Preparation of coloured silica glasses made by sintering of particulate gels

Abstract

Large pieces of silica glass can be easily made by sintering particulate gels prepared from fumed silica powders. These compacts can be doped by soaking with alcoholic solutions of salts of a large variety of colouring ions of the transition and rare earth elements. As the sintering of the compacts in a zone furnace with a silica glass tube inside is not restricted with respect to the atmospheres, higher states of valence of the dopants with additional colours can be achieved under oxidizing conditions in contrast to the conventional melting of silica glass in crucibles of molybdenum or tungsten which have to be operated under reducing conditions. In reducing sintering atmospheres red copper and gold ruby glasses can be prepared. Therefore, it is favourable to prepare compacts with smaller particles which show also smaller pores.The mechanism of the formation of the colloidal metal particles is not yet clear and needs further investigations.