Low Temperature Synthesis of Lanthanum Silicate Apatite Type by Modified Sol Gel Process

Abstract

Rare earth silicate apatite type is a very important and promising material for application as an electrolyte in IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell). Lanthanum silicate apatite, La9,33Si6O26, exhibits high conductivity and has high efficiency, long term stability, fuel flexibility, low emissions and relatively low cost compared to yttria stabilized zirconia (YSZ - yttria stabilized zirconia), at temperatures between 600 to 800 °C. One of the problems of YSZ is its high operating temperature which results in long starting times and problems of mechanical and chemical compatibility. The interest of investigating lanthanum silicate apatite as an electrolyte is to overcome the problems caused by high temperature operation required by YSZ electrolyte. In the present study, sol-gel method was used to synthesize La9,33Si6O26. Initially, the reagents (sodium silicate and lanthanum nitrate) were mixed to obtain colloidal silica. Then, this gel containing lanthanum nitrate was thermally treated to allow the melting of lanthanum nitrate salt distributed on colloidal silica. The aim of this study was to verify if this method permits the formation of La9,33Si6O26 pure apatite phase, in order to obtain fine powders and uniform particles for further processing and obtaining a ceramic body.