| Nickel-Zinc ferrites of nominal composition Ni0 •• Zno.,
Fe20 4 were prepared with small deviations from stoichiometry
by standard ceramic powder processing. Ferritisation
was carried out in the range 800-1100°C and the progress
was studied by X-ray diffractograms. For the final selected
material ferritisation was done at 850°C. The ground ferritised
material with a particle size of about 0.1 micron was
compacted into pellets for densification and microstructure
studies, and toroids for magnetic studies under identical
compaction pressures. Pellets and toroids were packed in
fireclay saggars with Ni-Zn ferrite powder of similar composition
to avoid loss of Zn at sintering temperatures.
Firing was done in silicon carbide tube furnace at 1150,
1170, 1200, 1250 and 1300°C for 5, 20 and 100 hrs. Bulk
density and porosity were determined and microstructure
analysis was made on polished and etched specimens of
fired pellets. Grain size and pore size distributions were
determined from optical micrographs. Maximum fired
density was 5 gmjcc (theoretical 5.345 gmjcc) and the
highest temperature and times of firing resulted in reduced
final density. Average sample grain sizes ranged between
7 micron and 43 micron. Exaggerated grain size of about
80 micron was also observed in high fired samples. Trapped
pores resulted in almost all samples. |
