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  • Oxidation of sintered Nd-Fe-B magnets with modified composition
    Škulj, Irena, 1972- ; Harris, Ivor ; Evans, H.E.
    Sintered Nd-Fe-B type magnets have been commercially widely used. They offer the highest energy product of any materials today and are available in a wide range of shapes, sizes and grades. However, ... their performance at elevated temperatures remains a problem, and this includes their propensity to oxidise. The Nd[sub](2)Fe[sub](14)B ferromagnetic matrix phase has a low Curie temperature (312[compositum]C). These factors limit the use of these magnets above 100[compositum]C, and this low maximum operating temperature has limited the range of applications for Nd-Fe-B magnets. Nd-Fe-B alloys have a very poor oxidation resistance. A lot of studies have already been made on the aqueous corrosion of many Nd-Fe-B alloys, but only a limited amount of research has been carried out on the oxidation behaviour. Oxidation is associated with the inward diffusion of oxygen, accompanied by an interval reaction to form a dispersion of Nd-oxides in an [alpha]-Fe matrix. Sintered Nd-Fe-B magnets were modified by Co and the influence of its addition on the oxidation kinetics was studied. Various EM techniques have been used to characterise the sample. Nd[sub](16)Fe[sub](76)B[sub]8 was powdered and used for different compositions magnets preparation by powder blending technique. Amount of additions add to the starting composition was up to 10at.% Co, 3at.% Dy and 0.3at.% Zr and V. All fully dense sintered and annealed magnets were oxidised at temperature range 250-500 [compositum]C for 24-120h exposed to the environmental atmosphere. The oxidation of these materials follows a parabolic rate, with oxidation taking place internally; i.e. oxygen diffuses into the magnet to form an internally oxidised layer and the reaction occurs at the interface between the unaffected magnet and the thick internally oxidised layer. Multilayered oxides are formed at the surface, with uniform thickness along the surface. The Co addition to a Nd[sub](16)Fe[sub](76)B[sub](8) alloy affects the rate of oxidation, while the oxidation kinetics remains parabolic. In the case of oxidation of Nd[sub](16)Fe[sub](76)B[sub](8) alloy the oxygen diffuses through internally oxidised layer [in relation]40% faster then through the layer formed on the Nd[sub](16)Co[sub](10)Fe[sub](66.9)B{sub](7.1) alloy.
    Vir: Zbornik sažetaka (2005, Str. 8-9)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2005
    Jezik - angleški
    COBISS.SI-ID - 565162

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