Influence of oxygen content on grain growth in Pr–Fe–B/Nd–Fe–B sintered magnets

The effects of annealing at 1000°C for 24h on the extrinsic properties of Pr–Fe–B and Nd–Fe–B-type sintered magnets

“…4) improvements are seen in the squareness factor on annealing for samples with initial oxygen contents 42000 ppm, where a progressive improvement is seen in the squareness factor (as a function of initial oxygen content) on annealing at 1000 1C for 24 h. This is in good agreement with previous work, which showed a regular and marked increase in the squareness factor with increasing oxygen content (also shown in Fig. 4-the solid line represents the as-sintered values) for Pr-Fe-B sintered magnets [14,15]. In comparison, for Pr-Fe-B samples with relatively low initial oxygen contents (o2000 ppm) a progressive reduction in the squareness factor is seen on annealing at 1000 1C for 24 h. It can also be seen from Fig.…”

“…5(a) and (b). The significant reduction in the squareness factor for Pr-Fe-B sintered magnets with low initial oxygen contents, on annealing, may be related to the relatively poor loop shape of the as-sintered magnets, which indicates that grain growth has taken place on sintering, as observed previously for Pr-Fe-B sintered magnets with low oxygen contents [14,15]. While a high initial oxygen content results in an improved squareness factor on annealing at 1000 1C for 24 h for Pr-Fe-B sintered magnets, it is interesting to note that low oxygen content Pr-Fe-B sintered magnets, in general, exhibit a higher coercivity, before and after annealing, although with inferior loop shapes, as shown by the permeameter demagnetisation curves in Fig.…”

“…The Pr 2 Fe 14 B, PrFe 4 B 4 and Pr-rich phases are indicated. [14,15]. Porosity is also present within the large f-grains, as well as throughout the matrix of smaller grains in the sintered magnet (although as-sintered density $7.41 g/cm 3 ).…”

“…Previous work has shown that oxygen content has a much greater influence on the melting temperature (1C) of the intergranular phase for Pr-Fe-B sintered magnets, as compared to that for Nd-Fe-B sintered magnets [15]. A change/ decrease in the melting temperature of the intergranular phase could lead to improved wetting behaviour, resulting in improved separation and isolation of the hard magnetic grains, and in enhancement of the intrinsic coercivity [34], as seen on annealing Pr-Fe-B sintered magnets at 1000 1C for 24 h. A reduction in the amount of Pr-rich phase due to evaporation may also explain the increases seen in the remanence on annealing at 1000 1C for 24 h, due to an increase in the proportion of the Pr 2 Fe 14 B phase [35], as shown in Fig.…”

Obtenção de ligas magnéticas à base de Pr-Fe-B por resfriamento super-rápido para a fabricação de ímãs permanentes de terras-raras

“…As etapas de manuseio e processamento de pós apresentam dificuldades devido à rápida oxidação dos pós-finos à base de TR. A produção ímãs HD sinterizados em escala de laboratório requer uma atmosfera com um teor de oxigênio inferior a 30 ppm, possível apenas em câmaras anaeróbicas (glove box) [90]. Para controlar o nível de oxigênio, a câmara anaeróbica deve ser operada com assistência contínua de gás nitrogênio, fluindo através da câmara principal.…”