جستجوی مقالات مرتبط با کلیدواژه « rheological behavior » در نشریات گروه « مواد و متالورژی »

In this study, the effect of slip casting parameters on the ultrafine microstructure and the density of pore-free YAG ceramic was evaluated. A stable, high concentrated aqueous YAG slurry using Dolapix-CE64 as a dispersant was prepared. The effect of dispersant concentration as well as the solid load on the stability and rheological behavior of the slurry was also studied. The optimal dispersant content for suspension was 1.5%wt which led to the slurry with minimum viscosity and near Newtonian behavior. The results show that increasing the solid load of the YAG slurry causes higher viscosity and alters the rheological behavior of slurry to slight shear thinning. By increasing the solid load of slurry up to a specific amount, 75%wt, relative green density of the slip cast sample was increased to about 65%, but further increase in solid loading reduced the green density. The density and the microstructure of the sintered body in the air and vacuum atmospheres bear a direct relationship to the green density of the slip cast body. Although, relatively the pore-free ultrafine YAG ceramic was obtained using vacuum sintering of the slip cast green body of 65% relative green density, the presence of nitrogen molecules in the air atmosphere inhibited full densification of YAG ceramic.

The effective shear and bulk viscosity, as well as dynamic viscosity, describe the rheological properties of the ceramic body during the liquid phase sintering process. The rheological parameters depend on the physical and thermo-mechanical characteristics of the material such as relative density, temperature, grain size, diffusion coefficient, and activation energy. Thermal behavior of the ceramic body during sintering process including the viscose flow deformation, anisotropic shrinkage, heterogeneous densification, as well as sintering stress, have significant influence on the both final body dimensional precision and densification process. In this paper, the numerical-experimental method has been developed to study both rheological and thermal behavior of hard porcelain ceramic body during liquid phase sintering process. After raw materials analysis, the standard hard porcelain mixture as a ceramic body was designed and prepared. The finite element method for the ceramic specimens during the liquid phase sintering process are implemented in the CREEP user subroutine code in ABAQUS. Densification results confirmed that the bulk viscosity was well-defined with relative density. It has been shown that the shrinkage along the normal axis of slip casting is about 1.5 times larger than that of casting direction. The stress analysis proved that the sintering stress is more than the hydrostatic stress during the entire sintering time so, the sintering process occurs completely. The inhomogeneity in Von-Misses, pressure, and principal stress intensifies the relative density non-uniformity. Dilatometry, SEM, XRD investigations as well as bulk viscosity simulation results confirmed that the “mullitisation plateau” was presented as a very little expansion at the final sintering stage, because of the highly amount of mullite formation.