Study on the shape of pores in ferrites. (Part 1)

Abstract

Microscopic observations of the intragranular pores were carried out to clarify the factors which determine the shape of pores during sintering in variously heat treated Cu-and Ni-ferrites.For prolonged annealing at the temperature range in which no change in pore size was observed, pores which consisted of (111) planes and curved surfaces were observed. The formation of such a poreshape is considered to be caused by minimization of surface free energy. At annealing temperature where the pore size changed, the pore under growing were apt to form the octahedral shape, but pores under shrinking formed the spherical shape. In the case of samples oxidized at lower temperatures, unsymmetrical pores which consisted of (111) planes on the surface and of spherical surfaces in the interior sides of samples were observed. In samples slowly cooled from temperatures above the solidus temperatures, the polyhedral pores having not only (111) planes but also (100), (110), (311) and (331) planes were observed. It is suggested that there exist some other factors than the surface free energy, which determine the shape of pores in actual sintered bodies.