MORPHOLOGY OF NICKEL ALUMINATE SPINEL (NiAl2O4) FORMED IN THE Al2O3-Ni COMPOSITE SYSTEM SINTERED IN AIR

The aim of this paper was to characterize the microstructure, especially the morphology of NiAl2O4 spinel phase in Al2O3-Ni composite system. The composites were prepared from the powder mixture contains: 90 vol. % of Al2O3 and 10 vol. % of nickel powder. Two series of samples were prepared: Series I with addition of nickel powder of average particle size 8.5, m and Series II with addition of nickel powder of average particle size 1.5, m. The presence of the spinel phase in composites was confirmed by both X-ray phase analysis and SEM observations. All tested samples were characterized by homogeneous distribution of NiAl2O4 phase in the whole volume of the material. The spinel has on oval shape with characteristic void inside. Two areas of spinel phase were identificated. The inner part is compact and consisted of large grains of spinel. In contrast, the outer part is porous and consisted of smaller grains of spinel. In aim to describe the spinel morphology the stereological analysis was done. Results showed that there is no evident influence of Ni initial grain powder size on the spinel formation and morphology. Formation of the spinel retarded the densification of the composites of Al2O3-Ni system.