnets discovered and developed independently by Masato Sagawa and John J. Croat have enabled energy-efficient and environmentally clean high-power motors integral to electric vehicles, high-torque servomotors in robotics and flying devices, renewable energy technologies, and hard disc drives. In early 1982, both researchers discovered that utilizing iron (Fe), the most abundant magnetic element in the continental earth’s crust; neodymium (Nd), the most abundant magnetic rare earth element; and a small amount of boron (B) led to the development of rare earth magnets with lower cost and much higher energy density. All Nd-Fe-B permanent magnets are based on the Nd2Fe14B. The discovery of these NdFeB magnets has overcame the cobalt crisis, which was the major obstacle for mass production of Sm-Co type permanent magnets during the 1970s. Sagawa is credited with the development of anisotropic sintered permanent magnets in which the principal axis of all crystal grains are aligned to produce strong magnetic flux using a powder metallurgy process. Sagawa further developed several key technologies including the development of high coercivity Nd-Fe-B magnets without the use of expensive and scarce heavy rare earth elements such as dysprosium. Croat's discovery resulted from his efforts to produce magnetically hard metastable phases by crystallizing rapidly solidified materials. His investigations led to the development of a family of highly stable resin bonded magnets produced from rapidly solidified NdFeB powders. These powders consisted of small flakes of rapidly solidified Nd-Fe-B alloys containing submicron magnetically isotropic grains of the Nd2Fe14B phase. Although these resin-bonded magnets produce significantly smaller magnetic flux density because of the nonmagnetic binder and the random orientation of the crystallographic axes, they can be rapidly processed into various shapes with high precision, specifically thin walled, high L/D ring bonded magnets now used in wide range of motor types. Magnets with these complex shapes are difficult to produce by the sintering process. Croat also played a principal role in the development of mass production technologies of the rapidly solidified Nd-Fe-B powders and compression bonded magnets.

Recipient of the 1994 Outstanding Engineering Achievement Award from the American Society of Metals, Croat is president of John Croat Consulting, Inc., Naples, FL, USA."