Manufacturing of pure and doped silica and multicomponent glasses from SiO₂ nanoparticles by reactive electrophoretic deposition

Abstract

Manufacturing of glasses by shaping of powders and sintering comprises several advantages, like near-shaping of complex structures. Furthermore, sintering to fully transparent glasses is typically obtained at temperatures significantly lower than via melt fabrication. Thus incorporation of functional dopants with lower decomposition stability becomes possible, significantly increasing the variety of possible doping materials and applications. However, nanosized particles with their significantly enhanced sintering activity have to be used for powder manufacturing of glasses to avoid crystallisation. Unfortunately, no suitable nanopowders with appropriate composition are commercially available, and the manufacturing techniques proposed so far are complicated and time-consuming, often resulting in inhomogeneous doping. In contrast, by means of the newly developed reactive electrophoretic deposition (EPD) fast shaping and doping of glasses in only one process step is possible, using pure nanosized fumed silica powders as starting material. Doping is achieved by electrophoretic co-deposition of the nanoparticles and functional ions, surrounding each particle homogeneously in the electrochemical double layer. Thus doping with anions as well with cations was possible, resulting in different colouration of the silica glass (blue or gold ruby), with the coefficient of absorption being a function of the ion concentration within the suspension. Furthermore, a decrease in sintering temperature was achieved by EPR with boric acid. Finally, co-doping with anions and cations resulted in the manufacturing of multicomponent glasses with a decrease in sintering temperature of 450 °C compared to pure silica OX50.