Accession Number : AD0776069

Title :   Structure of Grain Boundaries in Oxides.

Descriptive Note : Final rept.,

Corporate Author : NOTRE DAME UNIV IND DEPT OF METALLURGICAL ENGINEERING AND MATERIALS SCIENCE

Personal Author(s) : Kuczynski,G. C.

Report Date : DEC 1973

Pagination or Media Count : 90

Abstract : The magnetic properties of sintered alpha-ferric oxide were investigated as a function of grain size for three different kinds of powders. The coercive force was found to change drastically as soon as grain boundaries were formed by sintering, while the Morin temperature and the antiferromagnetic susceptibility were unaffected. The increase of magnetic hardness was identified as an effect of grain boundaries rather than the effect of crystal size only. The existence of grain boundaries appeared to be equivalent to the existence of strong uniaxial anisotropy of the order of 1000 ergs per g in the vicinity of grain boundary which could be visualized as a film possessing strong uniaxial anisotropy. The microscopic origin of the strong uniaxial anisotropy associated with grain boundaries is discussed on the basis of the dislocation structure of the grain boundary. The lowering of six fold symmetry of the crystal to two fold symmetry due to dislocations is suggested as the origin of this uniaxiality. (Modified author abstract)

Descriptors :   *Iron oxides, *Grain size, *Ferromagnetism, Coercive force, Sintering, Antiferromagnetism, Crystal structure

Subject Categories : Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE