Mechanochemical synthesis of magnetically hard anisotropic RFe10Si2 powders with R representing combinations of Sm, Ce and Zr

• Published in: Journal of magnetism and magnetic materials 2017-01, Vol.422 (C), p.43-48
• Main Authors: Gabay, A.M., Hadjipanayis, G.C.
• Format: Article
• Language: English
• Subjects: Coercivity; Mechanochemistry; Permanent magnet; Rare earth-lean magnet; ThMn12
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2016.08.064

Alloy synthesis consisting of mechanical activation followed by annealing was explored as a method of manufacturing medium-grade permanent magnet materials with a reduced content of the critical rare earth elements. Four RxFe10Si2 alloys with R=Sm, Sm0.7Zr0.3, Sm0.3Ce0.3Zr0.4 and Ce0.6Zr0.4 (nominal compositions) were prepared from mixtures of Sm2O3, CeO2, ZrO2, Fe2O3 and Si powders in the presence of a reducing agent Ca and a CaO dispersant. The collected alloy particles typically consisted of few joined submicron crystals. For R=Sm, X-ray diffraction analysis reveals a significant amount of the unwanted Th2Zn17-type compound forming alongside the desired ThMn12-type 1:12 compound. A more pure 1:12 phase could be obtained for R=Ce0.6Zr0.4, but it exhibited a room-temperature coercivity of less than 1kOe. The most pure 1:12 phase and the highest values of the coercivity (10.8kOe) and calculated maximum energy product (13.8MGOe) were obtained for R=Sm0.7Zr0.3 processed at 1150°C. The calculated maximum energy products of the Sm0.3Ce0.3Zr0.4Fe10Si2 particles, with half of their rare earths constituents represented by the relatively abundant Ce, was 10.1 MGOe. [Display omitted] •30% Zr substitution for Sm improves prospects of the alloys as permanent magnets.•Pure ThMn12-type structure could only be obtained in the Zr-substituted alloys.•Obtained powders exhibit better properties than nanocrystalline Sm(Fe,M)12 alloys.•If fully dense, alloy containing only 2.3at% Sm would energy product of 10MGOe.