Oxidative processes during heat treatment in intermetallic SmCo_5 powder

摘要

Understanding of the thermal stability of intermetallic SmCos powder is essential for designing the working atmosphere in all phases of the technological procedure in the produc- tion of sintered SmCo_5 magnets to obtain maximal magnetic properties. The thermal stability of the SmCo_5 powder with defined chemical composition and particle size was investigated in the interval from 20 to 900 ℃. It was found by thermogravimetric analysis (TGA) that up to 240 ℃, the oxidation of SmCo_5 does not occur. X-Ray diffraction of the thermogravimetric experimental residue of the SmCo_5 powder, heated at 240 ℃, yielded only the presence of the SmCo_5 phase. By X-ray diffraction analysis different crystal forms were identified depending on the maximal heating temperature. The following phases were identified: Sm_2O_3, Co, CoO, Co_3O_4 and SmCoC_3. According to T and X-ray results, for each of the investigated temperatures, the corresponding chemical reactions were established. The experimental data from both the thermal and X-ray investigations confirm that the phases of pressing and aligning the SmCo_5 powder, in the process of producing sintered SmCo_5 magnets, may be performed without a protective atmosphere.