The impact of a dispersed phase OF MgO on the course of sintering a material made of AgNi20
Stanisław Gacek, Irena Olszewska Akademia Górniczo-Hutnicza, Wydział Metalurgii i Inżynierii Materiałowej, al. Mickiewicza 30, 30-059 Kraków
Annals 4 No. 11, 2004 pages 254-259
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abstract This paper deals with the impact exerted by initial substances of Ag and Ni powders owing to their specific properties, as well as of an oxide phase of MgO on the course of sintering a material made of AgNi20 and of AgNi20 with some MgO quantities added to silver, their rates being 0.5, 1.0, 2.0, and 4.0% by volume. The silver powders used in the investigations differed by their properties: one silver powder was manufactured using electrolysis, and the other one during a process of chemical co-precipitation and reduction (Tables 1, 2; Fig. 1). MgO was incorporated into the Ag powder by: – chemical settling MgO on the surface of the electrolytic Ag powder, – settling MgO within the entire volume of Ag particles and by simultaneous co-precipitation and reduction. The compacts showing relative density values of 60, 70, 80, and 90% were sintered in the hydrogen atmosphere, at 1200 K, during 0,25; 0,5; 1; 4; 8 hrs. The density values and sizes of Ag grains were measured, and the measurement results allowed for the determination of the nature of changes occurring in the density and structure of sinters (Figs 2-4). MgO added to the Ag powder and settled on the particle surfaces of electrolytic powder made the mutual contact among the particles more difficult, and caused the following: – the swelling process of sinters during its first phase was either reduced or it totally vanished, – the intensity and magnitude of shrinkage was changed, – the silver grain growth was retarded (Figs 2-4). In case the magnesium oxide was uniformly distributed and arranged in the silver matrix of the sinters obtained from the co-precipitated mixes, then, it caused the following phenomena: – the entire sintering process progressed more difficult, – the intensity of both the swelling and the contraction was reduced during the first sintering phase, – the silver grain growth was retarded (Figs 2-4). Key words: electrical contact, sintered AgNi, particles MgO, microstructure