Fabrication of zirconia ceramics by sintering in a magnetic field

Abstract

An external magnetic field was applied for activating the process of sintering the ZrO2-based ceramic materials in order to lower high sintering temperatures and improve the quality of the ceramics. The regularities of the formation of the structure of crystalline phases and the strength properties of zirconium ceramics during sintering of compacts from ultradispersed powders in the presence of a constant magnetic field (H = 4.01·1010–7.87·1010 A/m) with the symmetry Fp = C3 have been investigated. Sintering was carried out in the volume of a resistance furnace. The magnetic field inside the furnace volume was created by a toroidal coil with a special symmetrized winding. It has been established that the crystal structure, morphology and shape of grains in ZrO2 ceramics sintered in the constant magnetic field at 1400 °C are characterized by more perfect crystallographic forms when compared with sintering without an applied magnetic field, and the degree of isometricity increases. In this case, the degree of crystallinity increases, on average, by 2.4 times its initial value. The observed formation and stabilization of high-temperature phases (high-temperature modifications of the о* and с phases) of zirconium dioxide when sintering in the presence of the magnetic field are associated with directional changes in the structural characteristics (a decrease in crystalline microdistortions, an increase in the degree of uniformity). The oxide ceramics sintered in the presence of a constant magnetic field (B = 0.02–1 T) with a given symmetry С3 possess improved physical and mechanical characteristics (the strength and density increase by 54% and 15% from their initial values, respectively) and more perfect crystalline forms of microstructures, as compared with sintering without the imposition of an external magnetic field.