Preparation of coloured glasses with nanosized secondary phases via sintering of colloidal gels

摘要

Silica glass can be produced via melting or via sintering of a green body of nanosized fumed silica powders, e. g. Degussa Aerosils A380 and OX50. Advantages of the sintering technique are the reduction of the processing temperatures from approx. 2,300 ℃ down to 1,250 ℃ and the possibility of near-shape manufacturing of silica glasses, which can be shaped at room temperature. Furthermore, it is possible to use the open pore structure for a modification of the silica glass, e. g. incorporation of a secondary phase. The doping can be added quite easily by soaking the green body with salt solutions. Here, size and distribution of the particles of the secondary phase can independently be controlled by the pore size of the compacts. For melting technology the secondary phase is precipitated during cooling of the glass and subsequent heat treatment to form particles with appropriate size. Since the processing temperature is much lower in the sintering route, even components with lower thermal stability can be incorporated into the glass network. The potentials of the sintering method are demonstrated by preparing and characterising ruby coloured silica glass. The pore sizes of the compacts measured by mercury penetration are correlated to the particle size of the secondary phase inside the sintered glass matrix measured by HR-TEM and EDXS. Furthermore, the possibility of doping silica compacts with other functional particles is discussed.