In a more recent work, silica (50 n

In a more recent work, silica (50 nm in size) synthesized by Stöber process was mixed with NaOH aqueous solutions to improve silica dissolution-precipitation process. Initially the blend was pressed by 190 MPa, followed by cold isostatic pressing at 500 MPa/5 min. The relative densities of the green bodies were in between 50 and 55%. These tablets were subjected to “hydrothermal sintering” using a modified HHP equipment operated at RT with 127 MPa pressure, then at 150℃, and finally at 300℃ under 350 MPa pressure for 90 min.