ELECTROCHEMICAL NUCLEATION FOR THE PREPARATION OF ORIENTED GLASS-CERAMICS

During cooling of a glass melt with the composition of 2BaO . TiO2 . 2 .75SiO(2) crystallization takes place at 1030 degrees C during DTA mea surements and at 1220 degrees C, if the glass melt is placed in a rota tion viscosimeter. If higher temperatures are used, e.g., 1300 degrees C, a cathodic current flow of 45 mA/cm(2) is achieved by attaching a dc-potential of 1.2 V and crystallization of fresnoite takes place at the cathode, leading to a highly oriented structure. The crystallites show fast dendritic growth and the crystallographic c-axis is oriented perpendicular to the electrode surface. Electrochemically induced nuc leation runs parallel with the reduction of Ti4+ of Ti3+ which is supp osed to decrease the viscosity, increase the diffusion coefficient and possibly alter the surface tension of the nuclei formed. (C) 1997 Els evier Science B.V.