Structure and stability of SmCo5

The structure of SmCo5has been investigated between 500°C and its melting point. It is found that SmCo5is a composite of two phases. One of them is unstable and decomposes below 1150°C giving rise to the neighboring phase Sm2Co17. No traces of Sm2Co7have been observed during this decomposition. The reaction of SmCo5with the container materials is discussed. The potential importance of RCo5compounds of the CaZn5- type structure for the manufacture of permanent magnets has resulted in intensive research on these materials. These materials have extremely high energy products and coercive fields. Several reports on the structure and stability of SmCo5have been presented in recent years. On the basis of measurements of the coercive field, Westendorp [1,2] concludes that SmCo5is a single phase above 1080°C and below this temperature a second phase precipitates out. The size of the particles of this precipitated phase controls the coercive field. Den Broeder et al. [3] and Buschow [4] have reported a eutectoid decomposition of SmCo5at about 750°C (SmCo5= Sm2Co7+ Sm2Co17). Although they detect the presence of Sm2Co7and Sm2Co17by metallographic methods, they are unable to find any traces of Sm2Co7by X-ray diffraction techniques. In this paper we report on the structure and stability of SmCo5at various temperatures and its reaction with various container materials.