Ceramics-Silikáty 44 (1) 9-13 (2000) 

OPEN-PORE GLASSES AND GLASS-CERAMICS BY SINTERING OF MODIFIED PYROGENIC SILICIC ACIDS

J. Vogel, Ch. Rüssel 

A pyrogenic silicic acid (Aerosil OX50) was used as glassy phase in salt sintering process. Aqueous disperoions of the Aerosil and ß-tricalcium phosphate (TCP) particles, acting as spacers during the sintering process, were dried and sintered at temperatures in the range of 1000 °C to 1500 °C. After sintering, the crystalline spacer was leached by aqueous hydrochloric acid and highly porous glasses or glass ceramics were obtained. By dissolution of water-soluble salts of other ions (Na⁺, Mg²⁺, Al³⁺...) in the aqueous dispersion, the pyrogenic silicic acid can be modified. The highly active surfaces of the SiO₂ particles are coated with the added compounds during drying the green compacts. The presence of sodium ions results in an enlargement of the silicatic network during sintering and the diffusion of these ions into the glassy phase is promoted. In this way, open pore glasses and glass ceramics possessing different chemical constitutions and pore diameters of 800 nm to around 15 ľm were obtained. The total open porosity of the glasses can be varied by the amount of incorporated spacer TCP.