The influences of varying cerium, neodymium, cobalt, and silicon concentrations on the magnetic properties of Ce-Fe-B type magnets were investigated. The results indicated that magnets containing 13.5 at.% of cerium exhibits superior magnetic properties to those exhibited by magnets with higher rare-earth element compositions. High-temperature annealing of the cast alloy containing 13.5 at.% cerium at 1010 °C for 120 min results in the elimination of the α-Fe phase. Increasing the cobalt concentration from 0 to 17 at.% raises the Curie point from 174 °C to 324 °C. The addition of 1 at.% of silicon to the alloy improves intrinsic coercivity by up to 100%. The substitution of up to 5.4 at.% of cerium by neodymium increases magnetic properties of sintered magnets with a 13.5 at.% total rare-earth content. Neodymium contents exceeding 5.4 at.% decrease coercivity. The highest maximum energy product of 27.2 MGOe was exhibited by magnets with a composition of Ce8.1Nd5.4Fe62Co17SiB6.5.
Nd-Fe-B powder produced by conventional methods is pyrophoric, and exhibits poor corrosion resistance. Magnets made from powder are also susceptible to corrosion. Conventional methods of production are complicated, potentially hazardous, and relatively expensive. A novel, low cost, less hazardous method of producing powder and magnets with high corrosion resistance and Curie point is discussed. Nd-Fe-B alloys are milled in water, vacuum dried, and passivated at a suitable temperature in a nitrogen or carbon dioxide medium. During passivation, a protective layer, comprised of nitride and/or carbide phases, is formed in the surface region of the powder particles. This powder is not pyrophoric, and may be stored in a laboratory air environment for an extended period of time with no loss in magnetic properties. Compacted and sintered magnets produced from this powder are also highly corrosion resistant, and exhibit a higher Curie point compared to conventionally produced magnets. A description of the novel technology, and a discussion of the properties of Nd-Fe-B-C/N powder and magnets is given.
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