Fabrication of Al2O3-Fe gradient composites by slip casting method
Katarzyna Konopka*, Mikołaj Szafran**, Ewa Bobrak** *Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa **Politechnika Warszawska, Wydział Chemiczny, ul. Noakowskiego 3, 00-664 Warszawa
Quarterly No. 1, 2006 pages 57-61
DOI:
keywords: ceramic-metal composites, gradient materials, slip casting
abstract The principal advantage of ceramic-metal composites is an increase of the resistance to brittle fracture compared to that of the ceramic matrix. Functionally gradient composites is the special kind of composites because the variation of the percent content of the metallic phase in ceramic matrix allow to change the fracture toughness as a function of the distance from the surface of material. Moreover, it is possible to modify its electric, thermal and magnetic properties. In the paper the way of ceramic-metal composites with gradient concentration of metal particles is presented. As a method of composites fabrication the slip casting method was chosen. The process of metal particles sedimentation under gravitation force and magnetic field (Fig. 1) was used to achieve the gradient concentration of metal particles. In slip casting method the mixture of powders with addition of liquidizers, surface-active agents and binders is used. The proper selection of components in slip casting mass is crucial for obtaining the material, especially composites in which powders with different density are mixed. In the paper the way of preparing of slip casting mass is discussed. The Al2O3-Fe composites were fabricated from the slip casting mass containing 40 and 50 vol.% of solid phase (volume % of Fe equal to 5). The microstructure of composites were characterized by optical microscope and scanning electron microscope. Process of metal particles with higher density than the density of ceramic powder sedimentation under gravity force is possible when the distance between the ceramic powder particles are bigger than the size of metal particles. When the size of metal particles is equal or higher than the distance between the Al2O3 particles the distribution of Fe particle is uniform as it is shown in Figure 2. Magnetic force leads to gradient concentration of metal particles according to the schema presented in Figure 1, moreover the metal particles are situated along the line of magnetic field (Fig. 3). In the composites the Fe particles make agglomerates (Fig. 4).