Influence of ageing phenomena on magnetic properties of dielectromagnetic - type powder composites
Tomasz Janta Politechnika Wrocławska, Instytut Maszyn, Napędów i Pomiarów Elektrycznych, ul. Smoluchowskiego 19, 50-372 Wrocław
Annals 4 No. 12, 2004 pages 384-388
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abstract Lately magnetic powder composites find ever wider use as active magnetic materials for magnetic cores of electric devices. Because of their proprieties and manufacturing technology, dielectromagnetics attract a great interest. They are powder composites made from soft magnetic powder with an admixture of, among others, dielectric in the form of resins which both bind and isolate the soft magnetic particles. The properties of manufactured dielectromagnetics and their constancy over time as well as the influence of the operating conditions (e.g. temperature) or the medium (e.g. humidity) on them are the main factors which determine the use of these materials. When the factors are examined and understood, it will become possible to design magnetic cores in such a way that the predictable changes in their properties will not disqualify the electric devices in the course of their service. Since the problem is a complex one it is difficult to explore. The changes depend on, among others, the kind of magnetically soft powder, the amount and kind of dielectric, the amount and kind of admixtures and finally, on the exposure. The affected properties include magnetic, electric and mechanical properties. In this paper changes in the magnetic properties of dielectromagnetics, made of soft magnetic powder ASC 100.29 with an admixture of epoxy resin Epidian 101 in the amount of 0.1 and 0.2% by weight, caused by ageing are described. The magnetic properties of the specimens were tested twice: immediately after they were made and one year later. The dielectromagnetics were stored in ambient conditions at a constant temperature of 22oC and a constant humidity of 50%. The magnetization curve values and shapes and the corresponding relative magnetic permeabilities are shown in Table 1 and in Figures 2-7. The research has shown that the effect of ageing phenomena on the magnetic properties of the tested dielectromagnetics is practically negligible. This is a proof of the high quality of the soft magnetic powder used whose properties remain stable over time. Key words: powder metallurgy, soft magnetic materials, dielectromagnetics, dielectrics, magnetic properties, ageing phenomena