Pore size control of porous silica ceramics by hydrothermal hot-pressing

Porous silica ceramics with homogeneous pore distribution were prepared by the hydrothermal hot-pressing of silica gels. The recovered porous ceramics had high mechanical strengths with large pore volumes. The ceramics prepared at 300 °C and 20 MPa for 1 h with 17.2 mass% water showed the following properties; high compressive strength (60 MPa), low bulk density (0.68 g/cm³), large pore volume (0.98 cm³/g), and uniform pore distribution with average pore size of 65 nm. The average pore diameter of the ceramics was controlled from 25 to 100 nm by selecting hydrothermal hot-pressing conditions and starting silica gels. The formation mechanism of large pores in the silica ceramics could be elucidated by capillary effects.