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An investigation of co-fired varistor-ferrite materials

2003; Elsevier BV; Volume: 24; Issue: 7 Linguagem: Inglês

10.1016/s0955-2219(03)00361-3

1873-619X

Aran Rafferty, Yurii K. Gun’ko, Ramesh Raghavendra,

Electromagnetic wave absorption materials

The purpose of this work was to co-fire crack-free varistor-ferrite ceramic multilayers fabricated via a dry pressing route.Multilayers were sintered using a standard industrial grade varistor sintering regime.Sinter shrinkages of both varistor and ferrite materials were measured using dilatometry and showed that the varistor shrunk significantly more than the ferrite material.X-ray diffraction analysis indicated that no significant phase changes occurred in the materials under investigation as a result of the sintering process.Scanning electron microscopy observations of the dry-pressed co-fired varistor-ferrite revealed vertical cracking in the ferrite due to thermal expansion mismatch between the materials.By pressing a mixed composition interlayer in the ratio 50:50, between the varistor and ferrite materials, a crack-free multilayer structure could be obtained.Energy dispersive X-ray analysis of the co-fired ferrite and varistor confirmed diffusion of Fe and Ni components from the ferrite into the varistor material.The degree of diffusion was reduced by using 50:50 ratio mixed composition interlayers.