 porosity, instead of grain size, grain-size strengthening is also observed in high-density ceramic specimens .Additionally, nanocrystalline ceramics have been shown to sinter more rapidly than bulk ceramics, leading to higher densities and improved mechanical properties, although extended exposure to the high pressures and elevated temperatures required to sinter the part to full density can result in coarsening of the nanostructure.The large volume fraction of grain boundaries associated with nanocrystalline materials causes interesting behavior in ceramic systems, such as superplasticity in otherwise brittle ceramics.